This space has continued to follow the discouraging advance of the Spotted Wing Drosophila (SWD), a destructive pest of cane fruits, cherries, strawberries, table and wine grapes, nectarines, among many others. Now with growing season well under way, the time has come for an update.
Firstly, for critical background on the original pioneering field work of Mark Bolda, farm advisor from of the University of California Cooperative Extension, and the historical and cultural dimension from Martin Hauser, Associate Insect Biosystematist with the Plant Pest Diagnostics Lab, California Department of Food & Agriculture (CDFA), Sacramento, please see my Spotted Wing Drosophila Emergency Meeting Results.
To get a sobering perspective of what is at stake for American growers, we read in the March 31st issue of the Australian paper Weekly Times, Now,
IMPORTED fresh fruit from the United States is unlikely to make its way to stores this winter after Biosecurity Australia invoked ”emergency measures” today in a bid to keep out a damaging pest.
BA announced it would begin a pest risk analysis for the Spotted Wing Drosophila fly (Drosophila suzukii), which has caused tens of millions of dollars damage to blueberries, raspberries, blackberries, strawberries, cherries, peaches, plums and grapes in the US in the past two years.
Australian Table Grape Association chief executive Jeff Scott said there was enormous concern about the pest which had the potential to devastate the table grape industry, and others, if it was allowed into the country.
Speaking from Canberra where he has been meeting with BA officials to discuss a range of quarantine issues, Mr Scott said table grape imports from the US had effectively been halted.
‘They won’t start again until BA is satisfied the US has demonstrated appropriate control measures,’ he said.
Neither has Europe been spared. In February the European and Mediterranean Plant Protection Organization (EPPO) put the SWD on Alert status. A quarantine of American imports may follow.
“Drosophila suzukii is an Asian pest of fruit crops which has almost simultaneously been introduced into North America and in Italy (in 2008 and 2009, respectively). Because the pest has a high potential for spread and can cause economic damage to many fruit crops, the EPPO Secretariat decided to add D. suzukii to the Alert List.”
The CDFA Weighs In
From the California Food and Agriculture’s Plant Pest Diagnostic Center–Entomology Laboratory may be read Martin Hauser’s just posted summation of SWD’s preferred hosts here in California and in Japan.
“The preferred hosts in California are various cherries and raspberries, but also strawberries, nectarines, boysenberries, Asian plums, plums, plumcots, Satsuma plums and blackberries. In Japan significant damage is reported from blueberries, as well as grapes and mulberries.”
Of considerable interest is the phrase ‘preferred hosts’, because the SWD’s potential for damage is not, therefore, limited to CDFA’s listed fruits. In fact, the SWD is now well known to infest vineyards in Oregon. From Oregon State University, in an Oct. ‘09 article titled Fruit Fly Pest Identified In Wine Grapes we read,
“A newly recognized pest in Oregon continues to concern fruit growers and researchers with the recent discovery of a Spotted Wing Drosophila fly in a sample of Willamette Valley wine grapes.
Since the tiny fly, Drosophila suzukii, was first confirmed in Oregon less than two months ago, there have been an increasing number of reports of its occurrence in a variety of fresh fruits, including blueberries, peaches, raspberries, strawberries, blackberries, plums – and now grapes, according to Amy Dreves, a research entomologist at Oregon State University.
‘This is an insect that, up to last year, had never been seen in the continental United States,” Dreves said. “Now, suddenly, it is showing up in lots of places.’”
[Please also see Oregon Dept. of Ag. Plant Division, Insect Pest Prevention and Management page]
And from a Washington State University Extension paper Spotted Wing Drosophila Could Pose Threat to Washington Fruit Growers:
“Spotted wind drosophila, Drosophila suzukii, was introduced into California in 2008 and has rapidly established populations along the Pacific Coast. There have now been confirmed infestations of the fly in the Willamette Valley, detections in Hood River, Oregon, and detections throughout western Washington, in locations including Bothel, Olympia, Puyallup, Seattle, Stevenson, Vashon Island, and Mount Vernon. [R]ecent evidence indicates they may feed on wine grapes.”
Further, from the EPPO web page linked here and above we may read a greatly expanded host range.
“D. suzukii has a wide host range and can attack many fruit crops, including small fruit crops, fruit trees and grapevine. Its host range includes: Actinidia spp. (kiwis), Diospyros kaki (persimmons), Ficus carica (figs), Fragaria ananassa (strawberries), Malus domestica (apples), Prunus avium (sweet cherries), P. domestica (plums), P. persica (peaches), Pyrus pyrifolia (Asian pears), Rubus armeniacus (Himalayan blackberries), R. loganobaccus (loganberries), R. idaeus (raspberries), R. laciniatus (evergreen blackberries), R. ursinus (marionberries), and other blackberries (Rubus spp.), Vaccinium spp. (blueberries), Vitis vinifera (table and wine grapes).”
All things being equal, table and wine grapes have been confirmed as hosts in Oregon and Europe. It is strongly suspected to be a potential threat to the Australian grape industry. In light of these announcements it remains a mystery why the CDFA continues to use the vague couplet ‘preferred hosts’. The phrase seems to encourage the grower of Vitis vinifera that they need not to be concerned. That is not, in my opinion, the most conscientious approach.
