Bean weevils get a kick out of mates

The battle of the sexes turns out to be a literal description of the domestic life of the bean weevil, say British researchers.

A male bean weevil unfurls these injurious spines during mating. Andrew Syred/Microscopix

These insects, Callosobruchus maculatus, breed in stored grain throughout the tropics. The male’s agenda apparently includes reducing the chances that a female will mate with any weevil after she has mated him, say Helen S. Crudgington and Mike T. Siva-Jothy of the University of Sheffield in England.

In the Oct. 19 Nature, they report that the male body part that enters the female reproductive tract bristles with spikes. During mating, it does considerable tissue damage. That’s hardly an inducement for multiple matings, and females that mate again despite the injury don’t live as long as those that mate once.

The females aren’t passive victims. While mating, they kick males vigorously, apparently shortening the encounters: When researchers kept females from using their legs, matings lasted longer and caused more injury.

Bean weevils, conclude the researchers, represent an unusually clear example of the evolutionary male-female arms race.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.