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

Population genetic structure and assessment of allochronic divergence in the Macoun’s arctic butterfly (Oeneis macounii)

Patterns in the genetic variation of species can be used to infer their specific demographic and evolutionary history and provide insight into the general mechanisms underlying population divergence and speciation. The Macounâ s arctic butterfly (MA; Oeneis macounii [W. H. Edwards, 1885]) occurs across Canada and parts of the northern US in association with jack (Pinus banksiana Lamb.) and lodgepole (Pinus contorta Doug. ex Loud.) pine. MAâ s current distribution is highly fragmented, and the extent of reproductive isolation among allopatric populations is unknown. Furthermore, although MA is biennial, adults emerge every year in some populations. These populations presumably consist of two alternate-year cohorts, providing the opportunity for sympatric divergence via allochronic isolation. Using mitochondrial (mt) DNA and amplified fragment length polymorphism (AFLP) markers, we analyzed MAâ s genetic structure to determine the current and historical role of allopatric and allochronic isolation in MA population divergence. Both markers revealed high diversity and a low, but significant, degree of spatial structure and pattern of isolation by distance. Phylogeographic structure was generally absent, with low divergence among mtDNA haplotypes. MA likely exhibits low dispersal and gene flow among most allopatric populations; however, there was no evidence of differentiation resulting from allochronic isolation for sympatric cohorts.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Contact toxicity of three insecticides for use in tier I pesticide risk assessments with Megachile rotundata (Hymenoptera: Megachilidae)

The current pesticide risk assessment paradigm may not adequately protect solitary bees as it focuses primarily on the honey bee (Apis mellifera). The alfalfa leafcutting bee (Megachile rotundata) is a potential surrogate species for use in pesticide risk assessment for solitary bees in North America. However, the toxicity of potential toxic reference standards to M. rotundata will need to be determined before pesticide risk assessment tests (tier I trials) can be implemented. Therefore, we assessed the acute topical toxicity and generated LD50 values for three insecticides: dimethoate (62.08 ng a.i./bee), permethrin (50.01 ng a.i./bee), and imidacloprid (12.82 ng a.i/bee). The variation in the mass of individual bees had a significant but small effect on these toxicity estimates. Overall, the toxicity of these insecticides to M. rotundata were within the 10-fold safety factor currently used with A. mellifera toxicity estimates from tier I trials to estimate risk to other bee species. Therefore, tier I pesticide risk assessments with solitary bees may not be necessary, and efforts could be directed to developing more realistic, higher-tier pesticide risk assessment trials for solitary bees

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

Background. Bumble bees (Bombus spp.) are important wild and managed pollinators. There is increased interest in incorporating data on bumble bees into risk assessments for pesticides, but standardized methods for assessing hazards of pesticides in semi-field and field settings have not yet been established for bumble bees. During semi-field studies, colonies are caged with pesticide-treated flowering surrogate plants, which must be attractive to foragers to ensure colony exposure to the test compound, and must produce an ample nectar and pollen to sustain colonies during testing. However, it is not known which plant(s) are suitable for use in semi-field studies with bumble bees. Materials and Methods. We compared B. impatiens foraging activity and colony development on small plots of flowering buckwheat (Fagopyrum esculentum, var. common), red clover (Trifolium pratense), and purple tansy (Phacelia tanacetifolia) under semi-field conditions to assess their suitability as surrogate plants for pesticide risk assessment studies with bumble bees. We also compared the growth characteristics and input requirements of each plant type. Results. All three plant types generally established and grew well. Red clover and purple tansy experienced significant weed pressure and/or insect pest damage. In contrast, pest pressure was extremely low in buckwheat. Overall, B. impatiens foraging activity was significantly greater on buckwheat plots than red clover or purple tansy, but plant type had no effect on number of individuals produced per colony or colony weight. Discussion. Because of the consistently high foraging activity and successful colony development observed on buckwheat plots, combined with its favourable growth characteristics and low maintenance requirements, we recommend buckwheat as a surrogate plant for use in semi-field pesticide toxicity assessments with B. impatiens

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.</p