Boletín de la AeE

All parasitoids face the problem that their offspring must either find or be provided with a host, typically another insect. The two alternative ways of achieving this aim is are either for the adult parasitoid to provide its offspring with a suitable host, that is to lócate one and to oviposit in, on or sufficiently near it. Alternatively, the adult may play little or no part in host location and simple deposit its eggs in more or less suitabíe places and to rely on its Ist instar larvae fmding their own hosts. For the most part, and probably ancestrally, the parasitic Hymenoptera follow the former strategy, whereas many, though by no means alL non-hymenopteran parasitoids make use of larval host-location. So why have the parasitic Hymenoptera been so successfull in their adherence to the former strategy? Two reasons: fírstly they have an ovipositor which is particularly well adapted to penetrating substrates enabling them to attack concealed hosts, and secondly, their ovipositors are furnished with many and various sensilla. In this talk we will focus on the latter.

Sense organs are present both on the truc ovipositor val ves and often also the ovipositor sheeths. Mechanoreceptors are typically present on the 2nd valvifers and proprioreceptors in first and sometime second valvulae are probably involved in perceiving movements of the different pieces and defonnations of the ovipositor during egg laying. Various morphological types of sensilla are found on third valvulae. They seem to be especially mechanoreceptors. Their number differs between species, according to the use of third valvulae in host exatnination. First and second valvulae bear sensilla of various types, number and distribution. From ultrastructural studies, they appear to be mechanoreceptors and contact chemoreceptors. They are probably involved in egg location inside the host host acceptance and recognition of already parasitized host. Compared with others insect groups, sense organs on female genitalia in parasitic Hymenoptera are characterised by i) reduced size, ii) peculiar morphological types iii) greater proportion of gustatory receptors compared to mechanoreceptors.

The types of sensilla present and their distributions on the ovipositor are related to the way the host is parasitised and also to the substrate on or in which the host lives. Much comparativa work on the ovipositor sensory system needs to be carried out, but some preliminary fíndings will be presented.