Concurrent Parasitism Alters Thermoregulation in Honey Bee (Hymenoptera: Apidae) Winter Clusters

Thermoregulation is crucial for honey bee, Apis mellifera L. (Hymenoptera: Apidae), colony survival in temperate regions, but possible interference by parasites is currently unknown. The small hive beetle, Aethina tumida Murray (Coleoptera: Nitidulidae), and the ectoparasitic mite Varroa destructor Anderson & Trueman are honey bee parasites and both overwinter in host colonies. The efficiency of thermoregulation might thus be affected in infested host winter clusters, due to altered worker activity. Here, we show for the first time that parasites can alter honey bee thermoregulation. Moreover, the data suggest that only combined infestations with V. destructor and A. tumida result in higher thermal maxima in the winter clusters, whereas infestations with one parasite alone had no significant effect compared with the controls. Due to the ubiquitous mite V. destructor combined infestations with parasites or combined infections with pathogens are almost inevitable. Therefore, our data indicate that an altered thermoregulation due to multiple infestations might be another widespread factor contributing to winter losses of honey bee colonies.