Combating Varroa destructor in Honeybee Colonies Using Flumethrin or Fluvalinate

Gregorc A. , M. I . Smodi‰ ·kerl : Combating Varroa destructor in Honeybee Colonies Using Flumethrin or Fluvalinate. Acta Vet. Brno 2007, 76: 309-314. Mite mortality in two apiaries, one with 32 and the other with 15 honeybee (Apis mellifera carnica) colonies, was recorded prior to and after flumethrin or fluvalinate treatments and after a control, oxalic-acid application. During the 42and 51-day pre-treatment periods, the average daily natural mite drop was 0.04 (± 0.04) and 2.82 (± 2.19), respectively, which represents 1.09% (± 1.06) and 3.84% (± 3.04) of the total number of mites found during the experiment. The flumethrin or fluvalinate applications resulted in an average mite mortality at the two apiaries of 214.46 (± 260.02) and 4,098.64 (± 2,508.31). The treatments resulted in a 19.11% (± 14.62) and a 39.28% (± 10.47) reduction in the number of mites in slightly infested colonies and 94.30% (± 4.26) and 96.24% (± 3.14) in highly infested colonies. The difference in treatment efficacy between both apiaries was significant (P < 0.001) and indicates that fluvalinate and flumethrin are highly efficacious in dealing with highly infested honeybee colonies with sealed brood. The importance of effective mite control in colonies with a high level of natural mite mortality is discussed in this study. Acaricides, control methods, Apis mellifera, oxalic acid, mite infestation Acaricides are regularly applied to honeybee colonies in order to maintain their productivity. These are usually synthetic and their lipophilic and persistent characteristics result in a build-up of their residues in the wax and honey (Wallner 1999). The varroa mite has already developed a resistance to several synthetic acaricides (Milani 1999; Lodesani et al. 1995; Miozes-Koch et al. 2000; Flor is et al. 2001; Spreaf ico et al. 2001) and beekeepers are increasingly turning to alternative treatments incorporating essential oils and organic acids (Mutinel l i et al. 1997; Melathopoulos and Gates 2003; Gregorc and Poklukar 2003). The efficacy of fluvalinate and flumethrin in killing mites is long-lasting. Fluvalinate is available under the trade names Apistan (used against varroa mites in bee colonies), Klartan and Mavrik, while flumethrin is available under the trade name Bayvarol, which is specific for varroa control. Oxalic acid (OA) has been found to be highly effective in treating colonies without brood (Imdorf et al. 1997; Br∅dsgaard et al. 1999). Efficacy of 95% was achieved after three treatments using a 5% OA solution (Mutinel l i et al. 1997) and efficacy of 24% after one springtime treatment administered by trickling when a capped brood was present (Br∅dsgaard et al. 1999). In our previous experiments the quantity of OA solution used to treat one normally developed colony was approximately 50 millilitres and we found that three OA treatments of colonies with brood had efficacy of 39.2%, and 99.4% when there was no brood present (Gregorc and Planinc 2001 and 2004a). This study was designed to evaluate the effectiveness of fluvalinate and flumethrin against varroa mites in honeybee colonies with sealed brood that are treated with oxalic acid during the period without brood. Data gathered during the experiment, such as the number of dead mites that had fallen onto the metal sheets at the bottom of the hives, was used to determine mite mortality both prior ACTA VET. BRNO 2007, 76: 309–314; doi:10.2754/avb200776020309 Address for correspondence: Prof. dr. Ale‰ Gregorc Agricultural Institute of Slovenia Hacquetova 17, 1001 Ljubljana SLOVENIA Phone +386 1 / 280-51-50 Telefax +386 1 / 280-52-55 E-mail: [email protected] http://www.vfu.cz/acta-vet/actavet.htm to and after both treatments. The objectives of this study were to evaluate the acaricidal efficacy of the treatments on honeybee colonies and their effects on the mite mortality rate as well as to establish the residual efficacy of both treatment methods. Materials and Methods Two apiaries, one with 32 and the other with 15 honeybee (Apis mellifera carnica) colonies populated in national standard AÎ “back load” hives (Zde‰ar 1998), were located at sites in Seniãno and Lesce, in the Gorenjska region of Slovenia, which is influenced by continental climatic conditions. The hives had ten 41 × 26 cm combs in each of the brood and honey compartments and 38 × 29.8 cm metal sheets were inserted on to the hive floors in the spring of 2005 in order to record natural mite mortality. Wire screens above the sheets prevented bees from coming into contact with the debris. On the sampling dates, the number of mites was recorded and the inserts were emptied. The level of mite drop in each colony was recorded both before and after the fluvalinate and flumethrin treatments and after the treatment with oxalic acid. While the pre-treatment periods of the two apiaries were different 42 days in one apiary and 51 days in the other, each was checked and cleared four times during this time. The first treatment of thirty-two colonies took place on July 21, after the honey had been harvested. Seventeen colonies each received four polyethylene strips containing 3.6 mg flumethrin (Bayvarol), while the remaining fifteen colonies each received two polyvinyl chloride strips containing 0.8 g tau-fluvalinate (Apistan). Seven of the fifteen colonies of the second apiary also received four Bayvarol polyethylene strips and the other eight colonies received two of the Apistan polyvinyl chloride strips. These strips were removed from the Seniãno and from the Lesce apiary on August 30. A final treatment was applied to all the colonies on November 11 when there were no broods present in the colonies. Mites were counted on December 8, 27 days after final OA treatment. Fifty millilitres of a 2.9% OA and 31.9% sucrose in water solution (w/w), which comprised oxalic acid dihydrate (Riedel-de Haen), sucrose (sugar) and de-mineralised water (Gregorc and Planinc 2001), was applied to every colony of the Seniãno and Lesce apiaries. During the application of the OA treatment the outside temperatures ranged from 5 °C to 8 °C and the operator wore a respiration mask, protective glasses and rubber gloves. The number of natural mite drops in pre-treatment periods or killed by the flumethrin or fluvalinate treatments during the brood period was estimated by counting the mite “drop-down” (T). The following formula was used to estimate the percentage of mites killed (PMK) by the treatments that began on July 21, 2005: PMK = (T/(T + OA) × 100)% The same formula was modified to calculate the percentage of mites that dropped before the treatments or after the removal of the medicated strips, as residual efficacy by excluding the number of mites collected in previous counts and in the first treatment. Colony strength and behavioural changes in the bees were evaluated visually and both treated groups compared. Data analyses were carried out by ANOVA (analysis of variance) with the aid of the Statgraphics programme (1991).