Functions Of Infochemicals In The Host Selection Of Plutella Xylostella,and Its Parasitoid,Diadegma Semiclausum

Some aspects of the interactions in the tritrophic system of two Brassica plants, the diamondback moth, Plutella xylostella, and the parasitoid, Diadegma semiclausum, were studied in the laboratory. Firstly, the host selection of P. xylostella and D. semiclausum were examined by choice tests using two host plants and cultivars. Secondly, the behavioural responses of P. xylostella and D. semiclausum to various plant volatiles were bioassayed. Finally, volatiles collected from the headspace of various plant treatments were collected and identified. In addition, the learning and the host foraging behaviour of D. semiclausum were studied. The resulte are summarized as follows:(1) The females of P. xylostella reared on radish were tested in the oviposition selection of P. xylostella between Chinese cabbage and common cabbage. The results showed adult females preferred to lay more eggs on the Chinese cabbage than on common cabbage. The amount eggs they laid on Chinese cabbage cultivars or common cabbage cultivars were difference.(2) The role of plant volatiles from the Chinese cabbage and common cabbage in host selection behaviour of P. xylostella adult was investigated by Y-tube olfactometer. Volatiles from the Chinese cabbage were more attractive to adult females than those from the common cabbage with the same treatments. However, volatiles from the same treatment plants of Chinese cabbage cultivars or common cabbage cultivars were no difference for adult females.(3) The females of D. semiclausum reared on radish were tested in the oviposotion selection of D. semiclausum between Chinese cabbage and common cabbage. When D. semiclausum wasps were provided with equal numbers of larvae of P. xylostella, the number of hosts parasitized on Chinese cabbage was more than on common cabbage. However, the number of hosts parasitized betwween Chinese cabbage cultivars, or commoncabbage cultivars was no difference.(4) The role of plant volatiles from the Chinese cabbage and the common cabbage in host selection behaviour of D. semiclausum females was investigated by Y-tube olfactometer. Compared to volatiles from intact plants, those from Chinese cabbage or common cabbage plants that were mechanically damaged, infested by P. xylostella and being infested by P. xylostella were more attractive to females. The volatiles from Chinese cabbage infested by P. xylostella and being infested by P. xylostella were more attractive to females than those from the mechanically damaged Chinese cabbage. However, their volatiles were no difference for attracting females. Volatiles from the mechanically damaged common cabbage and P. xylostella infested common cabbage or from common cabbage infested by P. xylostella and common cabbage being infested by P. xylostella were no difference for females. But the volatiles from common cabbage being infested by P. xylostella were more attaractive to females than those from mechanically damageed common cabbage. When plants were intact or mechanically damaged, the volatiles from Chinese cabbage and common cabbage were the same attractive to females. Only the plants were infested by P. xylostella or being infested by P. xylostellam, the volatiles from Chinese cabbage were more attractive to females than those from the common cabbage.(5) The host foraging behaviour of D. semiclausum was studied in the laboratory. The P. xylostella larvae and their feces, silk, regurgitant, exuviae could elicit host foraging behaviour by D. semiclausum females. The female showed different behaviour on different treatment plants. They had host foraging behaviour on plants infested by P. xylostella and plants being infested by P. xylostella. But they only had walking, stopping, cleaning behaviour on intact and mechanically damaged plant. They stayed significantly longer on plant infested by P. xylostella and plants being infested by P. xylostella than on intact and mechanically damaged plant.(6) The leraning of D. semiclausum was studied. It showed the host plant of D. semiclausum develop...