Parasitic wasps can turn spiders into zombies by hacking their internal code

Parasitic wasps lay their eggs on the back of a spider. This team proposes that by injecting the spider host the molting hormone, ecdysone, the wasp causes the spider to create a special web to the nymph of the wasp.

By unleashing a surprising chain of events, a parasitoid wasp can force a spider to weave a special web to suspend the wasp pupa just before it finishes killing its spider host. William Eberhard, researcher emeritus of the Smithsonian Tropical Research Institute and Marcelo Gonzaga of the Federal University of Uberlândia in Brazil have gathered a great deal of evidence that "zombification" involved hacking existing Web rotation mechanisms by diverting the spider molt hormone, ecdysone.

In a new article published in the Biological Journal of Linnaean society they combined an analysis of all known reports on different species of wasps known to zombify different species of spiders around the world; the results of a molecular study in Brazil; and new observations of Costa Rican spiders demonstrating several models until then unknown suggesting that wasp larvae use ecdysone.

Researchers are particularly concerned about the ability of a single species of wasp to induce an impressive diversity of changes in the webs of many species of spiders. In the most complex cases, the construction of the spider web is assigned to different stages: from the selection of a site to the modification of several key design elements that usually result in a secure and stable home for its nymphal cocoon.

This feat is dramatic because the wasp's larva does not have direct contact with the spider's nervous system: it's an external parasite, overlapping on the surface of the spider. Spider's abdomen. Its only access to the spider's brain is through injections of psychotropic substances into the spider's abdominal sperm, then to be transported through the circulatory system of the spider. spider to his central nervous system.

"Several studies have suggested that wasp-induced webs sometimes look like webs that unparalleled spiders build just before moulting," Gonzaga said. "We combined this observation with an earlier finding that, in one genus, spiders that had just constructed cocoon webs had unusually high concentrations of ecdysone in their body, and we predicted that the specificity of the effects wasp larvae may already be present in the spider's nervous system, in the form of its specific behavioral responses to the hormone that controls its own moult cycle.By pirating in this system, wasps guarantee the safety of their own offspring at the expense of their host. "

"Now that we have a proposed mechanism, we can ask a new set of questions," said Eberhard. "The lines of the spider webs depicting accurate records of their behavior, we were able to study the" zombification "with unprecedented detail by examining the lines in the cocoon and moult webs. types of canvases vary and, more importantly, overlap partially.

"Larvae probably alter the construction behavior of the spider's web for additional protection.The mechanisms by which these additional modifications are obtained may result from differences in timing or quantities of ecdysone, or of modifications of the ecdysone molecules themselves, but they remain to be determined, "continued Eberhard.