Daily production of spermatophores, sperm number and spermatophore size in two eriophyoid mite species

Abstract

Under dissociated sperm transfer, (non-pairing) males deposit spermatophores on a substrate, while females seek spermatophores and pick up sperm on their own. Spermatophore expenditures of non-pairing males should be high, due to the increased uncertainty of sperm uptake by a female. In this study I examined spermatophore expenditures in two eriophyoid species that differed in the degree of dissociation between sexes: (1) Aculus fockeui (Nalepa and Trouessart) males rarely visit quiescent female nymphs (QFNs), and mostly deposit spermatophores all over the leaves, whereas (2) Aculops allotrichus (Nalepa) males guard QFNs for many hours and deposit several spermatophores beside them. Males of both species were collected from the field and tested in solitude. Aculus fockeui males deposited on average 19.1 spermatophores per day, whereas A. allotrichus deposited only 3.6 spermatophores per day, and had a very large coefficient of variation. Males and spermatophores of A. allotrichus were significantly smaller and contained less sperm than those of A. fockeui. In both eriophyoids, spermatophore size was fitted to the size of female genitalia and the height of females. The ratio between the diameter of spermatophore head and the width of a female genital coverflap was 0.6, whereas the ratio between the female leg and the length of spermatophore stalk was 0.5. Several factors could be responsible for the discrepancy in spermatophore expenditures between species. Among other factors, the effects of male size, male reproductive strategy and female genitalia size on spermatophore output and size of spermatophores are discussed.