The remarkable biology of a new species of Gelis Thunberg, 1827 (Ichneumonidae, Phygadeuontinae), a solitary endoparasitoid of fresh eggs of Timarcha (Coleoptera, Chrysomelidae)

Mark R Shaw,Martin Schwarz,Pieter Kan,Brigitte Kan-Van Limburg Stirum

doi:10.3897/jhr.82.64657

Mark R Shaw, Martin Schwarz + Show 2 more

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https://doi.org/10.3897/jhr.82.64657

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Abstract

A new species, Gelis timarchae Schwarz, Shaw &amp; Kan, is figured and described from specimens reared as a solitary endoparasitoid of fresh eggs of Timarcha nicaeensis in the south of France. Oviposition behaviour of the adult parasitoid, directly into the host cytoplasm, is described and links to videos are given. This appears to be the first record of any ichneumonid developing as an endoparasitoid of an insect egg, and it is a major departure from hitherto known ectoparasitoid (or spiders’ egg-predation) behaviour in the genus Gelis. Fluid from the host egg issuing from the base of the parasitoid’s ovipositor early in the oviposition process is interpreted as a necessary reduction of hydrostatic pressure before the parasitoid egg can be forced down the ovipositor. The egg and first instar larva are figured; the latter is caudate, with the caudal appendage very unusual in being bifurcate. The complex phenology and diapause of the parasitoid were investigated partly experimentally; it is broadly bivoltine with a prepupal diapause in summer, but extra generations and prolonged diapause were both also seen.

Highlights

The phygadeuontine genus Gelis Thunberg exhibits a wide range of morphological forms, its various species being fully winged, brachypterous or apterous, sometimes with plasticity and often with sexual dimorphism in these respects
In this paper we describe a remarkable and quite profound departure from the normal biology of Gelis species: one that oviposits directly into the newly-laid large egg of another insect, in which the whole of the parasitoid’s larval development takes place as a solitary endoparasitoid in the cytoplasm
The univoltine Timarcha nicaeensis has two main oviposition periods, prolonged in each case: in autumn and again in early spring to early summer

Summary

Introduction

The phygadeuontine genus Gelis Thunberg exhibits a wide range of morphological forms, its various species being fully winged, brachypterous or apterous, sometimes with plasticity (as investigated by Salt 1952) and often with sexual dimorphism in these respects. Muesebeck and Dohanian 1927; Salt 1952; Harvey 2008), or successive egg predators within spider egg sacs and often developing gregariously. Host information is known for a number of species (see Schwarz and Shaw 1999), demonstrating that particular species show absolute fidelity either to spider egg sacs or to other hosts and that, within the last category especially, host ranges vary from being extremely specialised to remarkably catholic and often involving several orders of insects. In this paper we describe a remarkable and quite profound departure from the normal biology of Gelis species: one that oviposits directly into the newly-laid large egg of another insect, in which the whole of the parasitoid’s larval development takes place as a solitary endoparasitoid in the cytoplasm. The Gelis species proved to be undescribed, and it is described below

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