Semiochemicals Influencing the Host-finding Behaviour of Varroa Destructor

Abstract

Studies of Varroa destructor orientation to honey bees were undertaken to isolate discrete chemical compounds that elicit host-finding activity. Petri dish bioassays were used to study cues that evoked invasion behaviour into simulated brood cells and a Y-tube olfactometer was used to evaluate varroa orientation to olfactory volatiles. In Petri dish bioassays, mites were highly attracted to live L5 worker larvae and to live and freshly freeze-killed nurse bees. Olfactometer bioassays indicated olfactory orientation to the same type of hosts, however mites were not attracted to the odour produced by live pollen foragers. The odour of forager hexane extracts also interfered with the ability of mites to localize and infest a restrained nurse bee host. Varroa mites oriented to the odour produced by newly emerged bees (<16 h old) when choosing against a clean airstream, however in choices between the odours of newly emerged workers and nurses, mites readily oriented to nurses when newly emerged workers were <3 h old. The odour produced by newly emerged workers 18-20 h of age was equally as attractive to mites as that of nurse bees, suggesting a changing profile of volatiles is produced as newly emerged workers age. Through fractionation and isolation of active components of nurse bee-derived solvent washes, two honey bee Nasonov pheromone components, geraniol and nerolic acid, were shown to confuse mite orientation. We suggest that V. destructor may detect relative concentrations of these compounds in order to discriminate between adult bee hosts, and preferentially parasitize nurse bees over older workers in honey bee colonies. The volatile profile of newly emerged worker bees also may serve as an initial stimulus for mites to disperse before being guided by allomonal cues produced by older workers to locate nurses. Fatty acid esters, previously identified as putative kairomones for varroa, proved to be inactive in both types of bioassays.

Can We Disrupt the Sensing of Honey Bees by the Bee Parasite Varroa destructor?

“…This assay clearly showed that inhibition of EP responses to nurse honey bee volatiles correlates with a profound behavioral change: a total reversal of the commonly observed [15],[10]],[36] nurse preference by the mite. An expected behavioral effect of a chemosensory disruptive compound would be a lack of preference, yet in this case the inhibiting compounds caused an inversion in preference.…”

“…In laboratory bioassays Varroa has been shown to discriminate between bees from different task groups and to prefer a nurse over a forager [10], [11]. The host preference is apparently based on both low volatility compounds, such as cuticular hydrocarbons [12], and on volatile compounds emitted by the honey bees and their environment (such as larval food and brood pheromone) [13]–[15]. Despite much progress in the identification of host olfactory cues guiding Varroa , neither effective attractants nor repellents have been found so far.…”

Practical Sampling Plans for <I>Varroa destructor</I> (Acari: Varroidae) in <I>Apis mellifera</I> (Hymenoptera: Apidae) Colonies and Apiaries

“…Greater levels on brood combs were probably due to mites preferring nurse bees, which tend to stay on brood combs (Pernal et al 2005). The differences may have been underestimated in our study, to the extent that bees may have been redistributed among frames when colonies were opened for sampling.…”

The Biology and Control of the Greater Wax Moth, Galleria mellonella

“…Honeybees are among the most well studied living organisms [102]. They accumulate a variety of resources attractive to various arthropods including the small hive beetles, Aethina tumida Murray, the African large hive beetle, Oplostomus haroldi Witte and O. fuligineus Olivier, and the invasive mite, Varroa destructor Anderson & Trueman [102,103,104,105,106,107,108,109,110]. These invaders exploit hive resources as food for adults and immatures, and as oviposition sites [105].…”