docStudies on the Effect of Three Species of Heliotropium on the Life
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Studies on the Effect of Three Species of Heliotropium on the Life
Studies on the Effect of Three Species of Heliotropium on the Life System of Solitary Desert Locust Schistocerca gregaria (Forskål) (Orthoptera: Acrididae) By Atiyat Abdalla Fadoul Nori B.Sc. (Honour) Agricultural Studies, University Of Sudan Of Science And Technology (١٩٩٦) A thesis submitted in partial fulfillment of the requirements for the master degree of science in Agricultural Faculty Of Agriculture University Of Khartoum ٢٠٠٣ DEDICATION I would like to dedicate this thesis to My lovely family with my sincere appreciation and love. AKNOWLEDGEMENTS I would like to express my sincere appreciation and thanks to my supervisor, Professor Magzoub Omer Bashir for his supervision, guidance, encouragement and for providing many facilities. My deep thanks are due to the Red Sea University management for offering me the scholarship and financial needs to conduct this study. My deep thanks are also due to the staff members of Applied Science Faculty, especially Dr. Salah Mergany the Dean of the faculty, the Computer department and the Biology department for their patience, understanding, helping and enthusiasm. I am greatly indebted to Dr. Ahmed Abdelaziz for helping me to have this chance while he was the Dean of Applied Science Faculty. Thanks are also due to the staff members of ICIPE field station, Locust Research Program, Port Sudan, for helping and providing facilities. Thanks are extended to Mr. Sidi wad Ali Ph.D student and Mr. Adnan Khan M.Sc student University of Khartoum, ICIPE field Station for their helping hints. I am greatly indebted to Ustaz Nahid Abdalrahim, Faculty of Marine Science, Red Sea University and Ibrahim Tahir M.Sc Student Faculty Statistics of Gaezira University for helping me to understand SPSS analysis program. Special thanks are due to the staff member’s of the computer lab of the Red Sea University for providing many facilities. My sincere thanks are due to my friends and colleagues for their help, encouragement and cooperation. Also my sincere thanks are due to my family for their patience and support. Finally I render my all thanks to almighty “Alla” LIST OF CONTENT Page Dedication………………………………………………………. i Acknowledgments……………………………………………… ii List of contents…………………………………………………. iv List of tables…………………………………………………….. vii List of figures…………………………………………………… xi List of plates…………………………………………………….. xvi Abstract…………………………………………………………. xvii Arabic abstract…………………………………………………. xx Introduction…………………………………………………….. ١ Literature Review………………………………………………. ٥ ١ Host plant…………………………………………………….. ٥ ٢ The locust…………………………………………………….. ٦ ٢٫١ Identification………………………………………………… ٦ ٢٫٢ Desert locust ٦ classification…………………………………... ٧ ٢٫٣ Distribution………………………………………………….. ٨ ٢٫٤ Locust habitats………………………………………………. ٩ ٢٫٤٫١ Habitats of Solitarious Desert Locust…………………….. ١٠ ٢٫٥ Economic ١١ importance………………………………………... ١٣ ٢٫٦ Life ١٤ cycle…………………………………………………….. ١٥ ٢٫٧ Behaviour……………………………………………………. ١٧ ٢٫٨ Host plant……………………………………………………. ١٩ ٢٫٨٫١ Host finding……………………………………………… ٢٤ ٢٫٨٫٢ Factor’s in food selection………………………………… ٢٫٨٫٣ Effect of the food on the biology…………………………. Materials And Methods………………………………………... ٢٤ ١ Effect of Heliotropium spp. on the duration period, ٣٠ development period, weight, maturation, longevity, ٣٢ percentage survival and feeding rate…………………………. ٣٢ ١٫٢ Effect Of Heliotropium spp on oviposition………………….. ٣٢ ٢ Antifeedant experiments……………………………………… ٣٦ ٢٫١ Feeding on three species of Heliotropium………………...... ٣٧ ٢٫٢ Feeding on filter paper impregnated with juices of ٤٠ Heliotropium. …………………………………………………… ٤٠ ٣ Repellence experiment………………………………………. ٤٠ ٤ Data analysis…………………………………………………. ٤٠ Results…………………………………………………………... ٤١ ١ Effect of Heliotropium spp on the development of Solitary ٤٦ DL nymphs………………………………………………….. ٤٦ ١٫١ Duration period ……………………………………………... ٥٢ ١٫١٫١ Season ١٩٩٩- ٥٢ ٢٠٠٠…………………………………………. ٥٢ ١٫١٫٢ Season ٢٠٠٠- ٥٩ ٢٠٠١…………………………………………. ٦٨ ١٫٢ Developmental period……………………………………….. ٦٨ ١٫٢٫١ Season ١٩٩٩- ٦٨ ٢٠٠٠…………………………………………. ٦٨ ١٫٢٫٢ Season ٢٠٠٠- ٧٣ ٢٠٠١…………………………………………. ٧٣ ١٫٣ Weight of nymphs and fledglings…………………………… ٧٤ ١٫٣٫١ Season ١٩٩٩- ٧٤ ٢٠٠٠…………………………………………. ٨١ ١٫٣٫٢ Season ٢٠٠٠- ٨١ ٢٠٠١…………………………………………. ٨١ ١٫٤ Maturation ……………………..…………………………… ٨٦ ١٫٤٫١ Season ١٩٩٩- ٨٦ ٢٠٠٠…………………………………………. ٨٦ ١٫٤٫٢ Season ٢٠٠٠- ٩٥ ٢٠٠١…………………………………………. ١٠١ ١٫٥ Fecundity and ١٠١ fertility……………………………………….. ١٠٦ ١٫٥٫١ Season ١٩٩٩- ١١٧ ٢٠٠٠…………………………………………. ١٢٨ ١٫٥٫٢ Season ٢٠٠٠- ١٣٧ ٢٠٠١…………………………………………. ١٤٠ ١٫٦ Longevity……………………………………………………. ١٥٢ ٦٫١ Season ١٩٩٩- ٢١٧ ٢٠٠٠…………………………………………… ١٫٦٫٢ Season ٢٠٠٠٢٠٠١…………………………………………. ١٫٧ Percentage survival………………………………………….. ١٫٧٫١ Season ١٩٩٩٢٠٠٠…………………………………………. ١٫٧٫٢ Season ٢٠٠٠٢٠٠١…………………………………………. ١٫٨ Feeding rate…………………………………………………. ١٫٨٫١ Season ١٩٩٩٢٠٠٠…………………………………………. ١٫٨٫٢ Season ٢٠٠٠٢٠٠١…………………………………………. ٢ Antifeedant behaviour…………………………………………. ٤٫١ Consumption weight food……………………………………. ٤٫٢ Area consumed from impregnated filter paper………………. ٣ Repellency effect………………………………………………. Discussion……………………………………………………….. Conclusion………………………………………………………. References………………………………………………………. Raw data appendix……………………………………………... Analysis appendix………………………………………………. LIST OF TABLE Table page ١. Mean duration period in solitary DL nymphs reared on three species of Heliotropium (Season ١٩٩٩-٢٠٠٠)……………………..…٤٢ ٢. Mean duration period in solitary DL male nymphs reared on tow species of Heliotropium (Season ١٩٩٩-٢٠٠٠)………….. ………٤٤ ٣. Mean duration period in solitary DL female nymphs reared on tow species of Heliotropium (Season ١٩٩٩-٢٠٠٠)………………..٤٤ ٤. Mean Duration period of solitary nymphs of the DL reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)……….٤٧ ٥. Mean duration period of solitary nymphs male of the DL reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)…….…٤٨ ٦. Mean duration period of solitary nymphs female of the DL reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)………٥٠ ٧. Mean developmental period (from ١st instar to fledgling) of solitary of the Desert Locust males and females reared on tow species of Heliotropium (Season ١٩٩٩-٢٠٠٠)…………………٥٣ ٨. Mean developmental period (from ١st instar to fledgling) of solitary DL males and females reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)…………………………………..٥٥ ٩. Mean weight of solitary DL nymphs and fledgling reared on three species of Heliotropium (Season ١٩٩٩٢٠٠٠)………………….٥٧ ١٠. Mean weight of solitary DL male nymphs and fledgling reared on three species of Heliotropium (Season ١٩٩٩-٢٠٠٠)………٦٠ ١١. Mean weight of solitary DL female nymphs and fledgling reared on three species of Heliotropium (Season ١٩٩٩٢٠٠٠)……….٦٠ ١٢. Mean weight of solitary DL nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)………………٦٢ ١٣. Mean weight of solitary DL male nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)………..٦٥ ١٤. Mean weight of solitary DL female nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)…..……٦٦ ١٥. Onset of maturation solitary DL males and females reared on tow species of Heliotropium (Season ١٩٩٩٢٠٠٠)………………...٦٩ ١٦. Onset of maturation solitary DL males and females reared on tow species of Heliotropium (Season ٢٠٠٠٢٠٠١)………………...٧١ ١٧. Fecundity and fertility of solitary DL female reared on tow species of Heliotropium (Season ١٩٩٩٢٠٠٠)………………………..٧٥ ١٨. Fecundity, fertility and egg development of solitary DL female reared on tow species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………٧٦ ١٩. Fecundity and fertility of solitary DL female reared on tow species of Heliotropium (Season ٢٠٠٠٢٠٠١)………………………...٧٨ ٢٠. Fecundity, fertility and egg development of solitary DL female reared on tow species of Heliotropium (Season ٢٠٠٠٢٠٠١)…………٧٩ ٢١. Mean longevity of solitary DL male and female reared on three species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………………..٨٢ ٢٢. Mean longevity of solitary DL male and female reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)…………………..٨٤ ٢٣. Percentage survival of solitary nymphs and fledgling DL reared on three species of Heliotropium (Season ١٩٩٩٢٠٠٠)……….٨٧ ٢٤. Percentage survival of solitary nymphs and fledgling DL reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)……….٨٧ ٢٥. Mean weight dry food (gm) consumed by solitary nymphs and fledgling reared on three species of Heliotropium (Season ١٩٩٩٢٠٠٠)………………………………………………….٩٠ ٢٦. Mean weight wet food (gm) consumed by solitary nymphs and fledgling reared on three species of Heliotropium (Season ١٩٩٩-٢٠٠٠)………………………………………………….٩١ ٢٧. Mean weight dry food (gm) assimilated by solitary nymphs and fledgling reared on three species of Heliotropium (Season ١٩٩٩-٢٠٠٠)………………………………….٩٣ ٢٨. Mean weight dry food (gm) consumed by solitary nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)…………………………………………………٩٦ ٢٩. Mean weight wet food (gm) consumed by solitary nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)………………………………………………….٩٧ ٣٠. Mean weight dry food (gm) assimilated by solitary nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)…………………………………………………٩٩ ٣١. Mean weight wet food (gm) consumed by solitary nymphs and fledgling kept on three species of Heliotropium provided together in Banks each consisting of ١٠ cells (٦٠x٢٤x٣٠ cm) during ٢ days………………………………………١٠٢ ٣٢. Mean weight wet food (gm) consumed by solitary nymphs and fledgling kept on three species of Heliotropium provided together in Banks each consisting of ١٠ cells (٦٠x٢٤x٣٠ cm) during ٦ days……………………………………….١٠٤ ٣٣. Mean weight wet food (gm) consumed by solitary nymphs and fledgling kept on three species of Heliotropium provided together in small cages during ٢ days……………………………….١٠٧ ٣٤. Mean area of filter paper (cm٢) impregnated with juice of three species of Heliotropium eaten by solitary ٥th instar nymphs in ٢٤ hour in large cage (١٠٠ cm diameter), (Group and paired plant test.)……………………………………….١١٠ ٣٥. Mean area of filter paper (cm٢) impregnated with juice of three species of Heliotropium eaten by solitary ٥th instar nymphs in ٢٤ hour in small cages (٢٠ cm diameter), (group and paired plant test.)………………………………………..١١١ ٣٦. Mean area of filter paper (cm²) impregnated with the juice of three species of Heliotropium eaten by solitary male ٥th instar nymphs in ٢٤ hour in small cages (٢٠cm diameter), (group and paired plant tested)……………………………………..