The developmental cycles of two co-occurring sponge mites Unionicola crassipes (Müller) and Unionicola minor (Soar) (Acari, Hydrachnellae)

Abstract

A description is given of the annual cycles of the common sponge mites Unionicola crassipes and Unionicola minor, two very closely related species. In the Netherlands, both species have two cycles. The cycles were identified by collecting samples in the field and by breeding the different stages from sponge material.

Hibernating females of U. crassipes are active earlier in the spring than those of U. minor. Consequently the first generation peak of U. crassipes occurs about two weeks earlier than that of U. minor. The second generations of both species, following about two months later, roughly coincide. Niche overlap is prevented by the gap between the first generations of both species and possibly also by differences in prey selection. U. crassipes is larger than U. minor and able to select larger prey specimens (copepods) than U. minor.