1. Chemical espionage in nature may occur when predators or parasitoids home in on animal or plant communication signals.
Parasitoid wasps are known to use pheromones emitted by adults hosts to locate host eggs, larvae or pupae. The response of
Trichogramma egg parasitoids to a synthetic sex pheromone blend of moths has been shown in a number of studies over the past
2. Trichogramma pretiosum (Hymenoptera, Trichogrammatidae) is a tiny parasitic wasp, attacking the eggs
of the noctuid moth Heliothis virescens (Lepidoptera, Noctuidae). This study investigated whether T. pretiosum homes in on
the sex pheromone of H. virescens at close range. The arrestment response of the wasps to sex pheromone gland extracts of
two types of female moths, so-called high and low females, was also tested, referring to two selected extreme pheromone types
of H. virescens. The study also investigated whether the wasps would mount females, possibly to hitchhike with them.
The wasps were arrested by the common, ‘low’ pheromone, but not by the rare, ‘high’ pheromone or by extracts from male hairpencils.
The wasps did not show a preference for separate sex pheromone compounds, but when pre-exposed to the major sex pheromone
component of H. virescens before the tests together with H. virescens eggs, they did show a preference, indicating learning
behaviour. In the mounting experiments, mated females were mounted significantly more than virgin females or males, suggesting
that hitchhiking is a strategy used by these wasps to locate moth eggs.
4. This represents the first study to show
a differential response of parasitoid wasps to two different sex pheromone types in a single host species. The results warrant
further investigations into the potential role of parasitic wasps in the evolution of sexual communication in moths.