Here’s why. The pest’s life cycle centers on the female SWD piercing the skin and laying eggs within a ripe fruit. Owing to her diminutive size, so, too, does the break she makes in the fruit skin go undetected to the unaided eye. As the larva develops into progressively larger instars, feeding on the pulp as it grows, it remains protected from pesticides while inside the fruit. Equally as important as the fruit’s eventual destruction is the obvious fact that the site of the initial breach is clearly a pathway for infectious pathogens, of fungi and bacteria. Inasmuch as fruits may contain multiple larvae from multiple females, grapes harvested with significant laval loads may, therefore, also be contaminated with significant pathogen loads, pathogens potentially capable of altering the wine’s final phenolic expression.
Moreover, of equal concern is common vineyard hygiene. Dropped fruit, for example, now becomes a potential food reservoir for successive generations of SWD. Far from being a hypothetical matter, and regardless of whether grapes are a ‘preferred host’, it appears only proper that Vitis vinifera and associated vineyard hygiene practices deserve greater attention.
A final note. Dr. Martin Hauser informs me that his sources have not re-confirmed SWD in Spain this year. EPPO’s passing reference to the same, citing Dr. Hauser’s work, may now be considered up to date.
Admin
This is the third and final part of my sterling interview with Climatologist Gregory V. Jones. Here he discusses many of the practical agricultural effects climate change ushers in. Behind general, global headlines, the noisy political debates, there are very real changes taking place that simply escape our immediate, everyday notice. However attractive as a spiritual philosophy, ‘living in the moment’ has a clear downside. For like the sailing stones of Death Valley, despite no one having seen the phenomenon, surely they do move.
On a different note, man is a pest and pathogen vector, of course. During the course of our talk the spotted wing drosophila (SWD) fly came up, one of the most recent destructive insects to invade the United States, in this instance in refrigerated containers from Asia. It is a pest about which I have written a number of times. Today an AP story crossed my desk about the wherefores and the whys of yet another invasive pest, the European Grapevine Moth. In this instance it is strongly suspected the bug was brought to Napa by a winegrower smuggling cane cuttings from France. What goes around, comes around.
Part 1 On Wine and Climate Change
Part 2 The Science and Politics of Climate Change
Admin Perhaps you could speak more about insects and new pathogens…
Gregory V. Jones This is all about environmental thresholds, but it is also tied to people. The environmental thresholds that we know basically say that a given vector or a given bacterium or disease, whatever it may be, has some kind of environmental component. It can’t exist where it is either too hot or too cold. Or where there is not enough moisture. And so, as temperature and moisture conditions change from place to place, what that does is it changes the environmental geographical patterns that any of these vectors, pests, bacterium, diseases can exist in. So it is a natural kind of consequence of changing climates. The compounding factor is when you throw in the human component, the fact that we move things around very efficiently through our vehicles and transport of material and goods. So while there might be some great geographical barriers to the movement of material, and I’ll Oregon as an example, the mountains of Northern California have been very good at keeping certain things out of our state. Some people would laugh and say it doesn’t fully keep the Californians out (laughs)…
Yeah. My family nearly moved to Oregon. We were not given a warm reception!
GJ So the idea would be that the geographical barrier there, the mountains and the cooler conditions, would keep out or hinder a lot of pest and/or diseases from potentially coming to Oregon. But because humans travel, and we carry things around with us, whether they be plant material or fruits or soils, we can take things with us and cause an issue that might not have been there otherwise. There are a lot of examples. Oregon right now is concerned about mealy bugs. Mealy bugs are known to be hitting California vineyards pretty hard right now in terms of carrying leaf-roll virus that is in some cases necessitating large re-plantings of vineyards. So Oregon is all about quarantining material. What happens when a grower goes down to visit his cousin in Lodi and grabs a bundle of cuttings and brings them up, and they’re infected, and plants them? That infected material gets moved around. And we have an issue.
This has happened very recently with the spotted wing drosophila (SWD) about which I’ve written. What began as an infestation in Washington cherries quickly spread through out the United States. Actually, it had already spread, having initially been imported from Asia to Florida. The speed of the fruit fly’s life cycle is subject to temperature. So if you import a fruit in refrigerated containers and distribute it to markets around the country, the degree to which the damaging effects of the new pest are unknown, the ruined fruit is simply discarded into dumpsters and landfills. Now you have SWD everywhere. So widespread has the pest become in so short time, that the USDA has decided that a quarantine would be of no practical use.
GJ Exactly. People are talking about it big time in Oregon right now as an issue for many of the berry crops we have up here. So if you think about it, people are part of the problem. But yet there are these environmental limits: if the climate becomes warmer, dryer, moister, whatever those requirements are, and it meets that insect’s or disease’s needs, it is going proliferate. We shouldn’t expect it to be this ideal world, that we’re never going to see movement and change of that kind of thing. It’s going to happen.
Many of these other consequences when one discusses climate change, insects, disease vectors, new epidemiological patterns, these don’t often enter into the debate. Talk centers on temperature almost exclusively.
