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. 2019 Jan 18:6:e6278.
doi: 10.7717/peerj.6278. eCollection 2019.

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

Andrew J Frewin  1 , Angela E Gradish  1 , Graham R Ansell  1 , Cynthia D Scott-Dupree  1
Affiliations

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

Andrew J Frewin et al. PeerJ. .

Abstract

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.

Keywords: Non-apis; Risk assessment; Semi-field; Solitary bee.

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Conflict of interest statement

The authors declare they have no competing interests.

Figures

Figure 1
Figure 1. Field enclosure with nest box (A) and a close up of a nest box (B) used for semi-field experiments with Megachile rotundata in this study.
Figure 2
Figure 2. Mean number of active Megachile rotundata adults per observation period.
Adults were released on and confined to small plots of flowering alfalfa (A), buckwheat (B), or purple tansy (C) for up to 18 days. Open circles and dashed lines represent a release rate of 10♀/20♂(A, B) or 10♀/15♂(C), and closed circles and solid lines represent a release rate of 20♀/40♂(A, B).
Figure 3
Figure 3. Total number of foraging trips (collection of leaf pieces and/or pollen) made by Megachile rotundata adults per observation period.
Adults were released on and confined to small plots of flowering alfalfa (A), buckwheat (B), or purple tansy (C) for up to 18 days. Open circles and dashed lines represent a release rate of 10♀/20♂(A, B) or 10♀/15♂(C), and closed circles and solid lines represent a release rate of 20♀/40♂(A, B).
Figure 4
Figure 4. Total number of Megachile rotundata females resting in the nest box per observation period.
Adults were released on and confined to small plots of flowering alfalfa (A), buckwheat (B), or purple tansy (C) for up to 18 days. Open circles and dashed lines represent a release rate of 10♀/20♂(A, B) or 10♀/15♂(C), and closed circles and solid lines represent a release rate of 20♀/40♂(A, B).
Figure 5
Figure 5. Proportion of female Megachile rotundata observed at the nest box per observation period.
Adults were released on and confined to small plots of flowering alfalfa (A), buckwheat (B), or purple tansy (C) for up to 18 days. Open circles and dashed lines represent a release rate of 10♀/20♂(A, B) or 10♀/15♂(C), and closed circles and solid lines represent a release rate of 20♀/40♂(A, B).
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