Dynamics of falling varroa mites in honeybee (Apis mellifera) colonies following oxalic acid treatments

Abstract

The aims of the study were to establish the dynamics of the fallen mites after treating honeybee colonies and to establish the effectiveness of oxalic acid for the control of varroa in colonies during the bee-keeping season in order to reduce varroa populations to tolerable levels. This study presents data from the periodic checking of the number of mites that had fallen onto the bottom of hives in the pre-treatment periods and after treatments. Oxalic acid (2.9%) and sucrose-in-water solution (31.9%) (w/w) (OA) application in honeybee colonies triggered a significant increase (p < 0.01) in mite mortality. Two days after the August 8, 16 and 23 OA treatments, the mite mortality was estimated at 68.62 ± 12.29%, 65.31 ± 10.61%, and 33.35 % ± 13.99%, respectively. The mite mortality between the second and fourth day was estimated at 18.69 ± 7.43%, 22.98 ± 7.69%, and 14.06 ± 6.75%, respectively. Between the 2nd and 9th days after OA applications was a highly significant (p < 0.001) reduction and between the 9th and 11th days after the August 23 application the reduction in mite mortality was significant (p < 0.05). High correlation (R = 0.9896) was found between the natural mite-mortality and the number of mites that fell during three August OA treatments. Efficacy of treatments conducted in colonies with capped broods averaged 23.82 ± 1.52%. We can conclude mat in colonies with less than 1 natural mite-death per day following treatments should reduce their mite population by approximately 40 %. Our results could be used to establish a mite treatment programme in honeybee colonies and to evaluate in further research.