Application d’une stratégie de lutte intégrée contre le parasite Varroa destructor dans les colonies d’abeilles mellifères du Québec

For nearly 30 years, Varroa destructor has been responsible for the loss of many honey bee colonies around the world. The continued use of synthetic acaricides has resulted in their reduced efficacy against this pest in Canada and in other countries because of the selection of resistant mite populations. With this situation still present, it has become of utmost importance to develop efficient methods to control this apicultural pest. The major goal of this original work is to determine the fundamental parameters underlying the use of an integrated pest management (IPM) strategy against the varroa mite. The IPM strategy developed in this research is based on the periodic use of organic pesticides (oxalic acid, formic acid and thymol) and treatment threshold. Treatment thresholds were determined from linear regressions between the varroa mite levels and the zootechnical performances (honey production and colony strength) of honey bee colonies. A total of 154 honey bee colonies from the livestock of the “Centre de recherche en sciences animales de Deschambault” (CRSAD) were monitored from September 2005 to September 2006. Based on our findings, we propose economic treatment thresholds for three periods in the year: early May, late July and early September that are respectively 2, 10 and 9 varroa mites per day.  Efficacy of the various organic treatments: formic acid (FA), oxalic acid (OA) and thymol was evaluated in May (before the first honey flow), in July between two honey flows, in September (after the honey flow and before the fall feeding of colonies) and in November (before wintering). OA was applied using the trickling method (4% OA w/v in a sucrose syrup 1:1 w/v). FA was applied using MiteAwayII™ (pads imbedded with FA 65% v/v placed on top of brood frames), Mitewipe (Dri-Loc™ pads 10/15cm imbedded with 35 mL FA 65% v/v placed on top of brood frames), Flash (FA 65% poured directly on the bottom board of colonies, 2 mL per frame with bees). Thymol was applied using Apiguard™ (gel with 25% de thymol w/v placed on top of the brood frames). Efficacy trials were realised from 2006 to 2008 on a total of 170 colonies (98 from the CRSAD and 72 owned by a commercial beekeeper). Results show that treatments applied in spring give low efficacy on reducing varroa mite populations that are in full growth at this time because of large amounts of brood available for mite reproduction. Application of a FA treatment in mid-summer offers the opportunity to reduce mite populations at the 11 mites per day  September threshold but FA summer application is accompanied by a risk of incorporating residues in the harvested honey. Application of MiteAwayII™ in September followed by an oxalic acid treatment in November (trickling method 4% OA w/v in a sucrose syrup 1 :1 w/v, 5 mL between frames with bees) gave the best efficacy results: varroa mite levels are reduced below the 2 mites per day spring threshold. Our results also show that an early September management strategy of colonies for winter preparation (varroa treatment and fall feeding) gives greater varroa control, higher colony winter survival and stronger colonies in spring when compared to a later treatment in October. In conclusion, this work shows that varroa mite control in honey bee colonies in Québec is possible by using an integrated pest management strategy based on the application of a combination of organic acaricides in association with treatment thresholds.

Keyphrases: Varroa destructor, Apis mellifera, Pesticide organique, Thymol, Treatment thresholds, Organic pesticide, Formic acid, Oxalic acid