Engineered Microbe in Bees’ Guts Fends off Deadly Varroa Mite
Engineered Microbe in Bees’ Guts Fends off Deadly Varroa Mite

Engineered Microbe in Bees’ Guts Fends off Deadly Varroa Mite

The genetically modified bacteria spark an RNAi response in the parasite that leads to self-destruction—and perhaps a path to combatting colony collapse disorder.

Lisa Winter
Lisa Winter
Jan 31, 2020

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Genetically altering symbiotic gut bacteria in honey bees is successful at killing varroa mites, which tend to make bees sick and leave them at an increased risk of colony collapse disorder, according to a study published today (January 31) in Science.

Colony collapse disorder (CCD) occurs when the majority of a hive abandons ship, leaving behind the queen, honey and pollen stores, and young, immature bees behind. Without the workforce of a full hive, the colony fails. According to the US Department of Agriculture, there does not appear to be a single cause of CCD, rather, it is likely a combination of disease, parasites, poor nutrition, pesticide exposure, and other stressors on the hive.

One possible contributor to unhealthy hives are Varroa destructor mites, an invasive species that arrived in North America in the early 1980s. Not only do these parasites feed on the bees’ fat stores, but they also transmit a virus that leads to the deformation of their wings. As a bee’s health declines, it becomes more susceptible to contracting other illnesses. If a hive becomes infested with these mites, it might be enough of a threat for the healthy bees to bug out, leaving their hivemates behind. 

To fight back against Varroa, researchers looked to Snodgrassella alvi, a symbiotic bacterium found within the gut of honey bees. Genetic modification of the microbes enabled them to destroy the mites from the inside out through RNA interference (RNAi). The engineered bacteria produced double-stranded RNA that induced the mites to launch an RNAi defense to destroy those sequences. Because the bacterial sequences matched those from the varroa genome critical to the mites’ survival, the silencing mechanism wiped out the mite transcripts as well, killing the parasites

“It is a bit like a customized medicine for honey bees,” Jeffrey Scott, an insect toxicologist at Cornell University who was not involved with the study, tells Science. “Being able to engineer a gut microbe and specifically regulate gene expression in the host has enormous implications.”

By using S. alvi as a manufacturer, the team was able to provide a continued supply of the RNA, providing a useful window for the bees to fight back against the mites. The effects lasted for the duration of the 15-day-long experiment and bees with the altered bacteria were 70 percent more likely to kill mites within 10 days than those without it.

“If the technique works in the field, that could be the end of Varroa and the viruses,” Robert Paxton, a bee ecologist at Martin Luther University who was not involved with the study, tells Science.

While the results of this small-scale experiment are encouraging, the method won’t be used in the wild anytime soon. Releasing bacteria with gene-silencing potential invariably raises containment questions along with concerns that mutations may cause unintended consequences.

“You’re turning off genes [via RNAi],” honeybee epidemiologist Dennis vanEngelsdorp of the University of Maryland who was not involved with the study tells Science News. “There has to be a very healthy debate about ‘how do we regulate this?’” 

Lisa Winter is the social media editor for The Scientist. Email her at lwinter@the-scientist.com or connect on Twitter @Lisa831.