Parasitoid Wasp - Host Defenses

Host Defenses

The hosts of parasitoids have several levels of defense against them. Many hosts try to hide from the parasitoids in inaccessible habitats. They may also get rid off their frass (body wastes) and avoid plants that they have chewed on as both can attract parasitoids. The egg shells and cuticles of the prey are thickened to prevent the parasitoid from penetrating them. When they encounter the egg laying female, prey use defenses like dropping off the plant they are on, twisting and thrashing so as to dislodge or kill the female and even regurgitating onto the wasp to entangle it. The wriggling can sometimes help by causing the wasp to "miss" laying the egg on the host and instead place it nearby. Wriggling of pupae can cause the wasp to lose its grip on the smooth hard pupa or get trapped in the silk strands. Some caterpillars even bite the female wasps that approach it. Some insects secrete poisonous compounds that kill or drive away the parasitoid. Ants that are in a symbiotic relationship with caterpillars, aphids or scale insects may protect them from attack by wasps.

Even parasitoid wasps are vulnerable to hyperparasioid wasps. Some parasitoid wasps change the behaviour of the infected host to build a silk web around the pupa of the wasps after they emerge from its body to protect them from hyperparasitoids.

In endoparasitoids, host immune cells can encapsulate the eggs and larvae of parasitoid wasps. In aphids, the presence of a secondary endosymbiont, Buchnera aphidicola that carries a particular latent phage makes the aphid relatively immune to their parasitoid wasps by killing many of the eggs. However, wasps counter this by laying more eggs in aphids that have the endosymbiont so that at least one of them can hatch and parasitize the aphid.

Certain caterpillars eat plants that are toxic to both themselves and the parasite to cure themselves. Drosophila melanogaster larvae also self-medicate with ethanol to treat parasitism. D. melanogaster females lay their eggs in food containing toxic amounts of alcohol if they detect parasitoid wasps nearby. Despite the alcohol retarding the growth of the flies, it protects them from the wasps.