Will Bugs Warn of Vineyard Mildew?

Research under way with bees and beetles that identify powdery mildew in grapes

by Paul Franson
powdery mildew
Powdery mildew attacks a grape cluster. Source: University of Kentucky
Napa, Calif.—Every farmer knows of the importance of honeybees in fertilizing plants. Now researchers at the University of California, Davis, and Los Alamos National Laboratories find they also may help provide an early warning of powdery mildew.

They’re hoping this research will help them eventually develop a “smart nose” that can warn of the fungus and help both to destroy it in vineyards and reduce unneeded application of fungicides.

In related work, researchers are also finding that a widely distributed beetle also can help detect powdery mildew, and perhaps even reduce its incidence.

Powdery mildew is a huge problem for grapegrowers, and the last few years have brought cool, wet weather that exacerbates its incidence.

The bee research arose from interest by UC Davis professors Douglas Gubler and Andrew Sutherland, combined with work by the Los Alamos lab in developing ways to detect bombs and drugs in luggage. Gubler presented the research to a meeting of the Napa Vit Tech group Wednesday.

Sutherland, who received his doctorate in entomology from UC Davis and is a researcher with the Department of Plant Pathology, told the group that bees have excellent chemosensors on their antennae, so they're able to detect organic molecules. Plants that are threatened by predators or pathogens—like all living things—emit characteristic and perhaps unique volatile organic compounds (VOCs).

Using Ivan Pavlov's method of classical conditioning, researchers have learned that they can teach bees to detect these VOCs, in effect associating infected plants with a sugar reward. They respond by extending their probosci.

Harnessing bees’ abilities

The bees are placed in “harnesses” for these tests. After they learn to detect the odor, the bees are placed inside a box and taken to the field, where they extend their tongues in expectation of a sugar reward if they encounter the same compound. This is measured and recorded by sensitive instruments.

Gubler said it takes only a few hours for the bees to learn their tasks, although unfortunately, honeybees have short lives and typically die within a few days.

Initially, the researchers found that the bees detected extraneous odors in field trials, but this potentially could be minimized to detect the desired VOC by training them in the presence of other smells.

Along with this work, researchers Robert M. Wingo at Los Alamos National Laboratory Chemistry Division and Kirsten J. McCabe of Los Alamos National Laboratory Bioscience Division are attempting to identify the critical volatile compounds. They’ve identified at least two unrecorded compounds that could be unique to the powdery mildew.

Gubler said the aim is to create an instrument that detects the powdery mildew early, but said it won’t be “bees in a box.”

Treating—or failing to treat—powdery mildew is very expensive. The work is consequently being funded by a $450,000 grant; it has 18 months to go.

See a video of the experiment here.

Beetles also may reveal powdery mildew

powdery mildew
Unlike most other beetles known to destroy fruit crops, a tiny beetle similar in appearance to the ladybug feeds on powdery mildew.
Gubler also reported on other work using the presence of a type of beetle to detect incidence of powdery mildew. Researchers have found a small beetle that looks like a camouflaged ladybug and feeds on powdery mildew. When spotted, it indicates the fungus is present in a vineyard. The beetle is a fungus-eating member of the coccinellid family called psyllobora vigintimaculata.

No one is sure where the beetle overwinters or how far it can fly, but it appears when powdery mildew is present, and there’s a strong relationship between its population and the severity of powdery mildew infestation.

Gubler said that using traps and manual counting, the beetle was never found unless powdery mildew was present, and if the beetles were found, there was mildew. He said it’s fairly easy to trap and identify them using yellow sticky traps.

“If I found the beetles, I’d apply anti-fungal oil,” he said. He even postulated that millions of the beetles could be used to gobble up powdery mildew. “They could start at one end of the valley and eat their way to the other,” he said.

He noted that this research has been done without funding, so it’s taking some time. Dogs also are being trained to detect the mildew, but training is very expensive, a few hundred thousand dollars per dog, according to Gubler.

In added comments, Gubler mentioned the success in treating powdery mildew with chemicals, including organics and some not yet approved. He warned, however, that mildew quickly develops resistance to threats. “Rotate your treatments using different types of chemicals; don’t just depend on one, no matter how well it works on one application.”

He added that none of the “soft” (organic) chemicals worked well last year, which he said had the highest incidence of powdery mildew he’d seen.
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