١١٤ ٣٧. Mean area of filter paper (cm٢) impregnated with juice of three species of Heliotropium eaten by solitary ٥th instar female nymphs in ٢٤ hour in small cages (٢٠ cm diameter), (group and paired plant test.)………………………………….……١١٥ ٣٨. Mean walking, resting and total time and distance traversed to reach food in wind tunnel by solitary DL male and female ٥th instar nymphs……………………………………………………١١٨ ٣٩. Behavior analysis of solitary DL ٥th instar nymphs in wind tunnel until food is reached…………………………………………١١٩ ٤٠. Mean walking, resting and total time and distance traversed to reach food in wind tunnel by solitary DL male ٥th instar nymphs………………………………………………………………١٢ ٢ ٤١. Behavior analysis of solitary DL ٥th instar nymphs in wind tunnel until food is reached………………………………………….١٢٣ ٤٢. Mean walking, resting and total time and distance traversed to reach food in wind tunnel by solitary DL female ٥th instar nymphs………………………………………………………………١٢ ٥ ٤٣. Behavior analysis of solitary DL ٥th instar nymphs in wind tunnel until food is reached………………………………………….١٢٦ LIST OF FIGURES Figure Page ١ Diagram of the flat-bed wind tunnel made of transparent glass; ١.Exhaust fan; ٢. Heliotropium species; ٣. Doors for introduction and collection of insects; ٤. Ruler ١٤٠ cm long; ٥. Sliding glass door to release the test insect; ٦. Wire mesh box; ٧. Wind tunnel chamber; ٨. Insect test pre-release compartment…………………………………………………………٣٩ ٢ Mean duration period in solitary DL nymphs reared on three species of Heliotropium (Season ١٩٩٩٢٠٠٠)………………….٤٣ ٣ Mean duration period in solitary DL male nymphs reared on tow species of Heliotropium (Season ١٩٩٩-٢٠٠٠)………... ………...٤٥ ٤ Mean duration period in solitary DL female nymphs reared on tow species of Heliotropium (Season ١٩٩٩-٢٠٠٠)………… …….٤٥ ٥ Mean duration period in solitary DL nymphs reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)………………………..٤٩ ٦ Mean duration period in solitary DL male nymphs reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)………..٤٩ ٧ Mean duration period in solitary DL female nymphs reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)………..٥١ ٨ Mean developmental period of solitary nymphs reared on tow species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………٥٤ ٩ Mean developmental period of solitary nymphs reared on tow species of Heliotropium (Season ٢٠٠٠-٢٠٠١)……………٥٤ ١٠ Mean developmental period of solitary males and females nymphs reared on three species of Heliotrpium (Season ١٩٩٩٢٠٠٠)…………………………………………………..٥٦ ١١ Mean developmental period of solitary males and females nymphs reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)…………………………………………………٥٦ ١٢ Mean weight of solitary DL nymphs and fledgling reared on three species of Heliotropium (Season ١٩٩٩٢٠٠٠)……..…٥٨ ١٣ Mean weight of solitary DL male nymphs and fledgling reared on two species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………٦١ ١٤ Mean weight of solitary DL female nymphs and fledgling reared on two species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………..……٦١ ١٥ Mean weight of solitary DL nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)………..٦٣ ١٦ Mean weight of solitary DL male nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)………..٦٧ ١٧ Mean weight of solitary DL female nymphs and fledgling reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)… ……٦٧ ١٨ Onset of maturation of solitary DL fledgling stage reared on tow species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………٧٠ ١٩ Onset of maturation of solitary DL male and female fledgling stage reared on tow species of Heliotropium (Season ١٩٩٩-٢٠٠٠)…………………………………………...٧٠ ٢٠ Onset of maturation of solitary DL fledgling stage reared on tow species of Heliotropium (Season ٢٠٠٠٢٠٠١)…………٧٢ ٢١ Onset of maturation of solitary DL male and female fledgling stage reared on tow species of Heliotropium (Season ٢٠٠٠٢٠٠١)……………………………………………٧٢ ٢٢ Fecundity of solitary female reared on tow species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………………………….٧٧ ٢٣ Fecundity fertility and egg development in egg pods laid by solitary female reared on tow species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………………………….٧٧ ٢٤ Fecundity of solitary female reared on tow species of Heliotropium (Season ٢٠٠٠٢٠٠١)…………………………….٨٠ ٢٥ Fecundity fertility and egg development in egg pods laid by solitary female reared on tow species of Heliotropium (Season ٢٠٠٠-٢٠٠١)…………………………… ٨٠ ٢٦ Mean longevity of solitary nymphs, fledgling and adult reared on three species of Heliotropium (Season ١٩٩٩-٢٠٠٠)……….٨٣ ٢٧ Mean longevity of solitary males and females nymphs, fledgling and adult reared on three species of Heliotropium (Season ١٩٩٩٢٠٠٠)…………………………….٨٣ ٢٨ Mean longevity of solitary nymphs, fledgling and adult reared on three species of Heliotropium (Season ٢٠٠٠-٢٠٠١)…………………………………………...٨٥ ٢٩ Mean longevity of solitary males and females nymphs, fledgling and adult reared on three species of Heliotropium (Season ٢٠٠٠٢٠٠١)…………………………….٨٥ ٣٠ Survival of solitary DL nymphs and adults reared on three species of Heliotropium from ٢nd instar to adult mortality (Season ١٩٩٩-٢٠٠٠)………………………………...٨٨ ٣١ Survival of solitary DL nymphs and adults reared on three species of Heliotropium from ٢nd instar to adult mortality (Season ٢٠٠٠٢٠٠١)…………………………………٩٢ ٣٢ Mean weight dry food consumed by solitary DL nymphs and fledgling male and female (Season ١٩٩٩٢٠٠٠)…………..٩٢ ٣٣ Mean weight wet food consumed by solitary DL nymphs and fledgling male and female (Season ١٩٩٩٢٠٠٠)…………..٩٤ ٣٤ Mean weight dry food assimilated by solitary DL nymphs and fledgling male and female (Season ١٩٩٩٢٠٠٠)…………..٩٨ ٣٥ Mean weight dry food consumed by solitary DL nymphs and fledgling male and female (Season ٢٠٠٠٢٠٠١)………......٩٨ ٣٦ Mean weight wet food consumed by solitary DL nymphs and fledgling male and female (Season ٢٠٠٠٢٠٠١)…………١٠٠ ٣٧ Mean weight dry food assimilated by solitary DL nymphs and fledgling male and female (Season ٢٠٠٠٢٠٠١)…………١٠٣ ٣٨ Mean weight wet food consumed by solitary ٥th instar nymphs kept on three species of Heliotropium during ٢ days…………………………………………………١٠٣ ٣٩ Mean weight wet food consumed by solitary ٥th instar male and female nymphs kept on three species of Heliotropium during ٢ days…………………………………..١٠٥ ٤٠ Mean weight wet food consumed by solitary ٥th instar nymphs kept on three species of Heliotropium during ٦ days………...١٠٥ ٤١ Mean weight wet food consumed by solitary ٥th instar male and female nymphs kept on three species of Heliotropium during ٦ days…………………………………………...…….١٠٨ ٤٢ Mean weight wet food consumed by solitary ٥th instar nymphs kept on three species of Heliotropium in small cages during ٢ days……………………………………………..…١١٢ ٤٣ Mean eight wet food consumed by solitary ٥th instar male and female nymphs kept on three species of Heliotropium in small cages during ٢ days………………….١١٢ ٤٤ Mean area of impregnated filter paper eaten in ٢٤hour by solitary ٥th instar nymphs’ in-group and paired plant test in large cage (١٠٠ cm diameter)…………………..١١٦ ٤٥ Mean area of impregnated filter paper eaten in ٢٤ hour by solitary ٥th instar nymphs’ in-group and paired plant test in small cages ( ٢٠ cm diameter). ٤٦ Mean area of impregnated filter paper eaten in ٢٤ hour by solitary ٥th instar male nymphs’ in-group and paired plant test in small cages (٢٠ cm diameter). ٤٧ Mean area of impregnated filter paper eaten in ٢٤ hour by solitary ٥th instar female nymphs’ in-group and paired plant test in small cages (٢٠ cm diameter). ٤٨ Mean walking, resting and total time spend by solitary DL nymphs until food was reached. ٤٩ Behavior analyses of solitary DL ٥th instar nymphs in wind tunnel until food was reached. ٥٠ Mean walking, resting and total time spend by solitary DL male nymphs until food was reached. ٥١ Behavior analyses of solitary DL ٥th instar male nymphs in wind tunnel until food was reached. ٥٢ Mean walking, resting and total time spend by solitary DL female nymphs until food was reached. ٥٣ Behavior analyses of solitary DL ٥th instar female nymphs in wind tunnel until food was reached. LIST OF PLATES Plate page ١. a. Heliotropium ovalifolium old plant………………………………..٢٥ b. Heliotropium ovalifolium young plant ……………………………….٢٥ ٢. a Heliotropium arabianense old plant ………………………………٢٦ b. Heliotropium arabianense young plant……………………………… ٢٦ ٣. Heliotropium lignosum……………………………………………………..٢٧ ٤. a Solitary rearing cage in (Season ١٩٩٩-٢٠٠٠)……………………....٢٩ ٥. a Solitary rearing cup in (Season ٢٠٠٠-٢٠٠١)………………………..٢٩ ٦. a,b Paired cages………………………………………………………٣١ ٧. a,b Small cages used for Antifeedant experiments on plants in feeding………………………………………………………………..٣٣ ٨. a,b large cages used for Antifeedant experiment on impregnated filter paper……………………………………………………………٣٤ ٩. Small cage used for Antifeedant experiment on impregnated filter paper………………………………………………………………….٣٥ ١٠. Impregnated filter paper with the juice of A= Heliotropium ovalifolium, B=Heliotropium arabianense, C=Heliotropium lignosum……………………………………………………………...٣٨ ١١. Impregnated filters paper eaten by solitary ٥th instar nymphs in ٢٤ hour…………………………………………………………………..