Effects of larval densities and the duration since larval infestation on the host-searching behavior of Diadegma semiclausum, a parasitoid of diamondback moth larvae on plants

The host-searching behavior of Diadegma semiclausum, a parasitoid of diamondback moth (DBM) larvae, was studied in a wind tunnel. Wasps flew preferentially to a cabbage plant, freshly infested by 1 DBM larva, or one freshly infested by 10 DBM larvae, than to an intact plant. There was no significant difference between wasps' responses to plants infested by different DBM larvae densities. We also found that the duration since the last infestation by 10 DBM larvae (1 or 3 days) negatively affected the attractiveness of infested plants. We also studied the time wasps spent searching for larvae on a cabbage plant (residence time). The wasps spent ca. 400 s on a plant freshly infested by 1 larva. Residence time was significantly longer (ca. 1,200 s) on a plant freshly infested by either 5 or 15 DBM larvae. Residence time of D. semiclausum on a plant freshly infested by 5 DBM larvae was significantly longer than on a previously infested plant (1 or 3 days after the last infestation). These results showed that host densities on a plant and the duration since their last infestation affected the host-searching behavior of D. semiclausum.