Pesticide input data
To estimate average level of pesticide applied per crop at each field
site (1km buffer), we calculated a pesticide risk assessment
(RI ), including herbicides, insecticides, molluscicides and
fungicides, using the methodology described by Yasrebi-de-Kom et al.
(2019) as:
\begin{equation}
RI=\ \sum{HQ=\left(\frac{Application\ rate\ (\text{g.ha}^{-1})}{Toxicity\ (\text{LD}_{50}\text{\ in\ μg\ per\ bee})}\right)>50}\nonumber \\
\end{equation}with HQ the hazard quotient (HQ) of each active molecule and the
median lethal dose per bee (LD50 ). The median
lethal dose is one way to measure the short-term poisoning potential
(acute toxicity) of a substance. The LD50 is the
amount of a substance, given all at once, which causes the death of 50%
of a group of test animals. The hazard quotient ratio gives an
approximation of how close the likely exposure of bees is to a
toxicologically significant level. The pesticide risk index (RI )
was defined as the number of high risk active ingredients
(HQ>50 ; see EPPO, 2010) that were applied. IfHQ<50 , the active ingredient was categorized as low
risk to bees.
The LD50 of 390 active ingredients used in the UK
and the Netherlands were extracted from the “Pesticides
Properties DataBase ” (PPDB) from the University of Hertfordshire, UK
(https://sitem.herts.ac.uk/aeru/ppdb/en/index.htm;
Lewis et al., 2016; Lewis and Tzilivakis, 2019) (see list of active
ingredients in Appendix S1 in Supporting Information). As proposed by
EPPO (2010), the risk assessment was carried out selecting the lowest of
the oral and contact LD50 values available across
the different bee species (honey bees, bumble bees and other wild bees),
to take the most conservative approach for the entire bee community (see
Table S2). However, LD50 values were mainly
available for honey bees, sometimes for bumble bees, and much less
frequently for other pollinators (Lewis et al., 2016; Lewis and
Tzilivakis, 2019; Yasrebi-de Kom et al., 2019).
For the UK, the average annual application rate at 1km resolution (in
kg/km2/year) was obtained for 130 pesticide active
ingredients from the “CEH Land Cover® plus: Pesticides
2012-2016” (Jarvis et al. 2019) of the Centre for Ecology and
Hydrology (CEH, Wallingford, UK;
https://www.ceh.ac.uk), across a four-year period
(from 2012, 2013, 2014 and 2016). For the Netherlands, we created the
average annual allowed application rate at 1km2 (in
kg/km2/year) across a two-year period (2015 and 2016)
for 179 pesticide active ingredients, combining allowed application
rates produced by Yasrebi-de-Kom et al. (2019) and the BRP shapefiles
for crops in 2015 and 2016 obtained from the RVO
(https://english.rvo.nl).