2004 Volume 39 Issue 2 Pages 195-202
Laboratory tests were carried out in order to evaluate the insecticidal effect of the pyrethroids deltamethrin, beta cyfluthrin and alpha cypermethrin at the rates of 0.125 and 0.250 ppm, against the confused flour beetle Tribolium confusum on stored wheat. Therefore, clean untreated wheat was sprayed with these insecticides and stored for six months. During this period, four bioassays were carried out (32, 66, 101 and 171 days after insecticide application), in order to evaluate the residual efficacy of each pyrethroid. In each bioassay, pyrethroid-treated wheat was infested with T. confusum adults, and dead insects were counted after 24 h, 48 h and 7 d of exposure. In addition, in each bioassay, the progeny production was also examined. Mortality was notably higher after 7 d of exposure, as compared to 24 and 48 h counts. At the 7 d-exposure counts, beta cyfluthrin, at 0.250 ppm, was more effective as compared to the other treatments. This pyrethroid provided a satisfactory level of protection against T. confusum for a relatively long period, since the mortality 1 and 3.5 months after the treatment, was 98.6 and 88.7% at the rate of 0.250 ppm and 83.6 and 58.2% at the rate of 0.125 ppm, respectively. Similar mortality levels to the low rate of beta cyfluthrin were also recorded for the high rate of alpha cypermethrin (87.4 and 55.3%, respectively). Six months after the treatment, the efficacy of the high dose of beta cyfluthrin was 77.7%, while for the other treatments the respective figures were rather low (<48%). No progeny production was recorded on treated wheat, after the removal of the exposed adults, in any of the treatments. Finally, when adults that survived after a 7 d exposure interval on treated wheat were placed on untreated flour, progeny production was recorded only in the last two bioassays and only in the case of alpha cypermethrin.