١٠٩ ABSTRACT In this study the effect of three species of Heliotropium on the life system of solitary desert locust was investigated. This genus is the most important one among all desert plants in the Red Sea zone and forms the key species in desert locust distribution. There are six species in the area. Of these, three were used in this study; H. ovalifolium, H. arabianense and H. lignosum. All experiments were carried out at the International Centre of Insect Physiology and Ecology ICIPE, locust program –Port Sudan field station, during the period ١٩٩٩/٢٠٠٠-٢٠٠٠/٢٠٠١. The plants were collected from Sallom area ٣٠ Km south west of Port Sudan. The locusts used were offsprings of the solitary stock bred at ICIPE station. The effect of the three species on the life system of the DL was investigated using the parameters of development, weight, survival rate, feeding rate, maturation and longevity. Also the effect on the female fertility and fecundity and egg development was studied. The effect of antifeedant of the three species was carried out in two ways. First by keeping the locust on the three species in cells and small cages to know their preference to each species. Secondly by using juice extract from the plants impregnating on filter papers, and provided to the nymphs in multiple choice tests. The attraction of the solitary ٥th instar nymphs by the smell of food plants was carried out in a wind tunnel cage. The results indicated that the solitary locust nymphs develop well on H. ovalifolium and H. arabianense while they did not finish their development on H. lignosum, they died in the fledgling stage or after fledgling in a maximum of ٢ days. There is no clear effect on the nymphs weight gain between the three species. Solitary nymphs fed well on H. ovalifolium and H. arabianenes, while they fed little on H. lignosum. The fledglings on the first two species matured after a long period. The male matured before the female. The effect of these two species on the fertility and fecundity and egg development was in the same manner. Mating take place after a long period and also the egg laying rate was low compared to the solitary normal behavior. From antifeedant experiments it was clear that solitary nymphs fed on and preferred H. arabianense and H. ovalifolium and didn’t prefer H. lignosum. While large area was fed from the filter paper impregnated with H. lignosum juice compared to little areas of H. ovalifolium and H. arabianense. This indicates that some volatile phagostimulating material or materials were lost in the process of extracting the juice of H. arabianense and H. ovalifolium. On the other hand, some volatile antifeedant material or materials were lost in the process of extracting the juice of H. lignosum. This substance or substances need to be investigated and can be used as antifeedant substances in locust control. Attractiveness of H. lignosum to the DL was very slow. The tested individuals rested most of the time, then turned back or changed their direction in spite of that few numbers walked on for ١٤٠ cm but they didn’t clime the food or bit it. While the attraction to the other two species was clear. There is no significant difference regarding behavior (moving antenna, climbing and walking in many direction) between the three species. From this study it is clear that H. ovalifolium and H. arabianense are important species and can be used as an index in the locust survey. This makes the survey more limited, save a lot of time and effort. The wide spread of these species can be indicaters in the study of gregaraistion and swarming processes. This would help in obtaining early warning system for proper management and control strategies. Also the attractiveness of the two species can be used in the control strategies by incorporating poison in food traps. The third species volatiles can be extracted and used to repel locusts from crop plants. ﺍﻟﺨـــــــــﻼﺼﺔ ﺘﻡ ﺨﻼل ﻫﺫﻩ ﺍﻟﺩﺭﺍﺴﺔ ﺍﻟﺒﺤﺙ ﻋﻥ ﺘﺄﺜﻴﺭ ﺜﻼﺜﺔ ﺃﻨﻭﺍﻉ ﻤـﻥ ﺠـﻨﺱ Heliotropium ﻋﻠﻰ ﻨﻅﺎﻡ ﺤﻴﺎﺓ ﺍﻟﺠﺭﺍﺩ ﺍﻟﺼﺤﺭﺍﻭﻱ ﺍﻻﻨﻔﺭﺍﺩﻱ .ﻭﻴﻌﺘﺒﺭ ﻫﺫﺍ ﺍﻟﺠﻨﺱ ﻤﻥ ﺃﻫﻡ ﺃﺠﻨـﺎﺱ ﺃﻟﻨﺒﺎﺘﺎﺕ ﻓﻲ ﻤﻨﻁﻘﺔ ﺍﻟﺒﺤﺭ ﺃﻷﺤﻤﺭ .ﻭﻴﻌﺘﺒﺭ ﺍﻟﺒﻌﺽ ﻤﻔﺘﺎﺡ ﻟﺘﻭﺍﺠﺩ ﺃﻟﺠﺭﺍﺩ ﺒﺎﻟﻤﻨﻁﻘـﺔ. ﺘﻭﺠﺩ ﻤﻨﻪ ﺃﻜﺜﺭ ﻤﻥ ﺴﺘﺔ ﺃﻨﻭﺍﻉ ﺍﺴﺘﺨﺩﻤﺕ ﺜﻼﺜﺔ ﻤﻨﻬﺎ ﻓﻲ ﻫﺫﻩ ﺃﻟﺩﺭﺍﺴﺔ ﻭﻫﻲ ﺃﻷﻜﺜﺭ ﺘﻭﺍﺠﺩﺍ ﻓﻲ ﻤﻨﺎﻁﻕ ﺍﻟﺘﻭﺍﻟـﺩ ﻭﻫـﻲ H. ovalifolium, H. arabianense, H. . lignosum ﺃﺠﺭﻴﺕ ﺠﻤﻴﻊ ﺍﻟﺘﺠﺎﺭﺏ ﺒﺎﻟﻤﺭﻜﺯ ﺍﻟﺩﻭﻟﻲ ﻟﻔـﺴﻴﻭﻟﻭﺠﻴﺎ ﻭﺒﻴﺌـﺔ ﺍﻟﺤـﺸﺭﺍﺕ ICIPE ﺒﺭﻨﺎﻤﺞ ﺍﻟﺠﺭﺍﺩ ﺍﻟﺼﺤﺭﺍﻭﻱ ،ﻤﺤﻁﺔ ﺒﻭﺭ ﺘﺴﻭﺩﺍﻥ .ﻓﻲ ﺍﻟﻔﺘﺭﺓ ﻤـﺎﺒﻴﻥ ٢٠٠٠/١٩٩٩ – .٢٠٠١/٢٠٠٠ﺠﻤﻌﺕ ﺍﻟﻨﺒﺎﺘﺎﺕ ﺍﻟﻤﺴﺘﺨﺩﻤﺔ ﻓﻲ ﺍﻟﺘﺠﺭﺒﺔ ﻤﻥ ﻤﻨﻁﻘﺔ ﺴـﻠﻭﻡ ٣٠ ، ﻜﻴﻠﻭ ﻤﺘﺭ ﺠﻨﻭﺏ ﻏﺭﺏ ﺒﻭﺭ ﺘﺴﻭﺩﺍﻥ ﻭﺍﺴﺘﺨﺩﻡ ﺍﻟﺠﺭﺍﺩ ﺍﻻﻨﻔﺭﺍﺩﻱ ﻤﻥ ﻤﺯﺍﺭﻉ ﺍﻟﺘﺭﺒﻴﺔ ﺍﻟﺨﺎﺼﺔ ﺒﺎﻟﻤﺭﻜﺯ .ﺩﺭﺱ ﺘﺄﺜﻴﺭ ﺍﻟﺜﻼﺜﺔ ﺃﻨﻭﺍﻉ ﻋﻠﻰ ﻨﻅﻡ ﺤﻴﺎﺓ ﺍﻟﺠـﺭﺍﺩ ﻤـﻊ ﻤﺘﺎﺒﻌـﺔ ﺍﻟﺘﻁﻭﺭ ،ﺍﻟﻭﺯﻥ ،ﻨﺴﺒﺔ ﺍﻟﺘﻐﺫﻴﺔ ،ﺍﻟﻨﻀﺞ ﺍﻟﺠﻨﺴﻲ ﻭﺍﻟﻘﺩﺭﺓ ﻋﻠﻰ ﺍﻟﺒﻘﺎﺀ .ﻜﺫﻟﻙ ﺩﺭﺍﺴـﺔ ﺃﺜﺭﻫﺎ ﻋﻠﻲ ﻗﺩﺭﺓ ﺍﻹﻨﺎﺙ ﻋﻠﻰ ﻭﻀﻊ ﺍﻟﺒﻴﺽ ﻭﻤﺩﻯ ﺘﻁﻭﺭ ﺍﻟﺒﻴﺽ ﺍﻟﻨﺎﺘﺞ ﻋﻨﻬﺎ .ﻜﻤـﺎ ﺘﻤﺕ ﺩﺭﺍﺴﺔ ﻤﻀﺎﺩﺍﺕ ﺍﻟﺘﻐﺫﻴﺔ ﻟﻸﻨﻭﺍﻉ ﺍﻟﺜﻼﺜﺔ ﺒﻁﺭﻴﻘﺘﻴﻥ ،ﺍﻷﻭﻟﻰ ﺒﻭﻀﻊ ﺍﻟﺠﺭﺍﺩ ﻓﻲ ﺨﻼﻴﺎ ﺃﻭ ﺃﻗﻔﺎﺹ ﺒﻬﺎ ﺍﻟﺜﻼﺜﺔ ﺃﻨﻭﺍﻉ ﻤﻌﺎ ﻭﻤﻌﺭﻓﺔ ﻤﺩﻯ ﺘﻔﻀﻴﻠﻬﺎ ﻟﻜل ﻨﻭﻉ .ﺃﻤﺎ ﺍﻟﺜﺎﻨﻴـﺔ ﺒﺎﺴﺘﺨﺩﺍﻡ ﻤﺴﺘﺨﻠﺹ ﻋﺼﻴﺭﻱ ﺜﻡ ﻏﻤﺭ ﺃﻭﺭﺍﻕ ﺍﻟﺘﺭﺸﻴﺢ ﻓﻲ ﺫﻟﻙ ﺍﻟﻤﺴﺘﺨﻠﺹ ﻭﺘﺠﻔﻴﻔﻬﺎ ﺜﻡ ﻋﺭﻀﻬﺎ ﻋﻠﻰ ﺍﻟﺤﺸﺭﺍﺕ ﺒﻁﺭﻕ ﻤﺨﺘﻠﻔﺔ. ﻜﻤﺎ ﺘﻤﺕ ﺩﺭﺍﺴﺔ ﻤﺩﻯ ﺍﻨﺠﺫﺍﺏ ﺍﻟﻁﻭﺭ ﺍﻟﺨﺎﻤﺱ ﻟﺭﺍﺌﺤﺔ ﺍﻟﻨﺒﺎﺘﺎﺕ ﺍﻟﻤﺤﻤﻭﻟﺔ ﻤﻊ ﺘﻴـﺎﺭ ﺍﻟﻬﻭﺍﺀ ﻓﻲ ﻗﻔﺹ ﺃﻋﺩ ﻟﺫﻟﻙ. ﻤﻥ ﺍﻟﻨﺘﺎﺌﺞ ﺍﻟﻤﺘﺤﺼل ﻋﻠﻴﻬﺎ ﻟﻭﺤﻅ ﺃﻥ ﺃﻁﻭﺍﺭ ﺍﻟﺠﺭﺍﺩ ﺍﻻﻨﻔﺭﺍﺩﻱ ﺘﻜﻤل ﺩﻭﺭﺓ ﺤﻴﺎﺘﻬـﺎ ﺒﺼﻭﺭﺓ ﺤﺴﻨﺔ ﻓﻲ ﻨﻭﻋﻴﻥ ﻤﻥ ﺍﻟﻘﺭﻴﺭﺓ ﻫﻤﺎ. H. ovalifolium, H. arabianense ﺒﻴﻨﻤﺎ ﻻ ﺘﺘﻡ ﺩﻭﺭﺓ ﺤﻴﺎﺘﻬﺎ ﻭﺍﻥ ﺃﻜﻤﻠﺕ ﺘﻤﻭﺕ ﺍﻷﻓﺭﺍﺩ ﻓﻲ ﺍﻟﺘﺠﻨﺢ ﺃﻭ ﺒﻌﺩ ﻤﺩﺓ ﺃﻗـﺼﺎﻫﺎ ﻴﻭﻤﻴﻥ ﻋﻠﻰ ﺃﻟﻨﻭﻉ . H. lignosumﺃﻭﺯﺍﻥ ﺍﻷﻁﻭﺍﺭ ﻻ ﺘﺘﺄﺜﺭ ﺘﺄﺜﺭﺍ ﻭﺍﻀﺤﺎ ﻤﻥ ﻨﻭﻉ ﻵﺨﺭ .ﻨﺴﺒﺔ ﺍﻷﻜل ﺍﻟﻤﺴﺘﻬﻠﻙ ﻴﺯﻴﺩ ﻋﻠـﻰ H. ovalifolium, H. arabianense ﺒﻴﻨﻤﺎ ﻴﻘل ﻋﻠﻲ H. lignosum.ﺍﻷﻁﻭﺍﺭ ﺍﻟﻤﺠﻨﺤﺔ ﺘـﺼل ﻟﻠﻁـﻭﺭ ﺍﻟﺒـﺎﻟﻎ ﻋﻠـﻰ ﺍﻟﻨﻭﻋﻴﻥ ﺍﻷﻭﻟﻴﻥ ﻭﻟﻜﻥ ﺒﻌﺩ ﻓﺘﺭﺓ ﺯﻤﻨﻴﺔ ﻁﻭﻴﻠﺔ ﻭﺘﺼل ﺍﻟﺫﻜﻭﺭ ﻟﻠﻁﻭﺭ ﺍﻟﺒـﺎﻟﻎ ﻗﺒـل ﺍﻹﻨﺎﺙ .ﻜﺫﻟﻙ ﺍﻟﻨﻭﻋﻴﻥ ﺍﻟﺴﺎﺒﻘﻴﻥ ﺘﺄﺜﻴﺭﻫﻤﺎ ﻴﻜﻭﻥ ﺒﻨﻔﺱ ﺍﻟﻤـﺴﺘﻭﻯ ﻋﻠـﻰ ﺍﻟﺨـﺼﻭﺒﺔ ﻭﺘﻁﻭﺭ ﺍﻟﺒﻴﺽ ﺍﻟﻨﺎﺘﺞ .ﻭﻟﻜﻥ ﺒﻌﺩ ﻓﺘﺭﺓ ﻁﻭﻴﻠﺔ ﻤﻥ ﺒﻠﻭﻍ ﺍﻟﻁﻭﺭ ﺍﻟﺴﺎﻭﻱ ﻜﻤﺎ ﺃﻥ ﻨﺴﺒﺔ ﻭﻀﻊ ﺍﻟﺒﻴﺽ ﻗﻠﻴﻠﺔ ﻤﻘﺎﺭﻨﺔ ﻤﻊ ﺍﻟﺴﻠﻭﻙ ﺍﻟﻁﺒﻴﻌﻲ ﻟﻠﺠﺭﺍﺩ ﺍﻻﻨﻔﺭﺍﺩﻱ. ﻭﺠﺩ ﺃﻥ ﺃﻟﻌﻤﺭ ﺍﻟﻜﺎﻤل ﻓﻲ ﻫﺫﻴﻥ ﺃﻟﻨﻭﻋﻴﻥ ﻴﻁﻭل ﻭﻴﺼل ﻟﺤﻭﺍﻟﻲ ﺴﺘﺔ ﺍﺸﻬﺭ ﺃﻭ ﺃﻜﺜـﺭ ﺒﻴﻨﻤﺎ ﻴﻘﺼﺭ ﺒﺩﺭﺠﺔ ﻭﺍﻀﺤﺔ ﻋﻠﻰ ﺍﻟﻨﻭﻉ H. lignosum ﻤﻥ ﺘﺠﺎﺭﺏ ﻤﻀﺎﺩﺍﺕ ﺍﻟﺘﻐﺫﻴﺔ ﻴﺘﻀﺢ ﺃﻥ ﺃﻁﻭﺍﺭ ﺍﻟﺠﺭﺍﺩ ﺍﻻﻨﻔﺭﺍﺩﻱ ﺘﺘﻐـﺫﻯ ﻭﺘﻔـﻀل ﺍﻟﻨﻭﻋﻴﻥ H . ovalifolium, H. arabianenseﺒﻴﻨﻤﺎ ﺘﺘﻐﺫﻯ ﻋﻠﻰ ﻤﺴﺎﺤﺔ ﻭﺍﺴﻌﺔ ﻤﻥ ﺃﻭﺭﺍﻕ ﺍﻟﺘﺭﺸﻴﺢ ﺍﻟﻤﻐﻤﻭﺭﺓ ﻓﻲ ﺍﻟﻤﺴﺘﺨﻠﺹ ﺃﻟﻌـﺼﻴﺭﻱ ﻟﻠﻨـﻭﻉH. lignosum ﻭﺘﺘﻐﺫﻱ ﻋﻠﻰ ﻤﺴﺎﺤﺎﺕ ﻀﻴﻘﺔ ﺠﺩﺍ ﻤﻥ ﺍﻟﻨﻭﻋﻴﻥ ﺍﻵﺨﺭﻴﻥ .ﻤﻥ ﻫﻨﺎ ﻴﺘﻀﺢ ﺃﻥ ﻫـﺫﺍ ﺍﻟﻨﻭﻉ ﻴﺤﺘﻭﻱ ﻋﻠﻰ ﻤﻭﺍﺩ ﻁﻴﺎﺭﺓ ﺫﺍﺕ ﺭﺍﺌﺤﺔ ﻤﻤﻴﺯﺓ ﺘﺅﺩﻱ ﺇﻟﻰ ﻨﻔﻭﺭ ﺍﻟﺠـﺭﺍﺩ ﻤﻨـﻪ ﻭﻋﻨﺩﻤﺎ ﺘﻔﻘﺩ ﻫﺫﻩ ﺍﻟﻤﻭﺍﺩ ﺒﺎﻟﺘﺠﻔﻴﻑ ﻓﺎﻥ ﺃﻓﺭﺍﺩ ﺍﻟﺠﺭﺍﺩ ﺘﻔﻀﻠﻬﺎ ﻋﻠﻰ ﺍﻟﻨﻭﻋﻴﻥ ﺍﻟﺴﺎﺒﻘﻴﻥ. ﻜﺫﻟﻙ ﻴﻤﻜﻥ ﺍﻟﻘﻭل ﺒﺎﻥ ﻫﻨﺎﻟﻙ ﺒﻌﺽ ﺍﻟﻤﻭﺍﺩ ﺍﻟﺠﺎﺫﺒﺔ ﻓﻲ ﺍﻟﻨﻭﻋﻴﻥ H. ovalifolium, H arabianense ﺘﻔﻘﺩ ﺒﺎﻟﺘﺠﻔﻴﻑ .ﻭﺒﻬﺫﺍ ﻴﻤﻜﻥ ﺍﻻﺴﺘﻔﺎﺩﺓ ﻤﻥ ﺍﻟﻨﻭﻉ H.lignosum,ﻜﻤـﻭﺭﺩ ﻟﻤـﻭﺍﺩ ﻁﺎﺭﺩﺓ ﺘﺴﺘﺨﺩﻡ ﻓﻲ ﻋﻤﻠﻴﺎﺕ ﺍﻟﻤﻜﺎﻓﺤﺔ. ﻜﺫﻟﻙ ﻭﺠﺩ ﺃﻥ ﺍﻨﺠﺫﺍﺏ ﺃﻓﺭﺍﺩ ﺍﻟﺠﺭﺍﺩ ﻟﺭﺍﺌﺤﺔ H.lignosumﻴﻜﻭﻥ ﺒﻁﻴﺌﺎ ،ﺤﻴـﺙ ﺃﻨﻬﺎ ﺘﺄﺨﺫ ﻓﺘﺭﺓ ﺭﺍﺤﺔ ﻁﻭﻴﻠﺔ ﺜﻡ ﺒﻌﺩ ﺫﻟﻙ ﺘﺘﺭﺍﺠﻊ ﻭﺘﻐﻴﺭ ﺍﺘﺠﺎﻫﻬﺎ ﻤﺎﻋﺩﺍ ﺒﻌﺽ ﺍﻷﻓﺭﺍﺩ ﺍﻟﺘﻲ ﺘﻤﻜﻨﺕ ﺃﻭ ﻗﺎﺭﺒﺕ ﻤﻥ ﺍﻟﻭﺼﻭل ﻟﻠﻨﺒﺎﺕ ﻭﻟﻜﻥ ﺩﻭﻥ ﺘﻐﺫﻴﺘﻬﺎ ﻋﻠﻴﻪ .ﺒﻴﻨﻤﺎ ﺍﻻﻨﺠﺫﺍﺏ ﻜﺎﻥ ﻭﺍﻀﺤﺎ ﻟﻠﻨﻭﻋﻴﻥ ﺍﻵﺨﺭﻴﻥ ،ﺤﻴﺙ ﺘﻤﻜﻨﺕ ﺍﻷﻓﺭﺍﺩ ﻤﻥ ﺍﻟﻭﺼﻭل ﻟﻠﻨﺒﺎﺕ ﻓﻲ ﻓﺘـﺭﺓ ﺯﻤﻨﻴﺔ ﻭﺠﻴﺯﺓ .ﺃﻤﺎ ﺴﻠﻭﻜﻴﺎﺕ ﺍﻷﻓﺭﺍﺩ ﻤﻥ ﺘﺤﺭﻴﻙ ﻗﺭﻭﻥ ﺍﻻﺴﺘﺸﻌﺎﺭ ﻭﺍﻟﺤﺭﻜـﺔ ﻓـﻲ ﺍﺘﺠﺎﻫﺎﺕ ﻤﺨﺘﻠﻔﺔ ،ﻻ ﻴﻭﺠﺩ ﺍﺨﺘﻼﻑ ﻜﺒﻴﺭ ﺒﻴﻥ ﺍﻟﺜﻼﺜﺔ ﺃﻨﻭﺍﻉ. ﻤﻥ ﻫﺫﻩ ﺍﻟﺩﺭﺍﺴﺔ ﻴﺘﻀﺢ ﺃﻥ ﺍﻟﻨﻭﻋﻴﻥ H. ovalifolium, H arabianenseﻤـﻥ ﺃﻫﻡ ﺍﻷﻨﻭﺍﻉ ﺍﻟﺘﻲ ﻴﻤﻜﻥ ﺍﻻﺴﺘﻔﺎﺩﺓ ﻤﻨﻬﺎ ﻓﻲ ﺇﺠﺭﺍﺀ ﻋﻤﻠﻴﺔ ﺍﻟﻤﺴﺢ ﻟﻠﺠﺭﺍﺩ .ﻭﻫﺫﺍ ﻴﺅﺩﻱ ﻟﺘﻭﻓﻴﺭ ﺍﻟﻭﻗﺕ ﻭﺍﻟﺠﻬﺩ ﺒﺼﻭﺭﺓ ﻜﺒﻴﺭﺓ .ﻜﻤﺎ ﺃﻥ ﺘﻭﺍﺠﺩ ﻫﺫﻩ ﺍﻷﻨﻭﺍﻉ ﻭﺍﻨﺘﺸﺎﺭﻫﺎ ﺒﺼﻭﺭﺓ ﻭﺍﺴﻌﺔ ﻴﻌﺩ ﺴﺒﺒﺎ ﻭﺍﻀﺤﺎ ﻟﺘﻭﻗﻊ ﺇﻤﻜﺎﻨﻴﺔ ﺤﺩﻭﺙ ﺍﻟﻁﻭﺭ ﺍﻟﺠﻤـﺎﻋﻲ ﻭﺒﺎﻟﺘـﺎﻟﻲ ﺘﻜـﻭﻥ ﺍﻷﺴﺭﺍﺏ .ﻭﺫﻟﻙ ﻴﺴﺎﻋﺩ ﻓﻲ ﻭﻀﻊ ﺍﻟﺘﺩﺍﺒﻴﺭ ﺍﻟﻼﺯﻤﺔ ﻟﻠﻭﻗﺎﻴﺔ ﻤﻨﻬﺎ .ﻜﻤﺎ ﻴﻤﻜﻥ ﺍﺴﺘﺨﺩﺍﻡ ﺍﻟﻨﻭﻋﻴﻥ ﺍﻷﻭﻟﻴﻥ ﻜﻤﻭﺍﺩ ﺠﺎﺫﺒﺔ ﻓﻲ ﻋﻤﻠﻴﺎﺕ ﺍﻟﻤﻜﺎﻓﺤﺔ ﻋﻥ ﻁﺭﻴـﻕ ﺍﻟﻁﻌـﻭﻡ ﺍﻟـﺴﺎﻤﺔ ﻭﺍﺴﺘﺨﺩﺍﻡ ﺍﻟﻨﻭﻉ ﺍﻟﺜﺎﻟﺙ ﻜﻤﻭﺭﺩ ﻟﻠﻤﻭﺍﺩ ﺍﻟﻁﺎﺭﺩﺓ. INTRODCUTION Locusts belong to a large group of insects commonly called grass hoppers which belong to the super family Acridoidea, and the most important locusts are all in the family Acrididae (ALRC, ١٩٦٦.) The locusts are counted among the major pests in the Sahel zone of Africa.The desert locust, Schistocerca gregaria (Forskål), is one of the oldest insects known in history. Today, the desert locust is still occupying the whole of Arab world north Africa from west to east, including the Arabian peninsula, northern India, and southern central Asia. During the major plagues, the invasion area covers about ٢٩ million kilometres square, which is equivalent to one fifth of the earth surface. During the recession periods, the desert locust activities concentrate in the arid and semi arid areas covering about ١٦ million Km² (Meinzingen, ١٩٩٣). The desert locust has inflicted incredible losses, both in terms of money and crops to most of the countries it has invaded. One ton of Locusts (a very small part of an average swarm) eats much food in one day as ١٠ elephants or ٢٥ camels or ٢٥٠ people. (ALRC, ١٩٦٦). During (١٩٨٦-١٩٨٩), a desert locust plague occurred requiring mobilization of resources costing some US$ ٣٠٠ million and the application of some ١٥ million litters of pesticides over more than ١٧ million hectares In ١٩٩٢-١٩٩٤ yet another major upsurge occurred and about US$ ٤٥million was spent on chemical control over an area of ٤ million hectare. (Eltigani, ١٩٩٦). The most important feature of the desert locust is its ability to interconvert between two morphologically, physiologically and behaviourally distinct phases, the solitaria and the gregaria. During the solitarious phase, which is characterized by low population densities, the insect lives in areas that are not, or only minimally, used for agriculture. These so called recession areas, which have an average annual precipitation of no more than ٢٠٠ mm, are distributed across several Sahel countries. The solitarious phase the Desert Locust does not venture out of its original habitat. It is integrated into the food chain, constituting a useful component of the biotope. It does not have any injurious effect on agricultural production there (Herok, ١٩٩٥). The importance of solitary phase stems from its transformation from the solitarious to the gregarious phase. This is induced by a complex system of changing environmental conditions that has not yet been fully illuminated (Chandra, ١٩٩٠). The major locust out breaks are generally associated with improved rains and vegetation after a relatively long dry – weather spell. They begin with the migration of solitary – living locusts into areas where sufficient rain has recently fallen. Mating and egg – laying then occur. A sequence of appropriately timed rains in the winter and summer breeding areas, coinciding with the appearance of a new locust generations, may lead to high concentration and multiplication rates of the insect, which are then accompanied by gregarisation and swarming (Hassanali and Mahamat, ١٩٩١). Johnston (١٩٢٦) discovered in February ١٩٢٦ that the Red Sea coast of the Sudan was an area where S. gregaria could transform from the solitary to the gregarious phase. The Red Sea area is one of the habitats of solitary locusts. It is one of semi – permanent convergence of winter and comes under the influence of the Inter – Tropical Convergence Zone in summer. Most rains in the Red Sea area occur in winter, but there is also some rainfall in summer, in the south more than in the north. The prolonged rainfall in the south is probably one reason why the Red Sea coastal areas have locust populations very frequently. It is also rich with different species of desert plants, such as Heliotropium spp, Diptergim spp and Aerva spp. The Desert Locust is polyphagous (Evans and Bell, ١٩٧٩), especially in the gregarious phase. However, solitarious populations in semi – arid habitats have a limited choice of food plants (Kennedy ١٩٦٢). Despite the polyphagous nature of the species a hierarchy of preference exists. Some plants are preferred for sheltering and oviposition, like Heliotropium and Millet (El Bashir and Abd El Rahman, ١٩٩١; Bashir and Abd El Rahman, ICIPE report ١٩٩٥; Bashir, et al., ٢٠٠٠). The biology of locust is influenced by the type of food available in nature (Rao, ١٩٤٢ and ١٩٦٠; Uvarov, ١٩٦٦; Bhatia and A hlwalia, ١٩٦٧ and Ibrahim, ١٩٧٢) Recently, interest in the feeding activities has been prompted by the desire to understand the basic processes of host – plant selection by grasshoppers, and through this understanding to bring about more effective methods of crop and rangeland protection. Some of the plants with which solitarious Desert Locust are often associated in the Red Sea area are Heliotropium spp. Since the Red Sea area has been identified as one of the concentration areas where many workers in the Desert Locust problem feel that preventive control or upsurge suppression should be focused on (Van Huis ١٩٩٤), it will be very important to know the effect of the preferred host plants (Heliotropium spp) on the life system of the solitary Desert Locust. This study investigates the effect of (Heliotropium ovalifolium, Heliotropium lignosum and Heliotropium arabianense) on the life system of the solitary Desert Locust. There are more than six species of Heliotropium in the Red Sea area, but these three species are found frequently in the locust habitat. An advantage of this type of testing is that it is possible to know the preferred species, which will make the survey more limited because the surveyor only has to look for the common species. This will save a lot of money, effort and time. Also it helps to suggest and detect any gregarisation, which may happen. The locust must be controlled before they come together because it may be too late to stop the damage once they swarm and migrate. LITERATURE REVIEW ١ Host plant (Heliotropium spp) Heliotropium spp are herb or shrub plants. The flowers are yellow white, small, in leafless (at least in the upper part) scorpionid inflorescence, often ١sided cumes. Calyx ٥-parted, either persistent or deciduous with the fruit; corolla funnel shaped or salver – shaped with ٥-lobed limb. Style simple, terminal inserted on the top of the ovary. Stigma with broad base surrounded by a fleshy rim ovary at maturity breaking up into ٤ distinct drouplet, these rarely connate in pairs (Migahid, ١٩٧٨). Heliotropim ovalifolium Forsk. Agrey – hispid annual, herbaceous from a frutescent base, with elliptical-lanceolate, long petiole leaves and minute, bracteate flowers in narrow cymes, gets blackish-grey when dry. Heliotropium arbianense Fres (Hassan, ١٩٧٤), is prostrate, erect greenish white shrub lets, ٢٠ – ٤٠ cm. Stem hairy, leaves alternate, ovate-oblong densely hairy ١١٫٥cm long to a petiole leaf -apex acutish and margin wavy. Cymes ٥-١٠cm long, corolla ٨mm long, nearly twice as long as calyx flowers white. Nut lets four in number. Reported in Red Sea area between sea level and ٤٠٠٠ft. (Hassan, ١٩٧٤; Migahid, ١٩٧٨). Heliotropium lignosum Schweinf. Ex Bunge: Fruticose shrubby plant with short, woody ascending stems, densely clothed with whitish hairs. Leaves small, sessile, lanceolate, with short revolute margin, and densely and shortly bristly on both surfaces. Spikes short, dense, ٣-٦-flowered. Nut lets hispid (Migahid, ١٩٧٨). ٢ The locust ٢. ١ Identification According to COPR (١٩٨٢), Uvarov and Launois explain that Schistocerca gregaria (Forskål ١٧٧٥) has prosternal tubercle straight, blunt and slightly inclined backwards. Male subgenital plate bilobate, cerciflat and blunt. Tegmina marked with large irregular spots. Pronotum not crested, more constricted and saddle-Shaped in the gregarious phase. Adult coloration in the solitarious phase is sandy, gray or brownish, often with light. Coloured median stripe on pronotum. On the other hand the immature gregarious phase are pink, and the mature ones are bright yellow. ٢. ٢ Desert Locust Classification Schistocerca gregaria belongs to the sub family Acridnae of family Acrididea. Family Acrididea belong to the sub order Callifera of the order Orthoptera. Seven species are identified in the genus Schistocerca one of them is gregaria. The species gregaria has two sub species, gregaria (Forskål) and flaviwentris (Paster and Smolikowski, ١٩٨٩). ٢. ٣ Distribution The invasion areas of Schistoceca gregaria include mainly the semi desert and short grass Savannah, and is capable of invading the whole of N. Africa, Southern and western parts of Iberian Peninsula, Sardinia, the Azores, Madeira, Canary Is., Capverde Is., W.Africa, North of Equatorial, rain forest east words to N. E. Zaire and to S.Tanzania on the Indian Ocean, the Arabian Peninsula, Socotra, the middle east north to E.Turkey, Cyprus, the southern republics of the USSR, Iran, Afghanistan, the Indian sub-continent south to ١٠° N and east to the Burmes border (Régniér,١٩٣١). In the Sudan, Schistocerca gregaria has been recorded from the Red Sea littoral and along the central parts of the country. The Sudan lies at the heart of both the invasion and recession areas. It is mainly a summer breeding area, though breeding may take place in winter at the Red Sea littoral. However the country is subjected to infestation as far south as latitude ١٢° N (Maxwell-Darling, ١٩٣٦; Walloff, ١٩٦٦; Shumtterer, ١٩٦٩ and Karar, ١٩٧٢). According to COPR (١٩٨٢), Holst, Uvarov, Waloff, Rainey , Weidner, Dirsh and Krauss mentioned that the Desert locust has been recorded in the E. Atlantic, St Helena, British Is., possibly Denmark, Mediterranean region (Yugoslavia, Greece), Red Sea, Gulf of Aden, Arabia sea, Persian Gulf and Mozambique. Also there are records of individuals carried by ships from Madagascar to Srilanka and Australia. ٢. ٤ Locust Habitats On locust habitats according to Mulkern (١٩٦٦), a number of investigators found that distribution was related to vegetation composition as movement of individuals was much less in areas of favorable host plants than in area of un favorable host plants. The Red Sea region is mainly a winter breeding area, but spring breeding is believed to take place on the mountain range and summer breeding on the western slopes and plains descending from the plateau twoards the hinterland. The area is part of the central region considered as the primary source of up surges and potential plagues. The variety of host plants available for any species of grasshopper is limited because their restriction to distinctive habitats with associated vegetation has long been established (Cantrall, ١٩٤٣; Baccetti, ١٩٦٣). According to Mulkern, ١٩٦٦ many investigators came to the conclusion that food selection was primarily the consequence of habitat selection. The same author mentioned that distribution was related to vegetation composition as movement of individuals was much less in area of favorable host plants He suggested that this factor accounted for the concentration of grasshopper species in the favorable area. Anderson (١٩٦٤), also concluded that vegetation had definite influence on distribution as grasshoppers were never found in areas which did not include preferred host plants and the occupancy of this area was influenced by the physical structure of the vegetation. ٢. ٤. ١ Habitats of Solitarious Desert Locust Solitarious locusts live in fewer varieties of habitats than gregarious swarms. In general they occur in open sandy steppes with fewer or no trees. They are not usually present in places where the trees are on average less than ١٠ m apart. The vegetation generally consists of perennial bushes and herbs less than a meter high and annual plants which come up after rain. The habitats of solitarious locusts in the different regions are Pakistan, Iran and India (during summer) where the main food is Tribulus alatus and Aerva persica. In the rainy season parts of southern Arabia become suitable habitats for Desert Locust. Small concentrations can be found in patches of such plants as Chrozophora oblongifolia, Tribulus sp, Dipterygium glaucum and Aerva persica. The southern Red Sea area is one of semi- permanent convergence of winds in winter and comes under the influence of the ITCZ (Inter- Tropical Convergence Zone) in summer. This habitat is always cultivated with Pennisetum (dukhn). Also there are many plants like Heliotropium and Diptergium. In West Africa the Locust habitats are associated with the Saharan high lands and with the open steppes surrounding the Sahara. Schouwia thebaica, Tribullus alatus and Hyoscyamus muticus grow in this habitat (Steedman, ١٩٨٨). ٢. ٥ Economic importance Desert locust hoppers eat about their own weight of fresh vegetation each day, the amount increases from about ٢٠mg at the beginning of the first instar to about ١٫٥ g in the middle of the fifth instar (COPR, ١٩٨٢). Migrating immature adults need to eat at least their own weight (٢-٣g) of fresh vegetation each day, and possibly three times as much (Weis-Fogh, ١٩٥٢). Desert Locusts feed on a very wide range of plants. They also inflict considerable damage by actually feeding, and breaking branches with their weight when densely settled. Because swarms are so mobile there is great variation in the amount of damage caused seasonally, from country to country and from region to region. The greatest recorded crop losses occur when young migrating swarms of immature adults reach cultivated areas. Examples of crop losses caused by Desert Locust in Libya in ١٩٤٤ were ٧٫٠٠٠٫٠٠٠ tones grapevines/; ١٩٪ of total vine cultivated (ALRC, ١٩٦٦). In the Sudan according to ALRC (١٩٦٦), the value of losses was £ ٣٩٠،٠٠٠ in ١٩٤٤ and ٥٥،٠٠٠ tons of grain in ١٩٥٤. An area of ٣٫٧ million hectare were infested during ١٩٨٨ plague (Abass and Barsi, ١٩٩١). Also for the ٩year period ١٩٤٩-١٩٥٧ the FAO estimate of the total value of crop damage in ١٢ invaded countries was £ ١٥ million (FAO ١٩٥٨). During ١٩٨٦-١٩٨٩ a desert locust plaque occurred and required mobilization of resources costing some US $ ٣٠٠ million and the application of some ١٥ million litters of pesticides over more than ١٧ million hectares some of which were in ecologically sensitive areas. In ١٩٩٢-١٩٩٤ yet another major upsurge occurred and about US $٤٥ million was spend on chemical control over an area of ٤ million hectares. Also swarms were reported in the central region in Saudi Arabia, Somalia, Mali, Mauritania, Chad, Sudan and Eritrea in ١٩٩٥ (Eltigani, ١٩٩٦). ٢. ٦ Life Cycle The life cycle comprises three stages, egg, hopper and adult. Immature adults may become sexually mature in few weeks or few months, according to environmental conditions. The incidence of maturation can be recognized by the disappearance of the pink colour from the hind tibia (Steedman ١٩٩٠). Males mature