The ovipositor apparatus of basal Hymenoptera (Insecta): phylogenetic implications and functional morphology

The skeleto-musculature of the ovipositor apparatus and the external sculpture of the 1st and 2nd valvulae was studied in representatives from all 'symphytan' families. Nineteen informative characters were coded and scored. The distribution of character states are discussed with reference to recent cladistic treatments of the Hymenoptera. Putative autapomorphies of the Hymenoptera are the presence of cordate apodemes on T9 and basal articulations and associated musculature between the 2nd valvifers and the 2nd valvulae. It is a ground plan feature of the order to have the gonocoxites of abdominal segment 8 fused with the gonangula. The configuration of the musculature of the ovipositor apparatus did not display much variation among the taxa examined, except within the Pamphilioidea. There is considerable variation in the external ovipositor sculpture within the Tenthredinoidea. Putative synapomorphies for the tenthredinoid families except the Blasticotomidae are the presence of alternating strongly and weakly sclerotized zones on the first and/or second valvulae and the presence of serrulae on the sawteeth. The presence of transverse rows of large ctenidia on the 1st valvulae is an autapomorphy of the Diprionidae. Fusion of the 2nd valvifers and the 3rd valvulae is a synapomorphy for the Argidae + Pergidae. The ovipositor apparatus of the Pamphilioidea is highly derived, putative autapomorphies being the close association between T9 and the first valvifers, the reduction of the distal parts of the 1st valvulae, and the fusion of the 2nd valvulae for their entire length. The changes in the ovipositor apparatus of Pamphilioidea are associated with a decrease in the amount of work it has to perform during ovipositing, as the eggs are placed predominantly externally on the substrate. The ovipositor apparatus of the 'Siricoidea' is enlarged and modified for ovipositing into wood. Putative synapomorphies of the 'Siricoidea' + Orussidae + Apocrita are the presence of sawteeth only distally on the ovipositor and elongation of the cordate apodemes of T9.