Screening and evaluation of candidate chemical pesticides against bean weevils of stored legumes

Results of this study showed that pirimiphos-methyl at 4 ppm can provide protection against insect infestation (a hundred percent mortality rate) for six months of storage. It can also suppress the subsequent first filial generation (F1) and prevent the emergence of the second filial generation (T2) at least up to three months. This means that the residual activity of primiphos-methyl is still active as time progresses. Acceptable limits for this particular chemical insecticde is at the level of 10 ppm. On the other hand, permethrin proved to be effective at 1 ppm and deltamethrin at 0.8 ppm. Their MRL [Maximum Residue Limit] are set at 2 ppm and 1 ppm, respectively. Both are capable of suppressing both F1 and F2 in a three-month storage period. In fact, high mortality count on progenies were observed up to three months of mungbean storage. Efficacy of data on samples withdrawn at four and a half months and six months of storage are still to be assessed. Single insecticide per treatment was used since there is only one target pest. The effect of these reduced rates on the germination of stored seeds is virually nil. On the average, the germination rates of all the treatments after six months of storage is 86.3 percent. Initial quality is maintained throughout the duration of the storage. The chemical insecticides that passed that screening and evaluation proved to be effective protectants against bean weevils. When thes insecticides were admixed with mungbean intended for storage complete protection is achieved at the doses cited - 0.8 ppm for deltamethrin, 1 ppm for permethrin and 4 ppm for pirimiphos-methyl-for a six-month period of storage. However, they cannot provide complete prevention of the first filial and second filial generations. Instead, these generations were suppressed down to a level that infestation is not too severe. Hence, the application of protective spray using these chemicals may prove to be more effective and practical