Toxic and behavioral effects of selected insecticides on theHeliothis parasitoidMicroplitis croceipes

Abstract

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.

Disruptive Sublethal Effects of Insecticides on Biological Control: Altered Foraging Ability and Life Span of a Parasitoid after Feeding on Extrafloral Nectar of Cotton Treated with Systemic Insecticides

“…Studies, such as the present one, that also monitor altered foraging behavior of beneficial insects as a result of insecticide exposure, are rarely performed, even though this is a key behavior for beneficial insect effectiveness. Elzen et al (1989) showed a decrease in flight activity toward cotton plants by M. croceipes females sprayed directly with a fenvalerate/chlorodimeform mixture. Flight activity in this insect is usually considered to be an indicator of foraging efficiency.…”

“…(3) Mortality frequently is the only effect that insecticides are screened for, while more conspicuous sublethal effects in beneficial insects, such as altered behavior, reduced reproduction, and reduced longevity, are largely overlooked (Elzen, 1990). Like mortality, sublethal effects can severely reduce the performance of the biological control agent (Jacobs et al, 1984;Elzen et al, 1989;Roger et al, 1995).…”

Indirect Effects of Pesticides on Natural Enemies

“…Certain pesticides (insecticides and fungicides) may also exhibit repellent activity [16,[41][42][43][44][45][46] or alter host plant physiology [13,47] thus indirectly affecting the ability of natural enemies to regulate existing arthropod pest populations [48].…”

“…While evaluations associated with the direct effects of pesticides on natural enemies are important, what are actually more relevant are the indirect or delayed effects of pesticides because this provides information on the long-term stability and overall success of a biological control program when attempting to integrate the use of pesticides with natural enemies [12][13][14][15][16].…”

“…Any indirect effects, which are sometimes referred to as sub-lethal, latent, or cumulative adverse effects may be associated with interfering with the physiology and behavior of natural enemies by inhibiting longevity, fecundity, reproduction (based on the number of progeny produced or eggs laid by females), development time, mobility, searching (foraging) and feeding behavior, predation and/or parasitism, prey consumption, emergence rates, and/or sex ratio [2, 13,16,[17][18][19][20][21][22].…”