Neonicotinoids from coated seeds toxic for honeydew-feeding biological control agents

Miguel Calvo-Agudo,Jonathan Dregni,Joel González-Cabrera,Marcel Dicke,George E Heimpel,Alejandro Tena

doi:10.1016/j.envpol.2021.117813

Abstract

Seed coating (‘seed treatment’) is the leading delivery method of neonicotinoid insecticides in major crops such as soybean, wheat, cotton and maize. However, this prophylactic use of neonicotinoids is widely discussed from the standpoint of environmental costs. Growing soybean plants from neonicotinoid-coated seeds in field, we demonstrate that soybean aphids (Aphis glycines) survived the treatment, and excreted honeydew containing neonicotinoids. Biochemical analyses demonstrated that honeydew excreted by the soybean aphid contained substantial concentrations of neonicotinoids even one month after sowing of the crop. Consuming this honeydew reduced the longevity of two biological control agents of the soybean aphid, the predatory midge Aphidoletes aphidimyza and the parasitic wasp Aphelinus certus. These results have important environmental and economic implications because honeydew is the main carbohydrate source for many beneficial insects in agricultural landscapes.

Highlights

Seed coating (‘seed treatment’) is the leading delivery method of neonicotinoid insecticides (Frank and Tooker, 2020; Matsuda et al, 2020)
The longevity of female predatory midges that fed on honeydew produced by aphids feeding either on plants from seeds coated with thiamethoxam only or thiamethoxam plus fungicides was significantly shorter than of those fed on honeydew produced by aphids on untreated plants
The longevity of female A. certus parasitoids feeding on honeydew produced by aphids feeding on plants whose seeds had been coated with thiamethoxam only or with thiamethoxam plus fungicides was significantly shorter than that of females fed on honeydew produced by aphids feeding on untreated plants (Log-rank Test: X22 = 7.3, P = 0.03) (Fig. 3)

Summary

Introduction

Seed coating (‘seed treatment’) is the leading delivery method of neonicotinoid insecticides (Frank and Tooker, 2020; Matsuda et al, 2020). Seeds coated with neonicotinoids have been routinely used for major crops such as soybean, wheat, cotton and maize. The seeds of over 50% of soybeans, 52–77% of cotton, and 79–100% of maize sown in the United States were coated with neonicotinoids in 2011 (Douglas and Tooker, 2015; Hurley and Mitchell, 2017), they increased yield in less than 5% of the cases (Labrie et al, 2020). Neonicotinoids from coated seeds contaminate floral and extrafloral nectar because these pesticides are taken up systemically by the growing plant and distrib uted to all tissues (Goulson, 2013; Rundlof et al, 2015; Whitehorn et al, 2012). Many beneficial insects become exposed to neon icotinoids when they feed on contaminated nectar and pollen (Krischik et al, 2007; Rundlof et al, 2015)

Methods

Results

Discussion

Conclusion