Neuroethology of Parasitoid Wasps

Predators as diverse as snakes, scorpions, spiders, insects and snails manufacture venoms to incapacitate their prey. Most venoms contain a cocktail of neurotoxins and each neurotoxin is designed to target specific receptors in the nervous and muscular systems. Most neurotoxins act peripherally and interfere with the ability of the prey's nervous system to generate muscle contraction or relaxation, resulting in immobilization and often death of the prey to be consumed immediately. Unlike other venomous predators, some parasitoid wasps manufacture venoms to manipulate the host nervous system in ways that are tailored to the developmental needs of their offspring. The direct manipulation of the host nervous system and behavior may take several forms. In some instances the venom is purely paralytic, affecting either the peripheral or central nervous system to induce true paralysis, which can be transient or long-lasting. In other instances, the venom induces a neuro-chemical manipulation of specific behaviors of the host. Although the alteration of host behavior by parasitoids is a widespread phenomenon, the underlying neuronal mechanisms are only now beginning to be deciphered. As of today, only a few behavioral alterations can be unambiguously linked to alterations in the nervous system. The direct manipulation of the host nervous system and behavior may take several forms. In some instances the venom is purely paralytic, affecting either the peripheral or central nervous system to induce partial or total paralysis, which can be transient (seconds to minutes), long-term (hours to days). In other instances, the venom might affect behavioral subroutines to produce finer manipulations of the host behavior. A remarkable example of such manipulation is that of the braconid parasitoid wasp (Glyptapanteles sp.) that induces a caterpillar (Thyrinteina leucocerae) to behave as a bodyguard of its offspring. After parasitoid larvae exit from the host to pupate, the host remains alive but displays stunning modifications in its behavior: it stops feeding and remains close to the parasitoid pupae to defend these against predators with violent head swings. The parasited caterpillar dies soon after while unparasitized caterpillars do not show any of these behavioral changes. But the most formidable alteration of behavior ever attributed to a parasitoid wasp is probably the Ichneumonid wasp Hymenoepimecis's manipulation of its spider host. In this exceptional example of host behavioral manipulation, the parasitoid wasp takes advantage of the natural behavior of web waving of its prey to provide the larva with a shelter. Instead of paralyzing …