Interspecific competition and comparative cold tolerance in two egg parasitoids of sunn pest, Eurygaster integriceps

Trissolcus spp. are egg parasitoids of sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae). Direct (extrinsic) competition between female T. grandis and T. vassilievi was investigated in the laboratory by releasing different numbers (from one to 16) of one or both species into a multi-patch environment consisting different numbers of E. integriceps egg masses. Larval (intrinsic) competition was examined in host eggs multiparasitized at intervals ranging from 0 to 48 h. Survival of females was also assayed when stored at 4 °C. Trissolcus grandis reduced the searching efficiency of congeneric rivals more than did T. vassilievi, and was a superior intrinsic competitor within multiparasitized eggs, although both species benefited from a significant ‘first attack’ advantage. Trissolcus vassilievi was more efficient than T. grandis when parasitizing host eggs at high conspecific densities. Mortality at 4 °C was lower in groups ≥ 10 than in groups ≤ 5, and T. grandis survived longer than T. vassilievi.