نبذة مختصرة : Field performance of the Heliothis (Lepidoptera: Noctuidae) larval parasitoids Microplitis croceipes (Cresson) and Cardiochiles nigriceps (Viereck) (Hymenoptera: Braconidae) was assessed at various parasitoid densities and on different plants. Laboratory-reared M. croceipes were released in field plots of soybeans and peanuts at levels of ca. 400 and 1,350/ha. Observed and calculated data indicate that over a 4-day period parasitism levels of 45 and 95%, respectively, would be obtained with M. croceipes at these levels on soybeans. Performance of M. croceipes on peanuts was less consistent, but in one study, 71% parasitism was obtained during a 2-day interval after releases of 1,344 females/ha. The searching behavior and efficiency of C. nigriceps females were studied on the hyacinth bean (Dolichos lablab L.) and Florida beggarweed (Desmodium purpureum (Mill.)). Observed and calculated data indicate that populations of 2,622 and 5,371 females/ha on the hyacinth bean and beggarweed, respectively, would yield 80% parasitism, as compared to earlier studies showing that 988-1,142 females/ha yield this level of parasitism on cotton. These findings show that the efficiency of the parasitoids varies considerably on different host plants. The distribution of searching parasitoids within the experimental plots and the distribution of their eggs among the host larvae did not differ significantly from a random (Poisson) pattern.
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