1. ETH Zürich, Experimental Ecology, ETH-Zentrum NW, CH-8092 Zürich, Switzerland

Correspondence to: Paul Schmid-Hempel¹ Correspondence and requests for materials should be addressed to P.S.-H. (e-mail: Email: psh@eco.umnw.ethz.ch).

Abstract

In many species of animals, females typically mate with more than one male (polyandry). Some social insects carry this behaviour to extremes¹. For example, honeybee queens mate with ten to twenty (or even more) males on their nuptial flights². The reasons for this behaviour remain unknown, given the obvious costs of time, energy and exposure to predation. Several potential benefits of polyandry have been proposed¹,³,³,⁴, but none are well supported yet. Here we test the hypothesis that genetic diversity among a female's offspring may offer some protection from parasitism^{5, 6, 7}. We artificially inseminated queens of a bumble-bee (Bombus terrestris L.) with sperm of either low or high genetic diversity. The resulting colonies were exposed to parasitism under field conditions. High-diversity colonies had fewer parasites and showed greater reproductive success, on average, than did low-diversity colonies. We suggest that female mating frequency may be influenced in part by parasites.