Development of sampling methods for estimating levels of Varroa jacobsoni (Acari: Varroidae) infestation in colonies of Apis mellifera (Hymenoptera: Apidae)

Methods for estimating infestation rates of Varroa jacobsoni (Oudemans) on adult honey bees, Apis mellifera (L.), are not well developed. We calculated 3 measures of infestation in samples of adult bees from New York State and Washington, DC: (1) M/V, the ratio of the number of mites (M) to a constant volume of bees (V); (2) M/B, the ratio of the number of mites (M) to the number of bees (B); and (3) MIG, the ratio of the number of mites (M) to the wet weight of bees (G). Each measure requires a determination of the number of mites, or the number of mites and either the number or wet weight of bees. We calculated surrogates for these measures that are easier to obtain. An estimate (EM) of the number of mites in each sample was made using the ether roll technique. An estimate (EB) of the number of bees in each sample was estimated from the sample wet weight (G) by using a conversion factor (bees per gram). Surrogates for the 3 original measures were constructed using EM, EB, and G and compared with their corresponding original measures by using the concordance correlation coefficient r(c). Values of r(c) for EM/V with M/V were 0.97 and 0.85, in New York State and Washington, DC, respectively. Corresponding values for EMI B with Mi B were 0.97 and 0.85; values for M/EB with M/B were 0.99 and 0.98; values for EM/EB with M/B were 0.97 and 0.81; values for EM/G with M/G were 0.97 and 0.86. Infestation rates in samples obtained from the brood nest were approximately twice as high as in samples from the honey-storage area.