Saturday, October 9, 2010
The European honey bee (Apis mellifera) is a common pollinator worldwide. You can find them where there are flowers to feed on and suitable hive-building sites. Most of the individuals you see buzzing around your garden collecting pollen are females (workers), the males are significantly bigger and are very few in number. These social insects heat their hives with body heat and cool it by fanning their wings, this way they can live year-round in a place surviving on their honey reserves through the winter.
As you may have guessed by their common name, these honey bees are not native to the western hemisphere. They were brought over by early European colonists for their honey and wax production. Over time, beekeepers have experimented with the about two dozen subspecies, but they've found that Apis mellifera ligustica (a subspecies brought over by early Spanish settlers) is favorable.
Beginning in October 2006, beekeepers started reporting the losses of 30-90% of their hives. Some loss is normal, but this amount is highly unusual. Colony Collapse Disorder (CCD) is the name that has been given to this serious, mysterious die-off of honey bee colonies across the U.S. CCD is characterized by sudden colony death with a lack of adult bees in front of the die-outs. Honey stores and recent brood rearing are often evidenced, and sometimes the queen and a small number of survivor bees remain. Although there have been published incidences of honey bee disappearances - in the 1880's, 1920's, and 1960's - it is unclear if this same phenomena has happened before. Descriptions are similar to CCD but as it is yet unknown what causes CCD it is difficult to tell.
This year, 2010, CCD has once again devastated honey bee colonies in the US, at rates that are potentially higher than the occurrence in 2006-2007. Previous scientific studies, using sensitive genome-based methods, have found small RNA bee viruses and the microsporidia, Nosema apis and N. ceranae in healthy and collapsing colonies alike. However, no single pathogen has been linked to hive losses.
The study published this week in PLoS ONE used mass spectrometry-based proteomics (MSP) to identify and compare proteins from healthy and collapsing honey bee colonies. This particular method revealed two previously unreported RNA viruses, Varroa destructor-1 virus (VDV-1) and Kakugo virus. They also identified an invertebrate iridescent virus (IIV) (Iridoviridae), a DNA virus, and linked it to the CCD colonies. The CCD colonies were found to not only contain IIV but also Nosema (specifically N. ceranae). The IIV, in particular, is interesting because it was thought until now that small RNA viruses were the cause of bee diseases. The pairing of IIV and N. ceranae and their correlation with CCD colonies suggests that they track each other and they do not occur concurrently in healthy colonies. Laboratory cage trials add more evidence to support this hypothesis.
It is hypothesized that damage to the bees' gut epithelial tissue and other host cells by N. ceranae allows entry to IIV. Or, perhaps, the replication of N. ceranae in honey bee cells may decrease the bees' ability to ward off viral infections. The presence of IIV may prove to be a useful tool in identifying colonies in the early stage of CCD or a possible resistance to the virus in a strong colony. IIV's are not completely unstudied. In fact, a good amount of study has been done on them for use as biopesticides. IIV-3 and IIV-6 have had a complete genome sequencing, and 24 other IIV's have been partially characterized. Viral diseases are currently only manageable rather than curable, with infected bee populations needing culling. Nosema, however, is treatable with current management techniques. Since their pairing suggests increased lethality, disrupting the relationship may be an option to help reduce bee mortality.
You can read the paper here:
Bromenshenk, Jerry J., et al. (2010) Iridovirus and Microsporidian Linked to Honey Bee Colony Decline. PLoS ONE: 5(10): e13181. (DOI: 10.1371/journal.pone.0013181)
Also, here's a NY Times article on the subject:
Also, check out these links for more information on Colony Collapse Disorder:
Mid-Atlantic Apiculture Research and Extension Consortium (MAAREC)
United States Department of Agriculture: Agricultural Resource Service
United States Department of Agriculture: National Agricultural Library
The Ohio State University's Agriculture Network Information Center's Bees and Pollination Page
(image from nycgovparks.org)