Exploring the Pollinator Community: Diversity and Abundance of Flower-Visiting Insects on Cowpea in Bilone, Obala, Cameroon

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Abstract
Aims: Investigations in cowpea fields allowed the characterization of the community structure of flower-visiting insects. Study Design: Seeds were sown in 15 plots (6x5.5 m each). Place and Duration of Study: Campus of Obala Higher Institute of Agriculture and Management (OHIAM), Bilone agroecological farm (Obala-Cameroon), from May to June 2016 and 2017. Methodology: Insects were identified in-situ or captured and stored in papillotes (Lepidoptera adults) or labelled vials containing 70° ethanol (other insects). Abundances allowed the determination of 11 alpha diversity indices. Beta diversity was tested using Bray-Curtis dissimilarity index and the correlation between species occurrences. Results: A total of 929 specimens belonged to five orders, 10 families, 13 species were recorded. Hymenoptera was the most family-rich and abundant (four families, 94.3% of the collection) followed by Diptera and Lepidoptera (two families each). Neuroptera and Orthoptera (one family each). Apidae was the most species-rich and abundant (three species; 72.9%), then Formicidae (one, 10.1%), Megachilidae (two; 9.8%). Apis mellifera (Apidae) was the most abundant (35.5%), then Xylocopa olivacea (Apidae) (22.3%), Amegilla calens (Apidae) (15.1%), Myrmicaria opaciventris (Formicidae) (10.1%), and Megachile (Chalicodoma) cincta (Megachilidae) (8.2%). The afrotropical useful predator Ascalaphus africanus (Ascalapidae) and the phytophagous pest Pteropera carnapi (Acrididae) were recorded. Exotic myasigenic species Calliphora vicina (Calliphoridae) and Musca domestica (Muscidae) were recorded. Acrididae, Nymphalidae and Pieridae cumulatively represented 3.1% pest species in the collection. Assemblages showed low species richness, high species diversity, and highly even community. Numbers of simply abundant species were close to that co-dominants. A negative correlation was noted between Acraea acerata (Nymphalidae) and Apis mellifera adansonii (Apidae), Ap. mellifera and Calliphora vicina (Calliphoridae), Ap. mellifera and Synagris conuta (Vespidae). Several positive correlations were recorded. Conclusion: In Bilone, results highlighted the importance of flower-visiting insects for the cowpea pollination and crop yield. Species were moderately abundant and assemblages functioned on the base of niche partitioning nomocenosis (log-linear model) of more or less disturbed environments with strong competition between pioneer species for the available resources.

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