Field testing of formic acid (in Mitegone wafers) under autumnal mediterranean conditions

The negative impact of V. destructor on honey bees in Portugal has been known, at least since 1986. To cope with it, Portuguese beekeepers have focused on using fluvalinate and amitraz. As a result, Varroa populations increasingly resistant to these acaricides have been found, suggesting an adoption of “new approaches” to fight Varroa. In this line of thinking, we aimed at assessing the field efficacy of formic acid (in Mitegone wafers) in A. m. iberica honey bee colonies inserted in a traditional honey production system of southern Portugal. We tested 2 half parts of a Mitegone wafer, soaked in 65 % formic acid (left on external side of the last honey frame found in the brood nest), in Varroa infested colonies with normal amounts of capped brood. Monitoring of some environmental apiary variables (e.g. temperature or relative humidity) was put in place, as well as regular observations of honey bee behaviour towards wafers (removal, propolisation) and queen supersedure. We assessed colony condition (in terms of capped brood and in-hive adult bees) at the beginning and end of the experiment, as well as at the end of formic acid usage period. Collection of fallen mature Varroa on protected bottom boards (from bees and ants) was carried over the entire experimental period. In our beekeeping context, formic acid in Mitegone wafers appears to offer a relevant contribution to ‘traditional’ Varroa control, with an estimated average efficacy of 85 % (achieved within three weeks of treatment). This means that formic acid treatments, in release controlled ways, can also become a valuable alternative IPM tool against Varroa in Mediterranean climatic conditions (particularly if applied during early spring or autumn)

Varroa; Ácido fórmico; Protecção Integrada / Varroa; Formic acid; IPM.