Abstract
The utilization of native trichogrammatids for biocontrol of Helicoverpa armigera (Hbn.) and their potential integration with pesticide use are currently receiving attention. In this study the interaction of adults of Trichogramma sp. nr. mwanzai and Trichogrammatoidea sp. nr. lutea with commonly used pesticide products was investigated. The toxicity of eight pest control products commonly used in vegetable crops in Kenya, were evaluated by exposing the adults of the two species to detached potted tomato leaves at different intervals after spraying. Two biologically derived products, Achook® (neem-based) and Dipel® (Bt ssp. kurstaki)—were found to be harmless and had no persistent toxicity on both the trichogrammatid species. Two organophosphate products tested, dimethoate (Rogor®) and malathion (Malathion®) were found to be ‘slightly harmful’ and ‘moderately persistent’ respectively. Three other synthetic insecticides, lambdacyhalothrin (Karate®), bifenthrin (Brigade®) and alpha-cypermentrin (Fastac®) were found to be ‘moderately harmful’ and ‘persistent’ respectively. Polytrin® (mixture of cypermethrin and profenofos) was also found to be persistent but only ‘slightly harmful’. On the basis of five concentrations tested (0.032, 0.016, 0.008, 0.004 and 0.002 of the recommended field rates) the LC50 values for adult T. sp. nr. mwanzai were estimated as 285, 411, 435 and 1,916 (μg active ingredient (a.i) ml−1) for dimethoate; malathion; lambdacyhalothrin as well as cypermethrin + profenofos respectively. The corresponding values for T. sp. nr. lutea were 247, 251, 278 and 697 respectively. Further, Karate® appeared to be the least toxic among the four products, across all the respective concentrations. The study was an attempt to adopt the methodologies of the IOBC (International Organization for Biological Control) on non-target risk assessment for pest control products to cater for the local needs of integrating the use of the trichogrammatids along with other pest control products.
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