Karma is a real pest for parasitoids, tiny parasitic wasps that lay their eggs on caterpillars. That’s because the way they protect their hungry young from the caterpillar’s immune system sends out a chemical calling card that lures other parasites, which feast on the offspring, according to a new study.
For the parasitoid’s brood, a caterpillar is a walking nursery and buffet. But that brood is on the menu for wasps called hyperparasitoids, which lay their eggs on the parasitoid offspring. Researchers previously found that hyperparasitoids sniff out their victims using the distinctive aroma a plant emits when being munched by a parasitized caterpillar.
What’s ultimately responsible for the release of this odor, scientists report today in the Proceedings of the National Academy of Sciences, is a virus that parasitoids squirt into a caterpillar to suppress its immune system and shield their offspring. When the researchers injected caterpillars with the virus and let the insects gnaw on wild cabbage plants, they found that the scent of the plants was particularly attractive to the hyperparasitoid Lysibia nana (above, laying its eggs on the parasitoid’s cocoons). The study suggests the virus changes the chemical composition of the caterpillars’ saliva, which in turn causes the plant to release molecules that are wasp-nip for hyperparasitoids.