Ecology and behaviour of selected pollinating insects in cucurbit fields in Morogoro, eastern - central Tanzania
Loading...
Date
2022
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Sokoine university of agriculture
Abstract
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.
Description
Dissertation
Keywords
Cucurbits, Gamour, Agroecology, Conventional, Honeybees, Hoverflies, Pollination, Apis mellifera, Paragus borbonicus, Toxomerus floralis