Ecology and behaviour of selected pollinating insects in cucurbit fields in Morogoro, eastern - central Tanzania

Dissertation

Cucurbits are fruit vegetables belonging to the family Cucurbitaceae. They supply humans with essential compounds in edible products containing vitamins, minerals and phyto-protective compounds. The importance of cucurbits’ essential compounds to human health has raised the demand for its products. However, the production of cucurbit fruits is hampered by insufficient pollination services. Most of the cucurbits are monoecious, having both male and female flowers separately on the same plant. Male flowers have sticky and heavy pollens which for successful transfer to female flowers requires insect pollinators. Honeybees (Apis mellifera) are known to be the major pollinators of cucurbits. However, the population of the former is declining, this has negatively impacted cucurbits production. This is due to their territories being threatened by climatic change and agriculture intensification which involves the excessive use of pesticides. There is little hope in the efforts for enhancing the abundance of honeybees for effectiveness and sustainable pollination services in cucurbits. This situation entails the investigation of other insect pollinators who are attracted to cucurbits for supplementary pollination services. In Literature, the Syrphidae (hoverflies) family members have been reported to have pollination potential. Their bodies are covered with bristles which assist in carrying pollen grains from one flower to another. However, the foraging behaviour of most hoverfly species in cucurbits is not well understood, requiring further investigation. Therefore, this study investigated four dominant hoverflies species attracted to cucurbits namely Eristalinus megacephalus, Mesembrius caffer, Paragus borbonicus and Toxomerus floralis along with A. mellifera on: 1) the floral visitation of hoverflies and honeybees on the three cucurbit species; cucumber (Cucumis sativus), watermelon (Citrullus lanatus) and Squash (Cucurbita moschata) which are commonly grown in Tanzania, 2) how environmental variables; temperature, relative humidity and rainfall affect their diurnal visitation patterns, and 3) how different management practices in cucurbits production influence their foraging activities. A Randomized Complete Block Design (RCBD) in a factorial arrangement with four replications was used. The floral visitation was assessed based on pollinator visitation abundance per cucurbit species, visitation frequency (number of visits per pollinating species per cucurbit flower) and visitation rate (number of flowers visited by individual pollinating species). The influence of environmental variables on diurnal visitation patterns of pollinators were assessed based on pollinator visitation abundance on cucurbit flowers per specific time along the day: Five-time slots from 0800 h to 1700 h at the interval of 1 hour were considered. For the effects of cucurbits management practices on pollinator foraging activities; GAMOUR - Agroecology and conventional practices were evaluated and pollinators foraging activities were assessed based on their visitation abundance, visitation frequency, visitation rate and handling time (time spent on cucurbit flowers). The plots where no any management practices except weeding and irrigation during the dry season were used as a negative control. The experiments were conducted at two agroecological zones of Morogoro (plateau and mountainous) for two seasons (rainy and dry season). Results revealed a significant relationship between visitation abundance with flower density and relative humidity. Agroecological zones, cucurbit species and seasons had significant effects on the number of visits per cucurbit flowers and the number of flowers visited by pollinating species. Apis mellifera was the dominant species in cucurbit flowers at both agroecological zones during the two growing seasons and M. caffer was the least visitors on flowers of all three cucurbit species. Toxomerus floralis and P. bobornicus were dominant visitors of C. sativus and C. lanatus at the plateau zone during the season of May-June. Environmental variables had negative effects on the diurnal visitation patterns of flower visitors. The highest average visitation abundance for all pollinating species were recorded between 0800 – 1100 h and the least between 1600 – 1700 h. Environmental variables had less impact on hoverflies' diurnal visitation patterns as compared to honeybees because from 1200 – 1700 h the visitation abundance of honeybees was ceasing, whereas no significant difference in visitation abundance was found for hoverflies. Management practices applied during cucurbit production affected the visitation frequencies and handling time of pollinators on cucurbit flowers. The number of visits and the time spent by pollinators on cucurbit flowers in plots receiving GAMOUR - Agroecology practices were significantly higher than that in plots assigned Conventional practices and the control plots. This study concludes that, all the studied hoverflies can have pollination potentials in cucurbits, however their foraging activities are influenced by Agroecological zone, seasons, cucurbit species and management practices that are employed during cucurbit production. Therefore, cucurbit growers have to consider producing this crop during the season when pollinators are abundantly present and the practices that enhance pollinators’ abundance and their foraging activities. Also, this study recommends further investigations on the effect of cucurbits management practices on floral rewards quality and floral receptiveness longevity followed by an investigation of pollination efficiency of the studied hoverflies.

Agroecological Methodology in VEGetable crops (AGROVEG)