BackgroundThe ectoparasitic mite, Varroa destructor, is considered to be one of the most significant threats to apiculture around the world. Chemical cues are known to play a significant role in the host-finding behavior of Varroa. The mites distinguish between bees from different task groups, and prefer nurses over foragers. We examined the possibility of disrupting the Varroa – honey bee interaction by targeting the mite's olfactory system. In particular, we examined the effect of volatile compounds, ethers of cis 5-(2′-hydroxyethyl) cyclopent-2-en-1-ol or of dihydroquinone, resorcinol or catechol. We tested the effect of these compounds on the Varroa chemosensory organ by electrophysiology and on behavior in a choice bioassay. The electrophysiological studies were conducted on the isolated foreleg. In the behavioral bioassay, the mite's preference between a nurse and a forager bee was evaluated.Principal findingsWe found that in the presence of some compounds, the response of the Varroa chemosensory organ to honey bee headspace volatiles significantly decreased. This effect was dose dependent and, for some of the compounds, long lasting (>1 min). Furthermore, disruption of the Varroa volatile detection was accompanied by a reversal of the mite's preference from a nurse to a forager bee. Long-term inhibition of the electrophysiological responses of mites to the tested compounds was a good predictor for an alteration in the mite's host preference.ConclusionsThese data indicate the potential of the selected compounds to disrupt the Varroa - honey bee associations, thus opening new avenues for Varroa control.

-Honey bees and their ectoparasite Varroa destructor communicate through chemical signals among themselves, but they also eavesdrop on each other's chemical cues. We summarize semiochemicals of honey bees and Varroa , and their roles in honey bee-Varroa interactions. We also give an overview of current Varroa control methods, which can be classified into three categories: (1) chemical control methods with acaricides, (2) biotechnical intervention, and (3) bee breeding programs. Widely used synthetic chemical acaricides are failing due to the emergence of resistant mites. Therefore, new methods are being sought for Varroa control, and methods that target the semiochemical interactions between bees and mites are among the candidates. We review our discovery of compounds that alter the host choice of Varroa mites (from nurse to forager) in laboratory tests. Any semiochemicalbased methods are still in the experimental stage and need validation in the field.Apis mellifera / Varroa destructor / mite control / chemical senses / semiochemical

Chemosensing is a primary sense in nature, however little is known about its mechanism in Chelicerata. As a model organism we used the mite Varroa destructor, a key parasite of honeybees. Here we describe a transcriptomic analysis of two physiological stages for the Varroa foreleg, the site of primary olfactory organ. The transcriptomic analysis revealed transcripts of chemosensory related genes belonging to several groups. These include Niemann-Pick disease protein, type C2 (NPC2), gustatory receptors (GRs), ionotropic receptors (IRs), sensory neuron membrane proteins (SNMPs) and odorant binding proteins (OBP). However, no insect odorant receptors (ORs) and odorant co-receptors (ORcos) were found. In addition, we identified a homolog of the most ancient IR co-receptor, IR25a, in Varroa as well as in other members of Acari. High expression of this transcript in the mite’s forelegs, while not detectable in the other pairs of legs, suggests a function for this IR25a-like in Varroa chemosensing.

International audienceVarroa destructor Anderson and Trueman (Acari: Varroidae) is an obligatory ectoparasitic mite of honey bees. In view of limited success in mite control, the use of synthetic repellent was evaluated. The objective of the present study was to investigate the effect of common arthropod repellent N,N-diethyl-m-toluamide (DEET) on the chemosensing of the V. destructor and its hosts, the European honey bee (Apis mellifera L.), by electrophysiological and behavioural bioassays. In electrophysiological assays, the nurse headspace served as a positive stimulus for the V. destructor foreleg, whereas a queen headspace was used as a positive stimulus for honey bee antennae. Two effects of DEET on V. destructor host chemosensing were evaluated: short-term inhibition and long-term inhibition. The inhibition observed in the presence of DEET simultaneously with a positive stimulus was termed “short term inhibition”, while inhibition that occurred following the administration of the compound alone was termed “long term inhibition”. In V. destructor, DEET served as a long-term inhibitor to the response of the chemosensory organ to nurse bee headspace volatiles, whereas in honey bee, it caused short-term inhibition of antenna response to queen volatiles. Consistent with electrophysiological studies, DEET significantly inhibited host choice of mites, whereas even a 10 times higher dose did not alter honey bee behaviours (e.g. antennating, grooming, fanning etc.) or worker attraction to a queen. These data suggest that DEET may selectively disrupt the honey bee chemosensing of V. destructor