Hydropy and ultrastructure of egg envelopes in Aleochara bilineata (Coleoptera, Staphylinidae)

Aleochara bilineata oviposits in soil micro-habitats likely to contain the dipteran pupae that are hosts of its ectoparasitoid first instar larvae. Th e eggs of A. bilineata have a rigid chorion but they are nonetheless hydrop ic and, after 30 h of development, start to increase in volume and do so un til 50 h. This increase in volume is due to absorption of water. The eggs i ncrease their initial volume by a factor of 1.68 that corresponds to an inc rease of 44.44% of initial weight. To explain this augmentation in volume, we describe the modifications occurring in the egg chorion during hydropy. The increase in volume in such a rigid egg is made possible through the fra gmentation of the chorion which, initially dense and regular, becomes fragm ented. Such adaptation enables female A. bilineata to oviposit hydropic egg s in habitats where mechanical resistance is needed.