Foraging and pollination activity of Macronomia vulpina (Gerstaecker, 1857) (Hymenoptera: Halictidae) on Gossypium hirsutum L. (Malvaceae) flowers at Maroua, Cameroon

Abstract To evaluate the impact of Macronomia vulpina (Hymenoptera: Halictidae) on bolls and seeds of Gossypium hirsutum, its foraging and pollinating activities were studied in Maroua, during two seasons of flowering (August-October 2010 and 2011). Treatments included unlimited flowers access by all visitors, bagged flowers to avoid all visits and limited visits of Macronomia vulpina. Observations were made on 30 to 100 flowers per treatment. In addition, all flower visitors were recorded. The bee's seasonal rhythm of activity, its foraging behavior on flowers, its pollination efficiency, the fruiting rate, the number of seeds per fruit and the percentage of normal seeds were recorded. Among individuals from 40 species of insects recorded on flowers of Gossypium hirsutum after two seasons of observations, Macronomia vulpina was second with 7.5% and 6.52% of visits in 2010 and 2011 respectively. This bee intensely and exclusively foraged for pollen, almost throughout the day, with a peak between 8 and 9am. The foraging speed was 14.92 ± 8.24 flowers per minute. Macronomia vulpina foraging resulted in a significant increase in the fruiting rate by 7.50% in 2010 and 6.52% in 2011, as well as the number of seeds per boll by 41.19% in 2010 and 33.85% in 2011, and the percentage of normal seeds (well developed) by 21.83% in 2010 and 16.82% in 2011. The conservation of Macronomia vulpina nest in cotton plantations is recommended to increase fruit and seed yields of this species.