XXII CNIE - Accademia nazionale italiana di Entomologia

synergize each other, make the development of alternative approaches to varroa
management in commercial apiculture a high priority.
Nutrition?
Stress caused by poor nutrition has also been suspected to play a role in colony collapse
disorder. The high incidence of CCD among migratory beekeepers suggested that the
practice of maintaining bees for extended periods of time on monofloral food sources
might lead to nutritional imbalances and impaired resistance to disease. Yet another
source of concern was the routine use of sugar water or high fructose corn syrup, in
place of honey, to sustain colonies through the winter; such diets lack the myriad
micronutrients and antioxidants that are present in honey. Johnson (2008), using a
specialized “detoxification” microarray to identify inducers of detoxification gene
transcription, found that, unlike the P450s of most other insects examined, honey bee
P450 genes are not upregulated by synthetic substances or by table sugar; rather,
constituents of honey, propolis and pollen upregulate these genes, demonstrating in a
compelling way the extreme dietary specialization for floral tissues exhibited by the
honey bee. The finding that sucrose (table sugar) does not upregulate detoxification
genes suggests that feeding bees sugar water or possibly high fructose corn syrup, both
common apicultural practices, may alter their ability to metabolize pesticides.
Diagnostics
Some of the conflicting evidence regarding the causes of CCD can be accounted for by
virtue of the fact that diagnosis of the condition is imprecise. Debnam et al. (2009)
developed a 13-item visual inventory of symptoms that constitute evidence of incipient
collapse; although such diagnostics are useful in allowing beekeepers to take action to
reduce losses, the characteristic signs vary geographically and temporally and can be
difficult to quantify unambiguously.
By enabling high throughput quantitative analyses of whole genome RNA expression
levels, microarray analyses can be useful diagnostic tools (Bustin et al. 2002). Thus, we
recently undertook a whole genome microarray comparison of bees afflicted with CCD
with the objective of identifying a characteristic gene expression profile. Because the
gut is the major site of pesticide detoxification in honey bees (Yu et al. 1984) and is
integral to immune defense against pathogens (Lemaitre et al. 2007), it is likely a target
site for the development of CCD, irrespective of causative agents. We compared gene
expression in guts of adult worker bees from colonies afflicted with CCD with that in
guts of adult workers from colonies sampled prior to the outbreak of CCD. Samples
showing varying degrees of CCD were collected on the East and West Coasts of the US
in the winter of 2006-2007 and compared with healthy controls were collected in 2004
and 2005. Lists of genes differentially expressed between groups were categorized
according to Gene Ontology (Ashburner et al. 2000) and expression changes of a small
group of genes were verified using quantitative real-time PCR (qPCR) on a separate set
of bees afflicted from CCD that were collected in California in late 2007.
We found remarkable geographic variation in both gene-expression patterns and
pathogen loads. This variation likely reflects the multiple stresses experienced by bees
and underscores the necessity for extensive population surveys for diagnostic purposes.
Future work is needed to definitively establish the correlation between picornavirus
pathogen load and polyadenylated rRNA fragment abundance. Additionally, the
consequences of viral infection and CCD on the function of ribosomes should be
explored through assays of translational efficiency. In the interim, colony surveillance
via assay of rRNA fragment abundance may provide an earlier indication of CCD status
than has hitherto been available and allow beekeepers to take actions to reduce bee
losses.
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