Pollination and Foraging Activity of Amegilla sp. (Hymenoptera: Apidae) on the Flowers of Gossypium hirsutum (Malvales: Malvaceae) under the Influence of Biopesticides in Bocklé Nord, Cameroon

Abstract

Background: Botanical biopesticides are promoted as alternatives to synthetic insecticides, but their compatibility with pollinators remains insufficiently documented in cotton agroecosystems. Several botanical extracts have demonstrated insecticidal efficacy, their effects on pollinator foraging behavior and pollination services in cotton agroecosystems remain insufficiently documented, particularly in African contexts. Aims: This study evaluated (i) the effects of aqueous leaf extracts of Azadirachta indica, Cassia occidentalis, Eucalyptus camaldulensis and Hyptis suaveolens on flower-visiting insects, and (ii) the contribution of Amegilla sp. to cotton pollination and seed yield under these treatments. Place and Duration of Study: Field study was carried out in 2021–2022 (rainy and dry seasons) in Northern Cameroon. Fifty-six plots (3.5 × 4 m each) were arranged in a randomized complete block design (RCBD) with 14 treatments and four replications: an untreated control (Tem), the synthetic insecticide TEMA, and 12 botanical treatments corresponding to four plant species tested at three concentrations (5%, 10% and 15%). Methodology: Four pollination treatments at the flower level were established: (1) flowers left for open pollination; (2) flowers permanently bagged to exclude insects; (3) flowers bagged at bud stage, then exposed at anthesis to allow a single visit by Amegilla sp. before rebagging; and (4) flowers bagged at bud stage, briefly exposed at anthesis but prevented from receiving any insect visit, then rebagged. Results: Among 370 captured floral insects (10 species), Amegilla sp. was a major visitor (52.63% of visits in the rainy season; 25.12% in the dry season). Botanical extracts had contrasted effects on Amegilla activity: C. occidentalis and H. suaveolens were associated with higher abundance (≈49–60 individuals/1000 flowers) and higher foraging speed (up to 17 flowers/min), whereas A. indica and E. camaldulensis showed lower abundance (≈34–46 individuals/1000 flowers). Fruiting rates remained high for open-pollinated flowers and flowers visited once by Amegilla sp. (≈90–98%). Conclusion: Amegilla sp. is an important cotton pollinator in the study area. C. occidentalis and H. suaveolens extracts appear more compatible with pollination services than A. indica and E. camaldulensis during flowering.