TOXICOLOGICAL STUDIES OF SOME CHEMICALS AS POTENTIAL INSECTICIDES FOR CONTROLLING STORED GRAIN INSECTS

Abstract

The present study was carried out to throw the light on the toxicological effects of certain insecticides on some stored product insects, the grain weevil, Sitophilus granarius (L.) and the red flour beetle, Tribolium castaneum (Herbst.). Therefore, tests included study of the development of resistance and determination of carboxylesterase activity as possible mechanism of resistance to malathion in some strains of T. castaneum. In addition, the study included experiments on the determination of toxicity of some insecticides and their residual toxicity against the two insect species and tried to find out other alternatives of malathion to be used safely against insects in the warehouses during storage. applying the different insecticides were tested via different ways:

5.1. Development of resistance to malathion in a strain of T. castaneum: The development of resistance in a laboratory strain of T.

castaneum subjected to selection pressure with malathion for a number of generations was studied. The increase in LC50 of malathion to each generation was monitored using a residual film bioassay. Results showed that a high level of resistance was induced by malathion and the resistance factor was 62.8 folds after I 8 successive generations compared with the susceptible reference strain.

5.2. Carboxylesterase activity in susceptible, field and malathion­

resistant strains ofT. castaneum: Carboxylesterase activity was determined 111 adult insects of susceptible, the parental field and the malathion-resistant strains of T. castaneum. The obtained results revealed that the specific activity of carboylesterase was significantly higher in the resistant strain than in the parental field and susceptible strains ofT. castaneum.