Clothianidin In Bumblebees

ABSTRACT
Bees are important pollinators, worth over US$150 billion per year worldwide. Populations have been declining for many years due to a variety of stressors in their environment. Parasites and pesticides are a major interacting threat faced by bees. Clothianidin is a neonicotinoid pesticide widely used which comes into contact with bees while they forage on pollen and nectar. To investigate whether field realistic concentrations of clothianidin have an effect on the prevalence of gut parasites Crithidia bombi, Apicystis bombi and Nosema apis in Bombus terrestris, colonies were exposed for two weeks to clothianidin diluted to 1ppb in sugar water. Colonies treated with clothianidin had a higher prevalence of Crithidia bombi than control
colonies. Pesticide colonies also had a higher number of multiple infections than control colonies. These negative impacts of clothianidin on Bombus terrestris could have detrimental consequences for the survival of colonies and the pollination services they provide.
Keywords: Crithidia bombi, Apicystis bombi, Nosema apis, pesticide, bumblebee.

INTRODUCTION
Bees are the most economically important group of pollinators worldwide (Blacquière et al. 2012). 35% of the world’s food crop production depends on pollinators (Klein et al. 2007). Bumblebees make up 80% of insect pollination, and their populations have declined significantly over recent years, raising widespread concern (Potts et al. 2010).
Bees are simultaneously exposed to a combination of stressors in the field (Vanbergen 2013), these stressors can make bees more susceptible to infections.
Pesticides and parasites are major interacting threats to populations (Goulson et al. 2015). There is an increasing diversity of parasites in bumblebees, and infections may have a role in the declines of wild bee populations (Colla et al. 2006; Goulson et al. 2008). The extent to which pesticides can influence the prevalence of harmful gut parasites in bumblebees is little understood. It is important to know how pesticides effect the gut parasites in pollinators as the parasites can have a direct negative affect on colony mortality. The three most common gut parasites found in bumblebees are, Apicystis bombi which is a Neogregarine, Crithidia bombi which is a Trypanosome, and Nosema sp which are microsporidian
fungi.
A. bombi is a sub lethal and lethal parasite that causes sucrose sensitivity and a lower lipid/body mass ratio. Infection has been shown to cause a 22% mortality in Bombus terrestris (Graystock et al. 2016). C. bombi increases colony mortality and decreases queen fecundity and founding (Yourth et al. 2008). Queens infected with N. sp produce smaller colony sizes and reduced sexual offspring and N. sp can also affect the survival and efficiency of adult individuals (Otti & Schmid-Hempel 2007). Parasites can exhibit condition-dependent virulence, a high virulence has been seen when the host is under conditions of stress such as low food resources and being exposed to pesticides (Brown et al. 2000).
Pollinators are unintendedly exposed to neonicotinoid pesticides, these are ingested when they forage on the nectar and pollen of crops treated with the pesticides (Laycock et al. 2012). Neonicotinoids are among the most effective and widely used pesticides employed to control common insect pests such as aphid, moth and rootworm (Elbert et al. 2008). They are synthetic neurotoxins that act as agonists of acetylcholine receptors to disrupt the nervous system of pests to lethal effect (Goulson 2013; Moffat at al. 2016).
Using neonicotinoids as a seed dressing can cause residues of these systemic insecticides to be present at trace levels in the plant pollen and nectar (Blacquière et al.
2012), and can have devastating effects on pollinators (Rundlöf et al. 2015). The majority of the active ingredients (80 – 98%) leach out of treated plants and seeds into the surrounding soil and water, where nearby wild plants take them up and become toxic (Goulson 2014; Botias et al 2016), potentially exposing bees at a large scale to the residues. These residues aren’t at high enough concentrations to kill the bees outright, however they are enough to affect the ability of these insects to survive.
Studies have shown the detrimental effects, such as reduced production of brood and reduced food consumption, of neonicotinoids on pollinators in the laboratory (Mommaerts et al. 2010; Laycock et al. 2012), and reduced growth rate and queen production in semi-field studies where pollinator species are exposed to pesticide in laboratory conditions and then left to forage independently (Gill et al. 2012; Whitehorn et al.
2012).
The majority of previous studies use the neonicotinoid imidacloprid. However, newer neonicotinoids are available such as clothianidin and thiamethoxam, these are becoming more popular than imidacloprid. New studies are needed to assess the risk these newer neonicotinoids pose to pollinators. A statement from the European Food Safety Authority (EFSA) identified that neonicotinoids pose an unacceptably high risk to bees. Their review concluded, "A high acute risk to honeybees was identified from exposure via dust drift for the seed treatment used in maize, oilseed rape and cereals. A high acute risk was also identified from exposure via residues in nectar and/or pollen." (EFSA 2013). These pesticide stressors (Cresswell 2017) could be increasing the prevalence of parasites in bumblebee populations, which in turn may be contributing to their decline.
In 2012 Whitehorn et al. exposed Bombus terrestris colonies to imidacloprid in the laboratory for 2 weeks and then left them in the field for 2 months. Having the colonies in the laboratory first meant the amount of pesticide taken in by colonies could be controlled. This paper was used as a basis for our own study, however, the newer pesticide clothianidin was used instead of imidacloprid. Therefore Bombus terrestris colonies were used to investigate the effects of field realistic concentrations of clothianidin on gut parasite acquisition of C. bombi, N. apis and A. bombi.