Dendrolaelaps saprophilus n. sp. (Mesostigmata
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DENDROLAELAPS SAPROPHILUS N. SP.
(MESOSTIGMATA : DIGAMASELLIDAE),
FOUND WITH OTHER DENDROLAELAPS SPECIES IN FINLAND
Veikko H.!JHTA *
Dendrolaelaps saprophilus n. sp., described in this paper, is closely related
to D. arvicolus (Leitner 1949) and to D. insignis Hirschmann 1960. Masses of
D. saprophilus occurred in a mixture of sewage sludge and crushed bark deposited on
soi!, and this species was often found with D. arvicolus.
European species of the genus Dendrolaelaps
are relatively weil known from the thorough work
of Hirschmann (1960, 1971, etc.), who described
more than half the known species. Collections
from many parts of Europe, especially from northem and eastern areas, are very seant ; therefore
many species probably remain undescribed. In
the key for identifying Mesostigmata of the Soviet
Union (Ghilarov 1977) the genus is not treated to
species level. No records were available from
Finland before the work of Huhta et al. (1979).
The status of the genus Dendrolaelaps Halbert,
1915, in relation to Digamasellus Berlese, 1905,
has been disputed ; but Lindquist (1975) finally
settled the question by recognizing both as distinct
genera, with most known species belonging to
subgenus Dendrolaelaps (Dendrolaelaps) Halbert,
DESCRIPTION OF DENDROLAELAPS SAPROPHILUS N. SP.
• Female. Length of the idiosoma is 0.43 to
0.47 mm (extremes 0.41 and 0.50 mm), breadth
ca. 0.22 to 0.24 mm. Dendrolaelaps saprophilus
is the same size as and closely related to D. arvicolus (Leitner 1949) and D. insignis Hirschmann
1960. Drawings from females of D. arvico!us,
collected from the type locality of D. saprophilus,
are given here for comparison (Fig. la-e). Refer
to Hirschmann (1960) for comparison with D.
The dorsal setae (Fig. 2a) are slightly shorter
than in D. arvicolus (Fig. la), except Z5 and S5
(setal nomenclature according to Hirschmann 1960
and Karg 1971), which are the same length as in
* Department of Biology, University of Jyvaskyla, SF-40100 Jyvaskyla, Finland.
Acarologia, t. XXlll, fasc. 3, 1982.
~- -· -~
Dorsal view ; b. -
FIG. 1 : Dendrolaelaps arvicolus (LEITNER 1949), female .
Ventral view (microstructure not shown) ; c. - Insemination apparatus ; d. -
Chelicere ; e. -
-227D. arvicolus. Setae Z5 and S5 of the three species
differ in their curvature : in D. saprophi/us these
setae are usually straighter than in D. arvico/us,
where they always bend sharply outward (Fig. la).
This character can be used as an orientating feature in routine identifications. ln D. insignis
these setae are strongly curved (Hirsmann 1960,
The dorsal microsculpture is weakly developed.
The anterolateral region of the podonotal shield
and the area between setae Z3-Z4 are slightly
lineate. The opisthonotal shield is most distinctly
ornamented with punctate markings in the posterior region. Between setae pairs Z3 and Z4 are
relatively large pseudopores, as in D. insignis.
The peritremata extend forward farther (to the
leve! of r2) than in the other two species.
Ventrally, the sternal shield changes gradually
into a poorly defined sclerotized field (Fig. 2b),
while in D. arvico/us and D. insignis the sclerotized field has a well-defined anterior border and
a distinct transverse furrow behind setae stl
(Fig. lb). The ventrianal shield, bearing setae VI
to V4, V6 and V8, is shaped similarly to that of
D. insignis, with angles in front of V8. In sorne
specimens this angle is obtuse or absent, making
the shield more similar (but not identical) to that
of D. arvico/us (Fig. I b). The ventrianal setae in
D. saprophi/us are nearer each other than are
those of D. arvico/us (ratio of the distance between V3 to distance between V4 is ca. 1.5 in D.
saprophi!us, but is I. 75 in D. arvicolus ; distance
between pair VI is smaller than that between pair
V4, while the opposite is the case in D.
arvicolus). This pattern is similar to D. insignis,
but setae V4 are longer in D. saprophilus.
