Varroa-tolerant Italian honey bees introduced from Brazil were not more efficient in defending themselves against the mite Varroa destructor than Carniolan bees in Germany

RESUMO

In Europe and North America honey bees cannot be kept without chemical treatments against Varroa destructor. Nevertheless, in Brazil an isolated population of Italian honey bees has been kept on an island since 1984 without treatment against this mite. The infestation rates in these colonies have decreased over the years. We looked for possible varroa-tolerance factors in six Italian honey bee colonies prepared with queens from this Brazilian island population, compared to six Carniolan colonies, both tested at the same site in Germany. One such factor was the percentage of damaged mites in the colony debris, which has been reported as an indicator of colony tolerance to varroa. A mean of 35.8 of the varroa mites collected from the bottoms of the Italian bee colonies were found damaged, among which 19.1 were still alive. A significantly greater proportion of damaged mites were found in the Carniolan bees (42.3) and 22.5 were collected alive. The most frequent kind of damage found was damaged legs alone, affecting 47.4 of the mites collected from debris in Italian bees, which was similar to the amount found in Carniolan colonies (46). The mean infestation rate by the varroa mite in the worker brood cells in the Italian bee colonies was 3.9 in June and 3.5 in July, and in drone brood cells it was 19.3 in June. In the Carniolan honey bee colonies the mean infestation rates in worker brood cells were 3.0 and 6.7, respectively in the months of June and July and 19.7 in drone brood cells in June. In conclusion, the 'Varroa-tolerant' Italian honey bees introduced from Brazil produced lower percentages of damaged mites (Varroa destructor) in hive debris and had similar brood infestation rates when compared to 'susceptible' Carniolan bees in Germany. In spite of the apparent adaptation of this population of Italian bees in Brazil, we found no indication of superiority of these bees when we examined the proportions of damaged mites and the varroa-infestation rates, compared to Carniloan bees kept in the same apiary in Germany