The effect of annual flower strips on pollinator visitation and fruit set of avocado (Persea americana Mill.) in Kenya

Abstract

Wildflower strips are increasingly promoted in pollinator conservation schemes to maintain the stability of ecosystem services and increase crop yield. Yet, the increased area of avocado Persea americana Mill. cultivation in sub-Saharan Africa is not accompanied by measures of biodiversity conservation or the promotion of ecosystem services. We investigated the effects of flower strips on flower visitors and avocado fruit set in Kenya. A strip mixture of sunflower Helianthus annuus L., coriander Coriandrum sativum L., and alfalfa Medicago sativa L. was established at the border of four avocado plots, while four other plots with an unmanaged border served as control. The abundance of insect flower visitors and fruit set at 10 m, 55 m, and 100 m from the border of each plot were assessed during the early, peak, and late avocado flowering periods. The honeybee Apis mellifera L. and hoverflies Syrphidae spp. accounted for 22% and 71% of flower visitors, respectively. We found interactions between the treatment, distance to the border, and the avocado flowering intensity on the abundance of honeybees but not on hoverflies. Irrespective of the distance to the border and the avocado’s flowering intensity, flower strips acted as a sink for honeybees and hoverflies. Overall, the flower strip mixture of sunflower, coriander, and alfalfa did not increase pollinator abundance and avocado productivity, and it may be necessary to identify plant species for optimal benefits and study the long-term effects of floral strips on pollinators and crop production.