before females, but oviposition usually commences within about ٢days of copulation. Copulation some times occurs with female which appear not to be fully mature, that is, females in which the eggs are not fully developed. Once eggs are fully developed in side, the female can only keep them for about ٣days; then they may be oviposited. (Steedman, ١٩٩٠). Husain and Ahmed (١٩٣٦) recorded that a single female lays ٩ egg pods in the laboratory; while Hunter –Jones (١٩٥٨) reported an instance of ٢٥ pods laid by one female in the laboratory. On the other side according to Eltigani (١٩٩٦) Ripper and George, found that females lay an average of ٣ egg pods at an average interval of one week, minimum ٣ days maximum about ١٤ days. The numbers of eggs in pods of locust in swarms vary from ٢٠-to over ١٠٠. (Steedman, ١٩٩٠). However Ashall and Ellis (١٩٦٢), reported that the number of eggs per pod ranged from ٣٦ to ١٢٨. Females reared in the laboratory may lay from ١٠ to ١٤٠ eggs per pod (Norries, ١٩٥٢). On the other hand, Meinzingen (١٩٩٣) explained that solitary female mostley lays ٣ – ٤ pods, each pod containing ١٠٠ – ١٦٠ eggs, with egg pods laid at interval of ٧ – ١٠ days while gregarious female usually laid ٢ – ٣ egg pods each with about ٦٠ – ٨٠ eggs. Hunter- Jones (١٩٦٦), Uvarov (١٩٦٦), Waloff (١٩٦٦) and Wardhugh, et al., (١٩٦٩), mentioned that provided there is adequate soil moisture the rate at which eggs develop varies according to the soil temperature. Steedman (١٩٩٠) and Meinzingen (١٩٩٣) recorded that the egg incubation period ranges ١٢-٢١ days depending on the temperature. The period for development decreases from about ٧٠ days to ١٠-١٢ days, when the temperature ranged between ١٥°C to ٣٥°C; above ٣٥°C the period no longer decreases and high mortality occurs (COPR, ١٩٨٢). Moulting usually occurs five times during the development of the gregarious desert locust and five or six in solitarious individuals. The extra instars occurring between the third and the fourth. Each moult is indicated by a marked stripe on the eye. The rate of development depends on temperature. It varies from about ٢٢days under ‘hot’ conditions to over ٧٠ days under ‘cool’ condition (COPR, ١٩٨٢). The first, second, third fourth and fifth instar weights are ٣٠-٤٠, ٥٠-٨٠, ١٢٠-٢٠٠, ٥٠٠-٧٠٠ and ١٠٠٠ ١٢٠٠ mg r respectively. Also the developmental periods are ٥-٧, ٦-٨, ٧-٩, ٧-٩ and ٩-١٢ days respectively (Steedman, ١٩٩٠). The length of life of individual adults varies. Some have been kept alive in cages for over a year, but in the field they probably life between ٢٫٥ and ٥ months. Apart from accidental death the live span depends on how long they take to become sexually mature. The quicker they mature the shorter the total length of life (Steedman, ١٩٨٨). According to Eltigani (١٩٩٦), King, Uvarov and Bodenheimer were of the opinion that generally the desert locust has only one generation in the year, with a long diapause in the adult stage. While Ballard, et al., (١٩٣٢) was of the opinion that under favorable natural condition, there might be three generation in one year. ٢-٧ Behaviour Locusts are characterized by their ability to transform reversibly in a graded manner between two extreme phases, solitaria and gregaria, that differ in physiology, biochemistry, behaviour, pigmentation and morphology (Uvarov, ١٩٦٦). The Desert Locust Schistocerca gregaria is the race most sensitive to changes in population transformation from the solitarious to the gregarious phase and vice versa. This occurs rapidly and frequently (COPR, ١٩٨٢). In the solitarious phase, population densities can be extremely low (Uvarov, ١٩٧٧) and although patchy distribution of host plants may contribute to bringing the insects together, successful mate finding may depend on long – rang pheromone signals (Byer, ١٩٩١ and Hassanali and Mahamat, ١٩٩١). Rainey (١٩٦٢), Roffey and Popov, (١٩٦٨) and Uvarov, (١٩٧٧), mentioned that gregarisation is predicated on locust density which may be promoted by a variety of environmental and biotic factors, including covergent winds, habitat topologies, improved rains and distribution of food plants and oviposition sites. Some phase related traits, such as agregation behaviour (Roessingh and Simpson, ١٩٩٤ and Bouarchi et al., ١٩٩٥) and emission of the mediating aggregation pheromones (Torto et al., ١٩٩٤ and ١٩٩٦ and Deng et al., ١٩٩٦), change rapidly with density, others, such as morphometrics, take several generations (Pener, ١٩٩١ and Deng et al., ١٩٩٦). Bouarchi et al., (١٩٩٦) revealed that habitat microstructures, such as patchy distribution of food plants and perching sites, facilitated the concentration of and encounter between other wise reluctant desert locust solitarious hoppers. In time, this leads to active cohesive behaviour. This was consistent with the work of Deng et al., (١٩٩٦) which demonstrated that forced crowding of solitaria led to rapid production of the gregarious-phase aggregation pheromone. ٢. ٨ Host plant The Desert Locust is polyphagous, especially in the gregarious phase (Evan and Bell, ١٩٧٩). However, solitarious populations in semi arid habitats have limited choice of food plants (Kennedy, ١٩٦٢). Despite the polyphagous nature of the species, hierarchy of preferred host plants exists. Some plants are preferred for shelter, to oviposite close to, e.g. Heliotroium and millet (ElBashir and Abdel Rahaman ١٩٩١;Bashir and Abdel Rahaman, ICIPE report, ١٩٩٥). Also Bashir et al (٢٠٠٠) recorded that during the successive seasons and early during the rainy season, the incoming solitarious females, oviposited predominantly in the vicinity of Heliotropium species and millet seedlings. Solitarious nymphs also preferred to feed on these plants. More than six species of Heliotropium occur in the various habitats of the desert locust in the Red Sea Area. It appears that the Heliotropium in the eastern parts of the Central Zone takes the role that Shouwia pupurea (Forsk.) plays in West Africa (Ghaout, et al., ١٩٩١). ٢٫٨٫١ Host finding According to Uvarov (١٩٧٧), relative amount of grass and other plants in the crop of Schistocerca hoppers was correlated with the abundance of various plants in the habitat. Abundance being expressed in terms of the diameters of the plants. The finding of acceptable food is affected by the general behaviour pattern. For example species living mainly on the ground are more likely to feed on low plants and plant debris .The daily behaviour pattern also affects feeding, visual attraction, colour and olfactory orientation by the specific smell of particular plant, are of importance for locating the food. The attraction of Schistocerca hoppers by the smell of food plants was mentioned by Volkonsky (١٩٤٢), but without sufficient details. Experiments by Haskell et al., (١٩٦٢) in a wind tunnel proved that an air current carrying the smell of crushed grass and of a variety of odorous substances caused Schistocerca hoppers, which had been starved for ٢٤ hours and walking down wind, to reverse their direction and walk twoards the source of the odorous. This response was shown at a distance of some ٦٠ Cm. Williams (١٩٥٤), obtained no evidence of olfactory attraction in Locusta hoppers, but his experiments were inadequate for definite conclusion. Dadd (١٩٦٣) suggested that fourth - instar hoppers and adults of Schistocerca may be more able to follow odour signals than young hoppers. On the whole, if attraction to the smell of food plants exists, there is still very little evidence of its effective range and on this depends its influence on food selection in the field. Uvarov, (١٩٧٧) mentioned that once the insect is on a plant, the chemical properties of the latter appear to be examined by the antenna and palps repeatedly touching the plant. Following an examination of a plant by the palps, the insect usually takes a small bite, which is chewed, and then feeding because either continues or the insect moves away. According to Uvarov (١٩٧٧) Thomas suggests that the final selection is a matter of taste discrimination by the sensilla on the mouth –parts. Those plants, which are only nibbled, but not eaten, are rejected for their taste on chemical grounds. A well-known example is the tree Azadirachta indica that is unpalatable to Schistocerca (Rao, ١٩٦٠; Roonwal, ١٩٥٣). Another example of taste being responsible for the rejection of a normally favourite food-plant is that of Schistocerca hoppers refusing to eat Heliotropium undulatum after it had been dipped in ٥٪ salt solution for a minute and then dried (Rao ١٩٦٠). Refusal to feed on a plant after biting it, or its acceptance, led to the theory that this depended on the presence or absence of some specific substances termed phagostimulants (Goodhue, ١٩٦٣). An alternative view is that acceptance is affected by the presence of some nutrient substances, while rejection may be due to specifically repellent ones (Dadd, ١٩٦٣; Thorsteinson, ١٩٦٠). ٢-٨-٢ Factors in food selection The water content of plants is often regarded as affecting the selection. Williams (١٩٥٤), found that fresh grass (Holcus lanatus) was consumed more than dry one when both were offered in the same cage. While Isely (١٩٤٦) recorded that grasshoppers of dry habitats refused more succulent grasses in favour of the drier ones. Kaufman (١٩٦٥) also found similar preference for drier grasses in grasshopper from humid habitats. The chemical composition of plants may have major influence on selectivity by grasshoppers .The reception of chemical stimuli over distance or more than few centimeters is generally considered doubtful although experimentation in this regard is far from exhaustive (Dadd, ١٩٦٣). Plant volatiles play a significant role as cues in host selection by phytophagous insects. One group of host plant volatiles widely studied are the ‘green leaf volatiles` (GLVs) which are aldhydes and esters released when plant tissues are damaged either mechanically or by herbivory (Visser and Ave, ١٩٧٨; Visser, et al., ١٩٧٩; Dikens, et al.,١٩٩٣ and Light, et al., ١٩٩٣). Host plant recognition by grasshoppers has been examined in few studies. Air borne odours from damaged cabbage and damaged grass have been demonstrated to be attractive to the desert locust Schistocerca gregaria (Haskell, et al., ١٩٦٢; Kennedy and Moorhouse, ١٩٦٩ and Moorhouse ١٩٧١). Najagi and Torto, (١٩٩٦) found that nymphs of S. gregaria, generalist feeder, detect abroad range of GLVs in the volatiles of its