Short-term host discrimination in the parasitoid wasp Trissolcus basalis Wollaston (Hymenoptera : Scelionidae)

The ability of host discrimination allows insect parasitoids to avoid super parasitism (oviposition in a previously attacked host). However, superparas itism can sometimes be adaptive, so attempts to identify host discriminatio n must be made under appropriate ecological conditions. We tested the abili ty of the parasitoid wasp Trissolcus basalis to discriminate between self a nd conspecific-parasitised hosts (conspecific discrimination) under ecologi cally realistic conditions, in which conspecific discrimination should be a daptive. Data were analysed using a Monte Carlo simulation model that permi tted testing of several different ways in which conspecific discrimination could be achieved. We obtained the novel result that females avoided self-s uperparasitism on a patch consisting of a mixture of self- and conspecific- parasitised hosts, but that this avoidance was not due to true conspecific discrimination. Instead, it was due to short-term discrimination between ne wly and previously parasitised hosts. Two likely mechanisms for such discri mination are proposed: a short-lived host-derived volatile; and the presenc e of two or more chemical components in the marking pheromone.