Gene expression in honey bee (Apis mellifera) larvae exposed to pesticides and Varroa mites (Varroa destructor)

Honey Bee Research and Extension Laboratory, Department of Entomology and Nematology, University of Florida, Natural Area Drive, Gainesville, FL 32611, USA.
Journal of insect physiology (Impact Factor: 2.47). 04/2012; 58(8):1042-9. DOI: 10.1016/j.jinsphys.2012.03.015
Source: PubMed


Honey bee (Apis mellifera) larvae reared in vitro were exposed to one of nine pesticides and/or were challenged with the parasitic mite, Varroa destructor. Total RNA was extracted from individual larvae and first strand cDNAs were generated. Gene-expression changes in larvae were measured using quantitative PCR (qPCR) targeting transcripts for pathogens and genes involved in physiological processes, bee health, immunity, and/or xenobiotic detoxification. Transcript levels for Peptidoglycan Recognition Protein (PGRPSC), a pathogen recognition gene, increased in larvae exposed to Varroa mites (P<0.001) and were not changed in pesticide treated larvae. As expected, Varroa-parasitized brood had higher transcripts of Deformed Wing Virus than did control larvae (P<0.001). Varroa parasitism, arguably coupled with virus infection, resulted in significantly higher transcript abundances for the antimicrobial peptides abaecin, hymenoptaecin, and defensin1. Transcript levels for Prophenoloxidase-activating enzyme (PPOact), an immune end product, were elevated in larvae treated with myclobutanil and chlorothalonil (both are fungicides) (P<0.001). Transcript levels for Hexameric storage protein (Hsp70) were significantly upregulated in imidacloprid, fluvalinate, coumaphos, myclobutanil, and amitraz treated larvae. Definitive impacts of pesticides and Varroa parasitism on honey bee larval gene expression were demonstrated. Interactions between larval treatments and gene expression for the targeted genes are discussed.

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Available from: Aleš Gregorc,
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    • "LeConte et al. (2011) found that the levels of CYP4G11 expression in the brains of A. mellifera varied according to hygienic behaviour, suggesting that the enzyme 'might catalyse a reaction in some metabolic pathways that could be involved in hygienic behavior'. Additionally, honeybee larvae in colonies infested with varroa mites significantly decreased CYP4G11 expression by threefold (Gregorc et al., 2012) and adult honeybees in colonies diagnosed with Colony Collapse Disorder were characterized by significantly down-regulated CYP4G11 expression (Johnson et al., 2009). In the closely related congener Apis cerana cerana, the eastern honeybee, AccCYP4G11 was maximally expressed in epidermal tissue within an individual, and, across life stages, in 14-day-old adults (Shi et al., 2014). "
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    • "However, in a recent study (Boncristiani et al., 2012) examining five different pesticides (including coumaphos and two other pesticides commonly applied to manage Varroa mites, thymol and formic acid) the only P450 to be upregulated was CYP6A514 by thymol; however, several other detoxification, immune, and developmental genes were either up or downregulated by thymol, coumaphos, and formic acid. Another study examining the effects of pesticides (including coumaphos and fluvalinate) on larval development (Gregorc et al., 2012), found no changes in P450 gene expression, but expression of several genes involved in immune function and behavioral maturation were significantly impacted. Finally, exposure to neonicotinoids results in reduced activity of the NF-jB immune signaling pathway and increased titers of Deformed Wing Virus (Nazzi et al., 2012), suggesting that honey bees compromised by pesticide exposure may be more susceptible to pathogen infection. "
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    • "Primers were synthesized by Eurofins MWG Operon (Huntsville, AL, USA). Details of the primers a r e a s f o l l o w s : A m N O S : f o r w a r d , 5 ′ - TCCACTCGCAGGTACTTTCC-3′; AmNOS: reverse, 5′ -TCTGGAGGATCACCATTTCC-3′ (Gregorc et al. 2012); β-actin: forward, 5′-ATGCCA ACACTGTCCTTTCTGG-3′; β-actin: reverse, 5′- GACCCACCAATCCATACGGA-3′ (Yang and Cox- Foster 2005). "
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