host plants. However, quantitative and qualitative differences in components of the volatiles and previous exposure of the insects to the volatiles may affect their preference hierarchy for host plants in the field. It remains to be investigated what role these chemicals play in the host selection behaviour of nymphs and adults of the desert locust. No record of color being of important in attractive patterns has been made (Hjelle,١٩٦٤). Mulkern (١٩٦٦) in some preliminary trials found that grasshoppers would choose diet preparations containing commercially obtained chlorophyll powder over an identical diet without chlorophyll. It was not determined definitely whether the preference was due to the green color or to chemostimulation from chlorophyll. Dadd (١٩٦٠) reported that chlorophyll is not more effective than distilled water as a phagostimulant. The physical composition of plants texture, pubescence, turgidity, manner of growth, undoubtedly play an important part in food selection. The primary effect of the physical structure seems to be to modify feeding once the plant has been reached, although size or manner of growth may influence visual attraction. Many physical structures of plants have been mentioned as deterrents to feeding (Chapman, ١٩٥٧). ٢. ٨. ٣ Effect of food on the biology The biology of the locust is influenced by the type of food available to the insect in nature (Pfadt, ١٩٤٩; Rao, ١٩٤٢ and ١٩٦٠; Uvarov, ١٩٦٦; Bhatia and Ahlualia, ١٩٦٧ and Ibrahim, ١٩٧٢). Eltigani (١٩٩٦) recorded that under laboratory conditions, food plants have marked different effects on development, weight gain, survival, maturation, fertility, fecundity and longevity. According to him six plant species, Launaea capitata, Heliotropium undulatum, Pennisetum typhoideum, Crotalaria microphyla, Dipteryinm glauaum and Tribulus longipetallus, indused rapid growth and enhanced nymphal development, with closely synchronized moulting. It has been shown in several studies that food quality and quantity also influence insect reproduction (Jackson, et al., ١٩٧٨ and Injeyan et al., ١٩٨١). Rao (١٩٦٠) recorded that Schistocerca gregaria has different rates of development when fed on different stages of growth of the same plant. While Wardhugh et al., (١٩٦٩) showed that the development rates of S. gregaria in outdoor field cages were not significantly different when fed on eight different diets (millet, lucern, sorghum, and arafag). He investigated the incubation period of the desert locust under various conditions typical of the Tiahama and Hijaz of Saudi Arabia and found no significant difference between the development rates of hoppers fed on different species of plant. Though the result did suggest that hoppers reared on either barley or Sorghum required longer period to fledge than those reared on either millet or lucern. Also Rao (١٩٦٠) found that with the desert locust, Tribulus terresteis allowed rapid maturation while Panicum delayed it. Although the Sorghum provided to desert locust was not senescent, it seemed probable that some other factor delayed maturation. According to Mulkern (١٩٦٦), Stolyarov, and Waloff found S. gregaria survive better on some plants than on others. And Ellis, et al., (١٩٦٥), reported that the sexual maturity and moulting of S.gregaria was influenced by monoterpenoids and hormones from food plants. Variation in these substances in plants controlled the seasonal development of grasshopper. Water extract of plants was found to be essential to synthetic diets for complete development of several species of grasshoppers. However, there are striking differences among extracts from different plant species in their ability to promote growth and survival when incorporated into otherwise similar diet preparations (Mulkern, ١٩٦٦). Toy (١٩٧٣) investigated the effect of food on the development of the desert locust. He found that, the rate of development, mortality, feeding activity of nymphs and morphometrics of adults were more successful when reared on grasses (Agropron repens and Poa annua), than on other plant species like lime privet and spinach. The former (A.repens) gave well-fed mature adult, while the latter (spinach, Spinacia oleracea) gave brachypterous adults. Ba-Angood (١٩٧٤) found that the hopper development of S. gregaria at ٢٥-٣٢C° was ٣٢٫٧± ١٫٣٠ days on Pennisetum typhoideum Rich. It was ٢٧٫٩±٠٫٩٨ days on Sorgum vulgare pers. (Dura), ٣٥٫٨±٠٫٣٥ days on Medicago sativa L. (Berseem), ٣١٫٦±٠٫٣٥ days on mixed food (Cotton, Dura, and Berseem), it was٢٩٫٥± ٠٫٢٥ days. The highest survival percentage up to the adult stage was on mixed food reaching ٦٢٪, followed by ٥٨ % on Sorgum vulgare, and ٥٤٪ on Pensoutem typhodium. ٣٢ % ٠n Medicago sataiva and ١٦٪ on Gosspium barbadense. A marked high rate mortality was observed in the first hopper stage for those insects reared on Cotton and Berseem. According to Jackson et al., (١٩٧٨) food plants have markedly different effects on growth and development of the desert locust. P typhodeum, Dipterygium glacum, Tribulus longipetalus (plus T. terrestris) and (Chrozophora oblonifolia) support rapid growth and development. A pure diet of Sorghum sp, allows some hoppers to reach the adult stage in a normal period. But many are retarded. In general Pennisetum or Sorghum tended to enhance gregarious characteristics, while Dipterygium accentuated solitarious characteristics. They also reported that the reproductive capacity of these insects impaired by mono specific diet, even when it is adequate for non- reproductive growth. Bashir and Abdel Rahaman (ICIPE (International Center Of Insect Physiology and Ecology) report, ١٩٩٥) recorded that the solitarious nymphs under laboratory conditions attain sufficient weight and survive to fledgling stage on fewer plant species compared with gregaria. However, compilation and analysis of life tables data for solitaria was possible on still less number of plant species. In addition to being food source, plants play other roles in the life system of Desert Locust. Some plant species trigger the maturation process and many enhance gregarisation (Carlisle, et al., ١٩٦٥) while others inhibited gregarisation (Guichard, ١٩٥٥). In a study to evaluate the effect of moist air with fresh food, and dry air with dry food on phase characteristics Jackson, et al., (١٩٧٨) studied the effect of seven natural food plants on the phase status of the desert locust, and monitored changes in colour, morphometrics number of eye stripes and fecundity. Their result revealed that pennisetum typhoideum (Burm.f.) and Sorghum bicolor enhanced gregarious characteristics, while Dipterygium glaucum (oecn) accentuated solitary traits. MATERIALS AND METHODS The experimental food plants (Heliotropium spp) (plate ١ a, b, plate ٢ a, b, plate ٣) used in the study were naturally growing plants. They grew on seasonal rain fed flood plants, and standing near cultivated plants. They were collected from Sallom area, ٣٠ km south west of Port Sudan. Any part and age of the plants was used. All experiment were conducted inside the laboratory and carried out during ١٩٩٩ -٢٠٠١ seasons at the ICIPE field station in Port Sudan. The laboratory temperature ranged between ٢٨٫٢ ºC maximum and ٢٥٫٢ ºC minimum in summer, ٢٢٫٥ºC maximum and ١٨٫٥ºC minimum in winter. The mean relative humidity was ٣٧٫٢ % in summer and ٦٠٫٥ % in winter in season ١٩٩٩-٢٠٠٠. Whereas the laboratory temperature ranged between ٣٠٫٠ºC maximum and ٢٥٫٦ºC minimum in summer, ٢٢٫٨ºC maximum and ٢٠٫٢ºC minimum in winter. The mean relative humidity was ٤٠٫٥ in summer and ٦٩٫٣ % in winter in season ٢٠٠٠-٢٠٠١. ١ Effect of Heliotropium spp. on development, weight, maturation, longevity, survival rate and feeding rate The locusts used in the experiments were offspring of the solitary stock bred at the ICIPE station. Plate ١ a Heliotropium ovalifolium old plant. Plate ١ b Heliotropium ovalifolium young plant. Plate ٢ a Heliotropium arabianese, old plant. Plate ٢ b Heliotropium arabianese, young plant. Plat ٣ Heliotropium legnosum. First instars nymphs were collected and kept together for ٤ days, and fed on a mixture of the three species of Heliotropium (H. arabianense, H. ovalifolium and H. lignosum). The reason for keeping the hatchlings for such a period before the start of the experiment was that heavy mortality from natural causes usually occurs in the first days. Any mortality occurring during this period would have been unrelated to diet, and would have reduced the size of the population available for the study. The nymphs were then kept individually before starting the experiments because gregaraisation behaviour would occur when they are kept together more than ٢٤ hours. They were kept individually each in a separate cell of a ten-bank cage (Isolated cage), (plate ٤) The cage has the following dimensions; (٦٠ x ٢٤ x ٣٠ cm), representing the length, width and height respectively (season ١٩٩٩-٢٠٠٠). In season ٢٠٠٠-٢٠٠١ they were kept individually each in a separate cup (diameter, ١١٫٥ cm above and ٩٫٥ cm bottom), (plat ٥). The number of nymphs reared on each species was ٣٠. Each cup or cell containing the nymph was numbered. The tests on the three species were started at the same time. Every day cells and cups were cleaned and the uneaten food and faeces were removed and green fresh weighted food was provided. The uneaten food and faeces were raped with aluminium foil and put in the oven for ٢٤ hours at ٨٠ºC and weighted again to know the consumption and assimilation of food according to the following equation: Plate ٤. Solitary rearing bank cages (Season ١٩٩٩-٢٠٠٠). Plate ٥. Solitary rearing cups (Season ٢٠٠٠-٢٠٠١). In dry food = In wet food x Average dry weight / gm of each species. Consumed dry food = In dry food – (dry spill + remaining dry food). Consumed wet food = Consumed dry food x Average dry weight /gm Assimilated dry food = Consumed dry food – Dry faeces. At the same time observation on the locusts were carried out; dead locusts, moulting dates successive nymphal moults and newly emerging fledglings were recorded daily. Also locusts were weighted two days after each moult using an electric digital sensitive balance. Maturation dates were recorded, the sign of its occurrence is the yellowing of hind wings. The dead locusts were recorded daily to enable computation of the survival rate on the three species. ١. ٢ Effect of Heliotropium spp. on oviposition The number of mature