Antifeedant effect of Jatropha gossypifolia senescent leaf extract on Spodoptera exigua

Spodoptera exigua is one of the economic polyphagous pests that is widespread and has been able to develop rapid resistance, thus the development of pest control strategies are required urgently. Botanical insecticides have long been touted as attractive alternatives to synthetic chemical insecticides for pest management because the former pose little threat to the environment or to human health. This research studied the antifeeding effect of Jatropha gossypifolia senescent leaf extract on second instar larvae. J. gossypifolia leaves were extracted using a Soxhlet apparatus with ethanol as the solvent. Concentration in the range from 1 to 4 mg/mL was mixed with the artificial diet and then was put on a plate with the control diet as choice and no-choice assays. A dual standard check was run along with the treatment using no solvent (control A) and ethanol (control B). The mortality and behavior of larvae were observed every day whereas the weight of larvae was observed every 3 days. Observation continued until the larvae developed into the pupal stage. In the no-choice assay, at 4 mg/mL concentration, absolute mortality (100%) was recorded 17 days post-treatment. All concentrations showed toxicity at the first day of exposure. No toxicity was recorded in the control A or B groups. In the choice assay, the results showed that 70-85% of larvae seemed to ignore consumption of the treated diets. Larvae mortality occurred after 3 days of exposure, especially for the larvae that fed on the treated diet. The weight and rate of weight increase of the larvae feeding preferentially on the treated diet were less than for the control diet. However, when larvae moved to feed on the control diet, there was an increase in the rate of weight increase. Larvae that preferred to feed on the control diet reached the adult stage faster than larvae that preferred feeding on the treated diet. In addition, the treated diet produced some abnormal larvae at metamorphosis in the pupal stage from both assays.