20th International Congress of Arachnology

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DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
Student - oral presentation
Effect of increased habitat complexity on
pest suppression by winter-active spiders
*Radek Michalko1,2, Lenka Petrakova1, Lenka Sentenska 1,
Stano Pekar1
1Department of Botany and Zoology, Faculty of Sci-
ences, Masaryk University, Kotlářská 2, 611 37 Brno,
Czech Republic; 2Department of Forest Ecology, Faculty
of Forestry and Wood Technology, Mendel University in
Brno, Zem ědělská 3, Brno 613 00, Czech Republic
Increased habitat complexity often reduces intraguild
predation (IGP) among the top-predator and meso-
predator and consequently increases abundances of the
latter. However, reduced IGP may not necessary translate
to the increased predation pressure on a pest as the
increased habitat complexity can also provide shelters
for the pest. Moreover, increased abundances of the
meso-predator may lead to increased intra-trophic level
interference that decreases the per capita capture rate
of the meso-predator. Here, we investigated whether the
cardboard bands installed on pear trees in early winter
improve the suppression of the pear psylla, Cacopsylla
pyri, by winter-active spiders, Anyphaena accentuata
and Philodromus spp. We also investigated the effect of
abundances of philodromids on their functional response
and their overall predation on the pear psylla. The trees
with cardboard bands hosted less psylla than the control
trees in early spring. The decrease in abundances of
psylla can be attributed to the predation by spiders as the
molecular gut-content analysis showed that 35% of spiders
preyed on psylla. However, 58% of Anyphaena preyed also
on Philodromus. There was an asymptotic relationship
between abundances of winter-active spiders and the effect
size of psylla abundances. In the functional response
experiments, the per capita capture rate decreased with
abundance of conspecifics. Consequently, the overall pre-
dation pressure on psylla was lowest at low abundances
of philodromids but similar between moderate and high
abundances. Our results show that installation of card-
board bands in winter contributes to reduction of psylla
population. However, the effect of increased abundances
of winter-active spiders on overall predation pressure on
psylla is not additive, which can be partly explained by an
increased intra-trophic level interference.
Keywords: intraguild predation, food-web, biological
control, pear psylla, winter ecology
Student - poster presentation
Alteration of predatory behavior of a gener-
alist predator by exposure to two insecticides
Radek Michalko1,2, Booppa Petcharad3, Sara Bumrungsri3,
Ondrej Kosulic4
1Department of Botany and Zoology, Faculty of
Sciences, Masaryk University, Kotlarska 2, 611 37
Brno, Czech Republic; 2Department of Forest Ecology,
Faculty of Forestry and Wood Technology, Mendel
University in Brno, Zemedelska 3, Brno 613 00,
Czech Republic; 3Department of Biology, Faculty
of Science, Prince of Songkla University, Hat Yai,
Songkhla, 90112, Thailand; 4Department of Forest
Protection and Wildlife Management, Faculty of
Forestry and Wood Technology, Mendel University in
Brno, Zemedelska 3, Brno 613 00, Czech Republic
Predation pressure exerted by spiders on pests depends on
their prey choice as well as predatory activity. However,
both traits can be altered by exposure to pesticides. Pos-
sible influence of pesticides on the predatory activity of
spiders is known for quite a few preparations and the
predatory activity can be decreased as well as increased.
However, the effects of pesticides on prey choice of
natural enemies have not been studied yet. The prey
choice in euryphagous spiders might be altered either by
the blurred cognitive abilities or by increased voracity,
which are sometimes connected to lower prey choosiness
in euryphagous spiders. Here we tested the effect of two
insecticides, SpinTor® (a.i. spinosad) and Integro®
(a.i. methoxyfenozide), on the predatory activity and
prey choice of spider Philodromus cespitum (Araneae:
Philodromidae). We investigated the prey choice of P.
cespitum between the pest Cacopsylla pyri (Hemiptera:
Psyllidae) and spiders Theridion sp. (Araneae: Theri-
diidae). We evaluated the predatory activity as overall
20th International Congress of Arachnology