Impact of Mulches on Floral Visitors in Day-Neutral Strawberries and Contribution of Syrphid Flies to Strawberry Pollination

Animal-mediated pollination is essential for the production of many specialty crops, with insects, primarily bees, serving as the predominant pollinators in many agroecosystems. However, increasing management problems with honey bees and declines in native bee populations due to various environmental stressors have highlighted the importance of promoting wild bees and other insect pollinators to ensure sustainable pollination services. This study explores the impact of various mulches on the abundance and richness of floral visitations by insects and the role of syrphid flies in a day-neutral strawberry system. Four different types of mulches were evaluated at the University of Wisconsin West Madison Agricultural Research Station in Wisconsin, USA, during the 2022 and 2023 growing seasons, and included three polyethylene mulches of different colour (black, white on black, and reflective metallic) and one brown soil-biodegradable paper mulch. Observations of pollinator floral visitations were conducted, and insects were grouped into broad morphotypes. In addition, syrphid flies were sampled to assess their pollen loads. Mulch type did not significantly affect the overall abundance or richness of pollinators visiting flowers. Syrphid flies were the most abundant floral visitors, followed by small dark bees, green bees, Orius spp., and honey bees, while Bombus spp. were found in low numbers. Toxomerus marginatus, the margined calligrapher, was the most abundant syrphid species collected, representing 72% of all syrphid flies collected. Overall, 31% of syrphid flies captured carried strawberry pollen. A few syrphid species carried significant amounts (> 200 grains) of strawberry pollen on their body. The findings suggest that while mulch type did not impact pollinator visitation, syrphid flies may be important for strawberry pollination, as they were abundant, at least in 2022, and carry strawberry pollen. Our results underscore the need for further research to understand the complex role of non-bee pollinators in strawberry pollination and to further investigate the role of syrphid flies as pollinators in different agroecosystems.