Laboratory and field studies on the effect of sequential application of pesticides on susceptibility and on some biological aspects of mite Tetranychus cinnabarinus (Boisd.)

Laboratory and field evaluation on the effect of sequential application of dicofol, omethoate and cypermethrin insecticides on the susceptibility, biology and population density of the mite Tetranychus cinnabarinus were studied through the course of the present investigation. The results obtained may be sum.marized as follows: 1. The susceptibility of adult female mites to dicofol, omethoate and cypermethrin applied sequentially over three generations was studied. Susceptibility was varied due to the type of chemical as well as to the scheme of insecticidal sequences used. 2. Biological studies indicate that the life span of selected mites was extended, this was more pronounced in the schemes of (cypermethrin / cypermethrin / cypermethrin) - and (cypermethrin / dicofol / omethoate) - selected strains. Also, egg production was significantly increased in case of (cypermethrin / cypermethrin / cypermethrin) - selected strain, while decreased in case of (omethoate / omethoate / omethoate) - selected strain. The percent of hatchability was significantly decreased, this was highly occurred in (cypermethrin / omethoate / dicofol) - selected strain. 3. Field studies show that plots sprayed successively three times with dicofol recorded the highest reduction in mite population infesting soybean plants. The contrary was obtained in plots sprayed successively three times with cypermethrin. This indicate the necessity of using specific potent acaricide on soybean in case cypermethrin is used to control the cotton leafworm to avoid outbreak of mite infestation.