GJ And you’re right. This goes back the perception based thing as I told you. The idea that we’re in the immediate here and now, human-based mental framework. If you say to somebody temperature have warmed 2 degrees over the last 20 years they’ll say ‘Well, that’s great! I’m really enjoying it!’ What they don’t understand are the underlying things that happen to us within our environment, with things like insects and/or pests, and/or water availability, soil erosion, soil salinity, all that kind of stuff. I think that there is a real issue there: The magnitude of that number [2 degrees], I’ve even been quoted about saying this, we have a number problem. We all talk about how temperatures have gone up by whatever it is, 1, 2, 3 degrees regionally, but it is that number that humans take to mean it’s no big deal. But they don’t understand the entire environmental ramifications of it.
Yes. In one of your co-authored articles there is an interesting detail mentioned in passing about wine styles. The Parker palate has often been cited as driving winemakers to produce higher alcohol, more fruit forward wines. But in one of your papers you refer to an author who states that as much a 50% of the high alcohol wines could potentially be attributed to climate change. Could you talk about this?
GJ This is kind of a statistical relationship. If you throw data variables into a pot and you try to find out what describes what amount of variability, that’s pretty much what falls out. But let me tell you what I think is the background, and I would tell Parker to his face the same thing. I’ve even seen him write somewhere that climate change hasn’t changed these styles, so to speak, but the issue comes down to this, and it’s pretty damn straight forward: In 1960, 1970, you couldn’t produce the same styles of wines in Napa that you produce today. Period. End of sentence. You just couldn’t do it! The climate was too cool, you couldn’t have extended hang time because the climate wouldn’t let you. Period. So, while Parker, the Parker palate has driven wine styles to be different today than they were in the ’70s, you can’t say that the climate and maybe some other factors didn’t come into play with it. If you tried to do the hang time that they’re doing today back in 1970, it would not happen. You look at the issue of methoxypyrozines [See pgs.87-88 of R. Jackson's Wine Science Admin], well, we’ve been able to kind of manage that, the green flavors, through a lot of different characteristics, but the reason methoxypyrozines were also more prevalent back in the ’70s and ’80s is because the climate didn’t ripen the damn fruit! I can’t believe that there are that many people out there that think that climate doesn’t mean anything in this puzzle. But yet they are willing to say that climate is very important for how they produce this delicate style, or whatever it may be.
On a slightly different tack, for many wine drinkers just to become acquainted with the broad strokes of a concept like terroir passes for a kind of knowledge. They are comfortable with knowing just that, and going no deeper. Most people believe that terroir is the agricultural equivalent of some horrid neo-romantic landscape, terroir as painted by Thomas Kinkade. That is as far as perception is willing to go.
GJ Here’s another thing I think about the nature of climate in parts of California, and I’ll use Napa as an example because I think it’s really played out there. So the fruit is being left out on the vine for a long time. What people are trying to do is get this ideal flavor profile relative to it. Well, the issue there is that if the grape was being grown in its ideal climate then sugar ripeness and flavor ripeness would happen at the same time. Arguably, most people would agree that would be the case. Most years sugar and flavor ripeness would happen at the same time. In some years a little variability might cause it to be a bit disconnected, but not disconnected to the point that you’ve got to ripen something to 28 degree brix while you’re waiting for this ideal flavor profile. That’s just overdone!
And part of what I think is producing some of this is the fact that the growing seasons are just quite different today than they were before. Minimum temperature have gone up tremendously. This causes a major difference in respiration and metabolism in the vine and in the fruit. I think that because minimum temperatures have gone up we’re seeing less and less green flavors than we ever have. But I also think what that does is that when nighttime temperatures… put it this way, when the diurnal temperature range is sufficient, cool nighttime temperatures sets in flavor development. That is the final cue for the vine and the berries to do their thing. And if you have a place where you’re growing grapes and the nighttime temperatures are elevated, and that cue to get sugar and flavor in line, if it doesn’t happen? Then you have to hang the fruit. You have to hang it for a long time.
I really think that is part of the puzzle. It’s probably a bigger issue for some varieties than for others. For example, Pinot Noir and Tempranillo are two varieties that just would not do very well in a high nighttime temperature environment, while Cabernet Sauvignon and Merlot do a little bit better.
Yes. As I move toward a kind of finish, I was curious about your own drinking preferences.
GJ Honestly, I try everything. I don’t necessarily have the best palate in the world. Maybe I just haven’t figured out yet how to train it. But I think it’s pretty good. What I really, truly enjoy is the marriage of wine and food. I enjoy the fact that there many different styles and varieties of wine that contribute to that enjoyment. What I don’t like is wine that doesn’t go with food, that doesn’t have some kind of balance of alcohol relative to acidity. It just doesn’t work.
Of course, that is one of the difficulties with tasting notes and certainly scoring wines. It is just plain silly when one Cabernet after another requires that you essentially have a burned charcoaled steak every night. Wine is today often understood as a free-standing food in its own right. Many tasting notes would seem to suggest you’re eating bacon, raspberries…
GJ I buy a lot of local wine. I support the Oregon wine industry where I can. But when I go to the store I love playing the varietal game, finding something I’ve never seen; or maybe it’s a variety I have seen before, but from a different area. So I play that varietal game to try and get a broader palate and to understand the variety. I don’t specifically look at the alcohol content and say I’m not going to buy that. However, there are some varieties that a higher alcohol content typically means that I just won’t buy it. And Cabernet Sauvignon is one, Zinfandel is another. They just don’t work for me. So, even though I’m not looking specifically for a high alcohol level on a wine, there are some varieties that I do.
