BODY SIZE AND LIFETIME MATING SUCCESS OF MALE MIDGES (DIPTERA, CHIRONOMIDAE)

Among insects that mate on the wing, small males should have the mating advantage by being more aerobatic than large males. However, this benefit could be outweighed by costs to small size in other components of fitness. The hypothesis that mated males of the midge Chironomus plumosus L. are on average smaller than unmated males was tested. Small males were predicted to pay for any such success with a reduced longevity and a reduction in flight endurance. Hence small males should achieve a lower lifetime mating success than their larger conspecifics. A predicted, small males had the mating advantage. However, small size did not accrue the expected costs. Although body size correlated positively with lifespan and flight duration for starved males, when given access to food, small males lived and flew for as long as larger competitors. Ultimately, small size did run into constraints. The rare, smallest males in a population could not maintain continuous flight. Hence small size is beneficial to male midges but reduction in size by sexual selection is balanced by physiological constraints on flight. © 1990 The Association for the Study of Animal Behaviour.