Parasitic wasp tracks down fertilized butterfly by its smell

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Lev Bely, 20.02.2012 16:41

Parasitic wasp tracks down the Large White butterfly (Pieris brassicae) female which is ready to lay eggs by its special anti-sex smell that repels males. The wasp hangs on the butterfly and being carried suchwise to the Brussels sprout plants where the butterfly lays eggs.

A joint research project* of entomologists at Wageningen University and the Free University of Berlin (Freie Universität Berlin) pointed out some curious details about wasp's demeanor. “Parasitic wasps often hitch a lift with butterflies, but in this case we discovered that the parasitic wasps make use of an anti-sex scent emitted by the butterfly. It is an ingenious form of scent espionage that enables the parasitic wasp to ignore the sex female butterflies that are still virgins, and therefore will not lay eggs,” explains Nina Fatouros of the Freie Universität Berlin.

With colleagues from Wageningen University they made a series of scent experiments with P. Brassicae and parasitic Trichogramma wasp to know what's actually the mechanism of such kind of espionage. When mating Large White butterfly males transfer to their partners benzyl cyanide that's meant to repel other males. The small Trichogramma wasp which is a natural enemy of the Large White butterfly feels that smell and discerns fertilized butterflies ready to lay eggs. “If we treat virgin female butterflies with the scent they suddenly also become attractive to the parasitic wasps,” says Fatouros. So, the wasp can easily track down the butterfly, then it hangs on it and being carried right to the place for egg-laying in a Brussels sprout plant. Once eggs have been laid, the wasp climbs down the butterfly and lays its own eggs in the butterfly's ones. “It’s a clever strategy as Trichogrammas are not known for their good flying,” according to Fatouros.

Entomologists expect that the understanding of how parasitic wasps find butterfly eggs will improve biological control of caterpillars and make it more efficient.

*The results of a joint research project of entomologists at Wageningen University and the Free University of Berlin were published on 17 February 2005 in Nature.

Resource, http://resource.wur.nl

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