Effects of habitat management on diversity and abundance of cashew flower visitors: a case study of Mtwara region, south eastern Tanzania

Pollen vectors, most of which are insects contribute significantly to food production. Vectors such as bees pollinate over 75% of the world's flowering plan. Despite their importance in pollination, they are not adequately given attention as significant input affecting crop yield. This study was done in Mtwara Region-South eastern Tanzania with the general objective of assessing the effects of habitat management on diversity and abundance of cashew pollinators, and how the surrounding vegetation influences this diversity and abundance. The diversity of flower visitors was assessed through sweep netting at random pointsin cashew farms under different management categories (Highly Managed Farm- HMF, Well Managed Farm-WMF, Moderately Managed Fame-MMF and abandoned Farm-AF). Sweeping was replicated three times each month as from August to December 2009. A one-metre square visitation window was used to determine in- sects' relative abundance. Insects diversity were also assessed from weeds and sur- rounding vegetations. An exclusion bagging experiment was used to determine the influence of the diversity of flower visitors on fruits/nuts set. A combination of in- sects' behavioural observations, frequency of visits and the percentage of nut set fol- lowing a single visit by an insects was used to assess efficient/possible pollinators. Findings from the study have shown that the main flower visitors comprised of fourinsect orders: Coleopterans, Dipterans, Hemipterans and Hymenopterans. Hymenop- terans (Bees) contributed 78% of all the visitors sampled. A significant difference existed in the mean number of bee species visiting differently managed farms (F3, 20=5.906, P=0.004675). A WMF had the highest number of visiting bee species. while an AF had only 12 visiting bee species. Assessment of the influence of nectar production on insects' visitation rate has shown that number of visitors correlate positively to average nectar volume in WMF, HMF and AF (r=0.94; r=0.45 and r=0.63 respectively). The diverse and abundance of insects influenced fruit set, 17% of flowers exposed to single visit were recorded to have set seeds/fruits while 44% of flowers exposed to multiple visit were recorded to have set seeds/fruits. The differ-ences in seeds/nuts set between single and multiple visited flowers were statistically significant (T= 1.975092037; d.f=134; P=7.17x10 -08). The surrounding vegetation supported more than 50% of bee species encountered in respective cashew farms. The study has also revealed that Ceratina spp., Braunsapis spp. And Apis mellifera are efficient/possible pollinators of cashew flowers based on their high visitation rate, behaviours on flowers and their ability to influence fruits/nuts. The study concluded that, habitat management practices are crucial in influencing the diversity and abundance of cashew flower visitors. The surrounding vegetation needs to be maintained as they influence the diversity and abundance of flower visitors. This study has recommended pollinator-friendly activities like conservation of forest patches, shrublands, hedgerows, intercropping/mixed cropping and maintenance of flowering weeds in ensuring the continuity of free pollination services. Beekeeping activities are also recommended for farmers to earn multiple benefits. Further studies on pollination effiiciency of identified pollinators in this study are recommended