Critical links between biodiversity and health in wild bee conservation.

Wild bee populations are declining due to human activities, such as land use change, which strongly affect the composition and diversity of available plants and food sources. The chemical composition of food (i.e., nutrition) in turn determines the health, resilience, and fitness of bees. For pollinators, however, the term 'health' is recent and is subject to debate, as is the interaction between nutrition and wild bee health. We define bee health as a multidimensional concept in a novel integrative framework linking bee biological traits (physiology, stoichiometry, and disease) and environmental factors (floral diversity and nutritional landscapes). Linking information on tolerated nutritional niches and health in different bee species will allow us to better predict their distribution and responses to environmental change, and thus support wild pollinator conservation.

Metabolisation of thiamethoxam (a neonicotinoid pesticide) and interaction with the Chronic bee paralysis virus in honeybees.

Pathogens and pesticides are likely to co-occur in honeybee hives, but much remains to be investigated regarding their potential interactions. Here, we first investigated the metabolisation kinetics of thiamethoxam in chronically fed honeybees. We show that thiamethoxam, at a dose of 0.25ng/bee/day, is quickly and effectively metabolised into clothianidin, throughout a 20day exposure period. Using a similar chronic exposure to pesticide, we then studied, in a separate experiment, the impact of thiamethoxam and Chronic bee paralysis virus (CBPV) co-exposure in honeybees. The honeybees were exposed to the virus by contact, mimicking the natural transmission route in the hive. We demonstrate that a high dose of thiamethoxam (5.0ng/bee/day) can cause a synergistic increase in mortality in co-exposed honeybees after 8 to 10days of exposure, with no increase in viral loads. At a lower dose (2.5ng/bee/day), there was no synergistic increase of mortality, but viral loads were significantly higher in naturally dead honeybees, compared with sacrificed honeybees exposed to the same conditions. These results show that the interactions between pathogens and pesticides in honeybees can be complex: increasing pesticide doses may not necessarily be linked to a rise in viral loads, suggesting that honeybee tolerance to the viral infection might change with pesticide exposure.

Evidence for positive selection and recombination hotspots in Deformed wing virus (DWV).

Deformed wing virus (DWV) is considered one of the most damaging pests in honey bees since the spread of its vector, Varroa destructor. In this study, we sequenced the whole genomes of two virus isolates and studied the evolutionary forces that act on DWV genomes. The isolate from a Varroa-tolerant bee colony was characterized by three recombination breakpoints between DWV and the closely related Varroa destructor virus-1 (VDV-1), whereas the variant from the colony using conventional Varroa management was similar to the originally described DWV. From the complete sequence dataset, nine independent DWV-VDV-1 recombination breakpoints were detected, and recombination hotspots were found in the 5' untranslated region (5' UTR) and the conserved region encoding the helicase. Partial sequencing of the 5' UTR and helicase-encoding region in 41 virus isolates suggested that most of the French isolates were recombinants. By applying different methods based on the ratio between non-synonymous (dN) and synonymous (dS) substitution rates, we identified four positions that showed evidence of positive selection. Three of these positions were in the putative leader protein (Lp), and one was in the polymerase. These findings raise the question of the putative role of the Lp in viral evolution.

Social immunity in honeybees (Apis mellifera): transcriptome analysis of varroa-hygienic behaviour.

Honeybees have evolved a social immunity consisting of the cooperation of individuals to decrease disease in the hive. We identified a set of genes involved in this social immunity by analysing the brain transcriptome of highly varroa-hygienic bees, who efficiently detect and remove brood infected with the Varroa destructor mite. The function of these candidate genes does not seem to support a higher olfactory sensitivity in hygienic bees, as previously hypothesized. However, comparing their genomic profile with those from other behaviours suggests a link with brood care and the highly varroa-hygienic Africanized honeybees. These results represent a first step toward the identification of genes involved in social immunity and thus provide first insights into the evolution of social immunity.

Pheromones in a superorganism: from gene to social regulation.

Analogous to the importance of hormones in controlling organism homoeostasis, pheromones play a major role in the regulation of group homoeostasis at the social level. In social insects, pheromones coordinate the association of "unitary" organisms into a coherent social unit or so called "superorganism." For many years, honey bees have been a convincing model for studying pheromone regulation of social life. In addition, with the recent sequencing of its genome, a global view of pheromone communication is starting to emerge, and it is now possible to decipher this complex chemical language from the molecular to the social level. We review here the different pheromones regulating the main biological functions of the superorganism and detail their respective action on the genome, physiology and behavior of nestmates. Finally, we suggest some future research that may improve our understanding of the remarkably rich syntax of pheromone communication at the social level.

Regulation of brain gene expression in honey bees by brood pheromone.

Pheromones are very important in animal communication. To learn more about the molecular basis of pheromone action, we studied the effects of a potent honey bee pheromone on brain gene expression. Brood pheromone (BP) caused changes in the expression of hundreds of genes in the bee brain in a manner consistent with its known effects on behavioral maturation. Brood pheromone exposure in young bees causes a delay in the transition from working in the hive to foraging, and we found that BP treatment tended to upregulate genes in the brain that are upregulated in bees specialized on brood care but downregulate genes that are upregulated in foragers. However, the effects of BP were age dependent; this pattern was reversed when older bees were tested, consistent with the stimulation of foraging by BP in older bees already competent to forage. These results support the idea that one way that pheromones influence behavior is by orchestrating large-scale changes in brain gene expression. We also found evidence for a relationship between cis and BP regulation of brain gene expression, with several cis-regulatory motifs statistically overrepresented in the promoter regions of genes regulated by BP. Transcription factors that target a few of these motifs have already been implicated in the regulation of bee behavior. Together these results demonstrate strong connections between pheromone effects, behavior, and regulation of brain gene expression.

Differential gene expression of the honey bee Apis mellifera associated with Varroa destructor infection.

BACKGROUND: 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 that affect gene expression relevant to the bee's tolerance, as first steps toward unravelling 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 whose annotation has recently been enhanced by results from the honey bee genome sequence. We measured differences in gene expression in two colonies of Varroa-susceptible and two colonies of Varroa-tolerant bees. We identified a set of 148 genes with significantly different patterns of expression: 32 varied with the presence of Varroa, 116 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 and hygienic behavior, important behaviors known to be involved in Varroa tolerance. CONCLUSION: 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.