Diversified Farming in a Monoculture Landscape: Effects on Honey Bee Health and Wild Bee Communities

Abstract

In the last century, a global transformation of Earth's surface has occurred due to human activity with extensive agriculture replacing natural ecosystems. Concomitant declines in wild and managed bees are occurring, largely due to a lack of floral resources and inadequate nutrition, caused by conversion to monoculture-based farming. Diversified fruit and vegetable farms may provide an enhanced variety of resources through crops and weedy plants, which have potential to sustain human and bee nutrition. We hypothesized fruit and vegetable farms can enhance honey bee (Hymenoptera: Apidae, Apis mellifera Linnaeus) colony growth and nutritional state over a soybean monoculture, as well as support a more diverse wild bee community. We tracked honey bee colony growth, nutritional state, and wild bee abundance, richness, and diversity in both farm types. Honey bees kept at diversified farms had increased colony weight and preoverwintering nutritional state. Regardless of colony location, precipitous declines in colony weight occurred during autumn and thus colonies were not completely buffered from the stressors of living in a matrix dominated with monocultures. Contrary to our hypothesis, wild bee diversity was greater in soybean, specifically in August, a time when fields are in bloom. These differences were largely driven by four common bee species that performed well in soybean. Overall, these results suggest fruit and vegetable farms provide some benefits for honey bees; however, they do not benefit wild bee communities. Thus, incorporation of natural habitat, rather than diversified farming, in these landscapes, may be a better choice for wild bee conservation efforts.

Keywords: Apis mellifera; diversified farming; honey bee; wild bee.

Fig. 1.

Placement of honey bee colonies and bee-bowl pan traps in Mono-SOY (A) and Div-FV (B) farms in central Iowa in 2015 and 2016. In Mono-SOY farms, traps were placed parallel to honey bee colonies and 10 m inside of the field. In Div-FV farms, traps were placed in an area planted with grass directly adjacent to the crops and also parallel to honey bee colonies. Honey bee colonies were placed in the exterior grassy perimeter, 3 m from the edge of the crop and 10 m from the bee-bowls.

Fig. 2.

Coverage-based rarefaction/extrapolation curves with 95% confidence intervals (shaded areas, based on a bootstrap method with 200 replications) comparing wild bee species abundance (A) and richness (B) collected from bee-bowls for data of two farming types (Div-FV and Mono-SOY) in central Iowa in 2015 and 2016. Incidence-based rarefaction (solid lines) and extrapolation (dashed lines) sampling curves with 95% confidence intervals (shaded areas, based on a bootstrap method with 200 replications) comparing wild bee species richness (C). Observed samples are denoted by the solid circle (Div-FV) and open circle (Mono-SOY). Nonmetric, multidimensional scaling plot of the pollinator community found in Div-FV and Mono-SOY farms in central Iowa in 2015 and 2016 (D). The hulls (closed circles for Div-FV and open circles for Mono-SOY) are constructed from a representation of the pollinator community found at each of the 9 Div-FV and 20 Mono-SOY farms across the 2 yr.

Fig. 3.

Mean abundance (A), richness (B), and diversity (Shannon–Wiener Index; C) of the wild bee community observed in Div-FV (solid line and closed circles) and Mono-SOY (dotted line and open circles) in central Iowa across the season during 2015 and 2016. Error bars represent 1 SEM. Values represent the mean of bees collected at each farm per month. Asterisks signify post hoc least squares means comparison for differences between farm types at each time point.

Fig. 4.

Honey bee colony weight in Div-FV (solid line and closed circles) and Mono-SOY (dotted line and open circles) farms in central Iowa for 2015 and 2016 combined (A). Honey bee colony weight (B), capped brood area (C), and adult bee population (i.e., frame sides of honey bees; D) in colonies in Div-FV and Mono-SOY farms in central Iowa for 2016 only. Error bars represent 1 SEM. Asterisks signify post hoc least squares means comparison for differences between farm types at each time point. Results based on repeated-measure linear mixed effect model.

Fig. 5.

Mean percent honey bee lipid content (lipid mg bee-mass/mg) for colonies in Div-FV (solid line and closed circles) and Mono-SOY (dotted line and open circles) farm types in central Iowa in 2016. Error bars represent 1 SEM. Asterisks signify post hoc least squares means comparison for differences between farm types at each time point. Letters signify post hoc least squares means comparison for differences between sampling dates. Results based on repeated-measures linear mixed effect model.