ACTION OF FORMIC-ACID ON VARROA-JACOBSONI OUD AND THE HONEYBEE (APIS-MELLIFERA L)

In one series of experiments (in vitro tests), Varroa mites, honeybee larvae of different ages and newly emerged worker bees were treated with relatively high concentrations of formic acid (almost-equal-to 2 500 ppm in the air). In another series of experiments honeybee colonies in hives were treated with 20-40 ml 60% formic acid under practical beekeeping conditions (less-than-or-equal-to 500 ppm in the air). After both types of formic acid treatment the respiration of the animals was measured by the Warburg manometric method. In the in vitro tests formic acid inhibited oxygen consumption of the bee brood (figs 1, 2), of newly emerged worker bees (fig 3) and of Varroa mites (fig 4). This indicates that the mites, but also young larvae with their small body size and intensive respiration react more sensitively to formic acid than older larvae and young bees. Under conditions of formic acid treatments in bee hives there was no inhibition of the respiration of young And old larvae (fig 5). However, after prolonged formic acid treatments of bee colonies, a negative effect on brood care was observed. The resulting decrease in larval feeding might be the cause of the decrease in bee larvae respiration (fig 6). In the Varroa mites in a cage in the bee colony, respiration after one formic acid treatment was nearly arrested whereas the mites which fell from the bees during treatment showed only partial respiration inhibition (fig 7). The bodies of the animals with inhibited respiration were found to be strongly acidic as tested by pH indicator. However, no necrosis or corrosive effects on the in vitro treated animals could be detected after examination with light and electron microscopy. The faster respiration inhibition of the Varroa mites could thus be partly due to their lower buffering and metabolizing capacity. This at least explains the selective effects of formic acid on Varroa mites, however, the existence of neurotoxic effects on both bees and mites seems possible.