The effect of oil content and insecticides on insects attacking rice bran

Ephestia cautella (Walker) was unable to survive on rice bran of less than 5 per cent oil content and even on bran with 10 per cent oil it developed slowly and mortality was high. Tribolium castaneum (Herbst) survived on rice brans with oil contents of 0–10 per cent but the mortality and time taken for development increased as the oil content decreased. Latheticus oryzae Waterhouse survived and bred better on de-oiled rice bran than T. castaneum.Adult T. castaneum and L. oryzae were placed on batches of de-oiled rice bran treated with 20 or 16 ppm malathion, 8 or 4 ppm pirimiphos methyl, 8 or 4 ppm phoxim or 6 or 3 ppm fenitrothion, and mortality assessments were made over a period of 8 weeks after treatment. In general L. oryzae was more susceptible to the insecticides than was T. castaneum. Phoxim at 8 ppm gave highest mortality of T. castaneum and phoxim and pirimiphos methyl, both at 8 ppm, were equally effective in causing the highest mortality of L. oryzae. Malathion at 20 ppm or 16 ppm gave high mortality of both insects initially but began to lose effectiveness after 31 days. Fenitrothion did not give adequate control of either species. Phoxim at 8 ppm was the most successful treatment in preventing breeding of both species.The highest level of insecticide residue found 50 days after treatment was 13·7 ppm for malathion initially at 20 ppm, and by this time the other insecticides had lost about 60 per cent of their initial residue levels.