Abstract
Varroa destructor is one of the most common parasites of honey bee colonies and is considered as a possible co-factor for honey bee decline. At the same time, the use of pesticides in intensive agriculture is still the most effective method of pest control. There is limited information about the effects of pesticide exposure on parasitized honey bees. Larval ingestion of certain pesticides could have effects on honey bee immune defense mechanisms, development and metabolic pathways. Europe and America face the disturbing phenomenon of the disappearance of honey bee colonies, termed Colony Collapse Disorder (CCD). One reason discussed is the possible suppression of honey bee immune system as a consequence of prolonged exposure to chemicals. In this study, the effects of the neonicotinoid thiamethoxam on honey bee, Apis mellifera carnica, pupae infested with Varroa destructor mites were analyzed at the molecular level. Varroa-infested and non-infested honey bee colonies received protein cakes with or without thiamethoxam. Nurse bees used these cakes as a feed for developing larvae. Samples of white-eyed and brown-eyed pupae were collected. Expression of 17 immune-related genes was analyzed by real-time PCR. Relative gene expression in samples exposed only to Varroa or to thiamethoxam or simultaneously to both Varroa and thiamethoxam was compared. The impact from the consumption of thiamethoxam during the larval stage on honey bee immune related gene expression in Varroa-infested white-eyed pupae was reflected as down-regulation of spaetzle, AMPs abaecin and defensin-1 and up-regulation of lysozyme-2. In brown-eyed pupae up-regulation of PPOact, spaetzle, hopscotch and basket genes was detected. Moreover, we observed a major difference in immune response to Varroa infestation between white-eyed pupae and brown-eyed pupae. The majority of tested immune-related genes were upregulated only in brown-eyed pupae, while in white-eyed pupae they were downregulated.
Highlights
Pollinators are crucial in almost all terrestrial ecosystems, especially in those dominated by agriculture
The present study focuses on the effect of thiamethoxam and Varroa mites on honey bee immune-related gene expression in two developmental stages
The honey bees used in this study were from Apis mellifera carnica colonies maintained at the Biotechnical Faculty, University of Ljubljana, Slovenia
Summary
Pollinators are crucial in almost all terrestrial ecosystems, especially in those dominated by agriculture. High mortality rates in overwintering colonies have been documented over the last few years in North America and Europe [2, 3] Besides the impact this has on ecological balance, such declines have a great economic impact. By feeding developing honey bees contaminated food, entire colonies can be exposed to pesticides [4, 5]. Such sub-lethal exposure to pesticides can influence their physiology and behavior [6] and can cause changes in immune response and detoxification mechanisms [7,8,9]
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