Insecticidal Activity of Ten Plant Extracts on Cucumber [Cucumis sativus (L.)] Insect Pests in a Rainforest Transition Zone of Nigeria

Abstract

Cucumber, Cucumis sativus L. an important vegetable crop in southwestern Nigeria, faces significant threats from a diverse array of insect pests, requiring the application of synthetic insecticides for optimal fruit production. The associated drawbacks of insecticide usage, combined with its adverse effects on consumer health, highlight the need for an alternative control strategy. Field trials were carried out during the cropping seasons of 2013 and 2014, and subsequently repeated in the 2019, to assess the effectiveness of ten plant extracts against the insect pests of cucumber. The treatments were leaf extracts from ten plant species: Cymbopogon citratus, Carica papaya, Ocimum gratissimum, Vernonia amygdalina, Chromoleana odorata, Azadirachta indica, Gmelina arborea, Hyptis suaveolens, Alstonia boonei, and Ageratum conyzoides. Additionally, a synthetic insecticide, Lambdacyhalothrin, and water were applied as check and control treatments, respectively. The experiment was laid out in a randomized complete block design with three replicates. Data collected were subjected to analysis of variance at 5% probability. The major insect pests associated with cucumber were leaf pests such as Aulacophora nigripennis, A. hilaris, A. foveicollis, Epilachna chrysomelina, and the fruit borer Bactrocera cucurbitae. The application of leaf extracts resulted in a notable reduction (p < 0.05) in populations of cucumber insect pests. The densities of E. chrysomelina, Aulacophora spp., and B. cucurbitae, along with their associated damage to cucumber leaves and fruits, demonstrated a significant decrease when cucumber was treated with leaf extracts of A. conyzoides and G. arborea. The effectiveness of A. conyzoides and G. arborea leaf extracts in controlling pests was evident, leading to a substantial increase in cucumber fruit yield. Consequently, these could be used as a practical alternative to synthetic insecticides.