Abstract:
Toxicity of aqueous leaf extract of Piper betle L. on Aphis craccivora Koch, a serious insect pest on Yard-long beans, was determined, as a topical application and soil drench. In the topical application treatment, the effect of the extract on one-day and two-day-old-nymphs, and freshly emerged females, we.fe evaluated on detached Yard-long bean leaves whereas the drenching treatment was conducted with female aphids on potted Yard-long bean plants. Distill water was used as untreated controls. The topical application treatment replicated five times with four repetitions while the soil drench experiment had five replications with one repetition. The nymphal and female mortalities, and number of nymphs produced by females were recorded at 24, 48 and 72 h after the treatment. The findings indicated that the percentage cumulative mortality (PCM) of one-day-and two-day-old-nymphs were significantly (P<0.0001) higher compared to controls, at all the exposure times. Also, in both experiments, a significantly (P<0.0001) higher PCM was recorded in females compared to controls. PCMs of one-day-old-nymphs were significantly higher (P<0.0001) than that of two-day-old nymphs and females. A significant (P<0.0001) increase in PCM was detected in one-day-old nymphs over three exposure times with the maximum of 80.4% (±1.21). Though PCM of topically treated females had no significant increase over exposure time, soil drenching treatment caused a significant (P<0.0001) increase in PCM with a maximum of 50% (±4.47). Nymphal production of topically treated females showed 4 7% reduction whereas the females developed from two-day-old topically treated nymphs had 52% reduction relative to control, 72 h after the exposure to the extract. In the drenching experiment, maximum reduction in nymphal production was recorded as 57% of the control plants. This study proved that the leaf extract of P.betle has a potential of affecting survival and reproduction of A. craccivora via its contact and systemic toxicity.
