Hyperparasitoid defense strategies against spiders: the role of chemical and morphological protection

Abstract

The aphid endohyperparasitoid Alloxysta brevis (Thomson) (Hymenoptera: Charipidae) applies defensive chemicals stored in mandibular gland reservoirs against attacking ants. Alloxystines can be divided into species capable of exploiting ant-attended resources and into species exclusively reared from unattended aphid-parasitoid systems. Mandibular secretions are found in species of both groups, with little variation in chemical composition. We show that the mandibular gland secretion does not only protect against ant attacks but acts as an overall defense agent against generalist predators like spiders. The protective success differed with the spider species. The web-building spider Agelena labyrinthica (Clerck) (Araneae: Agelinidae) killed 57% of attacked A. brevis females, but sucked out only 8%. The smaller free-hunting jumping spider Salticus scenicus (Clerck) (Araneae: Salticidae) failed in overwhelming or severely injuring A. brevis. The pattern of interactions showed striking similarities with interactions between A. brevis and the ant Lasius niger (Hymenoptera: Formicidae). Primary parasitoids which are lacking chemical defense and sufficient morphological protection suffered significantly higher mortality due to spider predation. Our results indicate that - additional to chemical defense- parasitoid survival depends on the specific morphological resistance against grip pressure during capture, and on the predator - prey size relationship.