| heal.abstract |
Laboratory tests were conducted to assess the use of the pyrethroids, deltamethrin, beta-cyfluthrin and alpha-cypermethrin at the rates of 0.125 and 0.25ppm, as grain protectants in stored wheat against the rice weevil, Sitophilus oryzae (L.). For this purpose, clean untreated wheat was sprayed with these insecticides and stored for 6 months. During this period, four bioassays were carried out, in order to evaluate the residual efficacy of each pyrethroid. In each bioassay, treated wheat was infested with S. oryzae adults, and dead insects were counted after 1, 2 and 7d of exposure. In addition, S. oryzae progeny production was estimated on each bioassay, until the production of the F4 generation. The results indicated that deltamethrin and beta-cyfluthrin, both at 0.25ppm, were significantly more efficient than the other treatments. Efficacy was notably higher after 7d of exposure, than after 1 and 2d. At the same exposure level, 1, 2 and 3.5 months after treatment, at 0.25ppm, mortality for deltamethrin was approximately 89%, 92% and 86%, respectively, while the corresponding percentages for beta-cyfluthrin were 97%, 83% and 62%, and for alpha-cypermethrin 50%, 49% and 33%. However, at the rate of 0.125ppm, mortality was ≤58% in all cases. In all treatments appearance of F1-F4 generations was observed, with the exception of both deltamethrin and beta-cyfluthrin at 0.25ppm, where only a few F 1 adults were noted, without the production of subsequent generations. © 2003 Elsevier Science Ltd. All rights reserved. |
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