Some plants are known to attract parasitic wasps to eat the eggs laid on them by insects. However, the exact mechanisms of this complex defensive behaviour are not clear.
Nina Fatouros at Wageningen University in the Netherlands and her colleagues have determined that in one case the mechanism is triggered by a specific compound in male insect ejaculate. The ejaculate of male large cabbage white butterflies (Pieris brassicae) contains anti-aphrodisiac benzyl cyanide to reduce female re-mating. This compound is then present on or around their eggs.
Application of benzyl cyanide induced chemical changes in the leaves of Brussels sprout plants, Fatouros's team found. As a result, the parasitoid wasp Trichogramma brassicae spent more time on treated leaves than on controls. So, for P. brassicae males, the anti-aphrodisiac trick has some cost.
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Plant biology: An egg-spedient defence. Nature 454, 140 (2008). https://doi.org/10.1038/454140e