Insecticide effects on wild bee species and their ecosystem services

Plant pollination is an important ecosystem service which globally generates €153 billion per year. Biotic pollination is not just economically important but also essential for the preservation of native flora. Agricultural crops and wild plant are often pollinated by insects, particularly bees. There is growing evidence that global pollinator numbers are decreasing. In Germany half of all bee species are red listed. One of the possible causes of pollinator loss is agricultural pesticide application. This could lead to an under-supply of crop pollination demand in the future. The honey bee Apis mellifera is the main pollinator species employed by humans. Yet, there are already pollination deficits considering the existing honey bee stock in many European countries.

Wild insects have the potential to supplement pollination by managed honey bees or assure pollination where there is shortage of honey bee supply (e.g. due to Varroa destructor infestations). However, wild insect management schemes are money and labour intensive. Little is known about the effects of pesticides on wild bee species since only a few species have been subject to ecotoxicological experiments. In pesticide risk assessment only toxicity towards the honey bee is tested. It is deemed a surrogate species for all bees species (in fact all insect pollinators) though toxicity towards wild bees cannot be extrapolated from honey bee data. Recent studies show that wild bees are generally more susceptible to neonicotinoid insecticides than honey bees under lab and field conditions. The EU has already temporarily restricted the three most prominent neonicotinoids (imidacloprid, clothianidin, thiamethoxam) in use because of high acute risks for bees to reevaluate their registration. There is a need for further research on this matter including a wider range of non-managed bee species and more meaningful endpoints.

Through lab experiments we aim to collect acute toxicity data (LD50, median lethal dose) for multiple European wild bee species to generate a Species Sensitivitiy Distribution (SSD) for two insecticides (imidacloprid, dimethoate). In preliminary work we already gathered data for dimethoate toxicity towards a few species (Lea A. Franke, master thesis). Using the acute toxicity data we will also analyse the influence of certain traits (e.g. weight) on inter-specific sensitivity difference.

Furthermore, we want to study the impact of imidacloprid and dimethoate in a more realistic scenario. In an oilseed rape Brassica napus field we will set up micro tunnel tents (14 m²) and insert fertilised females of the red mason bee Osmia bicornis. Oilseed rape plants will be treated either with imidacloprid, dimethoate or be used as control. Inside every tent we will install a nesting aid were females lay eggs. Brood development will be monitored until eclosion in the lab. In addition, we will sample seeds to look for possible effects of both insecticides on the pollination service of O. bicornis in terms of yield. This experiment will be repeated in the following year using the eclosed brood of the first year to study insecticide impact on multiple generations through repeated exposure.


Carsten Brühl

Philipp Uhl

Related publications

Uhl P, Franke LA, Rehberg C, Wollmann C, Stahlschmidt P, Jeker L, Brühl CA (2016): Interspecific sensitivity of bees towards dimethoate and implications for environmental risk assessment. Scientific Reports 6: Article number: 34439. DOI:10.1038/srep34439