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

The aphid endohyperparasitoid Alloxysta brevis (Thomson) (Hymenoptera: Char ipidae) applies defensive chemicals stored in mandibular gland reservoirs a gainst 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 spe cies of both groups, with little variation in chemical composition. We show that the mandibular gland secretion does not only protect against ant atta cks but acts as an overall defense agent against generalist predators like spiders. The protective success differed with the spider species. The web-b uilding spider Agelena labyrinthica (Clerck) (Araneae: Agelinidae) killed 5 7% of attacked A. brevis females, but sucked out only 8%. The smaller free- hunting jumping spider Salticus scenicus (Clerck) (Araneae: Salticidae) fai led in overwhelming or severely injuring A. brevis. The pattern of interact ions showed striking similarities with interactions between A. brevis and t he ant Lasius niger (Hymenoptera: Formicidae). Primary parasitoids which ar e lacking chemical defense and sufficient morphological protection suffered significantly higher mortality due to spider predation. Our results indica te that - additional to chemical defense- parasitoid survival depends on th e specific morphological resistance against grip pressure during capture, a nd on the predator - prey size relationship.