Field-realistic exposure to the novel insecticide flupyradifurone reduces reproductive output in a bumblebee (Bombus impatiens)

Novel insecticides are continuously being developed for application in response to increased legal restriction of previously developed insecticides and resistance in target insects. These novel insecticides, such as flupyradifurone (FPF), remain relatively untested on non-target organisms, including bumblebees. Further, existing tests on honeybees tend to focus on adult mortality and thus sub-lethal effects, such as impacts on reproductive output, are neglected, despite their importance for population-level impacts.

To address if the novel insecticide FPF has sub-lethal effects on bumblebee reproduction and behaviour, we established microcolonies and chronically exposed them to field-realistic concentrations over a 14-day period.

We found that exposure to FPF reduced the bumblebees' reproductive output in terms of the number of larvae produced and the mean mass of each larval instar. FPF-treated bees also stored less sucrose and constructed fewer honeypots. However, adult bumblebee mortality was similar between control and FPF-exposed microcolonies.

Our results show that field-realistic FPF exposure leads to increased larval mortality and/or delayed larval development, as well as reduced nectar storage, without affecting adult mortality.

Policy implications. Insecticides that impair bumblebee reproduction can have long-term population-level consequences, even if adult bees do not experience increased mortality. Despite this fact, sub-lethal effects, such as impacts on reproduction, are not mandatorily assessed within the regulatory process. Our findings highlight the importance of determining sub-lethal effects of pesticides across developmental stages, as well as using pollinator species other than honeybees within the regulatory process.