A mechanism for movement of eggs along insect ovipositors

Abstract This paper aims to describe in detail the mechanism by which eggs are moved along the length of the ovipositor of insects. A series of posteriorly orientated scales, located along the inside of the ovipositor valves, catch the surface of the egg as it emerges from the oviduct and move it along the ovipositor as the valves oscillate back and forth. The morphology of ovipositor scales is examined by scanning electron microscopy, and is compared for 22 species in 20 Families of insects. The mechanism is also confirmed by direct manipulation of the ovipositor of an anaesthetized insect. Ovipositor scales vary in length from 1 to 30 μm and can be spine-like, comb-like or scale-like in structure in different species. Caddis-flies (Trichoptera) were the only group examined which did not possess ovipositor scales. One species, Philanisus plebeius Walker, has longitudinal ridges along the inside surface of its ovipositor valves. The lack of ovipositor scales in the caddisfly species examined in this study is discussed in relation to their behaviour and possible oviposition sites.

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