Functional Responses of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) to Ostrinia nubilalis (Lepidoptera: Pyralidae) Under Laboratory and Field Conditions

Abstract

Laboratory tests and field experiments were conducted to determine the functional response of Trichogramma ostriniae Pang & Chen to its host, eggs of the European corn borer, Ostrinia nubilalis (Hubner), under different conditions. Individual female wasps were offered different densities of host eggs for 16 h at 17, 20, and 27°C. Field experiments were carried out in a sweet corn field that was divided into 6 plots of equal size (120 m2). Sentinel European corn borer egg masses were exposed to wasps for 3 d, from day 0 to 3 and day 4 to 7 after releasing wasps. Both the laboratory study and field experiments indicated that egg parasitism was positively correlated with egg density. However, this relationship differed significantly for the 3 temperatures in the laboratory study and varied considerably for the different days of exposures (days 0–3 versus days 4–7) and for different replicates (time of the year). The Gompertz equation and a modified disc equation were fitted to the laboratory data categorized based on temperatures. The results showed that female T. ostriniae might exhibit the type II or type III functional response depending on temperature. The field data suggested a type II functional response when data were pooled for all replicates.