A virus that attacks grapeleaf skeletonizer – includes related articles on skeletonizers, registering viruses
Richard Steven Street
A virus that attacks grapeleaf skeletonizer
Wouldn’t you appreciate a pesticide that effectively controls the western grapeleaf skeletonizer (Harrisina brillians) and that is also non-toxic, costs pennies per acre and that allows immediate worker reentry into vineyards where it’s been applied? Sounds too good to be true, doesn’t it?
But it is true. The only problem is this pesticide is not a chemical. It’s a virus. And that is both its hope and curse.
One man who is betting on this virus is U.C.-Riverside entomologist Vern Stern, a well-known field researcher who has been developing the skeletonizer virus. Stern hopes to obtain EPA approval for his skeletonizer virus. But he doubts grape growers will ever be able to use it.
“The problem is with that word virus,” explains Stern, in what has become an oft-repeated speech. “When people hear it, they just go nuts. They start thinking about some ‘Andromeda strain,’ just like in the movie by that name. More than anything else, that’s why we’ve had to move slowly on this.”
Until recently, Stern was so fearful of adverse public reaction to his skeletonizer virus work that he kept his research under wraps. But six years of field experiments have convinced him that the skeletonizer virus ought to be registered for use on grapes. The virus, he says, could quickly eliminate the skeletonizer as a major pest, while also becoming a cornerstone in a program for total biological control of pests.
Last fall (1988), Stern traveled to Washington, D.C., to discuss registering his skeltonizer virus. He presented evidence showing the virus was naturally occurring, specific to the skeletonizer and no hazard to anyone or anything.
“Hell,” he says, holding a transparent vial of the virus up to an illuminated magnifier and eyeing it carefully, “you can even take a handful of this stuff and eat it. No problem. Try doing that with any other pesticide.”
And the EPA response? According to Stern, the regulators were unimpressed. “Our meeting was just a big waste of time,” says Stern. “I got nowhere. Their toxicology guys got up and left. And I got up and left. I might as well have been talking to a stone wall.”
At the end of 1988, EPA ruled that Stern’s skeletonizer virus would have to be evaulated just like any other “pesticide.” Toxicological tests must be done, as well as residue studies and a battery of associated tests. Such tests, argues Stern, are not only unnecessary, they are so expensive that Stern can’t possibly afford to finance even one of them.
To Stern it seems like a Catch-22 situation. “If you are a chemical company, you can use past data gathered on one chemical to register a similar one,” says Stern. “So I presented data from research and registration of the coddling moth virus, which is now a major biological control. What did the EPA say? You can’t do that. The viruses are not similar enough, even though they’re both granulosis viruses.”
If Stern were working with a chemical that showed such great potential for controlling any other grape pest, he could expect funding and support from a joint registration arrangement with a chemical company. But the skeletonizer virus lacks the commercial potential required to attract such support. “You aren’t going to sell a lot of something that works at minute rates — fractions of a gram per acre — and is applied to only a small part of California’s table grape and wine grape vineyards,” says Stern. “No chemical company is going to fund my work.
“It’s very strange,” says Stern, with unrestrained bitterness. “The EPA is supposed to protect us from pollution. But is it doing that in this case? I don’t think so. In fact, by holding up this virus, the EPA is forcing growers to continue using chemicals.”
Stern isn’t giving up. Two years ago EPA limited him to treating a single 10-acre block in one location. Because the restriction severely hindered his ability to monitor how well the virus spreads among the skeletonizer population, Stern has pushed hard to expand his spraying to 40 acres dispersed through the valley. EPA didn’t okay the larger acreage; but it did allow him to disperse his spraying — a row here, a section of vineyard there — so long as he did not go above the 10-acre limit.
Stern’s expanded experimental spraying yielded some unexpected and interesting discoveries. The first is that the virus works at even lower dosages than Stern had predicted. He now sets the effective application rate at .04 grams per acre. Even at that rate, he reports killing too many skeletonizers.
Not killing all the skeletonizers is important because of Stern’s second discovery: the virus doesn’t just work on skeletonizer larvae: it has residual effects on adult skeletonizer moths. Adult female skeletonizers surviving a treatment produce only 25% of the normal amount of eggs, most of which die upon hatching. Many females don’t even lay eggs. Most importantly, unexposed female skeletonizers mating with virus-infected males pick up the virus and lay half the normal eggs, which again die out in huge numbers.
“This virus is transmitted from one generation to another,” says Stern. “It’s a kind of AIDS of the insect world.”
Although Stern hopes the National Academy of Science of the National Institute of Health will lend support to his skeletonizer granulosis virus registration campaign, he doubts that will happen. “The skeletonizer is not a big enough problem to interest those people unless it’s evaluated as part of a larger strategy of looking at viral controls,” he says.
Stern also is pessemistic about prying the EPA loose from its anti-virus position. The main problem, he says, is that he only gets to see the lower-level bureaucrats. “They basically read definitions out of books and then say I’ve got to do this or that to comply with this or that paragraph of their book of regulations,” he explains. “Maybe we can kick the discussion to a higher level and get away from all this nonsense.”
Meanwhile, Stern is continuing his spraying program. Last fall, when we found him east of Delano, Stern was towing his portable spray rig from one infested vineyard to another, spraying a corner here, a section there, hoping in this way to distribute his virus around the valley and whittle away at the skeletonizer population.
“We’ve got to get this registered,” he remarked while spraying a patch of Red-globe grapes near Richgrove. “It’s not like something that’s been genetically engineered. This is a naturally occurring thing. I wish the EPA would just get that through its collective thick skull.”
(Richard Steven Street is a freelance writer and photographer who lives in San Anselmo, Calif. He is a regular contributor to California Farmer, among other publications.)
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