Abstract
Data on the webs, prey spectrum, density and fecundity of Theridion impressum from three different habitats [fields of sunflower, fiddleneck (Phacelia), and apple trees] are presented and discussed. The volume of webs were found to vary between 5 (the first free instar) to 117 cm3 (subadult and adult specimens). The mean density of adult spiders per plant was 0.7 (sunflower), 1.5 (fiddleneck) and 1.2 (per apple branch). Spiders preferred to build webs in the upper part of vegetation or at the extremities of tree branches. The prey spectrum was assessed by collecting webs and identifying their contents. Prey items were primarily aphids (73%), Diptera (7.5%), acid Coleoptera and Hymenoptera (both 5.4%). Pests comprised 90% of the prey; the remaining 10% was accounted for by natural enemies, pollinators and other insects. The number of insects captured in webs differed among study habitats (sunflower > fiddleneck > apple tree) though this difference was not statistically significant. Due to greater numbers of aphids in webs on sunflower, the mean prey length was significantly smaller on sunflowers than in other plots. An index of fecundity was obtained by counting the number of eggs in eggsacs. This varied from 48 to 156 per eggsac and was not significantly different between study plots. The number of eggs was strongly correlated with numbers of prey captured per spider.
Highlights
Serious study of the importance of spiders for the con trol of insect pests started fairly recently (e.g. Kiritani et ah, 1972)
I aimed to collect data necessary for parametrisation of variables that are going to be used in a mathematical model simulating the popula tion dynamics of this species
Later instars occurring in spring constructed larger webs (64.3 ± 13.9 cm3) which were spun between two stems of plants or twigs of tree branches
Summary
Serious study of the importance of spiders for the con trol of insect pests started fairly recently (e.g. Kiritani et ah, 1972). This pioneering research focused on the whole community of spiders. Koch was the most abundant canopy species It is one of the most com mon spiders in Europe so there is quite a lot known about its biology Nielsen, 1932; Kirchner & Kullmann, 1975), some aspects still remain to be unveiled This species prefers to construct webs on low vegetation. I aimed to collect data necessary for parametrisation of variables (such as web density, mean abundance, and fecundity) that are going to be used in a mathematical model simulating the popula tion dynamics of this species
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