Efficacy and Residual Effect of Abamectin and Chlorpyrifos-Methyl against the Second Larval Instar of the Cotton Leafworm, Spodoptera littoralis (BOISD.) Under Field and Semi-Field Condition

The initial mortality and residual effect of abamectin and chlorpyrifos-methyl against the second instar larvae of the leafworm, Spodoptera littoralis (Boisduval) and  beneficial arthropods were evaluated on tomato crop during 2019 and 2020 growing seasons under field and semi field conditions.The obtained data were revealed that Chlorpyrifos-methyl gave 100% initial mortality one to five days in 2019 and one to three days in 2020 growing season after application when the recommended rate was used in both seasons.Also, abamectin expressed 100 and 96% initial mortality during the first 24 hr after application in 2019 and 2020 growing seasons, respectively.When the recommended rate was applied,abamectin and chlorpyrifos-methylwere completely lost their toxic residues after 7.55 and 18.39 in 2019 and7.64 and 16.77 days during 2020 growing season of field application, respectively.On the other hand, abamectin had negatively effection on the population of predators at the first day after application then the population was turned back to its normal abundance after 48hr, particularly with half of the recommended rate as well as the field rate of application in both seasons. However, chlorpyrifos-methyl was showed negative impact on the predators, which resulted 100% reduction of predators' population within 96 hr post application, and then the percentage reduction continuously increased till day 13 then it decreased starting from day 14.Therefore, it could be recommended that using abamectin for controling Lepidopterous pests on vegetables to minimize the pre-harvest interval, which makes these crops edible for human use shortly after treatment and also to preserve beneficial predators.