Efficacy of aqueous and alcoholic extracts of Piper nigrum against Aphis gossypii and associated pest population dynamics on cucumber

Abstract

Cucumber (Cucumis sativus L.) cultivation is significantly threatened by various insect pests that reduce yield and quality. This study investigated the population dynamics of major cucumber pests during the spring season and evaluated the efficacy of black pepper (Piper nigrum) extracts against aphid nymphs under laboratory conditions. Monitoring of pest populations from March to May 2023 revealed fluctuating densities of whitefly nymphs (Bemisia tabaci), two-spotted spider mite nymphs (Tetranychus urticae), cotton leaf-worm larvae, and cotton aphid nymphs (Aphis gossypii). All pests exhibited peak densities early in the season, with the highest counts recorded between 1 to 8 March, and a gradual decline toward the end of the season (24 May). The maximum population densities observed were 79 whitefly nymphs, 80 spider mite nymphs, 10 leaf-worm punctures, and 78 aphid nymphs per leaf. A bioassay was conducted to assess the insecticidal potential of aqueous and alcoholic black pepper extracts against cotton aphid nymphs. Results indicated a concentration- and time-dependent increase in aphid mortality. At a 2 mg/L concentration, the highest mortality rates on day 7 were 18% (aqueous extract) and 29.83% (alcoholic extract), while the lowest mortality occurred on day 1 at 1 mg/L concentration (3.33% and 6.33%, respectively). The alcoholic extract was more effective than the aqueous form across all treatment levels. In conclusion, the findings highlight the temporal dynamics of key cucumber pests and demonstrate the promising potential of black pepper extracts, especially alcoholic formulations, as eco-friendly botanical insecticides for aphid management.