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
color (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.