Field evaluation of Varroa-resistance traits in surviving Apis mellifera colonies in Argentina.

Varroa destructor is one of the most important sanitary threats for the beekeeping industry and so far disease control is based mainly on chemical treatment. However, a long-term solution may arise from studying natural surviving colonies of Apis mellifera. We compared the Varroa infestation rate in six commercial colonies that received annual treatment against mites and six non-treated colonies that survived in absence of any treatment for the last 6 years. In addition, we evaluated two potential mechanisms that might be involved in colony survival: hygienic (HYG) and Varroa-sensitive hygiene behavior (VSH) by means of pin-killed and mite artificial infestation, respectively. HYG and VSH were negatively correlated with mite infestation independently of the colony group (treated or non-treated). Furthermore, colonies expressing high levels of pupae removal (≥ 80%) showed higher %HYG and lower mite infestation compared to colonies showing low pupae removal (< 80%). The analysis of reproductive status of mites from the non-removed infested cells evidenced that more infertile mites are found in colonies with more than 80% of pupae removal. To study non-treated colonies that survive for several years, it is a suitable approach for identifying the underlying mechanisms related to Varroa-resistance.