- Author: Ben Faber
New fungus strain could provide a chemical-free method to help honey bees
PULLMAN, Wash. -- A new fungus strain could provide a chemical-free method for eradicating mites that kill honey bees, according to a study published this month in Scientific Reports.
A team led by Washington State University entomologists bred a strain of Metarhizium, a common fungus found in soils around the world, to work as a control agent against varroa mites. Unlike other strains of Metarhizium, the one created by the WSU research team can survive in the warm environments common in honey bee hives, which typically have a temperature of around 35 Celsius (or 95 F).
"We've known that metarhizium could kill mites, but it was expensive and didn't last long because the fungi died in the hive heat," said Steve Sheppard, professor in WSU's Department of Entomology and corresponding author on the paper. "Our team used directed evolution to develop a strain that survives at the higher temperatures. Plus, Jennifer took fungal spores from dead mites, selecting for virulence against varroa."
Jennifer Han, a post-doctoral researcher at WSU, led the breeding program along with WSU assistant research professors Nicholas Naeger and Brandon Hopkins. Paul Stamets, co-owner and founder of Olympia-based business Fungi Perfecti, also contributed to the paper. Stamets is a fungi expert, well-known for using several species in applications ranging from medicine to biocontrol.
Varroa destructor mites, small parasites that live on honey bees and suck their "blood," play a large role in Colony Collapse Disorder, which causes beekeepers to lose 30-50% of their hives each year. The mites feed on bees, weakening their immune systems and making them more susceptible to viruses.
The main tools beekeepers use to fight varroa are chemicals, such as miticides, but the tiny pests are starting to develop resistance to those treatments, Naeger said.
Metarhizium is like a mold, not a mushroom. When spores land on a varroa mite, they germinate, drill into the mite, and proliferate, killing it from the inside out. Bees have high immunity against the spores, making it a safe option for beekeepers.
Stamets, who did some of the initial testing with Metarhizium that showed the fungus couldn't survive hive temperatures, was impressed by the work done by the WSU researchers.
"Science progresses through trial and error, and my technique wasn't economical because of the hive heat," he said. "But Jennifer did enormous amounts of culture work to break through that thermal barrier with this new strain. It's difficult to really appreciate the Herculean effort it took to get this."
Han and Naeger screened more than 27,000 mites for levels of infection to get the new strain.
"It was two solid years of work, plus some preliminary effort," Han said. "We did real-world testing to make sure it would work in the field, not just in a lab."
This is the second major finding to come from WSU's research partnership with Stamets involving bees and fungi. The first involved using mycelium extract that reduced virus levels in honey bees.
"It's providing a real one-two punch, using two different fungi to help bees fight varroa," Stamets said. "The extracts help bee immune systems reduce virus counts while the Metarhizium is a potentially great mite biocontrol agent."
The next step is to seek approval from the Environmental Protection Agency to use Metarhizium on hives used in agriculture. The team must also finalize delivery methods for beekeepers to apply the fungus in hives.
"We hope in 10 years that, rather than chemical miticides, Metarhizium is widely used to control Varroa mites," Sheppard said. "And that the mite problem for beekeepers has been significantly reduced."
The team thinks the methods they developed to evolve Metarhizium for varroa control could be used to improve biocontrol agents in other crop systems as well.
A female Varroa destructor Anderson & Trueman, feeds on the hemolymph of a worker bee. The mite is the oval, orange spot on the bee's abdomen. Photograph by James Castner, University of Florida.
- Author: Christina Herrick
This article is from Florida Grower News. Thanks for Jim Lloyd-butler for pointing it out.
A sister species of the Varroa destructor mite is developing the ability to parasitize European honeybees, threatening pollinators already hard pressed by pesticides, nutritional deficiencies, and disease, a Purdue University study says.
Researchers found that some populations of Varroa jacobsoni mites are shifting from feeding and reproducing on Asian honeybees, their preferred host, to European honeybees, the primary species used for crop pollination and honey production worldwide. To bee researchers, it's a grimly familiar story: V. destructor made the same host leap at least 60 years ago, spreading rapidly to become the most important global health threat to European honeybees.
While host-switching V. jacobsoni mites have not been found outside of Papua New Guinea, Purdue researchers Gladys Andino and Greg Hunt say vigilance is needed to protect European honeybees worldwide from further risk.
“This could represent a real threat,” said Andino, a bioinformatics specialist with Information Technology at Purdue. “If this mite gets out of control and spreads, we might have another situation like V. destructor.”
Varroa mites are obligate parasites, meaning their lifecycle is inextricably entwined with that of their bee hosts. The mites can do serious damage to their hosts' health due to their relatively large size – “think of a tick as big as your fist,” Hunt said. Mites latch on to bees and feed on their hemolymph, insects' rough equivalent to blood, leaving behind open wounds that are susceptible to infection. They can also transmit diseases such as deformed wing virus and have been linked to colony collapse disorder.
To gain insight into the biology behind V. jacobsoni‘s host switch, Andino and Hunt, professor of behavioral genetics and honeybee specialist, studied the differences in gene expression between V. jacobsoni mites that fed and reproduced on Asian honeybees and those that parasitized European honeybees. Knowing which host cues mites respond to and the genes involved could lead to potential control strategies, the researchers said.
“If we can understand the mechanism, we might be able to disrupt, block, or manipulate that,” Andino said. “But first we have to understand what is happening and which genes are involved in allowing the mites to shift to a new host.”
Andino and Hunt said the mites' leap to European honeybees likely occurred within the last decade. Previously, V. jacobsoni mites were occasionally found on European honeybees but seemed unable to produce healthy offspring, limiting their destructive capacity.
Catching the host transition in its early stages will allow researchers to continue to investigate the complex genetic details behind the shift and monitor infected European honeybees, Hunt said.
“This happened once with one species of mite, and it looks like it's happening again. Maybe if we catch this as it's beginning, we'll be able to figure out why it's happening or, down the road, stop it.”
The paper was recently published in BMC Genomics.
Funding for the study and an ongoing genome-sequencing project was provided USDA's-Agricultural Research Service and the USDA National Institute of Food and Agriculture.
This article is from Florida Grower News