Potency of selected plant extracts as biopesticides for the control of the wood termite (Coptotermis gestroi)

Abstract

This study aimed at evaluating the pesticidal potential of selected plant extracts against the wood termites (Coptotermis gestroi). During the study, extracts from chillies Capsicum fructescens, tobacco Nicotiana tobacum and garlic Allium sativum were evaluated for pesticidal effects on C. gestroi compared with a standard insecticide Rocket® (Cypermethrin). The variation of potency of the plant extracts with the solvents used in the extraction of plants namely acetone and water was also determined. Each plant extract was dissolved at three concentrations of 20, 40 and 80 grams per 100 ml of the respective solvents. Each concentration was replicated four times with 20 worker C. gestroi per replicate. The experiment was conducted for 60 minutes and mortality of C. gestroi was recorded at an interval of 10 minutes. Median Lethal Time (LT50), Median Lethal Concentration (LC50) and cumulative mortality of C. gestroi were compared across treatments. Results from the study revealed that apart from A. sativum extracts in water, the plant extracts were as effective as Rocket® in killing C. gestroi with no significant difference in the cumulative mortality and the LT50 of the bioactive plant extracts and the insecticide. The extracts of all the plant extracts in acetone had no significant differences in LC50 compared to Rocket® while of the extracts in water were lower than the LC50 of Rocket®. Mortality, LT50 and LC50 of C. gestroi were not significantly different in varying concentrations of water extracts of N. tobacum and C. fructescens. However, mortality, LT50 and LC50 of C. gestroi in the higher concentration of water extracts of A. sativum significantly differed from that in the other concentrations. These results support the use of botanical extracts as biopesticides for the control of C. gestroi. However, the need for development of cheap methods that can be used to extract the active compound and to characterize the bioactive compounds against C. gestroi from A. sativum, N. tobacum and C. fructescens is warranted.