solitary locusts from experiment (١) was low, therefore a new rearing was made to obtain ٢٣ pairs for each host plant species tests. The solitary nymphs were reared as in (١) where ٦٠ insects kept and fed on each species of Heliotropium. The date of maturation was recorded. The mature adults were sexed and paired in special cages (١٠ x ١٠ x ٢٤ cm), (plat ٦ a, b). When mating was recorded, then each cell was provided a metallic oviposition tube (size ١٢٫٥ x ٤٫٠ cm.), filled with sand with ١٠٪ soil moisture. The tubes were examined daily for the presence of egg pods and the tubes which contained egg pods were replaced with fresh ones, labelled and incubated in the laboratory. The Plate ٦ a, b Oviposition bank cages. (b) total number of eggs, number of hatched eggs, unhatched ones (fertile and un fertile) and the incubation period were recorded and counted once hatching was completed. Also the preoviposition, oviposition, postoviposition period, fecundity, and longevity of the females were recorded. ٢ Anti feeding experiments ٢. ١ Feeding on the three species of Heliotropium Twenty (١٠ male, ١٠ female) fifth and six solitary instar nymphs were fed on a mixture of fresh weighted plants of the three species of Heliotropium. Each nymph was kept separately in cells of the rearing cage ( plate ٤) and some in a small cage (٢٥ x ٢٥ x ٢٥) (plate ٧ a,b). The uneaten food, spill and faeces were wrapped and placed in the oven at ٨٠ºC for ٢٤ hours and weighed to know the consumption from each species. The tests were conducted with one set fed for ٢ days and another set of ٢٠ nymphs fed for ٦ days until fledging. ٢. ٢ Feeding on filter paper impregnated with juices of Heliotropium spp The three species of Heliotropium were crushed separately using a mortar and pestle. The juice of each species impregnated on filter paper was used to examine antifeedant effect for ٢٤ hours on old fifth and sixth solitary instar nymphs. Two sets of filter paper disks were used, one in a large cage (wooden circular cage of ٩٨ cm diameter) (plate ٨ a, b) and the other in a small cage (thick paper circular cage ٢٠ cm diameter) (plate ٩). The filter papers used in the large cage were ١١ or Plate ٧ a, b Small cage used in antifeedent experiment. (a) (b) Plate ٨ a, b large cage used in antifeedant experiment using host plant impregnated filter paper. (a) (b) Plate ٩ Small cages used in antifeedant experiment using host plant impregnated filter paper. ٩ cm in diameter while those used in the small cage were ٤٫٢٥ cm in diameter (plate ١٠). The papers were given in a multiple-choice test to ten nymphs (٥ males and ٥ females fifth and sixth instars mixed in the large cage) starved for ٢٤ hours. The cages were heated and lightened by electric bulbs. In the small cages males and females were put individually each in a separate cage. The filter papers were fixed with pins in different ways to facilitate group and paired testing. Three replicas were made in the big and small cage and the distance between the papers was equal. The test ended after ٢٤ hours. The eaten area from each paper was measured using graph paper. ٢٫٣ Repellence experiment Fifth and six instars nymphs (male and female) were put individually in a wind tunnel cage each side of which consist of glass except the front one made of mosquito wire net (plate ١١). The cage length (١٤٠-Cm) was sectioned and the sections were marked. A fan was used to blow air through the wire mesh side into the cage. The bottom of the cage is lined with sand. Seventy grams of tested host plant species were used and placed at the ١٤٠ cm zone of the cage in front of the fan. The insects each was released at the ٠٫٠ cm mark of the cage. Resting, walking and other behaviour was recorded. The tests on each plant species were replicated ٢٠ times. ٣ Data analysis All data collected were subjected to analysis of variance (ANOVA) and means were tested for significance using the Least Significant Difference (LSD). Two variable means was tested using Independent ttest. Plate ١٠ Filter paper impregnated with the juice of the three species of Heliotropium. A= H.ovalifolium, B= H. arabianense and C= H.lignosum. Fig.١. Diagram of the flat-bed wind tunnel made of transparent glass; ١. Exhaust fan; ٢. Heliotropium species; ٣. Doors for introduction and collection of insects ; ٤. Ruler ١٤٠ cm long; ٥. Sliding glass door to release the test insect; ٦. Wire mesh box;٧. Wind tunnel chamber; ٨. Insect test pre-release compartment. DISCUSSION The results of various experiments revealed that two species of Heliotropium (H. ovalifolium and H. arabianense) were suitable for rearing and sustaining development of solitary nymphs, while the third species namely H. lignosum was not. In season ١٩٩٩-٢٠٠٠ all nymphs reared on H. lignosum died before reaching the ٤th instar. The duration period of the ٣rd, ٤th and ٥th nymph instar periods were significantly long on H. ovalifolium compared to H. arabianense. The ٢nd nymph instar period was long on H. arabianense than H. ovalifolium and H. lignosum, but it was not significantly different compared to H. lignosum. The ٦th nymph instar period was long on H. arabianense, while the ٥th –fledgling periods was long on H. oavlifolium. In case of the male, the ٤th and the ٦th nymph instar periods were long on H. ovalifolium than on H. arabianense. The ٣rd and ٥th-fledgling nymph period were significantly long on H. ovalifolium compared to H. arabianense, while the ٢nd nymph instar period was significantly long on H. arabianense. Female ٣rd, ٤th and ٥th nymph instar periods were long on H. ovalifolium. In the ٢nd and ٦th instar the period was significantly long compared to H. arabianense. The total development period was not significantly different between the two species (ovalifolium and arabianense) in season ١٩٩٩-٢٠٠٠. In season ٢٠٠٠-٢٠٠١ the nymph instar development period was significantly longer in H. lignosum as compared to H. ovalifolium and H. arabianense. In case of male and female ٢nd, ٤th, ٥th, and ٦th the nymph instar periods were affected in the same manner. The ٢nd, ٤th and ٦th nymph instar periods were significantly long on H. lignosum compared to H. ovalifolium and H. arabianense. The ٥th nymph period was not significantly different between the species. The male ٣rd instar period was also significantly longer on H. lignosum as compared to the other two species. Also the ٥th to fledgling period was significantly different between the three species it was significantly longer on H. lignosum followed by H. ovalifolium and then H. arabianense. The female ٣rd nymph instar period was significantly long on H. lignosum followed by H. ovalifolium then H. arabianense. The ٥thfledgling nymph instar period was significantly long on H. lignosum compared to H. arabianense. In this season total development period was significantly long on H. lignosum. In case of the male and female it was significantly longer on H. lignosum followed by H. ovalifolium and H. arabianense. Pfadt, (١٩٤٩), Rao (١٩٤٢) and (١٩٦٠), Uvarov (١٩٦٦), Bhatia and Ahlualia (١٩٦٧) and Ibrahim, (١٩٧٢), mentioned the effect of food on the biology, and cleared that the biology of the locust is influenced by the type of food available to the insect in nature. In general it appears that H. arabianense is suitable for development followed by H. ovalifolium, while H. lignosum is not. In season ١٩٩٩-٢٠٠٠ there was no significant difference in the effect of H. ovalifolium and H. arabianense on the maturation of fledgling male and female, but when mixed data of male and female was taken negligible difference was detected. It was significantly rapid on H. ovalifolium compared to H. arabianense There is no significant difference in season ٢٠٠٠-٢٠٠١. Ellis, et al., (١٩٦٥) reported that the sexual maturity and moulting of Schistocerca gregaria was influenced by monoterpenoids and hormones from food plants. Also Steedman (١٩٩٠) mentioned that immature adults might become sexually mature in few weeks or few months, according to environmental conditions. From the previous studies it was clear that H. ovalifolium and H. arabianense enhanced maturation, so the two species influenced sexual maturation in the same manner. The longevity of all nymph instar was significantly prolonged on H. arabianense as compared to H. ovalifolium followed by H. lignosum in season١٩٩٩-٢٠٠٠, In season ٢٠٠٠-٢٠٠١ it was significantly prolonged on H. arabianense compared to H. ovalifolium which was significantly prolonged compared to H. lignosum. Male and female longevity was significantly short in H. ovalifolium compared to H. arabianense in season ١٩٩٩-٢٠٠٠. In season ٢٠٠٠-٢٠٠١ it was significantly prolonged on H. arabianense followed by H. ovalifolium compared to H. lignosum. In season ١٩٩٩-٢٠٠٠ all nymphs reared on H. lignosum died before reaching the ٤th instar. While in season ٢٠٠٠-٢٠٠١ few individuals reached the fledgling stage but died after fledgling and before maturation (in maximum ٢days after fledgling). Nymphs reared on H. ovalifolium in season ١٩٩٩-٢٠٠٠ and reached fledgling stage died before maturing except few individual, However most individuals matured in season ٢٠٠٠-٢٠٠١. Most individuals reared on H. arabianense reached the mature stage in the two seasons. It was mentioned in the literature that food plants affected individuals survival and the water content of food affected the food consumption rate. This has been confirmed by Williams (١٩٥٤), who found that fresh grass was consumed more than dry grass when both were offered in the same cage. According to Mulkern (١٩٦٦), Stolyarov and Waloff observed that Schistocerca gregaria survived better on some plants than on others The dry weight per gram was (٠,٣١٠, ٠,٢٦٥ and ٠,٢٩٤) in H. ovalifolium, H. arabianense and H. lignosum respectively in season ١٩٩٩-٢٠٠٠. Where as it was (٠,١٦٤, ٠,١٥٩ and ٠,٢٩١) respectively in season ٢٠٠٠-٢٠٠١. This may explain the variation in development and survival obtained in the two seasons during this study. The three species of Heliotropium has no clear effect on the weight of nymphs and fledglings. In season ١٩٩٩-٢٠٠٠ all nymph instars reared on H. arabianense weighted more than those reared on H. ovalifolium, except fledgling female, weight was significantly heavy in H. arabianense as compared to H. ovalifolium. The male ٤th instar and fledgling female weight were not significantly different. In season ٢٠٠٠-٢٠٠١ the ٣rd nymph instar weighted