Chemical cues in the host-seeking behaviour of tracheal mites (Acarapis woodi) in honey bees (Apis mellifera mellifera)

The tracheal mite, Acarapis woodi, is a widespread parasite of honey bees that can lead to colony death. A key determinant of colony mortality is the prevalence of the parasite within a colony. Prevalence depends upon transmission rates, which vary depending upon the age of potential hosts. Honey bee cuticular hydrocarbons change with age, and have been suggested to be the cue used by tracheal mites to determine whether they move to a potential host. Recently, honey bees pupated at a reduced temperature were found to have a significantly higher susceptibility to tracheal-mite infestation. In this study experiments were conducted to determine whether this susceptibility was due to a change in chemical cues. Cuticular compounds were significantly different between bees pupated at 34 degrees C and 30 degrees C, as predicted. However, behavioural tests showed conclusively that the increased susceptibility of bees pupated at the lower temperature could not be explained by these chemical differences. Other factors, such as changes in bee physiology, reduced mobility and cognitive ability, that have been shown to be caused by reduced pupation temperature, are suggested as potential mechanisms. Interestingly, these experiments provide evidence that tracheal mites only respond to gustatory and not olfactory cues. The implications of this for the behavioural strategies adopted by mites to maximise safe transmission, and a new model for mite transfer are discussed.