ACTION OF FORMIC-ACID ON VARROA-JACOBSONIOUD 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 wi th relatively high concentrations of formic acid (almost-equal-to 2 50 0 ppm in the air). In another series of experiments honeybee colonies in hives were treated with 20-40 ml 60% formic acid under practical be ekeeping 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 form ic 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 in dicates that the mites, but also young larvae with their small body si ze and intensive respiration react more sensitively to formic acid tha n older larvae and young bees. Under conditions of formic acid treatme nts in bee hives there was no inhibition of the respiration of young A nd old larvae (fig 5). However, after prolonged formic acid treatments of bee colonies, a negative effect on brood care was observed. The re sulting 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 th e bee colony, respiration after one formic acid treatment was nearly a rrested whereas the mites which fell from the bees during treatment sh owed only partial respiration inhibition (fig 7). The bodies of the an imals with inhibited respiration were found to be strongly acidic as t ested by pH indicator. However, no necrosis or corrosive effects on th e in vitro treated animals could be detected after examination with li ght and electron microscopy. The faster respiration inhibition of the Varroa mites could thus be partly due to their lower buffering and met abolizing capacity. This at least explains the selective effects of fo rmic acid on Varroa mites, however, the existence of neurotoxic effect s on both bees and mites seems possible.