We have an exciting project unraveling the causes of honeybee decline in the UK (and world-wide), focussing on the role of a new parasite, the varroa mite. The varroa mite, see Figure 1, was originally observed in Asia and has been invading European and the UK hives since the 1980s causing massive devastation, whilst similar problems of population decline are reported in the US. Given that the European honeybee is a principal UK crop pollinator its decline has wide economic and ecological impacts.

Honey bee pupae with 2 mites	Varroa mite	Varroa mite (EM)

Figure 1. Photos from Zachary Huang and USDA-ARS and International Bee Research Association.


Context.

The varroa mite has specialised to the bee lifecycle; bees protect their eggs and larvae by sealing them into egg chambers in the hive where the larvae develops through eating honey. The varroa tick enters the egg chamber before it is sealed. There the mite lays its eggs, which hatch and feed on the developing bee. The bee still develops into an adult but exhibits symptoms of this interaction - specifically they have a high incidence of deformed wing pathology, Figure 2, and thus are less able to fly and show evidence of a reduced ability to collect nectar. It is known that a virus, deformed wing virus (DWV), causes these symptoms suggesting that the varroa mite has upset the delicate balance between the honey bee and this virus which normally causes few symptoms. The varroa mite probably suppresses the bee immune system whilst feeding, and thus upsets the ability of the immune system to control the virus. Further, there is evidence of new more lethal strains of related viruses emerging, specifically a recombinant between DWV and a virus carried by the mite, Varroa Destructor virus. All this suggests that the viral-bee ecology is out of equilibrium experiencing invasion by an agressive new strain, exacerbated, and probably triggered by the immune suppressive effects of the varroa mite. Proving these claims will be a major part of the project.

Figure 2. Bee with severe deformed wing pathology (photo by by Michael Traynor, Vet. Res. (2010) 41:54)

The project.

Working as a collaborative team, headed by N.J. Burroughs (theory) and D.J. Evans (experiment), we propose to investigate the interaction of the varroa mite, the bee and its population of viruses. We will collect data (experimental PDRA) at both the interaction level (counting mites) and molecular level (viral load, strain/sequence and bee immune response (gene expression)), and analyse this data using both statistical analysis and bioinformatic tools. We will use a variety of statistical methodologies to develop a predictive (statistical) model of bee pathology within the context of known (bioinformatic) information on insect immunity, correlating the relationship between bee/viral genotype, antiviral responses and the presence and load of viral pathogens. The range of experimental data available represents state of the art in molecular biology, and only recently are they being used to study ecological systems, as here.

Statistical methods.
This is a high dimensional multi-variate problem. We will use predominantly linear regression multivariate techniques given their flexibility, although basic assessment of trends (and their significance) will be initially performed using correlation techniques and principal component analysis where appropriate. We will also explore expression QTL methods, and MCMC methods to implement more sophisticated models (eg sparsity priors) if needed. A key aspect throughout the project will be determining which of the proposed interactions are significantly supported by the data, and thus there will be a high emphasis on hypothesis testing and/or model selection. Given the high volume of tests, multiple testing corrections will be used.

Bioinformatic methods.

The honeybee is sequenced, and has about 12000 genes. However the function of many of the genes is unknown, so comparison to other better studied species can be invaluable. You will use standard bioinformatic tools and databases such as BeeBase, Biomart & ENSEMBL.

This project is funded through BBSRC/NERC on the insect pollination initiative.