Honeybee biomarkers as promising tools to monitor environmental quality

International audienceThe aim of this study was to distinguish the impacts of two different anthropogenic conditions using the honeybee Apis mellifera as a bioindicator associatedwith a battery of biomarkers previously validated in the laboratory. Both the urban (RAV, Ravine des Cabris) and semi-natural (CIL, Cilaos) sites in La Reunion Islandwere compared in order to assess the impacts of two types of local pollution using the discriminating potential of biomarkers. Hives were placed at the CIL and RAV sites and honeybees were collected from each hive every three months over one year. Honeybee responses were evaluated with respect to several biochemical biomarkers: glutathione-S-transferase (GST), acetylcholinesterase (AChE), alkaline phosphatase (ALP) and metallothioneins (MT). The results showed a significant difference between the localities in terms of GST, AChE and ALP activities, as regarding midgut MT tissue levels. Compared to the CIL site, ALP and MT tissue levels were higher at the RAV site, although AChE activity was lower. GST displayed more contrasted effects. These results strongly suggest that the honeybees based in the more anthropized area were subjected to sublethal stress involving both oxidative stress and detoxification processes with the occurrence of neurotoxic pollutants, amongst which metals were good candidates. A classification tree enabled defining a decision procedure to distinguish the sampling locations and enabled excellent classification accuracy (89%) for the data set. This field study constitutes a strong support in favour of the in situ assessment of environmental quality using honeybee biomarkers and validates the possibility of performing further ecotoxicological studies using honeybee biomarkers. (Résumé d'auteur

Development of biomarkers of exposure to xenobiotics in the honey bee Apis mellifera: Application to the systemic insecticide thiamethoxam

International audienceThis study describes the development of acetylcholinesterase (AChE), carboxylesterases (CaE1, CaE2, CaE3), glutathion-S-transferase (GST), alkaline phosphatase (ALP) and catalase (CAT) as enzyme biomarkers of exposure to xenobiotics such as thiamethoxam in the honey bee Apis mellifera. Extraction efficiency, stability under freezing and biological variability were studied. The extraction procedure achieved good recovery rates in one extraction step and ranged from 65 percent (AChE) to 97.3 percent (GST). Most of the enzymes were stable at −20 °C, except ALP that displayed a slight but progressive decrease in its activity. Modifications of enzyme activities were considered after exposure to thiamethoxam at the lethal dose 50 percent (LD50, 51.16 ng bee−1) and two sublethal doses, LD50/10 (5.12 ng bee−1) and LD50/20 (2.56 ng bee−1). The biomarker responses revealed that, even at the lowest dose used, exposure to thiamethoxam elicited sublethal effects and modified the activity of CaEs, GST, CAT and ALP. Different patterns of biomarker responses were observed: no response for AChE, an increase for GST and CAT, and differential effects for CaEs isoforms with a decrease in CaE1 and CaE3 and an increase in CaE2. ALP and CaE3 displayed contrasting variations but only at 2.56 ng bee−1. We consider that this profile of biomarker variation could represent a useful fingerprint to characterise exposure to thiamethoxam in the honey bee A. mellifera. This battery of honey bee biomarkers might be a promising option to biomonitor the health of aerial and terrestrial ecosystems and to generate valuable information on the modes of action of pesticides

Seasonal variation in the activity of selected antioxidant enzymes and malondialdehyde level in worker honey bees

The recent decline in managed honey bee populations, Apis mellifera L. (Hymenoptera: Apidae), has caused scientific, ecological, and economic concern. Research into the formation of reactive oxygen species (ROS), antioxidative defense mechanisms, and oxidative stress can contribute to our understanding of bee survival and conservation of this species. Activities of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) enzymes together with levels of malondialdehyde (MDA) were measured in summer and winter honey bees sampled from three colonies. One colony was stationary (C1), entering the winter period having accumulated Robinia pseudoacacia L. (Fabaceae) honey, and two were migratory (C2 and C3), entering the winter period with mainly Tilia (Malvaceae) and Brassica (Brassicaceae) honey, respectively. Compared to summer workers, winter worker bees had decreased SOD and GST activity, and MDA level, whereas CAT activity increased in all three colonies. We also demonstrated that seasonality is the main factor responsible for changes in antioxidant enzymes and MDA levels in worker honey bees. Overall, our results indicate a difference between summer and winter worker bees, pointing at a reduced level of antioxidant enzyme defenses during overwintering which may be due to a decrease in production of ROS. The decreased levels of MDA measured in winter honey bees confirm this. As ROS are actively used by insects as a defense mechanism to fight pathogens, we suggest that reduced production of ROS contributes to higher susceptibility of winter honey bees to infections and reduced overwinter survival