EFFECTS OF AIR-POLLUTION ON THE SEARCHING BEHAVIOR OF AN INSECT PARASITOID

To assess the impact of air pollutants on the population dynamics of h erbivores, the effects of pollutants an their natural enemies includin g predators, parasites, and pathogens must be evaluated in addition to direct effects and indirect effects mediated via the host plant. inse ct parasitoids are an important group of such natural enemies providin g many examples of partial or complete biological control of pest spec ies. This study examined the effects of air pollutants (ozone (O-3), s ulphur dioxide (SO2), and nitrogen dioxide (NO2)) on the searching beh aviour of insect parasitoids. A series of experiments comprising short -term, closed chamber fumigations of O-3, SO2, and NO2 (100 nl 1(-1)) of the braconid parasitoid (Asobara tabida) and aggregated distributio ns of its host larvae (Drosophila subobscura) was set up. Analysis of chamber results showed that the proportion of hosts parasitised and th e searching efficiency of the parasitoids were both significantly redu ced with O-3 fumigation, but not with NO2 or SO2 fumigations. O-3 fumi gation reduced percentage parasitism by approximately 10%. Parasitoids were able to avoid patches with no hosts, both in filtered air contro ls and when exposed to pollutants. However in the O-3 and NO2 treatmen ts they appeared less able to discriminate between different host dens ities, suggesting that pollutants may interfere with the olfactory res ponses of the parasitoids. These results indicate the potential for ai r pollutants, particularly O-3, to negatively influence the searching behaviour of parasitoids, and hence reduce the efficiency of natural e nemy control of many pest species.