Toxic and behavior-modifying actions of several formulated insecticides were determined for Microplitis croceipes (Cresson), a braconid parasitoid of Heliothis spp. Exposure of adult parasitoids to cotton plants sprayed at recommended field rates with a pyrethroid/formamidine mixture (fenvalerate/chlordimeform) resulted in significantly higher mortality rates (10.4 to 22.6 percent) than in controls. Exposure to the carbamate thiodicarb resulted in similar rates of mortality. Only methomyl, a type of carbamate different from thiodicarb, caused mortality significantly higher than all other treatments, ranging to about 70 %.Flight activity was measured by attraction to cotton in a laboratory wind tunnel bioassay. Females sprayed directly with a fenvalerate/chlordimeform mixture had significantly decreased flight activity up to 20 h post-treatment. Alternatively, attraction to cotton sprayed with either the fenvalerate/chlordimeform mixture or with methomyl to unsprayed females was significantly decreased, compared to plants sprayed with water only.These results suggest that the actions of insecticides, other than those of direct toxicity, may be important on beneficial parasitoids. Behaviors, such as flight activity and foraging, may be altered by even relatively non-toxic insecticides, thus potentially modifying the effectiveness of natural enemies.KEY-WORDS : Microplitis croceipes, insecticides, Hymenoptera, Heliothis, parasitoid, toxicity, behavior. spp. (Snow et al., 1966; Bottrell et al., 1968; Lewis & Brazzel, 1968) which has been cited as the most common parasitic insect among 6 species attacking Heliothis spp. in the southern United States (King et al., 1982). Microplitis croceipes comprised over 90 % of all parasitic insects reared from Heliothis spp. in cotton in southeastern Arkansas in 1981 and 1982, and rates of Heliothis parasitism by M. croceipes in cotton were found to be as high as 50 % (King et al., 1985). Microplitis croceipes is amenable to large scale rearing. This factor, along with its relative tolerance to pyrethroid insecticides (Poweli & Scott, 1985 ; Poweil et aL, 1986), makes it a prime candidate for use in augmentative releases for control of Heliothis in cotton (King et al., 1987).
Microplitis croceipes (Cresson) is a solitary endoparasitoid of Heliothis(i) This article reports the results of research only. Mention of a proprietary product does not constitute endorsement or a recommendation for its use by the U.S. Department of Agriculture.
