Arrestment responses of the parasitoid, Nemeritis canescens, to a contact chemical produced by its host, Plodia interpunctella

ABSTRACT. The locomotory response of walking parasitoids to a contact chemical from their host is reviewed, and in particular the response of the ichneumonid, Nemeritis canescens Grav., to the mandibular gland secretion of its host, Plodia interpunctella Hubn., is investigated. In response to the presentation of the host chemical on a surface, a walking Nemeritis exhibits a complex ortho-kinetic response involving stopping, walking at a reduced speed and probing with the ovipositor. In response to the removal of the chemical following presentation, as would occur when the insect left the edge of the chemical patch, the wasp exhibits a klinotactic response which directs it back to the patch at an average angle of 157° relative to the orientation at the moment of stimulation. This turning-back response at the patch edge greatly increases the time spent on a patch of contact chemical. The waning of this response determines when a host patch is abandoned. This waning is retarded by increasing the concentration of contact chemical on the patch and by opposition while on the patch.