Impact of chronic exposure to a pyrethroid pesticide on bumblebees and interactions with a trypanosome parasite

Abstract

Summary1. Bees are exposed to pesticides when foraging in agricultural areas and growing evidence suggests that such compounds can be harmful to managed and wild populations. Given the economic and ecological importance of bees, and the evidence of widespread population declines, the full impacts of pesticides and their interactions with other stressors in the environment need to be investigated. 2. Here, we focus on the impacts of chronic exposure to the commonly used pyrethroid pesticide lambda (k)-cyhalothrin on the bumblebee Bombus terrestris at both the individual and colony level. Furthermore, we investigated the interactions of pesticide exposure with a highly prevalent trypanosome parasite Crithidia bombi. Colonies were exposed to k-cyhalothrin in the laboratory, and colony growth and reproductive output were monitored for up to 14 weeks. The potential interactions between the pesticide and C. bombi were investigated by quantifying the impact of pesticide treatment on susceptibility to, and success of experimental infections, as well as the survival of workers. Male survival after larval pesticide exposure was also monitored. 3. Pesticide-treated colonies produced workers with a significantly lower body mass. However, out of the twelve variables of colony development measured, this was the only metric that was significantly affected by pesticide treatment and there was no subsequent significant impact on the reproductive output of colonies. 4. Lambda-cyhalothrin had no significant impact on the susceptibility of workers to C. bombi, or intensity of parasitic infection. 5. Pesticide exposure did not cause differential survival in workers or males, even when workers were additionally challenged with C. bombi. 6. Synthesis and applications. Chronic exposure to k-cyhalothrin has a significant impact on worker size, a key aspect of bumblebee colony function, particularly under conditions of limited food resources. This could indicate that under times of resource limitation, colonies exposed to this pesticide in the field may fail. However, the lack of other impacts found in this study indicate that further field trials are needed to elucidate this.

Pesticide use within a pollinator-dependent crop has negative effects on the abundance and species richness of sweat bees, Lasioglossum spp., and on bumble bee colony growth

“…These results are consistent with other studies that examined bumble bee responses to specific pyrethroid and neonicotinoid insecticides and found that the number of workers, but not gynes, was negatively affected (Gels et al 2002;Gill et al 2012;Baron et al 2014; but see Whitehorn et al 2012). While the number or size of workers may not directly contribute to bumble bee population growth rates, as only queens reproduce, workers could have an indirect effect on population growth via their effects on colony and gyne health.…”

“…Studies examining direct effects have found that many pesticides applied at recommended doses do not kill honey bees or other managed bees (Morandin and Winston 2003;Ladurner et al 2005;Morandin et al 2005;Abbott et al 2008;Cresswell 2011;Baron et al 2014). The indirect effects of pesticides on bees are generally less well known but may be as influential as direct, lethal effects.…”

Modulation of pesticide response in honeybees

“…In bumblebees, some studies have advanced into the investigation of the consequences of pesticide/pathogens or pesticide/pesticide combinations at the colony level (Gill et al 2012;Baron et al 2014;Fauser-Misslin et al 2014). Testing such combinations of exposures in honeybee colonies is more complex when compared to the small-size and annual life cycle of bumblebee colonies.…”

“…For example, recent work on bumble bees (Bombus terrestris ) has shown exacerbated impacts of a combined exposure to the trypanosome parasite Crithidia b om b i and neonicotinoid insecticides (clothianidin and thiamethoxam) ), but similar effects were not observed when B. terrestris was exposed to C. bombi infection coupled with exposure to a pyrethroid pesticide (lambda-cyhalothrin) (Baron et al 2014). The effect of this latter combination was no worse for these bumblebees than exposure to pyrethroid alone.…”

Protecting an Ecosystem Service

“…suggest that a combination of stressors may be sufficient to trigger failure of social bee 359 colonies (Bryden et al, 2013;Perry et al, 2015), yet empirical studies looking at interactive 360 effects are typically limited to two (or few) factors (Baron et al, 2014;Becher et al, 2013;361 Doublet et al, 2015;Fauser-Misslin et al, 2014;Gill et al, 2012;Gonzalez-Varo et al, 2013;362 Hoover et al, 2012;Kennedy et al, 2013;Kleijn and van Langevelde, 2006;Oliver et al, 363 2012;Pettis et al, 2013;Schweiger et al, 2010;Vanbergen et al, 2013). Land-use change 364 and management is seen as one of the leading drivers of insect pollinator declines (Garibaldi 365 et al, 2014;Ollerton et al, 2014;Vanbergen, 2014).…”