Comparison of buckwheat, red clover, and purple tansy as potential surrogate plants for use in semi-field pesticide risk assessments with Bombus impatiens

Results of Ring-Testing of a Semifield Study Design to Investigate Potential Impacts of Crop Protection Products on Bumblebees (Hymenoptera, Apidae) and a Proposal of a Potential Test Design

In Europe, the risk assessment for bees at the European Union or national level has always focussed on potential impacts on honeybees. During the revision of the European Food Safety Authority bee guidance it was explicitly stated that bumblebees and solitary bees should be considered as well and consequently concerns were raised regarding the representativeness of honeybees for these other bee species. These concerns originate from differences in size as well as differences in behavioral and life history traits of other bee species. In response to this concern, the non-Apis working group of the International Commission for Plant-Pollinator Relationships initiated a ring-test of a semifield tunnel study design using the bumblebee Bombus terrestris. Nine laboratories participated, validating and improving the proposed design over a 2-year period. The intention of the ring-test experiments was to develop and if possible, establish a test protocol to conduct more standardized semifield tests with bumblebees. In the present study, the results of the ring-tests are summarized and discussed to give recommendations for a promising experimental design. Environ Toxicol Chem 2022;41:2548-2564. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Comparison of Pesticide Exposure in Honey Bees (Hymenoptera: Apidae) and Bumble Bees (Hymenoptera: Apidae): Implications for Risk Assessments

To date, regulatory pesticide risk assessments have relied on the honey bee (Apis mellifera L.) (Hymenoptera: Apidae) as a surrogate test species for estimating the risk of pesticide exposure to all bee species. However, honey bees and non-Apis bees may differ in their susceptibility and exposure to pesticides. In 2017, a workshop ('Pesticide Exposure Assessment Paradigm for Non-Apis Bees') was held to assess if honey bee risk assessment frameworks are reflective of non-Apis bee pesticide exposure. In this article, we summarize the workshop discussions on bumble bees (Bombus spp.). We review the life history and foraging behavior of bumble bees and honey bees and discuss how these traits may influence routes and levels of exposure for both taxa. Overall, the major pesticide exposure routes for bumble bees and honey bees are similar; however, bumble bees face additional exposure routes (direct exposure of foraging queens and exposure of larvae and adults to soil residues). Furthermore, bumble bees may receive comparatively higher pesticide doses via contact or oral exposure. We conclude that honey bee pesticide risk assessments may not always be protective of bumble bees, especially queens, in terms of exposure. Data needed to reliably quantify pesticide exposure for bumble bees (e.g., food consumption rates, soil residue levels) are lacking. Addressing these knowledge gaps will be crucial before bumble bee exposure can be incorporated into the pesticide risk assessment process. Because bumble bees exhibit appreciable interspecific variation in colony and behavioral characteristics, data relevant to pesticide exposure should be generated for multiple species.

Potential surrogate plants for use in semi-field pesticide risk assessment with Megachile rotundata

BACKGROUND

Current regulatory pesticide risk assessments for bees are based primarily on the honey bee (Apis mellifera) and may not always be protective of solitary bees. To incorporate solitary bees into the risk assessment process, standardized methods to assess the hazard of pesticides under semi-field (Tier II) conditions will be needed. We conducted a series of experiments over 2 years to assess potential surrogate plants and adult release rates for use in semi-field experiments with the alfalfa leafcutting bee (ALB, Megachile rotundata).

METHODS

We compared ALB foraging activity and reproduction on 12 m2 plots of flowering alfalfa (Medicago sativa) and buckwheat (Fagopyrum esculentum) at low (10♀/20♂) and high (20♀/40♂) adult release rates. The following year, we assessed the same endpoints on plots of purple tansy (Phacelia tanacetifolia) at a release rate of 10♀/15♂.

RESULTS

Although ALB foraging activity was high on buckwheat plots, fewer adults were produced compared to alfalfa plots. On alfalfa, there were no differences in foraging activity, nesting, or reproduction between the low and high release rates. ALB readily foraged from purple tansy flowers, but females avoided purple tansy leaves for leaf cell construction.

DISCUSSION

Our study suggests that buckwheat alone cannot support ALB during semi-field studies on small plots. For alfalfa, we recommend a maximum release rate of 10♀/20♂ in 12 m2 plots. Further study of higher ALB release rates on purple tansy is warranted. A mixed planting of purple tansy and a plant suitable for leaf piece collection (e.g., buckwheat) may provide favorable conditions for ALB activity and reproduction during semi-field testing.