Understanding the mechanisms that influence the response of the parasitic wasp Dolichogenidea tasmanica (Hymemoptera: Braconidae) to the density of light brown apple moth

Understanding the functional response of a species is important in comprehending its population dynamics and capacity to contribute to biological control. Dolichogenidea tasmanica is a commonly collected parasitoid of light brown apple moth (LBAM), Epiphyas postvittana (Lepidoptera: Tortricidae). LBAM is a polyphagous native Australian species and the most destructive insect pest in Australian vineyards. We investigated the functional response of D. tasmanica attacking LBAM on grapes. Six densities of second instar LBAM larvae (1, 2, 4, 8, 16 and 32) were exposed to a 1-2 day-old mated female wasp for 2 h. The larvae were randomly placed on 20 small grape leaves in a small wind tunnel. D. tasmanica exhibited a type III functional response. A separate experiment was conducted to test if this parasitic wasp tends to learn slowly and to forget the value of a host unless they encounter it fairly often. In this experiment, experienced versus inexperienced females were released into wind tunnels containing 20 grape leaves which were randomly infested with 2 larvae.  Experienced wasps were exposed to 10 grape leaves, each infested with one larval LBAM for 1 hour in the wind tunnel before the experiment. Fisher's Exact Test showed that there is a highly significant difference between the parasitism by experienced and inexperienced wasps (p=0.001). We concluded that Type III curves are indicative some form of learning by D. tasmanica. Thus D. tasmanica will not search as actively for hosts at very low densities. The type III functional response may explain the relatively low levels of parasitism of LBAM that are typically observed in vineyards.