Abstract
Apical serrations of the hymenopteran ovipositor have been widely postulated to originally constitute adaptations for cutting through hard substrates. Simplifications of the ovipositor tip have occurred in several ichneumonid wasp genera associated with spiders. Despite such reduction in Clistopyga (Hymenoptera, Ichneumonidae), the ovipositor still possesses some apical serrations. Through the first detailed study, we believe, on the behaviour of an ovipositing Clistopyga species, we show that it can alter its ovipositor for different purposes and that the primary function of the apical serrations is clinging to its spider host as the spider attempts to escape. Intriguingly, we also discover a hitherto undocumented adaptation for the hymenopteran ovipositor. The female wasp seals openings in the silken spider nest by using its ovipositor on the silk in a highly sophisticated way that is comparable to how humans entangle wool by needle felting. By studying the ovipositor morphology through a scanning electron microscope, we elucidate how this works, and we hypothesize that by closing the nest the female wasp protects its developing kin.
Highlights
Female wasps typically have an ovipositor for inserting eggs into plant tissues or insect hosts
A few Clistopyga species have been reared from spider nests containing egg sacs [5,6], and there is a single record of a species reared from a cocoon found beside the dead body of a jumping spider (Salticidae) [7,8], indicating that at least some of the species act as idiobiont or even koinobiont ectoparasitoids of spiders [8,9]
The serrations at the apex of the lower valves show adaptations for three functional behaviours of the ovipositing female. (i) Solely by inserting the ovipositor tip into the host the female wasp clings to the struggling spider and prevents it from escaping during envenomation. (ii) With the aid of the ovipositor tip reinserted into the host after a successful paralysation, the female wasp performs physical manipulation of the host by repositioning the spider into a favourable posture for oviposition. (iii) after a successful oviposition, Clistopyga sp. instantly begins to stab the silk with its ovipositor around the site through which oviposition was accomplished
Summary
Female wasps typically have an ovipositor for inserting eggs into plant tissues or insect hosts. In most Ichneumonoidea, one of the superfamilies of parasitoid wasps including the families Ichneumonidae and Braconidae, the ovipositor serves a similar set of functions These are navigating or penetrating the substrate, locating and assessing the host, piercing and staying in the host, injecting venom and laying an egg [1]. The ovipositors can be used for infanticide by killing or removing eggs and larvae from already parasitized hosts prior to oviposition [2] Based on their life strategy, parasitoid wasps can usually be divided into two broad categories: idiobionts and koinobionts [3]. The studied species is an idiobiont ectoparasitoid of jumping spiders (NR Fritzen, in preparation) It attacks and permanently paralyses the host within its silken nest. We concentrate on the functional morphology of the ovipositor tip in the ovipositing female
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