Quantitative weight of evidence assessment of higher-tier studies on the toxicity and risks of neonicotinoid insecticides in honeybees 1: Methods

Abstract

A quantitative weight of evidence (QWoE) methodology was developed and used to assess many higher-tier studies on the effects of three neonicotinoid insecticides: clothianidin (CTD), imidacloprid (IMI), and thiamethoxam (TMX) on honeybees. A general problem formulation, a conceptual model for exposures of honeybees, and an analysis plan were developed. A QWoE methodology was used to characterize the quality of the available studies from the literature and unpublished reports of studies conducted by or for the registrants. These higher-tier studies focused on the exposures of honeybees to neonicotinoids via several matrices as measured in the field as well as the effects in experimentally controlled field studies. Reports provided by Bayer Crop Protection and Syngenta Crop Protection and papers from the open literature were assessed in detail, using predefined criteria for quality and relevance to develop scores (on a relative scale of 0-4) to separate the higher-quality from lower-quality studies and those relevant from less-relevant results. The scores from the QWoEs were summarized graphically to illustrate the overall quality of the studies and their relevance. Through mean and standard errors, this method provided graphical and numerical indications of the quality and relevance of the responses observed in the studies and the uncertainty associated with these two metrics. All analyses were conducted transparently and the derivations of the scores were fully documented. The results of these analyses are presented in three companion papers and the QWoE analyses for each insecticide are presented in detailed supplemental information (SI) in these papers.

Quantitative weight of evidence assessment of higher tier studies on the toxicity and risks of neonicotinoids in honeybees. 3. Clothianidin

“…The source of studies, papers, and reports used in this QWoE analysis and the methods used to assess quality and relevance of the data are described in the first paper in the series (Solomon and Stephenson 2017). Reviews and papers lacking sufficient information to allow for assessment of quality and relevance were not included in the analysis (see discussion in Solomon and Stephenson 2017).…”

“…The methods used to score the papers and reports for quality and relevance and how these scores were used to produce the QWoE diagrams in this paper are also provided in the text and supplemental information in Solomon and Stephenson (2017). These methods are common to this and two other companion papers and are not discussed in detail here.…”

Quantitative weight of evidence assessment of higher tier studies on the toxicity and risks of neonicotinoids in honeybees. 4. Thiamethoxam

“…As for all neonicotinoid insecticides, TMX acts as an agonist at the insect nicotinic acetylcholine receptor (nAChR) (Jeschke et al 2011). The companion paper (Solomon and Stephenson 2017a) presents a generic conceptual model for exposure of honeybees to neonicotinoids. This assessment of TMX was based on that conceptual model.…”

“…Toxicity tests at the level of the colony integrate lethal and sublethal effects at the apical endpoints (see Solomon and Stephenson 2017a) and data for higher-tier assessments were provided in wholehive feeding-and dust-exposure studies conducted over an extended period of time (Syngenta 2010a). These reports were reviewed using the guidelines for effect-studies as described in the supplemental information, SI Table 2a of Solomon and Stephenson (2017a). The feeding study (Syngenta 2015) exposed honeybees via sugar syrup and colony-relevant responses for survival and productivity were measured over 42 d with a follow-up the next spring.…”

“…This paper is the fourth in a series of quantitative weight of evidence (QWoE) analyses on the effects and risks to honeybees from neonicotinoids used as seed treatments. The methodology used for the QWoE analysis is described in the first paper in this series (Solomon and Stephenson 2017a). Moreover, this paper reports on a QWoE of the effects and risks of the neonicotinoid, thiamethoxam (TMX), in honeybees.…”