But the bigger thing is that I just love to try different varieties. I had a bottle of wine the other night, I don’t even know how to say the variety, B-o-n-a-r-d-a. It’s grown in Argentina. I’ve never had this variety before. It wasn’t necessarily the cleanest and best wine I’ve ever had, but it was unique, it was different. That’s what I appreciated about it.
Yeah, I understand. I’m baffled by folks who stick to the same variety. I don’t get it. The point is to drink as widely as is possible, not only for understanding but for pleasure. The obsession with variety labeling as well has always been puzzling to me.
GJ Yes, appreciate the surprise and anticipation component of it. If I buy a wine that is something I have never seen or had before and it’s not good, if I have to use it to cook with (or dump it out if it’s really not good), that’s OK. That’s part of the experience. But, boy, it is the gems that stand out that make you say, “Yeah, this is what it’s all about!”
Exactly right. That’s one of the reasons I’m doing the film on Portuguese wines with Virgilio. There are so many flavors completely unknown to most folks here in the states. Perhaps people can be persuaded to ask for them.
Well, it has been an extraordinary pleasure to speak with you. Is there anything you’d care to add? What about your father’s wines? How is his work coming along?
GJ In my personal opinion? His wines are very good. We came to Oregon wanting to grow Iberian varietals and so we produce mostly Tempranillo, Grenache, Albariño, Tinta Cão, and Tinta Amarela. We make some very traditional Iberian wines from them. And I think one of the interesting things is that across everything we make I don’t know that I’ve ever seen one place able to produce that wide of a range of wines with that kind of typicity. Maybe I should chalk it up to my dad, how he grows the grapes, his attention to winemaking, but I’ve had other people say the same thing. I’ve heard them out of context that they were just amazed.
And to do that in Oregon, a place that’s known for Pinot Noir, is something special. I tasted our 2009 Albariño last night. It had only been in bottle for few hours, but it is liquid gold. That’s the best thing I can say. It’s liquid gold.
END
For further reading
Oregon Wine Press
Climate and Wine: Quality Issues in a Warmer World
Admin
Dr. Helmuth Rogg, entomologist for the Integrated Pest Prevention Management section of the Oregon Dept. of Agriculture Plant Division, has confirmed that both table and wines grapes have been attacked by the Spotted Wing Drosophila (Drosophila suzukii). In an email to this blog, Dr. Rogg wrote,
“[W]e hand picked wine grapes and table grapes from various vineyards in the Salem area and hatched out the SWD. So, we do know that SWD attacks wine and table grapes but we do not know the level of infestation, difference in variety, crop damage, etc. Unfortunately, we cannot conduct these experiments. We passed on our information to our colleagues from OSU and its Extension Service.”
A second email provided me reads,
Oregon Department of Agriculture has confirmed the presence of Drosophila suzukii in the following 11 counties of Oregon:
Multnomah
Washington
Yamhill (new)
Clackamas
Marion
Polk (new)
Benton
Lane
Douglas
Hood River
Umatilla
We also have confirmed the following hosts:
Strawberries
Cherries
Blackberries
Blueberries
Raspberries
Plums
Peaches
Table grapes
Wine grapes
(10/14 Update.) Please also read this 10/13 release from Oregon State.
All the fruit listed above have also been attacked by SWD here in California, with the notable exceptions of table grapes and wine grapes. I wrote a follow-up email about this development to Dr. Martin Hauser, entomologist with the California Dept. of Agriculture. He responded,
“that is bad news… I still do not have any confirmed SWD from California grapes. With the first batch of suspects, the PCR failed [owing to a technical issue]. But maybe I will have new news tomorrow.”
PCR is short for polymerase chain reaction, a DNA sequencing technology. It clearly differs from Dr. Rogg’s more field-oriented approach. The question begs whether the simple gathering of grapes from a variety of suspect California vineyards and allowing SWD larvae, if present, to emerge, might prove more diagnostically helpful. Which is to say that ‘confirmation’ of SWD in California wine and table grapes should properly be done using with both field and lab taxonomic identification protocols.
Important gains from primary field research have already been accomplished by Mark Bolda of the University of California Cooperative Extension. His focus, though principally cane berries, has resulted in great insight into early detection of the pest, how to set up traps, the appropriate baits, pesticides, both conventional and organic, and field sanitation requirements. For a recent account of his work please see my August 30th post Spotted Wing Drosophila Emergency Meeting Results and follow the various links.
Very important questions remain. What is the intensity of vineyard infestation? Are grapes a ‘preferred’ host for SWD or a fruit of last resort? What was the ratio, if any, of damaged vs. intact grapes in the Oregon samples? What grapes varieties are especially vulnerable? What ought a grower do with respect to vineyard sanitation? Will the common practice of ‘dropping’ fruit have to controlled? Will the composting of grape pomace have the unintended consequence of maintaining or even cultivating damaging populations of SWD? The list goes on, as must the research.
