Relative effectiveness of methods that sample worker honey bees to estimate Varroa destructor populations in Apis mellifera colonies

Abstract

Honey bee (Apis mellifera) colonies usually survive less than 16 months if populations of parasitic mite (Varroa destructor) are not controlled. The timing of when to control Varroa populations is aided by using methods that estimate the number of Varroa in hives. The relative efficacy of eight methods used to calculate the number of Varroa in samples of 300 adult bees was established: icing sugar shake (78%), low-suds detergent wash (86%), ethanol wash (72%), 10-min exposure to Apistan^® (42%), ether roll (42%), a 30-s exposure to grapefruit leaf smoke (5%), a 30-s exposure to fluvalinate smoke (0%), and a 30-s exposure to tobacco leaf smoke (0%). A range of approaches were investigated to improve the efficacy and reliability of some of the methods. The following approaches improved the efficacy of four methods so that more than 95% of the Varroa were recovered: two 15-s shakes with at least 10 g of icing sugar; three 15-s washes with low-suds detergent; three 30-s washes with ethanol; and a 35-min exposure to an Apistan^® strip.