Agroscope Bern Switzerland

1 Introduction The proximity of a large number of individuals makes the colonies of social insects a favourable ground for infestations by parasites and infections by pathogens (Schmid-Hempel 1998; Cremer et al. 2018). Parasites and pathogens of the honey bee have been particularly well studied because of the important economic role these insects play by providing crop pollination and hive products (Gallai et al. 2009; Khalifa et al. 2021).

1 INTRODUCTION The need to decrease the use of pesticides is widely recognized1 to reduce the risk for pollinators and other terrestrial organisms.2 This has been reflected in the agricultural policies of many countries and in the EU and Switzerland.3-5 For example, in 2017, the Swiss Federal Council set out the Federal Act on reducing pesticide risks by 50% by 2027, using 2012–2015 as a reference period.4 Therefore, having information on the occurrence of pesticides in different...

1 INTRODUCTION Insects comprise the most diverse class of the animal kingdom (Stork et al., 2015). These species are key components of natural ecosystem functioning and human food security by providing a wide range of services ranging from pollination, natural pest control, and soil fertilization (Basset & Lamarre, 2019; Straub et al., 2015). However, insect diversity is crumbling in many regions globally (Powney et al., 2019; Wagner, 2020).