McGraw and Farrier (1973) and Shcherbak
(1973) drew attention to the female insemination
apparatus as a diagnostic character in the taxonomy of Dendro/ae/aps. In D. saprophi/us this
organ closely resembles that of D. arvicolus and
D. insignis, but can be distinguished by careful
inspection. When it is more or Jess curved
throughout" its length in D. arvico/us (Fig. le), it
is clearly divided into a thicker arc-shaped proximal part, and thinner, irregularly curved distal
part in D. saprophilus. A transversal eut can be
seen in the proximal part and usually another one
between the proximal and distal parts (Fig. 2c).
The insemination apparatus of D. insignis is intermediate between these two types, the proximal
part being shorter than in D. saprophi/us (Shcherbak 1973).
The tectum, hypostome, and chelicera (Figs. 2df) cannot be distinguished from those of D. arvicolus or D. insignis.
• Male. Length of the idiosoma is ca.
0.43 mm. The male closeÏy resembles that of D.
arvico/us (see Hirschmann I960, Fig. llc; the
male of D. insignis has not been described). The
dorsal microstructure, relative length of setae, and
position of peritremata ali are the same as those
of the female. Posterior setae Z5 and S5 are
generally straighter than those of D. arvicolus. The main feature that distinguishes D.
saprophi!us from D. arvicolus is the extension of
the peritremata anteriorly, ending in front of r2
(Fig. 3a) ; in D. arvicolus they only extend between r4 and r5. On the ventral surface are relatively large pseudopores at the leve! of anus ; they
become smaller anteriorly and change into reticulate microsculpture about the leve! of V2
(Fig. 3b). Leg chaetotaxy (Fig. 3c, d) is similar to
that of.D. arvicolus, femur IV possesses a series
of 3 ventral protuberances, two normal setae on
the prolateral side, two thickened setae on the
dorsal side, and two on the retrolateral side.
• Deutonymph. Length ca. 0.40 mm. The
deutonymph also closely resembles that of D.
arvicolus, but can usually be distinguished from
the latter on the basis of the straighter posterior
setae Z5 and S5 (Fig. 4a). The dorsal microstructure is similar to that of adults. The peritremata end anteriorly in front of r2, but in D. arvicolus they may reach almost the same leve!. The
ventrianal shield bears setae V3, V4 and V8
(Fig. 4b), but V3 is situated right at the margin
and may lie outside the shield. The same variation is also found in D. arvicolus. Thus, the
deutonymphs of these species can probably not be
identified with certainty.
FIG. 2 : D. saprophilus n. sp., female.
a.- Dorsal view; b.- Ventral view; c.- Insemination apparatus; d.- Hypostome; e.- Chelicere; f.- Tectum.
FIG. 3: D. saprophilus n. sp., male.
a. -Dorsal view ; b. - Ventral view ; c. - · Leg II (modified anteroventral setae indicated by punctate areas) ; d. e. - Tectum ; f. Hypostome ; g. - Chelicere.
femur of leg IV ;
Type loca/ity and eco/ogy.
The species was found in 1977 at Tikkurila, ca.
20 km north of Helsinki, Finland. It was very
numero-us in a test plot made of a mixture of
fresh activated sewage sludge 1 and crushed bark
(Huhta et al. 1979). Four months after the experiment was established D. saprophilus occurred
abundantly : 1 000 specimens per dm 3• The following year it was still numerous and then occurred with D. arvicolus, which was equally abun- '
dant by the second autumn (together these species
made up roughly half of ali Mesostigmata). At
the same time D. arvicolus was numerous in a
control plot made only of crushed bark ; there
it reached max~mum numbers when the material
had aged 1.5 to 2 years (the test plots were established during different years). When the plots
were established, the test materials were almost
devoid of mites, but populations of sorne species
found later in the plots may have originated from
the bark, which had been stored in heaps for
sorne weeks before use. Since the Dendro/ae/aps
species mentioned were not found until 3 months
after th_e plots were established, they probably
arrived phoretically from the surroundings.
