Impact of aqueous extracts of Cassia occidentalis, Eucalyptus camaldulensis and Hyptis suaveolens on the entomofauna and the seed yield of Gossypium hirsutum at Boklé (Garoua, Cameroon)

There is a frightening decline in the population pollinators around the world due to the over usage of synthetic pesticides, leading to the directly reduce of plant production. Plant extracts with insecticidal properties could be eco-friendly alternatives to synthetic pesticides in maintaining the pollinator population and the diversity of the ecosystem. The impact of aqueous extracts of Cassia occidentalis L., Eucalyptus camaldulensis Dehnh. and Hyptis suaveolens L. was investigated on the entomofauna and the seed yield of Gossypium hirsutum L. cotton. The study was carried out in RCBD, four times replicated: 3 extracts x 1 standard synthetic insecticide (TEMA) x 1 control x 4 groups of flowers (group 1: flowers free to insect visits, group 2: flowers protected from insects using gauze bags, group 3: protected flowers and opened exclusively to Amegilla sp. and group 4: protected flowers opened from time to time without any visit of insect). Gossypium hirsutum was found to be visited by the insects belonging to five orders, 10 families and 18 species. Amegilla sp.1 and Apis mellifera were the major pollinators during the rainy and dry seasons, respectively. The number and quality of seeds visited exclusively by Amegilla sp.1 were significantly improved by H. suaveolens extract. During the dry season, E. camaldulensis and H. suaveolens extracts as well as the standard insecticide improved the number of seeds and the percentage of normal seeds harvested from the flowers allowed to be visited by insects; that was probably due to their insecticidal effects which protected plants from pest damage. Therefore, aqueous extracts of E. camaldulensis and H. suaveolens are good candidates for incorporation in integrated pest management programs to minimize the risk of synthetic pesticides to pollinators, hence to increase the yield and the quality of seeds.