Pollination of strawberry in Kenya, by stingless bees (Hymenoptera: meliponini) and honey bee (hymenoptera: apini) for improved fruit quality
The essence of pollination in crop and fruit production, for increased food production, in quantity and quality, is undisputed. A wide range of agricultural crops rely on pollinators, particularly bees for their pollination requirement. Strawberry, for instance, is self-pollinated, wind and bee-pollinated. The production of strawberry fruits is heavily dependant on efficient and effective pollination, such that when properly pollinated, the fruits become heart-shaped, suitable for market at premium prices. Besides pollination by honey bees, stingless bees and solidary bees are suitable alternative pollinators, in the wake of declining honey bee colonies, due to anthropogenic factors, hence declines in food production. Pollination studies in Africa have, in the past been initiated but abandoned due to prioritization challenges. The study aimed at testing the pollination efficiency of three stingless bee speciesﾷ Hypotrigona sp., Meliponula sp. Plebeina sp.) and the honey bee, Apis mellifera scutellata, on two strawberry varieties, rotunda and chandler, in enclosures, in order to recommend their utilization by commercial farmers to increase horticultural production and for improved fruit quality. Specific objectives were: a) To determine the pollination efficiency of the selected stingless bee species and the honey bee, Apis mellifora scutellata, on strawberry plants in net enclosures, cages. b) To determine the quality and quantity of strawberry fruit production through stingless and honey bee pollination. c) To establish strawberry fruit variation due to: ecological zone, stem age, season, bee species, strawberry variety and crop husbandry. Experiments were set up in three ecological zones of Kenya, with differing Agricultural land productivity: Kakamega, high potential; Nairobi, medium potential and Kima, low potential. Using a randomized split block design, five stingless bee species, Hypotrigona gribodoi, Hypotrigona ruspo/ii, Meliponula ferruginea, M bocandei, Plebe ina hildebrandti and the honey bee, Apis mellifera scutellata, were tested for their suitability in the pollination of two strawberry varieties, rotunda and chandler. This was done on 6 x 11 Metre split plots. The study incorporated two control strategies: In the first control, strawberry cultivars were planted in the open with free pollination and could therefore be pollinated by self, wind or any other pollinator in the viscinity. In the second control, the study plots were enclosed by an insect net, to keep off would be pollinators, hence, no external pollinator was used such that only self pollination occurred. The total number of fruits harvested per day, their weight, size and quality classification, were used as the response variables, whereas bee species, strawberry variety and location, were the main explanatory variables. Rainfall and daily temperature data were recorded. Regression analysis revealed significant association between rotunda strawberry variety and bee species (d.f=6; P<O.OOI, 505). Similarly, between chandler variety and bee species (d.f =9; P<O.OOI, 2055). A chisquare test to establish association between fruit quality and stingless bee species, and fruit quality and strawberry variety, were both highly significant (d.f=21; X2 =62.95; P<O.OOI and d.f=7; X2 =2909; P<O.OOI respectively). Pearson chi-square test for association between strawberry variety and bee species was highly signi!icant (d.f=7; X2=2909; p<O.OOI). The mean number of fruits picked per day for chandler strawberry variety was 4, whereas that of rotunda was 2 (d.f 424; P<O.OOI). The study showed that strawberry variety and quality of fruits for, Kima and Nairobi sites were significant (d.f 3; P=0.05). There was high significant association between strawberry variety and quality of fruits for, Kakamega and Nairobi sites (d.f=3, X2=46.79, P<O.OOI). The honey bee pollination improved fruit yield and quality. The Pearson Chi-square test showed significant association between strawberry variety and fruit class (d.f=3; P=0.05, 9.24). It further revealed significant association between quality of fruits and ecological zones (d.f= 3; X2 =7.83; p< 0.050). There was significant seasonal effect on productivity of strawberry varieties (d.f=3; P<0.001,709). There was significant interaction between season and strawberry variety (d.f= 3; F<O.OOl, 3.82). Some bee species responded differently with change of environment, from endemic site to an introduced site (Plebeina hildebrandti, from Kima to Nairobi site). There was positive correlation between the number of fruits picked per day and the warm temperature (coefficient 7.5 with a p-value 0.04). Season and location were found to be important factors that influence the number of fruits picked per day. In conclusion, the two strawberry varieties, rotunda and chandler, require differrent stingless bee species for optimal pollination. Hypotrigona species were more efficient pollinators of strawberries than meliponula and plebe ina species. It was recommended that farmers in Kakamega be advised to cultivate chandler strawberry variety for increased food and nutrition security, whereas those in Kima should cultivate rotunda, since it is capable of withstanding stress conditions, to some extend, as opposed to chandler variety. Farmers in Nairobi may cultivate both, rotunda and chandler, and use the bee species best adapted to the climatic condition for their pollination requirement.