Seasonal dynamics of prey utilization and individual specialization in a generalist spider in a pear orchard

Abstract

Populations of generalist predators are often comprised of a mixture of specialist and generalist individuals and this intraspecific variation in prey utilization may affect pest suppression. However, little is known about seasonal changes in prey utilization by generalist predators, especially during winter, when some generalist predators exert strong biocontrol effects. We used prey preference experiments on Philodromus cespitum (Araneae: Philodromidae) and molecular gut-content analyses of Philodromus spp. (dominated 85% by P. cespitum) to study the dynamics of spider specialization in a pear orchard during the non-growing season. In the laboratory, P. cespitum preferred springtails (Collembola) over the pear psylla, Cacopsylla pyri, an important pest of pear. The presence of springtails in guts of Philodromus spp. did not affect detection of psylla by molecular gut-content analysis in specimens collected from the pear orchard. The philodromid population comprised of a mixture of specialists and generalists in winter, but was composed mainly of generalists in spring. Greater variation in prey utilization during winter most likely reflects a patchy distribution of prey and philodromids switching to a less active hunting mode. Seasonal specialization of individual generalist predators could be the result of their ability to change hunting mode in response to changing environmental conditions and prey distribution. Our study demonstrates that alternative (collembolan) prey are unlikely to affect philodromid predation on psyllids and suggests that changes occur in the spatial structure of predator-pest interactions from winter to spring.