Authors: Kate D.L. Umbers; Matthew R. E. Symonds; Hanna Kokko.
Source: The American Naturalist, Vol. 185, pp.417-432, March 2015.
Brief summary of the paper: Male moths are well known for their exquisite antennae and ability to find female moths over long distances via pheromone plumes.
On the other hand, the problems that female moths face are more subtle. Females have to emit pheromones for males to find them, but they also try to avoid becoming too conspicuous. How ‘loud’, chemically speaking, should a virgin moth be, when she can’t be sure of how many males are around her? If she calls too quietly, she might die before she is found; if she is too loud, she might attract too many males, and maybe eavesdropping predators too.
In this paper we develop new theory to investigate optimal calling strategies females and show that the optimal strategy is for a female to start out relatively quietly and then, if night after a night she is still a virgin, gradually increase her calling effort.
Our survey of previous studies of calling finds that this is indeed the strategy most species adopt, but only in one respect. Traditionally, researchers have measured two aspects of female calling: how long they call each night and the concentration of pheromone they produce.
The data show that females of the majority of moth species so far studied do increase the amount of time they spend calling as they age as virgins, but there is no clear trend in the amount of pheromone they produce.
This, together with another mathematical model of how precisely a plume of pheromone spreads in the environment, suggests that changes in the amount of time a female spends signalling is a better way for her to adjust the number of males she attracts than trying to adjust the concentration of the pheromone cloud.