Immune gene expression in developing honey bees (Apis mellifera L.) simultaneously exposed to imidacloprid and Varroa (Varroa destructor Anderson and Trueman) in laboratory conditions

Authors: TESOVNIK, TANJA - University Of Ljubljana; ZORC, MINJA - University Of Ljubljana; GREGORC, ALES - Mississippi State University; Rinehart, Timothy - Tim; Adamczyk, John; NARAT, MOJCA - University Of Ljubljana

Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2019
Publication Date: 7/4/2019
Citation: Tesovnik, T., Zorc, M., Gregorc, A., Rinehart, T.A., Adamczyk Jr, J.J., Narat, M. 2019. Immune gene expression in developing honey bees (Apis mellifera L.) simultaneously exposed to imidacloprid and Varroa (Varroa destructor Anderson and Trueman) in laboratory conditions. Journal of Apicultural Research. https://doi.org/10.1080/00218839.2019.1634463.
DOI: https://doi.org/10.1080/00218839.2019.1634463

Interpretive Summary: The impact of widespread pesticide use in agriculture has been a major concern to the beekeeping industry. Accumulating evidence suggests that pesticides may have a negative impact on honey bees. Additionally, honey bees exposed to different stressors, such as parasites and the pathogens they vector, may further affect their health. The aim of this study was to investigate the combined effect of two stressors on developing honey bees under laboratory conditions where larvae were treated with realistic field doses of the noenicitinoid, imidacloprid, and infested with the parasitic mite, Varroa destructor. Here we present a gene expression profile of 15 immune related genes in different honey bee development stages (white-eyed, brown-eyed pupae, and emerged honey bees). The influence of neonicotinoid imidacloprid exposure in the larval stage showed that most immune related genes are downregulated in white- and brown-eyed pupae. However, two immune related genes were still significantly upregulated. The gene expression pattern of varroa infested honey bees changed during development, where we can see that a number of significantly elevated genes increased from white-eyed pupae to newly emerged honey bees. The effect of both stressors have significant synergistic effect on antimicrobial peptides and other genes involved in defense of honey bees in different developmental stages. The impact of varroa infestation alone on honey bees treated with imidacloprid during the larval stage was reflected as downregulation and upregulation of certain genes in the white-eyed pupal stage. In the brown-eyed pupal stage, treatment with imidacloprid varroa infestation caused an upregulation of certain genes was detected, whereas newly emerged bees had a downregulation in two genes.

Technical Abstract: The impact of widespread pesticide use in agriculture has been a major concern to the beekeeping industry. Accumulating evidence suggests that pesticides may have a negative impact on honey bees. Additionally, honey bees exposed to different stressors, such as parasites and the pathogens they vector, may further affect their health. The aim of this study was to investigate the combined effect of two stressors on developing honey bees under laboratory conditions where larvae were per os treated with realistic field doses of imidacloprid and infested with Varroa destructor. Here we present a gene expression profile of 15 immune related genes in different honey bee development stages (white-eyed, brown-eyed pupae, and emerged honey bees). The influence of neonicotinoid imidacloprid exposure in the larval stage showed that most immune related genes are downregulated in white- and brown-eyed pupae. However, two immune related genes, lysozyme-2 and PPO, were still significantly upregulated. The gene expression pattern of varroa infested honey bees changed during development, where we can see that a number of significantly elevated genes increased from white-eyed pupae to newly emerged honey bees. The effect of both stressors have significant synergistic effect on antimicrobial peptides and other genes involved in defense (apidaecin, hymenoptaecin, defensin-1, lysozyme-2, and PPO) of honey bees in different developmental stages. The impact of varroa infestation alone on honey bees treated with imidacloprid during the larval stage was reflected as downregulation of dorsal, lysozyme-2, and PPO and upregulation of basket, kayak, and relish genes in white-eyed pupae. In brown-eyed pupae treated with imidacloprid varroa infestation caused an upregulation of genes defensin-1 and relish was detected, whereas newly emerged bees had a downregulation in genes defensin-1 and PGRP LC 710.