Oviposition behaviour and eggshell structure in some libellulid dragonflies, with particular reference to Brachythemis lacustris (Kirby) and Orthetrum coerulescens (Fabricius) (Anisoptera)

The eggshell of Brachythemis lacustris contains a trabeculate endochorion and an exochorion perforated by aeropyles; that of Tholymis tillarga is similar but it has a much higher density of aeropyles. In both spp. wetting the exochorion at oviposition causes it to become sticky and to attach firmly to the substrate. Later it hardens to form a more or less continuous, perforated covering over the eggs: no evidence for the addition of a spumaline in the vagina was obtained. It is suggested that the shells in these species act as plastrons with properties adjusted to the differing epiphytic modes of each. — The eggshells of Orthetrum coerulescens and Sympetrum danae are not trabeculate. On being wetted they produce, after a variable latency, a thick, sticky coat of jelly probably derived from material in the exochorion. It surrounds each egg, separating the eggs within a cluster, and it remains deformable throughout development.