Paralyzing Spray Used in Female Combat

Scientists have found that the tiny parasitoid wasps can use a kind of pepper spray in their heads, when fighting other individuals. Many species of parasitoid wasps are used in biological pest control, so knowing more about their behavior could improve their use.

The chemical weapon was found for the first time on the females of a bethylid wasp - Goniozus legneri, when they fight over larvae to lay their eggs. The chemical was always sprayed by the losing wasp. The larvae of the parasitoid wasps develop inside the larvaer of pest insects, devouring them while alive, and at the end, they finish their hosts. Killing this way pest insects are very useful in non invasive biological pest control, in an ecological agriculture.

"Bethylid wasps kill the larvae of many insects that are pests of crops, such as almonds, coffee and coconut, ruining harvests and costing industry thousands of pounds. These wasps could be used as a cheap and effective biological control to kill the larvae, avoiding the use of expensive and polluting pesticides. But for successful biological control, we need a good knowledge of wasp behavior, including how wasps from the same and different species interact. Understanding these patterns can inform us of the best combinations of species to release against a given crop pest." explained Dr Ian Hardy, from the University of Nottingham.

The researchers introduced it in a transparent chamber where one "owner" female had already paralyzed a host larva for its eggs 24 hours before the other wasp. The experiment was repeated many times. Using a new real-time chemical analysis technique, Atmospheric Pressure Chemical Ionization Mass Spectrometry (APCI-MS), and video recordings, the researchers could see and, at the same time, study the visible and chemical behavior of the insects. The wasps displayed chasing, biting, stinging and full-on fighting. The analysis proved that a volatile chemical, a type of spiroacetal, was sprayed by the wasps when losing fight.

Dr Hardy said: "Our research suggests that wasps which have lost a fight release spiroacetal to temporarily and partially incapacitate the winner, it could be likened to the insect version of pepper spray. The volatile chemicals released by the wasps may prompt females to disperse away from the target area. If we understand how to reduce chemical release behavior we can improve the efficacy of these wasps in pest control".

Professor Julia Goodfellow said: "This research highlights the benefits of understanding animal behavior and the impact this can have on finding solutions to tackle costly problems such as pest control."

Photo credit: Sonia Dourlot