Wasps Squirt "Pepper Spray" From Heads in Fights, Study Says

November 28, 2006

When female bethylid wasps are losing a vicious fight, they squirt an insect version of pepper spray from their heads before beating a retreat, new research suggests.

The chemical release is undetectable to humans, but it could represent a crucial behavior that may help biologists use the parasitic wasps as natural pest controls.

(Related news: "Drug-Sniffing Wasps May Sting Crooks" [October 27, 2005].)

Bethylid wasps kill the larvae of several species of crop pests by using them as hosts for their eggs.

For example, the bethylid species Goniozus legneri targets the larvae of pests that plague almond plants.

Female wasps often fight over prime hosts, says Ian Hardy, a biologist at Nottingham University in the United Kingdom.

"Hosts are rare, so [the wasps] don't get too many chances to reproduce," Hardy said.

"So when they do get an opportunity, they make the most of it. They guard the host. When they find one that's being guarded by another female, they try to get it off her" by starting a fight.

Wasp Fights

To better understand the nature of these wasp fights, Hardy and colleagues staged 47 bouts between pairs of G. legneri wasps inside a transparent chamber built to resemble the inside of an almond nut.

Using a combination of video cameras and real-time chemical analysis, the team found that after particularly violent encounters, the loser wasp released a chemical from her head as she ran away.

"The more nasty the fights are in terms of aggression … the much higher the chance of there being a chemical release," Hardy said.

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