Impact of Three Local Plant Extracts on Okra Flower-Visiting Insects in Bokle, North-Cameroon

Abstract

Background: Okra production is often constrained by insect pest infestation, leading to significant crop damage and yield loss. Excessive use of synthetic pesticides for pest management adversely affects non-target organisms, including beneficial flower-visiting insects essential for pollination and ecosystem balance. Therefore, eco-friendly botanical extracts are being explored as sustainable alternatives for pest control. Objective: The present study aimed to characterize the composition, structure, and functioning of the flower-visiting insect community in okra fields and to determine the impact of aqueous leaf botanical extracts on these insects for achieving effective and environmentally safe pest management. Study Design: Ecological survey was conducted in 11 trials (four plots each). Place and Duration of Study: Investigations were carried out in Bockle from June 15 to October 10, 2022. Methodology: Plants were identified in-situ when possible or photographed and a sample of leaves, bark, flowers and fruits (when available) allowed identification in the laboratory by botanist colleagues. Collected insects were identified to the species level in the Laboratory of Applied Zoology (Department of Biological Sciences, Faculty of Science, University of Ngaoundere) where voucher specimens were deposited. Aqueous extracts were sprayed and flowers inspected two days a week. Results: A total of 4,406 specimens belonged to six orders, 11 families and 14 species. Lilioceris lilii (42.2%) and Apis mellifera adansonii (12.0%) highly occurred. Extracts affected exclusively Li. lilii. Species richness was low (d=0.012 in the pooled Azadirachta indica extract to d=0.044 in 15% Eucalyptus camaldulensis plots; pooled assemblages: d=0.003). Species diversity was slightly median in pooled assemblages (H’=2.064, H’max=2.639), low in experiments (H’=1.908; H’max=6.644 in untreated to H’=2.255, H’max=5.781 in 15% Senna occidentalis); highly even (J=0.723 in untreated plots to J=0.855 in 15% Se. occidentalis; J=0.782 in the pooled assemblages), four co-dominants in untreated plots, 5% and 10% Az. indica and Se. occidentalis respectively to eight species in the pooled assemblages. Assemblages fitted Zipf’s model with a high decay coefficient and fractal dimension (γ=0.986, 1/γ=1.014 in 15% Eu. camaldulensis to γ=1.362, 1/γ=0.734 in 10% Eu. camaldulensis; pooled assemblages: γ=1.203 and 1/γ=0.831). Assemblage  from  15% Az. indica plots fitted Zipf-Mandelbrot with a high decay coefficient (γ=2.152), high niche diversification (β=2.578) and low fractal dimension (1/γ=0.465). Six dominant pollinators and flying insects strongly tolerated each other, repelled eight pests and shredders that in turn were weakly correlated each other.  Conclusion: Promoting pollinators and flying insects, breaking solidarity among pests and shredders, and using pollinators and butterflies as indicators (their decrease indicate imminent pests invasion) would optimize the health of Okra plants. However further studies are needed to validate reliability.