Pollination efficiency of Apis mellifera (Hymenoptera: Apidae) on Cosmos sulphureus (Asteraceae) capitula at Dang (Ngaoundéré, Cameroon)

To study the foraging activity of Apis mellifera (Hymenoptera: Apidae) on Cosmos sulphureus (Asteraceae) and to evaluate its impact on fruits yields, C. sulphureus capitula were observed on Dang (Ngaoundéré, Cameroon) from September to November 2016 and from August to October 2017. Each year, observations were made every day, from 06.00 am to 6.00 pm on 540 capitula divided in four treatments: 120 capitula left in free polliniation, 120 capitula protected from insects ; 200 capitula protected, then uncovered, exclusively visited by A. mellifera and rebagged ; 100 capitula protected, then uncovered and rebagged without insect or any other organism visit. The foraging behaviour on A. mellifera capitula, its pollination efficiency, the fruiting rate, the percentage of mature achenes and the percentage of normal (well developed) achenes were evaluated. The results show that among 10 insect species recorded on C. sulphureus capitula after two seasons of observation, A. mellifera was the most represented with 95.57 % of 1128 visits. This bee harvested intensely nectar and pollen on C. sulphureus florets. The fruiting rate, the percentage of mature akenes and the percentage of normal achenes of treatments with unprotected capitula were significantly higher than those of treatments with capitula protected from insects. Through the pollination efficiency of a single capitule visit, A. mellifera increased the fruiting rate, the percentage of mature achenes and the percentage of normal achenes by 50.58 %, 14.37 % and 40.52 % respectively. The installation of A. mellifera colonies close to C. sulphureus fields is recommended to increase achenes and honey yields, as well as pollen production as a hive product.