Biological and morphological studies on the parasitoids (Hymenoptera, Ichneumonidae) of Aprosthema tardum (Klug) (Hymenoptera, Argidae, Sterictiphorinae) in Var, southern France

Abstract

Field surveys at four neighbouring but discrete sites in southern France revealed the presence of five ichneumonid parasitoids of the Lathyrus-feeding sterictiphorine argid sawfly Aprosthema tardum. Four of these parasitoids, Lathrolestes erythrocephalus, Ischyrocnemis goesi (both Ctenopelmatinae), Terozoa quadridens and Thibetoides aprosthemae (both Tryphoninae), could be identified and, by also incorporating laboratory studies, the developmental biology of each was elucidated and illustrated. A little supplementary information from a site in Italy is also presented. The fifth species was detected only once and failed to develop in its cocoon; it remains unidentified but the cephalic sclerites of its final instar larva are illustrated. The identified parasitoids are all more or less rare and little-known species and prior to this study only L. erythrocephalus had a known host; the others were biologically unknown even at the generic level and not recorded from France. The egg of L. erythrocephalus bears prominent hooked structures at its capital end, not reported in other studied Lathrolestes species. From its biology as an endoparasitoid of a sawfly and from larval characters, Ischyrocnemis is confidently assigned to Ctenopelmatinae. Both ctenopelmatines could successfully parasitise the host during any of its 2nd to 5th instars, but the tryphonines were less flexible. Terozoa monitors hosts until the moult to the final instar before ovipositing on them, usually affixing the egg to the head and often an eye (stemma), while Thibetoides parasitises much younger hosts, placing its strongly anchored egg behind a thoracic leg where it remains through successive host moults. Some characters used in the past to determine Terozoa species are discussed, and a new provisional key to the known species of Terozoa is presented. The very different developmental biology of Terozoa and Thibetoides may challenge views that they are closely related genera. Terozoa bituberculata (Constantineanu, 1973), stat. rev. is raised from synonymy with T. quadridens Perkins, 1962. Reinterpretations of several cephalic structures of final instar larvae as well as larval spiracles are discussed, and a new interpretation and terminology for describing the latter is introduced.