One of the more serious questions, if and when SWD is found in California wine grapes, is whether the presence of larvae in the interior of harvested fruit might adversely affect some quality of the must during fermentation or taste in the finished wine. This would be in addition to the skin break created by the laying of the egg, of course, clearly already a pathogen pathway. We already know that common fruit flies are effective vectors of Brettanomyces and other spoilage yeasts. Similarly do Ladybugs, very fond of vineyards, produce chemicals capable of ruining fermenting wine. This new kind of MOG (material other than grapes), the Spotted Wing Drosophila larvae, will be of pressing interest to winemakers in the very near term.
—– More breaking news on another exotic pest just detected in Napa vineyards, the European Grapevine Moth (Lobesia botrana).
Admin
10/12 Please see this urgent update.
9/22 Correction I wrote to Terry Witt, Executive Director, of Oregonians For Food and Shelter, the organization that appears to have been the original source for the ‘confirmation’ of Spotted Wing Drosophila in Oregon grapes. I asked him for an elaboration of the results of the meeting held earlier today. He wrote,
“We just had the meeting where ODA, APHIS and OSU were present to discuss what is know about the Drosophila suzukii. It appears that the “news” about it being confirmed in Oregon grapes may have come from our email alert about the meeting and at this time has NOT been verified, but growers have just now begun looking at all fruit across the state.’
I further contacted Helmuth Rogg, Entomologist, IPPM Program Manager, Plant Division, of the Oregon Department of Agriculture (ODA). And he wrote,
“Dear Ken,
Yes indeed, today we held an informational meeting on the SWD which was attended by industry, OSU, USDA and USDA-ARS.
And no, we have not recorded SWD in grapes!!!
There is no official record of SWD from grapes. So far we collected SWD from blackberries, blueberries, raspberries, and peaches. We collected SWD from about 6 counties, mainly in the Willamette Valley, of Oregon.
We will prepare a public website on which all interested parties can contribute and receive information. The main objective of this website will be to present information, data and results of work done by ODA, OSU and USDA-ARS. As soon as we have it ready to go live, I will let you know.
We have more information on our Oregon Dept of Agriculture (ODA) website with links to ODA and OSU’s pest alert.”
——
The information about outbreaks in Japan, however,still stands. Read the balance of this post and also see THIS LINK.
——–
The news we have dreaded to hear has been confirmed. The Spotted Wing Drosophila, America’s latest invasive pest, has been found infesting grapes in Oregon. From the Oregon Natural Resources Report:
The spotted wing Drosophila (often named “Dragon Fruit Fly”) has invaded Oregon from California and has already been confirmed in several Oregon fruit crops – blueberries, caneberries and grapes. Stuart Olson, a local peach, apple and cherry grower, believes this could literally shut down fresh fruit sales from Oregon. Unlike the vinegar fruit fly that takes to rotted fruit, this critter infects ripening fruit and is visible in the fruit as a small maggot.
A meeting to discuss the matter has been set for September 22nd. (Follow the ONR link above.)
——
According to Martin Damus, Entomologist for the Canadian Food Inspection Agency,
“I contacted officials of our National Plant Protection Organisation that work in Japan, to clarify some questions about the spotted wing drosophila’s hosts, primarily the reports on grapes and apples. Our official there just had to look at Japanese websites (which I cannot do) and found that spotted wing drosophila is classed as an agricultural pest in nearly every prefecture of Japan, and that it has recently been in “outbreak” conditions in blueberries in Aomori prefecture (the northernmost prefecture of the main island, Honshu) and also in outbreak conditions on grapes on Hokkaido (the island north of Honshu, with a very cool-temperate climate).
What no-one has yet told me is if grapes are a “preferred host”, or if they only go to them under outbreak conditions, that is when all preferred hosts are already attacked. I also have no specific information of under what conditions grapes are attacked — are the grapes sound or damaged? Are they ripe? Are they over-ripe? These are questions I still hope to have answers to.
Unfortunately though there is at least evidence that this fly does attack grapes, and that it does so in a cool climate.
Sorry not to be of more help. It would certainly be prudent, I would suggest, of vintners to hang out a few traps and see if they have the fly. The traps are not pheromone lures, so they don’t have to worry about drawing the fly in from other crops. It will only be found if it is already in the wine crop.”
—-9/22 Update. I’ve just received a second email from Martin Damus, Entomologist from the Canadian Food Inspection Agency. He provided THIS LINK to a Japanese website with relevant info on the SWD.
He also adds,
“The webpage also indicates that there are no chemicals registered in Japan for this pest on grapes. This could mean two things: either they haven’t any (not so good), or it is a sufficiently rare occurrence that none are regularly needed (better news). Not sure which is true, if either.”
For further info please see my summation of a presentation given August 26th by UCCE Farm Adviser Mark Bolda and Martin Hauser of the California Dept. of Food and Ag. Spotted Wing Drosophila Emergency Meeting Results
Admin
Planned only a week and a half before, University of California Cooperative Extension (UCCE) Farm Advisor Mark Bolda’s August 26th emergency meeting in Watsonville on the Spotted Wing Drosophila (SWD) was thorough and informative. His up-to-the-minute research presentation, and that of his charming colleague, Martin Hauser, Associate Insect Biosystematist with the Plant Pest Diagnostics Lab, California Department of Food & Agriculture (CDFA), Sacramento, provided the assembled growers, foremen, and associated persons, representing an estimated 75% of the caneberry acreage in Santa Cruz county, with insight into the history of the pest, the fruits under threat, the critical importance of early detection and identification, bait and capture techniques, the basics of field sanitation, and pesticide options for both the conventional and organic producer. But much work remains.
