Objective: Foraging and pollination activity of flowers of Gossypium hirsutum (Malvaceae) by Apis mellifera Linné (Hymenoptera: Apidae) have been observed in Garoua (North Cameroon), to determine the impact of worker bees on fruit and seed yields of this plant species. Methodology and results: From June to November 2010 and 2011, for each year, 200 flowers were labeled and divided in to two treatments, differentiated according to the presence or absence of protection against insect's activities. The foraging behavior on flowers, the fructification rate, the number of seeds per pod and the normal seeds rate were evaluated. Results show that A. mellifera foraged on G. hirsutum flowers from 6 am to 17 pm and throughout the whole blooming period. Through its pollination efficiency, A. mellifera increased significant fructification rate in the order of 20.55 %, the number of seed yields per pod was 26.21 % and the percentage of the normal seeds was 25.01 %. Conclusion and application of results: The installation of A. mellifera colonies close to G. hirsutum field could be recommended to improve its pods and seeds production.

To evaluate the impact of the honeybee Apis mellifera adansonii Latreille on fruit and seed yields of Callistemon rigidus R. Br. 1819, its foraging and pollinating activities were studied in Ngaoundéré for two seasons (June -August 2009 and July -September 2010). Each year, observations were made on 120 inflorescences per treatment. The treatments included unlimited flower access by all visitors, bagged flowers to deny all visits and limited visits by A. m. adansonii only. In addition, all flower visitors were recorded. The worker bee's seasonal rhythm of activity, its foraging behaviour on flowers, its pollination efficiency, the fruiting rate, the number of seeds per fruit and the percentage of normal seeds were recorded. Individuals from five and ten insect species that visited C. rigidus flowers were recorded in 2009 and 2010, respectively. Apis mellifera adansonii was the most frequent, followed by Myrmicaria opaciventris Emery. Apis mellifera adansonii intensely and preferably foraged for nectar. The fruiting rate, the number of seeds per fruit and the percentage of normal seeds of unprotected inflorescences were significantly higher than those of inflorescences protected from insects. Apis mellifera adansonii foraging resulted in a significant increase in the fruiting rate by 92.04% in 2009 and 64% in 2010, as well as the number of seeds per fruit by 38.67% in 2009 and 59.16% in 2010, and the percentage of normal seeds by 84.67% in 2009 and 82.30% in 2010. Cultivation of C. rigidus plants could be recommended to increase seeds, fruits and honey production.

To evaluate the effect of the carpenter bee, Xylocopa olivacea Lepeletier 1841, on the pod and seed yields of Phaseolus coccineus L., in this study, its foraging and pollination activities were examined in Ngaoundéré during the June -July 2010 and July -August 2011 cropping seasons. Treatments included open floral access to all visitors, bagging of flowers to avoid all visits and floral access to limited visits of X. olivacea. Observations were made on 120 flowers per treatment. In addition, all flower visitors were recorded. The seasonal rhythm of the activity of the carpenter bee, its foraging behaviour on flowers and its pollination efficiency (fruiting rate, number of seeds/pod and percentage of normal or well-developed seeds) were recorded. Phaseolus coccineus flowers were visited by 13 insect species in 2010 and by 14 insect species in 2011. Xylocopa olivacea was the most frequent visitor and intensely and exclusively foraged the flowers for nectar. The mean foraging speed was 9.28 flowers/min. In 2010, the foraging activity of X. olivacea resulted in a significant increase in the fruiting rate (27.49%), number of seeds/pod (45.43%) and percentage of normal seeds (89.38%). In 2011, the corresponding values were 56.14% (fruiting rate), 74.44% (number of seeds/pod) and 66.44% (percentage of normal seeds). These results reveal that this crop experiences a pollination deficit, considering that flowers visited by X. olivacea had higher yields than those under unlimited access to all visitors. Hence, the conservation of X. olivacea nests close to P. coccineus crop fields is recommended for improving pod and seed production.

