Metabolisation of thiamethoxam (a neonicotinoid pesticide) and interaction with the Chronic bee paralysis virus in honeybees.

Pathogens and pesticides are likely to co-occur in honeybee hives, but much remains to be investigated regarding their potential interactions. Here, we first investigated the metabolisation kinetics of thiamethoxam in chronically fed honeybees. We show that thiamethoxam, at a dose of 0.25ng/bee/day, is quickly and effectively metabolised into clothianidin, throughout a 20day exposure period. Using a similar chronic exposure to pesticide, we then studied, in a separate experiment, the impact of thiamethoxam and Chronic bee paralysis virus (CBPV) co-exposure in honeybees. The honeybees were exposed to the virus by contact, mimicking the natural transmission route in the hive. We demonstrate that a high dose of thiamethoxam (5.0ng/bee/day) can cause a synergistic increase in mortality in co-exposed honeybees after 8 to 10days of exposure, with no increase in viral loads. At a lower dose (2.5ng/bee/day), there was no synergistic increase of mortality, but viral loads were significantly higher in naturally dead honeybees, compared with sacrificed honeybees exposed to the same conditions. These results show that the interactions between pathogens and pesticides in honeybees can be complex: increasing pesticide doses may not necessarily be linked to a rise in viral loads, suggesting that honeybee tolerance to the viral infection might change with pesticide exposure.

Tetracycline residues in honey after hive treatment.

Tetracyclines are used to control bacterial diseases such as European and American foulbrood, which may cause severe losses in the honey bee population and honey production. By using 24 hives randomly distributed into four groups of six hives, this study was performed to measure the occurrence of tetracycline hydrochloride (TC) residues in honey following two types of TC application. Two groups of colonies were treated three times with 0.5 g TC in 1 litre syrup (group S) or in 10 g powdered sugar (group P). Six hives of a first control group (C) fed with untreated syrup were installed at 20 and 45 m from groups S and P, respectively. A second control group (DC) was set up 3 km away. Honey was sampled at different times from all hives, and honey artificially contaminated with TC was stored in the laboratory at 4, 20 and 35 degrees C; all samples were analysed by ELISA and HPLC methods. One day after the last application, the mean TC concentration in brood chamber honey was ten times higher in group S (40.7 mg kg(-1)) than in group P (4.34 mg kg(-1)). After 8 days, TC residues were detected in all hives of group C. After 146 days, the mean TC concentration in harvested honey was 1.54, 0.35 and 0.15 mg kg(-1) for groups S, P and C, respectively. The control group C had been contaminated with TC by drifting. In all hives of group DC, no residues were detected at any time during the study. The honey collected at day 504 did not contain any detectable TC residues, except in one super from group C (0.026 mg kg(-1)). The half-life of TC in honey from supers was similar in groups C, S and P: 65 days. This duration was twice lower than in honey stored in laboratory in similar conditions: at 35 degrees C in the dark (t(1/2) = 121 days). In honey stored at 20 degrees C, TC was quite stable and its half-life was 242 days. The data from these experiments indicate levels of TC residues in honey after a treatment in hives, their persistence and diffusion into the apiary. These results show that the TC must be used with precaution in honey production.