AsianScientist (Mar. 7, 2017) – The genome of the parasitic bee mite Tropilaelaps mercedesae suggests that existing methods to prevent bee colony collapse might be ineffective. These findings have been published in GigaScience.
Although there are many potential causes for the decline in honey bee colonies, pathogens and parasites of the honey bee, particularly mites, are considered major threats to honey bee health and honey bee colonies. The bee mite T. mercedesae is honey bee parasite prevalent in most Asian countries, and has a similar impact on bee colonies that the globally present bee mite Varroa destructor has. With the global trade of honey bees, T. mercedesae is likely become established world-wide.
To preempt the impact of T. mercedesae infestation, an international team of researchers from Jiaotong-Liverpool University sequenced its genome and compared it to the genome of free-living mites.
As opposed to the free-living mites, T. mercedesae has a very specialized life history and habitat that depends strictly on the honey bee inside a stable colony. The researchers found that the T. mercedesae genome has been shaped by interaction with the honey bee and colony environment.
Interestingly, the authors found that the mite does not rely on sensing stimulatory chemicals to affect their behavior. The researchers noted that this discovery meant that, “control methods targeted to gustatory, olfactory, and ionotropic receptors are not effective.” Instead, control measures will have to use other targets when trying to disrupt chemical communication.
“There will be a need to identify targets for biological control,” they added.
Furthermore, the researchers found that T. mercedesae is enriched with detoxifying enzymes and pumps for the toxic xenobiotics, which help them quickly acquire resistance to miticides.
However, the study also revealed a potential alternative to miticides. The researchers found that Rickettsiella grylli commonly infect T. mercedesae, suggesting that targeting these bacteria might be one way to control the mite population.
They also found that R. grylli was involved in horizontal gene transfer of Wolbachia genes into the mite genome. Wolbachia is a bacteria that commonly infects arthropods, but is not present in T. mercedesae.
Although up to a horizontal gene transfer has been detected in as many as a third of all sequenced arthropod genomes, this is the first example of horizontal gene transfer in mites and ticks, the authors noted. Since Wolbachia bacteria do not currently infecting the mites, these findings indicate that Wolbachia was once a symbiont for T. mercedesae or its ancestor but has been replaced with R. grylli-like bacteria during evolution, they added.
The extent of honey bee colony destruction remains a complex problem, but one that has an extensive impact crop productivity since honey bees are needed for pollination of a variety of plants. Indeed, in several places in China, farm workers have begun to carry out manual pollination to maintain high crop yield in orchards. Thus, research and resources to help combat this global threat are needed now. These genome, transcriptome, and proteome resources from the T. mercedesae study add another weapon in the fight to save bee colonies.
The article can be found at: Dong et al. (2016) Draft Genome of the Honey Bee Ectoparasitic Mite, Tropilaelaps Mercedesae, is Shaped by the Parasitic Life History.”
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Source: GigaScience.
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