Comparative study of the foraging activity of Apis mellifera L. (Hynemoptera: Apoidae) on the capitula of Helianthus annuus in two agroecological zones of Cameroon

The impact of Apis mellifera L. (Hymenoptera: Apidae) foraging on Helianthus annuus yields in two agroecological zones of Cameroon (the Sudanese-Sahelian zone and the humid equatorial zone) was assessed. The observations were made in Maroua and Yaoundé, during the 2019 and 2020 rainy seasons. In each agroecological zone, 480 flower heads were labeled and 2 treatments carried out, one left in open pollination and the other isolated from insects. The diversity of flower-visiting insects, their foraging behavior, regularity index, fruiting rate, and the percentage of achenes with seeds were evaluated. The results showed that A. mellifera was the most abundant floral visitor at both sites. In Maroua, out of 16 species of insect visitors recorded on the flowers of H. annuus, A. mellifera accounted for 41.40% of 5715 visits, while in Yaoundé, 11 species of flower-visiting insects were recorded, and A. mellifera accounted for 51.38% of 3400 visits. In Maroua as in Yaoundé, A. mellifera harvested nectar intensively (80.85% and 85.19% of the foraging time). The mean abundance per 1000 flowers of A. mellifera on the capitula of H. annuus was 107.5 ± 9.90 and 138.95 ± 39.05 respectively in Maroua and Yaounde. The regularity index of A. mellifera and the flowers of H. annuus was 0.41 (Maroua) and 0.51 (Yaounde). Flower-visiting insects, including A. mellifera, increased the fruiting rate, the number of achenes with seeds and the percentage of achenes with normal seeds was 37.91%, 17.20% and 30.22% respectively. The corresponding values (Yaounde) were 49.65%, 19.07% and 43.63%. In Maroua as in Yaoundé, the conservation of colonies of A. mellifera near plantations of H. annuus is recommended to increase yields of this plant.