Effects of prey type and mixed dites on survival, growth and development of a generalist predator, Pardosa lugubris (Araneae: Lycosidae)

Spiders are generalist predators with a wide food spectrum which is considered to predominantly consist of qualitatively equivalent prey. To prove this assumption, laboratory feeding experiments were conducted with the lycosid spider Pardosa lugubris (Walckenaer) (Araneae: Lycosidae). Survival, growth and development of juveniles reared on single and mixed diets differed strongly. Spiderlings feeding on single prey species of the Collembola Folsomia candida, the aphid Rhopalosiphum padi and conspecifics did not develop or grow. Spiderlings feeding on the Collembola Heteromurus nitidus or the Diptera Drosophila melanogaster lived considerably longer and grew bigger. Feeding on E candida resulted in survival rates equal to those of spiderlings with food deprivation. Of the single prey species diets, H. nitidus resulted in maximum rates of survival, growth and development. D. melanogaster ranked second which was due to high mortality during or after molting to the fourth instar. Compared to single prey species diets, a mixed diet consisting of H. nitidus and D. melanogaster increased survival, growth and development of spiderlings. Adding E candida to the mixed diet consisting of H. nitidus and D. melanogaster resulted in a dramatic decrease in overall food quality. Survival, growth and development of spiderlings decreased strongly. The results document that the nutritional quality for generalist predators differs significantly between prey species. Mixed diets may be beneficial but also detrimental. P. lugubris appears to be unable to recognize and refuse detrimental prey species in mixed diets. The presence of toxic or low quality prey species may therefore counteract the benefits of mixed diets for generalist predators.