Fending for thyself : honey bees from Ethiopia inflict physical damage on varroa destructor

Abstract

The ectoparasitic mite Varroa destructor and its associated viruses threaten the health of honey bee (Apis mellifera L.). Yet, African populations survive mite infestations without miticide treatment largely due to social immunity behaviors. However, little is known about these defense mechanisms in A. m. simensis populations from the Amhara region of Ethiopia. Therefore, this study investigated grooming and hygienic behaviors across lowland, midland, and highland areas during the wet and dry seasons in this region. Grooming behavior was quantified by measuring adult mite infestation rates, daily natural mite fall, and the proportion of mites showing physical damage per colony. Hygienic behavior was evaluated via the removal of pin-killed brood cells. Results were compared with Kenya's resistant A. m. scutellata and susceptible European hybrids in the USA. Honey bees in the Amhara region maintained low mite infestations (< 3.5 mites/100 honey bees) and exhibited higher grooming rates, ranging between 15% to 43% and inflicted more frequently damage to legs and gnathosoma comparable to Kenya's resistant honey bees. In addition to the 10 previously known damage categories inflicted on the mites by honey bees, two new mite damage combinations were identified. Their hygienic behavior was also high, ranging between 79.9% to 98.6% within 24 h and reached 98.8% to 100% after 48 h. While adult grooming and hygienic behaviors significantly varied with landscape and/or season, neither significantly correlated with mite infestation loads, suggesting these traits confer tolerance rather than resistance. Other resistance mechanisms, such as suppressed mite reproduction in worker brood cells, may further reduce colony mite infestations and should be evaluated in future studies.