The ectoparasitic mite Varroa destructor is one of the main plagues of honey bees Apis mellifera. Grooming behavior is a resistance mechanism through which parasitized bees can dislodge mites by themselves (autogrooming) or by the action of other bees (allogrooming). The objective of this study was to evaluate grooming behavior in Italian (A. m. ligustica) and Africanized (hybrids of A. m. scutellata) bees at the individual, group, and colony levels. Firstly, five behaviors were recorded observing bees individually placed on a Petri dish and after placing a mite on their thorax. Secondly, 30 bees of each colony were placed in a Petri dish along with 20 mites and 24 h later fallen mites were counted. Lastly, the proportion of injured mites collected in the hive floor was determined. At the individual level, Africanized bees showed a higher total number of reaction behaviors to V. destructor than did Italian bees (U = 182.5; p = 0.02). Groups of Italian bees could dislodge 60.8 ± 20.0% of mites and Africanized bees dislodged 65.9 ± 15.6% of mites, without showing significant differences (t = 0.735; p = 0.47). Colonies of Africanized bees showed a higher proportion of injured mites (29.0 ± 8.6%) than colonies of Italian bees did (17.7 ± 9.8%) (t = 2.92; p = 0.009). Africanized bees are characterized by presenting higher resistance to V. destructor than European bees. This study shows that such difference can be, partly due to grooming behavior. The importance of auto and allogrooming regarding resistance to V. destructor is discussed.

Chalkbrood disease affects the larvae of honeybees Apis mellifera L. and is caused by the fungus Ascosphaera apis. Infected larvae die when they are stretched in the cap cell and suffer a gradual hardening that ends in a very hard structure (mummie). Several studies have demonstrated that colonies that express an efficient hygienic behaviour (uncapping of cell and subsequent removal of dead brood) exhibit a higher resistance to the disease. However, it remains unclear whether the advantage of hygienic colonies over less hygienic ones lies in the ability to remove mummies or in the early detection of infected larvae and its cannibalization before they harden. To elucidate this aspect, the hygienic behaviour of 24 colonies, which were subsequently provided with pollen cakes containig A. apis, was evaluated. The number of mummies and the number of partially cannibalized and whole larvae in uncapped cells were recorded. The most hygienic colonies controlled the disease better. These colonies also had a higher tendency to uncap cells that contained infected larvae and cannibalize them. The presence of A. apis in partially cannibalized and whole larvae in uncapped cells indicate that the advantage of hygienic colonies over less hygienic ones lies in the early detection of infected larvae death and their quick removal from the cell before they become mummies.

The ectoparasite Varroa destructor is the greatest biotic threat of honey bees Apis mellifera in vast regions of the world. Recently, the study of natural mite-resistant populations has gained much interest to understand the action of natural selection on the mechanisms that limit the mite population. In this study, the components of the A. mellifera–V. destructor relationship were thoroughly examined and compared in resistant and susceptible honey bee populations from two regions of Uruguay. Mite-resistant honey bees have greater behavioral resistance (hygienic and grooming behaviors) than susceptible honey bees. At the end of the summer, resistant honey bees had fewer mites and a lower deformed wing virus (DWV) viral load than susceptible honey bees. DWV variant A was the only detected variant in honey bees and mites. Molecular analysis by Short Tandem Repeat showed that resistant honey bees were Africanized (A. m. scutellata hybrids), whereas susceptible honey bees were closer to European subspecies. Furthermore, significant genetic differentiation was also found between the mite populations. The obtained results show that the natural resistance of honey bees to V. destructor in Uruguay depends on several factors and that the genetic variants of both organisms can play a relevant role.