Different species of Dendrolae/aps, in fact
mesostigmatid mites in general, possess a welldeveloped ability to differentiate between substrates ; each species dominated in test materials of
different age and origin. D. strenzkei Hirschm.
characterized the medium and late stages of succession in material containing anaerobically digested sludge. D. zwoeljeri Hirschm. was found
almost exclusively in a compost heap of digested
sludge and bark. D. stammeri Hirschm. was
characteristic in fresh · test plots made of the same
materials. D. punctatosimi/is Hirschm. occurred
abundantly in test plots made of fresh activated
sludge and bark, and fresh limed sludge and bark,
but at an earlier stage of succession than D.
saprophilus ' ; when the latter species reached its
peak density, the former bad almost totally disap-
peared. D. foveolatus (Leitner) was characteristic
on the adjacent arable sail, but was not found
during 3 years of observation in artificial sail
made of composted mixture of digested sludge
These observations confirm Karg's (1968 a) statement that predatory Mesostigmata can be used
as indicators of substrate properties. This seems
to fit the genus Dendrolaelaps particularly weil ;
several Dendrolaelaps species are among the first
colonists in accumulations of fresh organic materials. Regrettably, data from the current literature provide only meagre information for camparing the ecology of these three closely related species : D. saprophilus, D. arvico/us, and D. insignis. According to Hirschmann (1960), D. arvicolus is found in raw humus, stacks of manure,
and nests of ants and wild bees. Hirschmann
(1971) states that it occurs most commonly in cultivated sail, but is also found in manure and
decaying wood. Karg (1971) mentions D. insignis as occurring sparsely in deciduous and coniferous forests, under bark and in decaying
stumps. Neither species was included in the
material of Karg (1967, 1968 a, 1968 b) collected
from manure, composts, arable land, and forest
soils. Because the species are so similar, previously D. saprophilus n. sp. may have been misidentified as D. arvicolus. Another related species
is D. punctatu/us Hirschm., which lives subcorticolously according to Hirschmann (1971).
• Type specimens are stored in the Zoological
Museum of the University of Helsinki.
GHILAROV (M. S.), ( rHJIHpOB, M. C.) (ed.), 1977. Détermination des peuplements des Acariens du sol.
Mesostigmata. - 718 pp. Izdatelstvo ' NAUKA ',
HIRSCHMANN (W.), 1960. - Die Gattung Dendrolaelaps Halbert 1915 . - Acarologie. Gangsystematik der
Parasitiformes, 3 : 1-27.
HIRSCHMANN (W.), 1971. - Ursprüngliche und abge- ·
leitete Merkmale. Vorkommen von Dendrolaelaps-
1. Sludge produced by sewage treatment plants using the activated sludge method ; dried to 20 OJo dry matter content, without further
Arten. - Acarologie, Schriftenreihe für Vergl. Milbenkunde, 15 : 22-28.
HUHTA (V.), lKONEN (E.) ~ VILKAMAA (P.), 1979. Succession of invertebrate populations in ardficial soi!
made of sewage sludge and crushed bark. - Ann.
Zoo!. Fennici, 16 : 223-270.
KARG (W.), 1967. - Synëkologische Untersuchungen
von Bodenmilben aus forstwirtschaftlich und land.wirtschaftlich genutzten Baden. - Pedobiologia, 7 :
KARG (W .), 1968 a. - Bodenbiologische Untersuchungen über die Eignung von Milben, insbesondere von
parasitiformen Raubmilben ais Indikatoren. - Pedobiologia, 8 : 30-39.
KARG (W.), 1968 b. - Okologische Untersuchungen an
Milben aus Komposterden im Freiland und unter Glas
besonders im Hinblick auf die Uroobovella marginata
C. L. Koch. - Archiv für Pflanzenschutz, 4 : 98122.
KARG (W.), 1971. - Acari (Acarina), Milben. Unterordnung Anactinochaeta (Parasitiformes). Die freilebenden Gamasina (Gamasides), Raubmilben. - Die
Tierwelt Deutschlands, 59 : 1-475.
LINDQUIST (E. E.), 1975. - Digamasellus Berlese, 1905,
and Dendrolaelaps Halbert, 1915, with descriptions of
new taxa of Digamasellidae (Acarina : Mesostigm.;:tta).
- Canadian Entomol., 107 : 1-43.
McGRAW (J. R.) & FARRIER (M. H.), 1973. ~ Taxonomically useful parts of the insemination apparatus
in females of Dendrolaelaps (Mesostigmata : Dîsamasellidae). - Ann. Ent. Soc. Amer., 66 : 1075·1077.
SHCHERBAK (G. J.), (~ep6aH, f.l1.•), 1973. - On a
new diagnostic character of mites from the genus
Dendrolaelaps Halbert, 1915. - Vestnik .Zoo!. Inst.
Zoo!., Akad. Nauk. Ukr. SSR 4 : 86-90,
Paru en sept§!mbre 1982.
FIG. 4 : D. saprophilus n. sp. deutonymph.
a . .- Dorsal view ; b. - Ventral view.