Efficacy of Three Plant Species on the Mortality and Food Consumption of Epilachna vigintioctopunctata

Abstract

The Evaluation of Azadiracta indica (Neem), Annona reticulata, (Custard apple) and Annona squamosa (Sugar apple) under laboratory conditions showed their potential as antifeedants and insecticides for the control of Epilachna vigintioctopunctata. Methanol extracts of all three plants elicited a highly significant reduction in food consumption from the Epilachna larvae. When compared with the other two plant extracts, .A. squamosa produced a very strong antifeedant effect on the larvae at all concentrations tested. At the highest concentration (20.0gll)., none of the larvae consumed leaf disks treated with A. squamosa extract at all, but all larvae died immediately after they were introduced to the test medium, indicating a strong contact toxic effect on the larvae. With all the plants, the food consumption decreased with the increase of the concentration. Among the three plants tested, A. squamosa was the most effective against the Epilachna larvae causing significantly very high mortality even after 24 hours. A. indica extract on the other hand, elicited a much more delayed toxic action in the larvae. When treated with extracts of A. indica, a positive relationship was observed between larval mortality and concentration of extracts and also between larval mortality and time. Larval mortality increased with the increase of concentration and also with time. However, no larval deaths were recorded for 4 days with any concentration tested and 100% mortality was recorded on the 12thday after treatment at the highest concentration (20.0g/l).