significantly less when reared on H. lignosum compared to H. ovalifolium and H. arabianense. The ٦th instar weight was significantly higher on H. ovalifolium compared to the other two species. The ٤th, ٥th and fledgling instar weight was not significantly different. In case of male and female nymph instars the weight was affected in the same manner and there was no significant difference except that the male ٦th instar weight was significantly heavy in H. arabianense than other species and the female ٤th instar weight was significantly heavy on H. lignosum compared to H. ovalifolium. The weight gain of nymphs and fledglings in season ١٩٩٩-٢٠٠٠ was higher in those fed on H. arabianense than on H. ovalifolium, followed by H. lignosum but the fledgling female gained more weight on H. ovalifolium than on H. arabianense. It was significantly heavy in (٣rd and ٥th nymphs instar), (male ٣rd and ٥th) and (female ٣rd, ٤th, ٥th) nymph instar. In season ٢٠٠٠-٢٠٠١ weight gain was not significantly different, However in case of the ٤th nymph instar it was significantly high in H. lignosum and H. arabianense as compared to H. ovalifolium. The female ٣rd instar weight was significantly high in H. lignosum compared to H. arabianense followed by H. ovalifolium. The feeding rate of nymph instars increased gradually until the ٦th nymph instar, then declined in the fledgling stage. In season ١٩٩٩-٢٠٠٠ the ٣rd and ٤th nymph instar consumed significantly few grams of wet H. lignosum compared to the other species. Also the ٣rd and ٥th instar consumed significantly few grams of wet food on H. ovalifolium as compared to H. arabianense. The ٤th instar consumed significantly few grams of wet food of H. arabianense. There was no significant difference in the ٦th and fledgling stage. In season ٢٠٠٠-٢٠٠١ the nymphs consumed significantly few grams on H. lignosum as compared to the other two species. The ٥th instar nymphs consumed significantly more grams from H. arabianense followed by H. ovalifolium then H. lignosum. In season ١٩٩٩٢٠٠٠ dry food consumed by solitary ٣rd and ٤th nymph instar was significantly less in H. lignosum followed by H. arabianense as compared to H. ovalifolium. In the other nymph instars and fledgling there was no significant difference and it was slightly high on H. ovalifolium compared to H. arabianense. In season ٢٠٠٠-٢٠٠١ only the ٤th instar, nymphs consumed significantly few grams of dry H. lignosum compared to H. ovalifolium and H. arabianense. Also the ٥th instar consumed significantly more grams from H. arabianense compared to H. ovalifolium. Dry food assimilated by solitary nymphs was significantly high in H. ovalifolium compared to H. arabianense and H. lignosum in season ١٩٩٩-٢٠٠٠. In season ٢٠٠٠-٢٠٠١ it was significantly high in the ٣rd instar in H. lignosum, significantly high by ٥th instar in H. arabianense and significantly low by ٦th instar in H. lignosum compared to the other two species. There was no significant difference in the other instars. In conclusion and as mentioned above solitary nymphs fed well on H. arabianense and H. ovalifolium while they fed little on H. lignosum. However the assimilated food from H. lignosum was high compared to the food consumed and nymphs excreted few grams of faeces. The average fecundity and egg development was affected in the same manner in the two species (H. ovalifolium and H. arabianense), except in season ١٩٩٩-٢٠٠٠ the incubation period and number of pods per female was higher on H. arabianense. Fertility of solitary females was affected by the food species. In season ١٩٩٩-٢٠٠٠ females mated in significantly few days on H. ovalifolium compared to H. arabianense. The oviposition period took significantly short time on H. ovalifolium compared to H. arabianense. H. arabianense significantly prolonged the life span compared to H. ovalifolium. The influence mentioned above probably reflect the effect of the seasonal climatic conditions that in turn affected the quality of the two species. Nymphs kept on the three species of Heliotropium together for ٢ days fed equally well on the three species, but when they were kept for ٦ days they consumed significantly few grams from H. lignosum compared to H. ovalifolium and H. arabianense. Consumption rate was high on H. arabianense than on H. ovalifolium. Also when they were kept in small cages for two days negligible difference was found between H. arabianense and H. ovalifolium, and nymphs consumed significantly few grams on H. lignosum. This indicates that nymphs prefer H. arabianense and H. ovalifolium than H. lignosum. The preference was not cleared when the nymphs were left to feed for two days but it was clear when they were kept to feed for ٦ days. According to Uvarov (١٩٧٧), Thomas mentioned that the final selection is a matter of taste discrimination by the sensilla on the mouthpart. Plants, which are only nibbled, but not eaten, are rejected for their taste on chemical grounds. When filter paper impregnated with the juice of the three species was presented, nymphs consumed large areas of filter paper impregnated with H. lignosum juice compared to H. arabianense and H. ovalifolium in all paired and group tests. There was no significant difference between H. ovalifolium and H. arabianense except in male nymphs and male + female nymphs in paired test in small cages, where they consumed large area of H. arabianense compared to H. ovalifolium. This indicates that some volatile phagostimulating material or materials were lost in the process of extracting the juice of H. arabianense and H. ovalifolium. On the other hand, some volatile antifeedant material or materials were lost in the process of extracting the juice of H. lignosum. Goodhue (١٩٦٣), mentioned that refusal to feed on a plant after biting it, or its acceptance, led to the theory that this depended on the presence or absence of some specific substances termed phagostimulants. Nymphs tested in wind tunnel to know their behavior during their search for and finding the food spend significantly more time in walking and resting. They jumped and climbed the walls significantly few times in the presence of H. lignosum and most of the nymphs did not reach the food. The average distance traversed was significantly short with this plant. In case of the male there was no significant difference in the behavior and the average distance traversed. Females spend significantly long time in walking and resting and they significantly walked right, left and back a lot of times when provided H. lignosum in the tunnel compared to the other two species. The nymphs traversed significantly short distance and didn’t reach the food. The attraction of Schistocerca gregaria hoppers by the smell of food plants was mentioned by Volkonsky (١٩٤٢). Also Haskell et al., (١٩٦٢) mentioned that in wind tunnel with air current carrying the smell of crushed grass and of variety of odorous substances, these odorous caused Schistocerca hoppers, starved for ٢٤ hours, walking down wind to reverse their direction and walk twoards the source of the odours. From the previous data nymphs prefer H. ovalifolium and H. arabianense odours and walked down towards and reached the food. Whereas they did not prefer H. lignosum odorous so they did not reach the food in spite of few numbers walked the whole ١٤٠ Cm length of the wind tunnel but they did not climb the food or bite it, instead they turned back. CONCLUSION The Influence of three species of Heliotropium on the development, weight, feeding rate, maturation, fertility and fecundity, longevity, antifeedent and repellency on the desert locust Schistocerca gregaria solitary phase was carried out in this study. H. ovalifolium and H. arabianense are suitable for male and female nymph development, while H. lignosum was not suitable. Nymphs developed fast on H. arabianense followed by H. ovalifolium. There was no clear effect of the three species on the weight gain of nymph instars and fledglings, in spit of the more weight gain on H. ovalifolium in season ١٩٩٩-٢٠٠٠. Nymphs and fledglings’ male and female consumed more food when they fed on H. arabianense or on H. ovalifolium, whereas they consumed less on H. lignosum In spite of this the assimilation rate of the consumed food was high on H. lignosum due to the fact that comparatively less food was taken and few faeces pellets were voided Fledgling male and female took a long time before maturing. The male became mature before the female, on both the two species (H. ovalifolium and H. arabianense). H. ovalifolium and H. arabianense affected the fertility and egg development in the same manner, but all females preoviposition period was long and laid few egg pods compared to literature reports. H. ovalifolium and H. arabianense prolonged individual life. Most of the male and female nymphs reared on these species completed development, but nymphs reared on H. lignosum died before fledgling and the few that fledged died after a maximum period of ٢ days. Male and female ٥th instar nymphs kept on the three species of Heliotropium together prefer H. arabianense, than H. ovalifolium especially when they were kept for ٦ days. Nymphs provided with filter paper impregnated with juice of the three species individually in-group and paired test, consumed large areas from those impregnated with H. lignosum and a small area from those impregnated with the other two species. The male preferred filter paper impregnated with H. arabianense than those impregnated with H. ovalifolium in paired test, while the female fed equally on them. Generally nymphs didn’t prefer filter paper impregnated with these two species. This indicates that some volatile phagostimulating material or materials were lost in the process of extracting the juice of H. arabianense and H. ovalifolium. On the other hand, some volatile antifeedant material or materials were lost in the process of extracting the juice of H. lignosum. Effect of plant smell on the behavior of male and female ٥th instar nymphs as tested in a wind tunnel, cleared that nymphs prefer the smell of H. ovalifolium and H. arabianense and they went towards the smell until they reached the food. During that they moved their antenna some time, jumping and walked left, right and back. The nymphs didn’t prefer H. lignosum smell as they walked and rested for long periods, then turned back or climbed the wall. 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