Saturday, October 22, 2016

Sexual transmission of a bee virus

A queen honeybee. Via wiggledanceforme.

When sexually transmitted infections are discussed, one might think of human viruses, such as HIV or herpes. However, other organisms can become infected with viruses from sex. A new study describes how one of the more debilitating bee viruses, Deformed Wing Virus (DWV), can be sexually transmitted from infected male drones to otherwise healthy queens after mating. As the name might suggest, DWV severely deforms the wings of infected bees (see picture below) and impairs their cognitive function, specifically impairing the learning behavior and memory retention. Because of this, it wasn't known if infected drones would be successful at mating or not.

Carniolan honey bee with Deformed wing virus. Photo credit, Xolani90, via Wikipedia. 

In order to test this, the researchers took extensive steps to ensure that queen honeybees were free of viruses. They came from the same virus-tested colony as larvae and were then reared in nurse colonies that lacked a queen. That colony was screened for the varroa mite (300 bees were examined and none had the mite) and common bee viruses tested for in 60 worker bees. These include DWV, Black Queen Cell Virus, Sacbrood Virus, Chronic Bee Paralysis Virus and the ABPV complex made up of Acute Bee Paralysis Virus, Kashmir Bee Virus and Israeli Acute Paralysis Virus. A total of 30 queens met this criteria and were used in the study. They were then allowed to mate with DWV-infected male drones for at least 7 min; nine did not mate for the full time leaving 21 queens that fulfilled the requirements. If the drone's endophallus was still present in the queen after mating, then it was removed and tested for DWV; three of these had high levels of DWV. They found that seven of the queens developed high levels of systemic DWV infection; one of these queens died shortly after ovipositing (laying eggs) due to the infection. A further 15 queens had medium levels of DWV that varied in titer by tissue and eight queens had low levels of DWV.

This study answers an important question: can DWV-infected drones pass the virus on to queens by mating? The answer is a clear yes. Part of the reason why this study is important is because DWV is one of the major viruses associated with colony collapse disorder. Complicating matters, previous work has demonstrated that the varroa mite prefers drone brood (the varroa mite transmits all the viruses listed in this post to bees). 
Another issue is that if a queen dies, then the colony will be lost. Up to 25% of lost colonies are the result of loss of the queen. This new discovery could have implications for managing honeybees and lead to the development of strategies to mitigate these losses.