For a female butterfly, a male has to look and smell right before she'll choose him as a mate. Green-veined white butterfly males, Pieris napi, release a lemony smelling compound called citral, but up until now researchers didn't know what its role was. So Anna-Karin Borg-Karlson and her colleagues at KTH, Stockholm and Stockholm University, investigated whether citral would help males snare a mate(p. 964).

To find out when male butterflies release citral, the team measured how much they released as they flew in a sealed cylinder in the presence of male and female butterflies, of the same and different species. They found that males released citral whenever they flew, not specifically in the presence of females. But were females more responsive than males to citral? Next, the team measured the electrical response of male and female antennae as they wafted citral over them. They found that female antennae were 10 times more sensitive to the compound than males.

Finally, they tested the effect of citral on female mate acceptance behaviour. Virgin females accepted models of male butterflies with citral on their wings as potential mates, but paid no attention to citral free models. This behaviour, plus the sensitivity of females to citral, suggests that it functions as a sex pheromone in these butterflies, helping males attract a mate.

Andersson, J., Borg-Karlson, A.-K., Vongvanich, N. and Wiklund,C. (
). Male sex pheromone release and female mate choice in a butterfly.
J. Exp. Biol.