Mr. Bolda began with the acknowledgment of the group effort required for his summation. “I am standing up here by myself but in no way or form did I do all this wok on my own. I had a lot of support from people in the industry.”
What follows is a distillation of his talk, followed by that of Martin Hauser’s. My focus, of course, is on the wine industry, of the pest’s threat to vineyards. Hence, my notes taken from Messrs. Bolda and Hauser will faithfully report what might be the basics that a vineyard manager ought to know in advance of a potential crisis. For on-going research and breaking news, Mr. Bolda’s farm blog, Strawberries and Caneberries is a ‘must read’. And it is with his work that I begin.
History of the SWD in California
In 2007, in a vineyard in Paso Robles a suspect grape was picked up, but as no specimens were kept, it remains a rumor that SWD was the agent.
Late summer of 2008, in over just a few weeks, multiple reports came in of the presence of vinegar larvae in unharvested cane fruit. Something was different. Research established it was a different species of vinegar fly than hitherto known. Samples were sent to CDFA. That it was in the family of Drosophilidae was confirmed, but the matter was not further pursued. Fruit producers, however, knew it was a damaging pest. Independent studies, without CDFA’s assistance, were initiated by concerned growers and the UCCE.
Spring 2009. Colossal infestations of the new vinegar fly in cherries were reported. People sat up and took notice. It was then provisionally named the Cherry Vinegar Fly. The cherry industry was not pleased so the name was soon changed to the Spotted Wing Drosophila. It has now been picked up in plums, strawberries, blueberries, blackberries, raspberries, and olallieberries, but not yet in wine grapes. Additional infestations have been reported in Oregon and Washington.
The male is identified by the presence of black spots on the wings. For most people the female looks like a regular vinegar fly. But should spotted wing males be present in a field the presence of females may be confidently extrapolated. [Photo by Dr. M. Hauser]
SWD is native to South East Asia: India, Bangladesh, South East China. It has spread to Japan, Korea, it is in Hawaii, Florida, California, Oregon, Washington, British Columbia. Neither the CDFA or the USDA has given any indication that this will become a quarantine pest. The entirety of California was infested at the same time, therefore it is not possible to create a quarantine around it. Because eradication is not possible the effort will be to bring down SWD to manageable levels.
Life Cycle
Fruits attacked by SWD reveal only a soft spot on its surface, slightly indented. No hole is casually visible. [See Mark Bolda's blog for pics.] When the fruit is cut open at the sunken spot a larvae may be observed. The female lays one to two eggs per fruit, with an overall capacity to lay 300 eggs. More than two larvae indicates multiple females laying eggs on the same fruit. The damage of the fly is not the feeding by the adult on fruit but from larval development.
Normally fruit flies most people are familiar with lay eggs on the surface of things. The ovipositor is benign. It does not insert eggs. The SWD, by contrast, possesses an ovipositor designed to saw through the surface of fruit. Not a needle-point but a saw-like structure. An egg’s deposit depth is believed to be approx. 1 mm or 2 mm.
The colder it is the longer it takes for the SWD to develop. At 54 degrees it takes 50 days to develop from egg to adult. At 64 degrees it takes 19 days to mature. At 77 degrees 8.5 days; 82 degrees, 7 days, one generation a week. Beyond 85-86 degrees the males become sterile. Reproduction ceases at that point.
Monitoring and Management
Early detection is critical. As is the use of preventative sprays and enhanced sanitation protocols. Cane berry growers are especially hard hit owing to the practice of closed canopies and tunnels. Once SWD is well established it becomes very difficult to control them. Sanitation methods currently enjoyed are insufficient.
SWD is a very mobile pest. It is felt trapping is the best method for early detection. Early expert advice (Dec. 2008) suggested using banana slices placed at the base of the canes. Extremely limited success was achieved. Next was banana slices and apple juice in a mason jar hung on a stake in a raspberry field. It worked far better trapping SWD but it required a lot of service by the larger grower. More efficient trapping methods were sought.
The next trap experiment used was GF120, a fruit fly bait, this time hung at a lower level in the canes because the SWD does not like the sun, it prefers shade. The bait worked moderately well but its attractiveness to the fly declined over time.
What do the adult flies like to eat? They like old stuff, fermenting materials. Again, only the larvae are destructive. Of other attractants, a strawberry purée or GF 120 were still working; methyl eugenol, currently advocated by the CDFA as a bait, did not prove effective in field experiments. In fact, it never picked up a single fly.
(It is important to add that only the male SWD was used as an indicator of their presence in the field. The females are simply too similar to vinegar flies when examined in the field to be of much diagnostic help.)
Other fruit purées were explored. Yeast and sugar mixed with water proved the most effective bait (one package of Baker’s yeast, four teaspoons of sugar and 12 ounces of water). Mr. Bolda then offered traps (see pic) to folks. He had assembled them for use in SWD detection with the recommended bait solution mentioned above to be added later.
Note that the sugar is added not for the SWD but for the yeast. The idea is to produce a rapidly fermenting liquid attractive to SWD. The monitoring traps are then placed throughout the field. Attention should also be paid to the direction the SWD appear to be coming from.
