Habitat manipulations increasing spider densities in agroecosystems: possibilities for biological control?

Abstract

Field experiments with habitat manipulations were conducted in Belgian crop fields in order to follow changes in abundances and species composition of the spider taxocoenosis. Spider densities increased spectacularly in plots with holes (up to 13 times) in the soil. Moreover, this density increase depends on the diameter of the holes, with diameter 9.5 and 5 cm being the most effective. Species composition in the plots with holes also changed considerably compared to control plots. Exclusively web building Linyphiidae (Bathyphantes gracilis and Lepthyphantes tenuis) took far more advantage of the new possibilities offered by the habitat for web construction than non web‐building spiders. B. gracilis preferred holes with a diameter of 5 cm whereas L. tenuis was more abundant in the D9.5 cm plots. It is concluded that this kind of relatively simple habitat manipulations are advantageous for population levels of certain beneficial polyphagous predators, such as spiders. This might offer possibilities for biological control of pest populations.

Effects of agricultural diversification on the abundance, distribution, and pest control potential of spiders: a review

“…There was also a tendency for the magnitude of the enhancement of spider abundance to be greater for interspersed than for aggregated diversification (Table 1). The largest enhancement factors were × 13 for increased ground zone heterogeneity (Alderweireldt, 1994) and × 10 for mulching with straw . We suggest that spiders tend to remain in diversified patches where conditions are optimal and that to increase spider density on and below crop plants, where they can impact maximally on pests, it is necessary to extend the diversification throughout the entire crop, as in interspersed diversification.…”

“…Weed cover improves the microclimate and increases the amount of alternative food in the form of herbivores and detritivores (Altieri & Whitcomb, 1979;Purvis & Curry, 1984). Weediness and undersowing increase the availability of structural support for webs, but there is also, as we have seen, potential for augmenting the density of ground zone web spiders by increasing the structural heterogeneity of the soil surface (Thornhill, 1983;Alderweireldt, 1994;Samu et al,1996). Rich structure and the close spatial packing of different microhabitats could also support higher spider densities by reducing mortality, since there are various strands of evidence that have led authors to consider the risk of predation to be high when spiders move between microhabitats (Edgar, 1969;Enders, 1975Enders, , 1976Enders, , 1977Vollrath, 1985;Bradley, 1993;Gunnarsson, 1996).…”

“…We suggest that spiders tend to remain in diversified patches where conditions are optimal and that to increase spider density on and below crop plants, where they can impact maximally on pests, it is necessary to extend the diversification throughout the entire crop, as in interspersed diversification. One of the convincing diversification experiments was performed by Alderweireldt (1994), who increased the heterogeneity of the ground in Belgian maize fields by spreading out clods of earth and by creating 10 cm deep circular holes of various diameters. The clods of earth did not result in a significant increase in spider density but the holes were colonised by web-building Linyphiidae, with Bathyphantes gracilis preferring 5 cm diameter holes and Lepthyphantes tenuis preferring holes with a diameter of 9.5 cm.…”

Do spiders respond to global change? A study on the phenology of ballooning spiders in Switzerland

“…We also revealed a clear difference in the population trends according to habitat use: most ground-level species decreased, while most upper-strata species increased. Management to improve habitat quality in agroecosystems could counteract this impoverishment (Haaland, Naisbit & Bersier, 2011;Nentwig, 2000), e.g., manipulation of microhabitats (Alderweireldt, 1994;Marc, Canard & Ysnel, 1999). Ecology c d 1994d 1995d 1996d 1997d 1998d 1999d 2000d 2001d 2002d 2004d TOTAL 1994d -2004d 1994d -2002 Thomisidae …”

Chemical Control of Spiders and Scorpions in Urban Areas

“…Spiders are not only considered targets of pest control programs. They can be used for the control of insects in integrated agricultural pest management programs [3,26,27]. Most of the studies on the susceptibility of spiders to pesticides are based on an evaluation of agricultural products used in the field.…”