Les investigations ont été faites sur les fleurs de Cajanus cajan en vue d’estimer l’impact de l’activité de Dactylurina staudingeri sur la pollinisation, la production en gousses et en graines à Dang, en 2016 et 2017. Pour  chacune de ces années, 540 boutons floraux ont été étiquetés sur 120 plantes réparties en quatre traitements: 120 fleurs laissées en libre pollinisation, 120 fleurs protégées des insectes, 200 fleurs protégées, puis découvertes, visitées exclusivement par D. staudingeri et de nouveau protégées et 100 fleurs protégées, découvertes et à nouveau protégées, sans visite d’insectes ou de tout autre organisme. Le taux de fructification, le nombre moyen de graines par gousse et le pourcentage de graines normales ont été comparés entre ces traitements. Sur 33 espèces d’insectes recensées, D. staudingeri était majoritaire avec 12,19% de 6037 visites. Cette abeille prélevait fortement le nectar et récoltait faiblement le pollen au niveau des fleurs de C. cajan. La vitesse moyenne de butinage était de 7,14 fleurs/min. Via l’efficacité pollinisatrice d’une visite florale, D. staudingeri a augmenté le taux de fructification de 14,71%, le nombre moyen de graines par gousse de 35,29% et le pourcentage de graines normales de 17,31%. La conservation des colonies de D. staudingeri à proximité des exploitations de C. cajan est recommandée pour assurer la hausse des rendements de cette culture et favoriser une bonne pratique de la méliponiculture dans la région.Abstract Investigations were made on the flowers of Cajanus cajan in order to estimate the impact of the activity of Dactylurina staudingeri on pollination and yields at Dang, in 2016 and 2017. For each of these years, 540 flowers buds labeled on 120 plants were divided into four treatments: 120 open-pollinated flowers, 120 bagged flowers, 200 flowers protected, then unbagged, exclusively visited once by D. staudingeri and rebagged, and 100 flowers bagged, unbagged and rebagged without insect or any other organism visit. The fruiting rate, the mean number of seeds per pod and the percentage of normal seeds were compared between these treatments. Among 33 insect species recorded, D. staudingeri was prominent with 12.19% of 6037 visits. This bee harvested intensely nectar and collected slightly pollen from C. cajan flowers. The mean foraging speed was 7.14 flowers/min. Through the pollinating efficiency of a single flower visit, D. staudingeri increased the fruiting rate by 14.71%, the mean number of seeds per pod by 35.29% and the percentage of normal seeds by 17.31%. The conservation of D. staudingeri colonies close to C. cajan farms is recommended to improve yields of the crop and to promote the good meliponiculture in the region.

Most plant species require pollen transfer to produce fruits and set seeds. Although some insects visit flowers for nectar or pollen, not all flowering insects bring about pollination. To evaluate the impact of Apis mellifera Linnaeus on fruit and seed yields of Solanum nigrum Linnaeus, foraging and pollinating activities of worker bees were studied at Meskine in January 2019 and February 2020. The experiments were carried out on 540 flowers divided in four treatments: two treatments differentiated according to the presence or absence of protection of flowers regarding A. mellifera and other insect visits; the third with flowers protected and uncovered when they were opened, to allow A. mellifera visits and the fourth with flowers protected then uncorvered and reprotected without the visit of insects or any other organism. The foraging behaviour of A. mellifera on flowers, its efficiency pollination, the fruiting rate, the number of seeds per fruit and the percentage of normal seeds were evaluated. Results indicate that among 27 insect species recorded on flowers, A. mellifera ranked first accounting for for 34.16% of 2652 visits. This worker bee intensely harvested nectar and pollen. The mean foraging speed was 10.39 flowers / min. The mean abundance per 1000 flowers was 519.46. For the two years, throughout its pollination efficiency, A. mellifera increased the fruiting rate by 16.29%, as well as the percentage of normal seeds by 15.57%. Hence, the installation of honeybee colonies close to S. nigrum fields is recommended to improve fruit yields, seed quality, pollen as a hive product and honey production.