Meeting Abstract
Parasitic wasps of the superfamily Ichneumonoidea use ovipositors to lay eggs in or on arthropod hosts which are often hidden in substrate. The physical properties of the substrate can differ significantly. Some hosts use soft substrates, such as rotten fruit, and others use hard substrates, such as wood. Field observations show that ichneumonoid species prefer single host species often found in a specific substrate. It may be assumed that during evolution the ovipositor adapted to the physical properties of the specific substrate. For 113 species we obtained morphologies and host preferences from literature, and used these to find morphological adaptations for specific substrates. The egg-laying preferences were categorized in six classes varying from drilling in hard substrate to non-penetrating egg-laying on exposed hosts. We used morphological characters relevant for ovipositor stiffness and internal stress reduction, which limit buckling and avoid breaking of the ovipositor. The ovipositors consisted of three moving parts, which are linked via a tongue and groove (aulax-rachis) mechanism. A multivariate discriminant analysis showed that the largest differences between animals in different substrate classes are in this tongue and groove mechanism. The mechanism is large when hard substrates are used, and smaller in species that use exposed larvae. This indicates that drilling creates stress on the sliding mechanism, and that the valve movement might be important for drilling. Other parts of the morphology seem less affected by substrate characteristics, but might be affected by other functions such as egg transport or sensory functions.
