Sept. 28, 2007 — An unusual benefit of mating may be taking place right now in your kitchen pantry.
A common food pest has evolved a unique way to survive in dry conditions — say, inside a bag of dried beans — says biologist Martin Edvardsson, who discovered that female bruchid beetles, also known as bean weevils, mate more when thirsty. Their male partners, it seems, give up a lot of water in exchange for the opportunity.
Mating as a means of survival (for at least one of the partners) could be widespread among insects, since males store up to 10 percent of their bodyweight as ejaculate, which has a high water content.
It's doubtful the same incentive exists for people and other mammals, although human semen does contain essential vitamins and minerals, as well as sugars.
"Female mammals are too big and need too much food and water for this to be feasible," said Edvardsson, who is currently working at the University of Exeter but conducted the beetle study at Sweden's Uppsala University..
He explained that men "would have to increase the size of their ejaculates by about 2,500 times to 2 gallons to be able to match the beetles.".
Bruchid beetles, also known as bean weevils, are tiny black, brown or mottled insects that bore into seeds or beans as young larvae. They become more visible when they mature and leave their legume hideaways.
Get the skinny on smooching. Get more Discovery News video here.
Since water and nutrients can be scarce after life in the legume, females may mate when thirsty, to obtain life-saving nutrients and water from the male's substantial offering. The females require more such resources to produce and lay eggs.
For the study, which has been accepted for publication in the journal Animal Behavior, Edvardsson maintained the promiscuous bugs on black-eyed beans in Petri dishes. Different groups of virgin females were kept with or without access to water and allowed to mate with virgin males.
Overall, the parched females mated more than the females with access to water.