Control
GF 120 (not a spray, but OMRI certified). Sprays: Spinosads (permitted for organic use, [but broad spectrum]), Mustang, PyGanic (permitted for organic use), and Malathion were all discussed. As was the importance of preserving predators and parasitoids.
Mustang proved very effective, as did Malathion, even after five days. Spinosad (Trust), gave good results but lost efficacy over that same five day period. PyGanic was of minor efficacy.
A single application is not enough in a heavily infested field. Three applications, one every five days, was recommended to break the cycle. But early detection may reduce the need for repeated applications.
Rotating the chemicals was stressed. Without rotation resistance will develop. And these are not the only sprays available. The ones tested were ready at hand. The idea was to provide immediate research results into the efficacy of some commonly available pesticides. Other chemical alternative may well, indeed, probably exist.
March, 2010 update on Control of SWD An email from Mark Bolda reads, “We did find just before the holidays that spinetoram is pretty useful on SWD, giving some 3 weeks of control at least.”
Sanitation
Dropping fruit to rot in the field is strongly discouraged. As is leaving incompletely harvested fruit. If not disced, the discarded fruit must be removed from the field and be physically destroyed.
Mr. Bolda stressed that the berry industry is only as strong as its weakest link. All growers must do their part to implement the research findings.
—–
Here now is a partial summation of the talk given by CDFA’s insect specialist, the very engaging and downright hilarious, Martin Hauser. It was his primary research that led to the identification of this new California pest, what is now known as the Spotted Wing Drosophila. [Martin Hauser's PDF to come.]
He acknowledged Mr. Bolda’s thorough presentation. His talk was to be a kind of positive reinforcement.
CDFA History of SWD
Last September UCCE sent flies to the CDFA. They were identified to genus level as a Drosophila and was considered completely harmless. The larvae always develop in rotten fruit, some in fungi, occasionally elsewhere. They normally eat the fungus which develops in rotten fruit. Again, the first estimation of the flies sent were considered completely harmless. CDFA was wrong.
Spring brought more and more calls from growers, especially of cherries. After a close look at the larvae specimens sent in it was again determined by the CDFA to be a harmless Drosophilid. Mr. Hauser said that in his defense it was rather like hearing from ranchers that there were rabbits attacking and eating their cows. Rabbits don’t eat cows! (laughter) They eat carrots. After a while one no longer believes these people, these ranchers.
A summary was given of other dangerous agricultural flies. But the fruit and vinegar flies were, up until now, thought to be drawn only to rotten fruit. Of no real economic importance. Though a single fly which falls into your glass of red wine can ruin it.
The larval samples initially received from cherry growers were too difficult to identify. Taxonomic identification could not proceed beyond the Family level. Indeed, there are 3,000 different species of Drosophilids in the world. And nobody over 100’s of years of agriculture in California, nobody ever reported or described the SWD here. It must be coming from outside. With increased trade and shipping the fly could be from anywhere in the world. So began a search through the scientific literature on the 3,000 species.
Identification
Only 125 Drosophilid species live in North America. There are 600 species in Hawaii. The islands’ isolation, abundant fruit, and absence of competitors allowed considerable speciation. But they are all harmless and restricted to Hawaii. The SWD could not be one of those well-described species. So, Dr. Hauser’s job is to identify insects, to give them a name, the scientific name. And this step is crucial. Everything is connected to the name. The scientific name is the key to the literature. One can then learn of a pest’s predators, parasites, biology, among many other things.
Deep in the literature was found the first description of California’s newest pest, suzukii (the Genus [Leucophenga] was not proper). In 1931 Matsumura Suzuki described the species as new to science in Japan. Just a few years later the species was then described as a pest in Japan. Dr. Hauser’s theory is that the species was not native to Japan. It was introduced from elsewhere, South East Asia, perhaps.
When a new species of insect is first introduced to a new area you have a massive, invasive explosion. It just eats. It has no natural enemies. There follows a few years of explosive populations. Then pathogens and parasites move in. The invasive insect population then begins its decline. In the Japan of today the SWD still causes trouble but not the catastrophic trouble California et. al. have here right now.
Description
The male fly has spots on its wings. There is no other Drosophila in North America with spots on its wings. Other flies have spots, there can be some confusion, but this characteristic makes it easy for even the relatively inexperienced person to identify them. No microscope needed. The females are harder to identify. They are relatively big and heavy Drosophilids. The large ovipositor is key. With it the female cuts through a fruit’s skin “like butter”.
Life Cycle
The eggs are very small. They cannot be seen in the field. There are three instars of increasing size. The third, the largest, is the one most often seen because the damage already done to the fruit has now become easy to see in the field. Then there is a pupa, the last transitional form to the fly.
The average time for one generation is about 12 days. [Mark Bolda's collaborative field research must take precedence here. See his comments above.] From adult to another adult, 12 days. Varies with season and temperature, as Mr. Bolda’s work shows. The female lays 350 to 400 eggs. The egg stage is between 12 and 72 hours, a very short time. Larval stages are between 3 to 14 days. The pupa, 3 to 15 days, depending on the temperature.
