By M. Navajas, A. Migeon, C. Alaux, Ml. Martin-Magniette, G. E. Robinson, J. D. Evans, S. Cros-Arteil, D. Crauser and Y. Le Conte in BMC Genomics 2008, 9:301, reprinted from Catch the Buzz, produced by Bee Culture Magazine

The parasitic mite, Varroa destructor, is the most serious pest of the western honey bee, Apis mellifera, and has caused the death of millions of colonies worldwide. This mite reproduces in brood cells and parasitizes immature and adult bees.

We investigated whether Varroa infestation induces changes in Apis mellifera gene expression, and whether there are genotypic differences in the bee's tolerance, as first steps toward unraveling mechanisms of host response and differences in susceptibility to Varroa parasitism.

Results: We explored the transcriptional response to mite parasitism in two genetic stocks of A. mellifera which differ in susceptibility to Varroa, comparing parasitized and non-parasitized full-sister pupae from both stocks.

Bee expression profiles were analyzed using microarrays derived from honey bee ESTs (Whitfield et al. 2002b) whose annotation has recently been enhanced by results from the honey bee genome sequence (Consortium 2006).

We measured differences in gene expression in two colonies of Varroa susceptible and two colonies of Varroa-tolerant bees.We identified a set of 127 genes with significantly different patterns of expression: 30 varied with the presence of Varroa, 99 varied with bee genotype, and 2 with both. Varroa parasitism caused changes in the expression of genes related to embryonic development, cell metabolism and immunity.

Bees tolerant to Varroa were mainly characterized by differences in the expression of genes regulating neuronal development, neuronal sensitivity and olfaction. Differences in olfaction and sensitivity to stimuli are two parameters that could, at least in part, account for bee tolerance to Varroa; differences in olfaction may be related to increased grooming ßand hygienic behavior, important behaviors known to be involved in Varroa tolerance.

Conclusions: These results suggest that differences in behavior, rather than in the immune system, underlie Varroa tolerance in honey bees, and give an indication of the specific physiological changes found in parasitized bees.

They provide a first step toward better understanding molecular pathways involved in this important host-parasite relationship.

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