Determination of Acute Lethal Doses of Acetamiprid and Cypermethrin for the Native Bee <i>Apis mellifera</i>(Hymenoptera: Apidae) in Cameroon

Honey bees are important pollinators and are essential in agriculture;as such they get exposed to a wide range of pesticides while foraging in contaminated fields or during the spray of chemical on crops. It is therefore important to know the toxicity and evaluate the impacts of bees’ exposure to these molecules. Acetamiprid and cypermethrin are two pesticides widely used in Cameroon and other countries. The objective of this study was to determine the toxicity of acetamiprid and cypermethrin on the native subspecies of Apis mellifera L. in agricultural areas in Adamaoua-Cameroon and to evaluate the impact on honeybee foragers exposed to lethal and sublethal doses of these two insecticides. The results obtained in laboratory conditions show that acetamiprid and cypermethrin are toxic to A. mellifera. The symptoms of neurotoxicity and first mortality appear 15 min after the ingestion of the high concentrations and about 30 to 45 min after the inoculation of the pesticides through contact route and the mortality increases with the concentration and time. The LC50 of acetamiprid obtained after 24 h are respectively 5.26 ng/μl for the topical application and 4.70 μg/μl by the oral route. At the same time, the LC50 of cypermethrin are respectively 2.27 ng/μl for topical application and 2.68 ng/μl for oral toxicity. For a sustainable agriculture and beekeeping, it is, therefore, important to establish quality measures on these insecticides in the ecosystem and to set up a phyto-pharmacovigilance and awareness system to the population.

Impact of <i>Amegilla calens</i>and <i>Apis mellifera</i>Pollination on <i>Gossypium hirsutum</i>var. QR₁302 Flowers at Tchabbal-Mounguel (Ngaoundéré, Cameroon)

The investigations were carried out from September 10 through October 13, 2017 at Tchabbal-Mounguel. On Gossypium hirsutum flowers, investigations were done on many aspects of the pollination services of Amegilla calens and Apis mellifera. G. hirsutum flowers were observed to study the activity of A. calens and A. mellifera and to evaluate their impacts on fruits and seed yields of this Malvaceae. The treatments consisted of 120 flowers left for free pollination, 120 flowers protected from insects using gauze bag nets, 200 protected flowers and visited exclusively by A. calens and A. mellifera and 100 protected flowers then opened and closed without any visit of insects or any other organisms. The results show that on cotton flowers, foragers of A. calens and A. mellifera highly collect nectar and pollen on its flowers. The highest mean number of individuals simultaneously active per 1000 flowers is 587 for A. calens and 526 for A. mellifera. Through their pollinating efficiency, A. calens and A. mellifera caused a significant increase in the fruiting rate by 7.00% and 17.33%, the number of seeds per fruit by 44.20% and 18.32% and the normal seeds by 47.78% and 5.66% respectively. Therefore, the conservation of the nests of A. calens and colonies of A. mellifera around G. hirsutum plantations are to be recommended to improve the fruit and seed yields of this Malvaceae.

Pollination Efficiency of <i>Ceratina cyanea</i>(Hymenoptera: Apidae) on <i>Helianthus annuus</i>(Asteraceae) Flowers at Dang (Ngaoundere, Cameroon)

To evaluate the impact of Ceratina cyanea on fruit and seed yields of sunflower, experimental field was set up from June to July in 2016 and 2017 at Dang. Observations were done on 540 capitula divided in four treatments: two treatments differentiated according to the presence or absence of protection on capitula regarding Ceratina cyanea and other flowering insects’ visits;the third with capitula protected and uncovered when florets were opened, to allow C. cyanea visits and flowers bagged uncovered and rebagged without the visit of insects or any other organisms. Bee’s daily rhythm of activity, its foraging behavior on florets and its pollination efficiency were evaluated. Bee’s daily rhythm of activity, its foraging behavior on flowers and its pollination efficiency were evaluated. Results show that, C. cyanea foraged on Helianthus annuus flowers throughout its whole blooming period. Among 32 insect species recorded on H. annuus capitula, C. cyanea ranked second accounting for 10.79% all visits, after Apis mellifera (76.06%). On florets, individual bees intensely harvested nectar and slightly collected pollen. The mean duration of a visit per floret was 3.62 sec for nectar harvest and 9.58 sec for pollen collection. For the two years, through its pollination efficiency on H. annuus, C. cyanea has increased the fruiting rate by 65.90%, the percentage of fruit with seed by 63.56% and the percentage of normal seeds by 76.11%. Based on these results, we recommend the protection of C. cyanea nests at the vicinity of sunflower fields to increase its fruit and seed yields in the Adamaoua Region of Cameroon.