Scent of a moth

Natural History, March, 2007 by Nick W. Atkinson

Female moths of the species Utetheisa ornatrix boost their chances of attracting a mate by pumping out sex pheromones in unison--the olfactory equivalent of chorusing frogs--according to new research. Hangkyo Lim and Michael D. Greenfield, both behavioral ecologists at the University of Kansas in Lawrence, tested females in the laboratory to find out whether they adjust their chemical signaling in the presence of other females. Females housed in groups began releasing pheromones sooner and continued to signal longer and with fewer interruptions than did isolated females. They also appeared to signal more vigorously: the group-housed females pumped their abdomens more rapidly, a behavior thought to enhance the release of pheromones.

Until now, biologists had described sexual communication in moths largely as a straightforward interaction between signaling females and responsive males, which fly upwind toward the source of the pheromones they detect. Lim and Greenfield's findings, however, show that female U. ornatrix moths also keep track of what their competitors are doing, suggest ing that the story in that species is more complex.

Unlike the males of most other moth species, U. ornatrix males mate infrequently compared with females, because it takes the males several days to produce a spermatophore--a kind of insect prenuptial gift that carries nutrients, toxins to ward off predators, and sperm. That valuable gift entices females to mate multiple times, another behavior unusual in moths. Those quirks lead to a circumstance fairly uncommon in nature: the sexually receptive females outnumber the males. Lim and Greenfield suspect that the competitive signaling behavior of U. omatrix females stems from the surplus. (Behavioral Ecology)