Are temporal trends in bee and non-bee abundance similar in Plymouth County, MA?

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Wes V. Walsh, Michael Bankson, Adam Germaine, Andrew Oguma, Prisca Sanon and Christina Orazine, Division of Science and Mathematics, Massasoit Community College, Brockton, MA

Background/Question/Methods
As a keystone species, bees often dominate discussions about pollination. However, while bees are thought to be the most efficient pollinators, non-bee insect pollinators provide pollination services similar to bees when the number of visits and productivity per visit are both considered. Multiple pollinator types are associated with a greater diversity of organisms and more fertile plants. Plants also benefit from predatory insects, like wasps, that control the number of plant-eating insects, as well as detritivorous insects, such as flies, which promote nutrient cycling. Some studies suggest that non-bee insects may be declining and likely react differently than bees to environmental changes. If the non-bee insect pollinator community is more resilient in the face of ecosystem disruptions, they could mitigate the effect of bee declines. However, if both groups respond negatively to the same environmental changes it could increase the ecological damage. This pilot study compares changes in bee and non-bee pollinator abundances to gauge whether these groups share similar trends over time. Specimens were collected bi-weekly at six sites in southeastern Massachusetts through systematic sweep netting. Sampling spanned from spring to early fall during 2016-2019.
Results/Conclusions
Repeated measures ANOVA showed no significant change in overall insect pollinator abundance over five years (p = 0.08). Insect abundance declined from 2016 to 2019 (p = 0.03), but this trend weakened with the addition of 2020 data suggesting no strong trend of pollinator decline. Bee and non-bee abundance remained relatively stable over five years and there is no evidence the groups do not covary (interaction, p = 0.62). Not surprisingly, insect abundance varied within seasons (at biweekly resolution, p < 0.001). However, these within-season abundance patterns differed between bees and non-bees (interaction, p < 0.001). Non-bees were more abundant in early spring, whereas bees became the more abundant pollinators in late summer after non-bee abundance waned. Thus, non-bee insects could be important pollinators for early blooming plants. Even with a stable bee population, a subset of the ecosystem’s plants may suffer from a decline in non-bee pollinators. Overall, these results suggest that bee and non-bee insects may play differing temporal roles in regards to plant pollination in southeastern Massachusetts. Thus, we recommend that studies investigating the potential for pollinator decline may be incomplete without non-bee insect monitoring.