Genomic analysis of the interaction between pesticide exposure and nutrition in honey bees (Apis mellifera)

Authors: SCHMEHL, DANIEL - Pennsylvania State University; Teal, Peter; FRAZIER, JAMES - Pennsylvania State University; GROZINGER, CHRISTINA - Pennsylvania State University

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2014
Publication Date: 12/1/2014
Citation: Schmehl, D.R., Teal, P.E., Frazier, J.L., Grozinger, C.M. 2014. Genomic analysis of the interaction between pesticide exposure and nutrition in honey bees (Apis mellifera). Journal of Insect Physiology. 71:177-190.

Interpretive Summary: Pollinators are critical to production of approximately 70% of our agricultural crops, particularly nutrient-rich fruits, vegetables and nuts (Eilers et al., 2011 and Klein et al., 2007). However, populations of honey bees and other pollinators are in decline globally (González-Varo et al., 2013 and Potts et al., 2010), with US beekeepers losing approximately 30% of their colonies each winter (vanEngelsdorp et al., 2012). These declines have been attributed to multiple factors, including pathogens, parasites, habitat loss and fragmentation, and intensive mono-cropping systems which lead to reduced floral resources and nutrition (Potts et al., 2010). In addition to these factors, there have been mounting concerns about the effects of pesticides (Council, 2007, Godfray et al., 2014 and Sanchez-Bayo and Goka, 2014). Indeed, residues from over 120 different pesticides have been found in honey bee colonies in the US, with an average of six pesticides found in the stored pollen of these colonies (Mullin et al., 2010). Two pesticides in particular, fluvalinate and coumaphos, are the most prevalent (found in ~98% of the 749 colonies surveyed) and are found at the highest concentrations in hives, with maximum detection levels of 204 and 94 ppm in the wax, respectively (Mullin et al., 2010). More recently, (Berry et al., 2013) found coumaphos concentrations of 514 ppm following colony treatments of coumaphos (Checkmite+™) at the recommended label dose. These pesticides are commonly applied by beekeepers to control Varroa mites, a widespread and devastating parasite of honey bees ( Anderson and Trueman, 2000 and Rosenkranz et al., 2010). Since the half-life of fluvalinate and coumaphos is ~5 years in wax ( Bogdanov, 2004), these pesticides can accumulate to unsafe levels in colonies ( Haarmann et al., 2002) (the LD50 of coumaphos is 46.3 ppm, while that of fluvalinate is 15.86 ppm ( Mullin et al., 2010)). Coumaphos, an organophosphate, inhibits acetylcholinesterase, while fluvalinate, a pyrethroid, targets the sodium channels of mites and insects ( Eiri and Nieh, 2012). While there have been many studies examining the impacts of pesticides on the behavior and longevity of individual honey bees ( Aliouane et al., 2009, Burley et al., 2008, Ciarlo et al., 2012, Collins et al., 2004, Decourtye et al., 2004, Decourtye et al., 2005, Decourtye et al., 2011, Eiri and Nieh, 2012, Frost et al., 2013, Haarmann et al., 2002, Henry et al., 2012, Pettis et al., 2004, Rinderer et al., 1999, Teeters et al., 2012, Williamson and Wright, 2013, Wu et al., 2011 and Zhu et al., 2014), our understanding of the molecular and physiological mechanisms mediating these impacts, and the related pathways that convey resistance to these chemicals, remains limited.While acute doses of pesticides can kill individual honey bees and colonies outright (reviewed in Atkins, 1992 and Johnson et al., 2010), chronic exposure to low doses leads to sub-lethal effects in individual bees, which, in turn, may result in colony-level effects (reviewed in Johnson et al., 2010 and Thompson and Maus, 2007). Honey bee colonies consist of a single reproductive female queen that lays all of the female eggs and the majority of unfertilized male eggs, tens of thousands of facultatively sterile female workers that perform all colony tasks (including feeding the developing larvae, building honeycomb, and foraging for food) and males (drones) (Graham, 1992). Sub-lethal effects of coumaphos and fluvalinate have been demonstrated in all three castes (queens, workers, and drones). Coumaphos and/or fluvalinate exposure can reduce learning, memory, and orientation in adult worker bees (Frost et al., 2013 and Williamson and Wright, 2013), alter adult worker locomotion and feeding behavior (Teeters et al., 2012), and reduce larval longevity (Wu et al., 2011 and Zhu et al., 2014). In drones, coumaphos a

Technical Abstract: Populations of pollinators are in decline worldwide. These declines are best documented in honey bees and are due to a combination of stressors. In particular, pesticides have been linked to decreased longevity and performance in honey bees; however, the molecular and physiological pathways mediating sensitivity and resistance to pesticides are not well characterized. We explored the impact of coumaphos and fluvalinate, the two most abundant and frequently detected pesticides in the hive, on genome-wide gene expression patterns of honey bee workers. We found significant changes in 1118 transcripts, including genes involved in detoxification, behavioral maturation, immunity, and nutrition. Since behavioral maturation is regulated by juvenile hormone III (JH), we examined effects of these miticides on hormone titers; while JH titers were unaffected, titers of methyl farnesoate (MF), the precursor to JH, were decreased. We further explored the association between nutrition- and pesticide-regulated gene expression patterns and demonstrated that bees fed a pollen-based diet exhibit reduced sensitivity to a third pesticide, chlorpyrifos. Finally, we demonstrated that expression levels of several of the putative pesticide detoxification genes identified in our study and previous studies are also upregulated in response to pollen feeding, suggesting that these pesticides and components in pollen modulate similar molecular response pathways. Our results demonstrate that pesticide exposure can substantially impact expression of genes involved in several core physiological pathways in honey bee workers. Additionally, there is substantial overlap in responses to pesticides and pollen-containing diets at the transcriptional level, and subsequent analyses demonstrated that pollen-based diets reduce workers’ pesticide sensitivity. Thus, providing honey bees and other pollinators with high quality nutrition may improve resistance to pesticides.