Effect of Insecticides on Development and Adult Survival of Trichogramma chilonis (Trichogrammatidae: Hymenoptera)
Abstract
The effect of insecticides on development and adult survival of Trichogramma chilonis was investigated under laboratory condition. Insecticides tested were endosulfan, coragen, monocrotophos and deltamethrin+triazophos on following concentrationi.e. 0.009%, 0.010%, 0.020%, 0.022% and 0.024%. Treating eggs with all the concentration of chemical insecticides caused death of the emerged adults within few hours post emergence when the treatment was carried out 4 days post parasitism or one day before adult emergence. The number of host eggs turned to black (the parasitoid larvae developed to pupae) varied according to timing of treatment. Adult emergence rate varied according to the used insecticide, the parasitoid stage and the generation. All the concentration of insecticides, with the exception of endosulfan and some cases coragen, adversely affected T. chilonis emergence from Corcyra cephalonica host eggs when exposed at 1st, 2nd, 3rd, 5th and 6th day of developmental stages (larval and pupal) of T. chilonis. Regardless of the developmental stage treated, none of the insecticides tested had a significant effect on the emergence and survival of T. chilonis male and a female significantly varied among insecticide treatments, and were significantly affected by the developmental stage of parasitoid when treated. Based on toxicity, deltamethrin+triazophos was the most toxic followed by monocrotophos, which was comparatively less toxic compounds to adult male and female T. chilonis. No parasitoids emerged from parasitized eggs treated with deltamethrin+triazophos in second generation.
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Introduction
Recently, integrated pest management strategy has recommended, minimizing the use of chemical pesticides. It is very important to study the side effect of insecticides on the natural enemies to exclude the ones that have detrimental effect on such natural enemies. Trichogramma spp. has been extensively used as biological control agent. During the past two decades, Trichogramma spp. wasps have been evaluated as biological control agents for pest suppression indifferent crops. Numerous laboratory and field studies have shown that Trichogramma spp. wasps are highly susceptible to most broad-spectrum insecticides (Bull and Coleman 1985). Consequently, use of insecticides and Trichogramma spp. has historically been considered incompatible. In an attempt to combat insecticide resistance, conserve arthropod natural enemies, and reduce health risks, several new insecticides (e.g., tebufenozide, methoxyfenozide, spinosad) have been developed and tested against T. exiguum (Duttle et al. 1997, Harrison et al. 1997). Studies were conducted to assess the effects of selected insecticides on T. chilonis preimaginal development in Biocontrol laboratory S.V.P. Uni. of Agric. & Tech., Meerut,
Conclusion
Preliminary studies indicated that endosulfan and coragen had less adverse effect on preimaginal development or adult survival, indicating that these compounds are compatible with T. exiguum wasps. In response to the adverse effect of insecticides on preimaginal development in our study, it should be noted that eggs were completely drenched with an insecticide solution. Consequently, eggs received the maximum possible dose in our study. However, further research should focus on the impact of insecticide exposure on Trichogramma parasitism and overall effectiveness under field conditions to determine the compatibility of Trichogramma wasps and insecticides. More emphasis should be placed on conserving or enhancing naturally occurring populations of Trichogramma as well as other natural enemies infield condition
