Arthropods (Sep 2012)
Effect of male densities on sex ratio variations of the predatory gall midge, Aphidoletes aphidimyza (Diptera: Cecidomyiidae)
Abstract
Monogeny, the production of unisexual broods by individual females, is a well-known characteristic in several species of gall midges (Diptera: Cecidomyiidae). Theoretical models have proposed that monogeny may provide a system by which the arrhenogenic/thelygenic females can optionally raise or lower the number of their male/female eggs in response to changes in environmental conditions. In polygynous species, where the males mate with several females, a sex ratio bias toward females is expected to occur when environmental conditions such as food and temperature are suitable. In this paper, first, we evaluated the occurrence and intensity of monogeny in native populations of the polygynous predatory gall midge Aphidoletes aphidimyza. Then, we examined the sex ratio variations in relation to different densities of males in the populations. Two proportions of male gall midges (5 and 12 unmated males vs. 10 virgin females) were obtained in plastic cages and the sex ratio of progenies was determined in each density. There was no difference between sex ratio of progenies when the females were exposed to high or low densities of males. Apparently, females cannot regulate the number of female-producing and/or male-producing progenies in response to male densities. Our results incline us to think about other benefits that may have been achieved through transition to monogeny.
