Oxalic acid treatments for varroa control (review)

Abstract

Oxalic acid (OA) is one of the most common natural acaricides used against varroa throughout Europe. Its activity is well known since the middle 1980s at least, due to experiments performed mainly in Eastern-Europe and Asia on the spraying and sublimation administration techniques (OKADA and NEKANE, 1987; POPOV et al., 1989). However, only one decade later OA became increasingly popular in West-European beekeeping community due to massive trials performed in Germany (RADETZKI et al., 1994) and further experiments (NANETTI et al., 1995; IMDORF et al., 1995) showing high efficacy of weak solutions sprayed onto the bees of broodless colonies. Although many beekeepers used (and still use) to treat their colonies with the spraying technique, this complicate and time consuming method limited OA adoption to relatively small scale beekeeping farms. Many attempts had been made during time to find more practical and less invasive treatment methods and considerable progresses were achieved when the trickling technique was set-up in Italy (NANETTI and STRADI, 1997). In that case, a concentrate sugar syrup (60%) added with 4.2% OA was trickled by the means of a syringe (5 ml per Dadant-Blatt comb occupied by the bees) onto the comb top bars of broodless colonies. The efficacy averaged 96.8% and a weaker OA concentration resulted in significantly lower acaricidal effect. Further experiments showed steady performances even when the treatments were made in cold middle winter period. Several hobbyists and professional beekeepers successfully embraced the new technique, especially in Italy, but further trials were needed to corroborate its use in other European climates and technical circumstances. The general lack of knowledge about OA needed a special interest of the European Group for Integrated Varroa Control, that decided to create a working group to investigate on the substance. Part of the involved researchers focused on setting-up the trickling method, in order to verify the possibility to extend this application method also in other areas. The needed experiments were performed according to agreed protocols in order to compare the results. This paper summarises the main achievements resulting by this corporate research.