Dissipation and cross-contamination of miticides in apiculture. Evaluation by APIStrip-based sampling

The active substances coumaphos, tau-fluvalinate and amitraz are among the most commonly employed synthetic miticides to control varroa infestations in apiculture. These compounds can persist inside the beehive matrices and can be detected long time after their application. The present study describes the application of a new passive sampling methodology to assess the dissipation of these miticides as well as the cross-contamination in neighboring beehives. The APIStrips are a recently developed sampling device based on the sorbent Tenax, which shows a remarkable versatility for the sorption of molecules onto its surface. This avoids the need of actively sampling apicultural matrices such as living bees, wax or reserves (honey and pollen), therefore allowing to obtain representative information of the contamination in the beehive environment in one single matrix. The results show that the amitraz-based treatments have the fastest dissipation rate (half-life of 11-14 days), whereas tau-fluvalinate and coumaphos remain inside the beehive environment for longer time periods, with a half-life up to 39 days. In the present study, tau-fluvalinate originated an intense cross-contamination, as opposed to coumaphos and amitraz. This study also demonstrates the contribution of drifting forager bees in the pesticide cross-contamination phenomena. Moreover, the sampling of adult living bees has been compared to the APIStrip-based sampling, and the experimental results show that the latter is more effective and consistent than traditional active sampling strategies. The active substances included in this study do not migrate to the honey from the treated colonies in significant amounts.