Spatial analysis of Mopani worms distribution in Botswana, Africa: A

GCK SCIENCE LETTERS
Vol. 3(1), January 2014, pp. 34-43
Spatial analysis of Mopani worms distribution in Botswana,
Africa: A preliminary study using GIS
A.N. Manoharan1* and M. Praseedakumari2
1
Department of Post-Graduate Studies and Research in Geology, Government
College Kasaragod, P.O. Vidyanagar, Kasaragod-671123, Kerala, India.
2
Krishi Bhavan, Pallikkara, P.O. Panayal, Kasaragod, Kerala, India.
Abstract
Mopani worms are important forestry resource products of mopane
woodland in Botswana. It has high protein content and an important trading
commodity in southern Africa. In the present study geographical distribution of
Mopani trees have been analyzed using Google earth imagery and aerial
photographs with field verification using GPS. Mopani worm harvesting,
processing and trading etc are observed and analyzed especially in Selebi Phikwe
area of Botswana. Protein content of the worms was assessed using secondary
data.
Keywords: Mopani worm, Mopani tree, spatial analysis, harvesting and
processing.
__________________________________________________________________
*Corresponding
author:
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[email protected].
+91-9447693860,
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Introduction
Mopani worms (Imbrasia belina) generally known as Phane in Botswana
is the larva of the emperor moth. It is one of the best – known and most
economically important forestry resource products of the mopane woodland in
Botswana. Originally, the mopane worm used to be an important food source for
the rural communities occurring within the range of mopane woodland, but it is
now widely eaten across southern Africa where it has become an important
trading commodity. Mopani worm have high protein content and are considered a
traditional delicacy. Women and children are usually involved in Mopani worm
collection but in recent years, men and youth have participated in the gathering of
this product, attracted by the income earning opportunities from the supply and
trading of Mopani worm food products. Mopani worms are used as a protein
source by people in semi-arid environments of Botswana, Namibia, South Africa
and Zimbabwe (Marais, 1996; Moruakgomo, 1996; Styles, 1996), and also
exported to South Africa is used as animal feed (Mpuchane et al. 2000). Mopane
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worm is a high quality nutrient source (Ohiokpehai et al. 1996; Madibela et al.
2007). The mopane worm, the edible larvae of the Saturnid moth Imbrasis beilina
peaks in abundance of this species are between November and January (major)
and March – May (minor), though population numbers and location of outbreaks
vary from year to year. Outbreaks of Mopni Worms although seasonal, are very
timely in that they occur during the early months of the rainy season, when most
rural households are in need of cash for food and school fees. However, the high
inter annual variability in production means that these products are not a very
reliable income source.
In the present study an attempt has been made to spatially analyze the
geographical distribution of Mopani worms in Botswana using Google earth
imagery and high resolution aerial photographs and limited ground truth
verification. Extensive field work have been carried out to observe and understand
the worm harvesting, processing and trading especially in Selebi Phikwe and
along Phikwe to Gabarone tract in Botswana.
Study area
The study area is Botswana, a landlocked country located at south central
Africa in between Longitude 19° 59’ 38” to 29° 22’ 16.957” E and Latitude 26°
55’ 12.192” to 17° 44’ 57.572” S (Fig. 1).
Fig.1 Location of the study area.
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The country is bounded North by Zambia and Namibia, East Zimbabwe,
West Namibia and South by South Africa. Geographically, Botswana is
predominantly flat tending toward gently rolling table land, with up to 70% of its
territory being the Kalahari Desert. The Okavanga Delta, one of the world’s
largest inland deltas is in the North West. The Makgadikgadi Pan, a large salt pan,
lies in the north. Botswana is one of the most sparsely populated country the
world. The total geographical area of the country is 5, 81,730 Sq.km.
Materials and methods
The studies carried out attempting digital aerial photo/satellite imagery
interpretation of the areas using image processing software ERDAS Imagine 9.1
and GIS software ArcMAP 9.2 On screen image interpretation have been carried
out to delineate the areas of Mopani trees in the study area. Garmin etrex GPS
receiver was employed to ground check the interpreted features. The entire
analysis was carried out on a GIS platform in order to overlay and integrate the
interpreted features to the available geo-spatial data and the same collected from
the field during the course of the work. The output of the interpretations is
overlaid on road, settlement and other administrative divisions of the country.
Secondary data have been used to analyze the protein content of the Mopani food
products. Methodology used for study is shown in Fig.2 Different stages of image
processing are shown in Figs 3-8.
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Manoharan and Praseedakumari /GCK Science Letters 3-1 (2014) 34-43
Google imagery
Download Google earth imagery with
higher resolution as .jpg format.
Import to .img format
Geo-reference the imagery with GCPs
marked on the imagery
Aerial photograph
Import orthorectified aerial photograph
tiles covering an area of 0.25sq.km from
.tiff to .img format. (789 tiles)
Mosaic 789 tiles in to 12 mosaics
Subset as per the required area
Enhance the photograph for better clarity
Enhance the imagery for better clarity
Subset by trimming darker edges
Mosaic the imagery tiles
Resolution merge
Merge high resolution monochrome aerial
photograph with low resolution multi-color
Google imagery in order to get high
resolution multi-colour imagery.
Subset the mosaic as per required area
Image interpretation
Interpret the imagery onscreen (use different image enhancements as and
when required) for Mopani trees.
Fig.2. Methodology of the study.
