Aliphatic alcohols and aldehydes of the honey bee cocoon induce arrestment behavior in <i>Varroa jacobsoni</i> (Acari: Mesostigmata), an ectoparasite of <i>Apis mellifera</i>

The ectoparasitic mite <i>Varroa jacobsoni</i> reproduces in the capped brood of the honey bees <i>Apis cerana</i> and <i>Apis mellifera</i>. Observations on the reproductive behavior of the mite have shown a well-structured spatial allocation of its activity using the bee or cell wall for different behaviors. The resulting advantages for the parasite of this subdivision of the concealed brood environment suggests an important role for chemostimuli in these substrates. <br> Extracts of the European honey bee cocoons induce a strong arrestment response in the mite, as indicated by prolonged periods of walking on the extracts applied on a semipermeable membrane and by systematically returning to the stimulus after encountering the treatment borders. Two thin-layer chromatography fractions of the cocoon extract eliciting arrestment were found to contain saturated C₁₇ to C₂₂ primary aliphatic alcohols and C₁₉ to C₂₂ aldehydes. <br> We analyzed extracts of the cocoon and different larvae, pupae, and adults of both worker and drone A. mellifera to determine the relative amounts of these chemostimuli in the different substrates employed by <i>Varroa</i>. Both aldehydes and alcohols were more abundant in the cocoon than in the cuticle of adult or developing bees. <br> Mixtures of the aliphatic alcohols and aldehydes at the proportions found in the cocoons acted synergistically on the arrestment response, but this activity disappeared when mixed in equal amounts. When these oxygenated chemostimuli were mixed with C₁₉ to C₂₅ alkanes at the proportions found in the cocoon extract, we observed a significantly lower threshold for the chemostimulant mixture. These results indicate how <i>Varroa</i> may use mixtures of rarer products to differentiate between substrates and host stages during its developmental cycle within honey bee brood cells.