A systematic scoping review of the methodological approaches and effects of pesticide exposure on solitary bees
Background: Pollination services provided by solitary bees, the largest group of bees worldwide, are critical to the vitality of ecosystems and agricultural systems alike. Disconcertingly, bee populations are in decline and while no single causative factor has been identified, pesticides are believed to play a role in downward population trends. The effects of pesticides on solitary bee species have not been previously systematically cataloged and reviewed. Objectives: This scoping publication examines available evidence for effects of pesticide exposure on solitary bees to identify data gaps and research needs. Methods: A systematic literature search strategy was developed to identify reports on solitary bee pesticide exposure-effects studies. Literature was subsequently screened for relevance using a Population, Exposures, Comparators, and Outcomes (PECO) statement and organized into a systematic evidence map. Studies were organized by effect category (lethal effects on immatures, lethal effects on adults, sublethal effects on immatures, and sublethal effects on adults), species, pesticide class, and study year. Results: A comprehensive literature search of Web of Science and ProQuest Agricultural & Environmental Science supplemented by targeted internet searching and reference mining yielded 137 reports and publications for title and abstract screening and 53 that met PECO criteria (27 included lethal and 46 included sublethal effects endpoints). Relevant study details (pesticide, test compound configuration, study type, species, sex, exposure duration) were extracted into literature inventory tables to reveal the extent endpoints have been studied and areas in need of additional research. Conclusions: Evidence mapping revealed diversity in the pesticides and endpoints studied across the database. However, study dilution across bee species, lack of complementary laboratory work and paucity of replicated studies complicate efforts to interpret and apply available data to support pesticide risk assessment.