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Manoharan and Praseedakumari /GCK Science Letters 3-1 (2014) 34-43
Results and discussion
The large outbreak populations of mopane worm in Botswana largely follow
that of the host plant (colophosperum Mopane), which occurs in a broad band
extending from the northern parts of South Africa into Zimbabwe, Botswana and
west into Northern Namibia. The majority of these areas lie in regions of low
natural resource potential, where cultivation is risky and extensive livestock
production is the most suitable form of agriculture. Unreliable climate causes
regular failure of staple grains and a high level of vulnerability to food insecurity.
Mopane trees were identified in the field areas of Selebi Phikwe, Eastern
Botswana. The corresponding locations were marked on resolution merged
imagery (Google earth imagery + Aerial photograph) using a hand held GPS. On
screen image interpretation have been carried out with help of interpretation keys
identified at the marked area of the imagery. The Mopani forest area have been
delineated and shown in Fig. 11.
Fig. 10. Mopani forest area delineated on google earth imagery.
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Around 1, 61,496.64 Sq. Km. area is covered with Mopani forest. The
Mopani forest coverage is mostly confined to north and north eastern regions of
the country. Harvesters in the Botswana study identified collection of Mopani
Worms to be a vital source of income despite outcry over low buying prices.
Nevertheless, all harvesters are involved in other forms of livelihood including
cropping; rearing livestock, selling traditional beer and working for the drought
relief programme Harvesters in Botswana also use the proceeds of Mopani Worm
sales for various household supplies (Taylor, 2003).
Dried Mopani Worms from the rural areas increasingly find their way into
both the formal and informal national distribution network via a wide variety of
marketing chains (Kotsanyi and Frost, 2002 and Stack, 2002). Mopane worms
reach urban markets via a number of pathways (Collectors, rural traders urban
based middlemen) and are marketed in a wide variety of places including urban
bus termini, open markets, roadside vendors, wholesalers, supermarkets, and tuck
shops. In some instances the marketing chain is quite long.
Table 1 Composition of dried Mopani worm. The protein content is found to be
the highest, it is higher than that of Biltong (55.4%) and cooked beef
(22.6%).
Ingredients
Moisture
Ash
Proteins
Carbohydrates
Fats
Potassium
Sodium
Phosphorous
Iron
Calories (KJg-1)
Content in % by dry
weight g/100g
7.31
9.28
59.03
8.16
15.7
0.581
0.516
0.0169
0.2992
24.21
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Fig. 11 (a) Hatching Mopani larvae (b) Different stages of Larvae, (c) Mopani worms
(MW) eating Mopani tree leaves (d) MW collection, (e) Collected worms,
(f) Drying worms (g) Frying, (h) Drying on wire net and (i) Cooking.
Composition of dried Mopani worm is given in Table.1.
The MW has a tough skin and is protected along the length of the dorsal
surface by six parallel rows of black or dark reddish brown spines. The spines can
be painful and cause lacerations and the spines and associated hairs seem to have
a slight irritating effect. In addition, when the larvae are handled, they often exude
a slimy green fluid from the mouth. This fluid irritates any scratches on the hand.
Hand protection therefore helps with harvesting and degutting. In an attempt to
prevent excessive damage to their hands, some collectors’ tie barks fibers around
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their fingers (Kozanayi & Frost 2002). As it has been noticed that harvesters in
Botswana often wear gloves.
Traditional cooking is done on a fire. The MWs are placed in a container
with some water and salt. This system relies on the use of wood and regular
stirring, in order to allow even cooking and prevent the MWs at the bottom of the
pot burning. Solar cooking was tested as an alternative as it decreases the amount
of wood used and the physical labour/time spent on cooking. Solar cooking
allows the items to be evenly cooked without stirring.
Drying is one of the major problems in processing. It can take many days
and during this time of the year (in particular the December/January harvest) the
humidity is often high, making drying difficult. If the MWs are not dried properly
they spoil rapidly. Traditionally, after cooking the MWs, they are laid for drying
on a swept piece of ground. The piece of ground varies depending on the
harvesting situation and hence the amount of contamination is likely to vary. In
Botswana the MWs are also sometimes placed on hessian bags. The traditional
ground drying method takes 2-4 days depending on weather conditions, about 3
days with cloud cover of 30-40%. It also allows easy access for other insects.
Insects such as dermestids and flies can cause significant levels of contamination
(Allotey et al. 1996 & Nyakudya 2004).
There are problems associated with the storage of MWs (Nyakudya 2004).
Traditionally they are kept in woven polypropylene bags in which maize or a
similar product has been stored, plastic or metal buckets and clay pots. In all these
items they are subject to contamination and spoilage (Allotey et al. 1996). In
many cases the MWs are sold as soon as possible in order to prevent losses due to
spoilage. In order to decrease the deterioration both from micro-organisms and
insects the mopane worms are taken out of the bags and spread on the floor in the
sun. In Botswana some people have started a sterilization system by placing a
black plastic sheet over the MWs while they are in the sun, in an attempt to kill
the unwanted insects. Better prices are obtained later in the year and for this
reason traders who store the MWs fumigate them with Phostoxin gas (Taylor
2003). However, Phostoxin gas is dangerous and only registered pest control
operators are allowed to fumigate with it.
Conclusion
The mopane worm (MW), Imbrasia belina, and mopane woodland products
are key resources to poor farmers and landless poor people across Botswana. A
detailed study of aerial photographs and google earth imageries of the country
have been carried out to delineated the spatial distribution of mopane forest in
Botswana. Extensive field verification also has been carried during the mopane
worm rearing season as well as off season. The study reveals that around
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1,61,496.64Sq.Km. ie. 28% of the total geographical area covers mopane forest
area in Botswana. Field photographs of various stages of Mopani worms growth,
worm collections, processing etc. have been collected during the field work.
Ingredients of the dried Mopani worms have been analysed using secondary data.
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