Distribution
The fly is originally from Asia, very likely China. But also Japan, Korea and Thailand. When calling colleagues around the world Dr. Hauser heard from an entomologist in Switzerland that he had just found it in Spain last year! It was also found in the early 2000’s in Hawaii, in fruit fly traps. It was not attracted to the fruit fly attractant but to the traps already full of fruit flies. It seems the rotting fruit inside the fruit flies attracted the Drosophilid. But there are no reports of agricultural damage there. The same for Spain.
The presence of SWD was detected in San Diego, all over the LA Basin, they are everywhere along the Coast and the Central Coast, the Central Valley up to Sacramento, the Bay Area. A lone maggot was trapped in Humboldt. Suzukii was recently detected in Florida. Dr. Hauser predicts SWD is all throughout the mid-west owing to shipping and distribution patterns. A fruit may be deemed sub-standard and tossed into the dumpster, for example, thereby allowing SWD to reproduce. The fly will eventually be found in every state with significant fruit production and that is not too cold.
As a side note: CDFA used Methyl Eugenol which attracts male fruit flies through mimicking the scent of the female. The male climbs into the trap and drowns. A good lesson, Dr. Hauser suggests! But the reason SWD is attracted to M. Eugenol is because of the presence of already fermenting fruit flies. This attracts the Drosophilids into the fruit fly traps. Therefore, the primary attractant that is used for fruit flies does not work, absent rotting flies, with SWD. It is agreed the use, the addition of yeast is ideal.
Natural History of SWD
A Japanese paper from 1939 was found describing the biology of the SWD. Eyebrows were raised when it was read that the fly infests cherries and grapes severely. Also apple, peach, plum and persimmon. Cherry infestation reached as high as 75% according to the ‘39 paper. SWD can have 13 generations in a year. They are active all year round in Japan. (And here. There is no snow or severe weather. Further up north they might try to hibernate. They probably could survive a ‘normal’ winter.) They are hardy flies. But the 1939 report also held out promise: it seems the larvae are parasitized by a specific wasp. The CDFA is looking hard to find natural enemies in other countries and to import them here for enhanced natural control.
What will it hit next? Cherries have been hit hard. The Spotted Wing Drosophila was initially called the Cherry Vinegar fly. But neither the Cherry industry nor the Vinegar industry wanted a fly named after them! Perhaps call it the Japanese Fly? No. The Japanese might not like this. So CDFA came up with the Spotted Wing Drosophila. It is also found in raspberries, strawberries, and recently, plums, Asian, Satsuma and Plumcots, blackberries, boysenberries, and surprisingly, nectarines. This is what has been found in California. But it is not thought they will go into apples or oranges.
And of grapes? This is always floating around. It is kind of a political issue. There have been reports of tomatoes, apple and apricots. Sometimes you can’t really trust these literature reports. People may have just found a maggot. The reports must be taken with a grain of salt pending DNA analysis. This is just the potential of the fly. There is still no proof they go into grapes.
10/13 This has changed. Please see this update.
UC Davis may have done some experiments where grapes were offered to SWD. They more or less forced them into the grapes. They gave SWD no alternative. Eventually the females laid their eggs where the stem enters the grape and grapes were infected. But the experiment was unnatural. It is still unclear whether SWD is a danger for grapes. There is no confirmed damage to wine grapes in Nature, so to say. Why might that be? It is felt grapes have a stronger skin the SWD cannot really penetrate. But there are many different varieties of grapes. Some may prove more susceptible than others. Dr. Hauser felt it improper to exclude healthy grapes at this point. SWD, however, does go into already damaged or rotting grapes. It is not clear whether SWD caused the damage or arrived after the grapes had already been corrupted in some way. More work needs to be done.
The USDA is currently taking no regulatory action because the SWD is already everywhere. And in a few years it will be everywhere in the world. Everybody will have it. There will be, therefore, no export restrictions on cherries to Japan, for example, because they already have the SWD.
END
Special thanks to UCCE’s Mark Bolda for extending me an invitation to the Watsonville meeting.
Admin
Here is a supplemental piece of some interest. More to come.
The agricultural industry in California is working rapidly to meet the threat of a new fruit pest, the spotted wing Drosophila (Drosophila suzukii). According to an August 24th posting by the Western Farm Press titled New Name For Cherry Pest, though recently discovered, the fly is already well established and has been found from San Diego to Humboldt counties, but also in Washington, Oregon, and British Columbia. It seems to have a preference for the cooler, more moist climes along the Pacific Coast.
After its initial discovery in cherries, the article points out the growing varieties of fruit where the fruit fly may now be found.
So far SWD has caused economic damage to sweet cherries, strawberries, blueberries, raspberries, blackberries, Ollalieberries and in backyard Santa Rosa plums in the San Jose area.
Can grapes be far behind? University of California, Berkeley entomologist, Bob Van Steenwyck is quoted as saying:
“Will it damage grapes? That is the $64,000 question. I believe it will hit grapes as they start to sugar. I think, however, it will not be a problem in the Central Valley because it is too hot for suzukii. I think the problem will be in the cooler (wine grape producing) areas of the state. It likes cooler climates.”
And it is for this reason, as assorted fruit harvests and the grape Crush looms, that an SWD Emergency Meeting will be held in Watsonville, August 26th. In an email exchange, Mark Bolda describes the meeting as “the most complete presentation of SWD biology and management to date”.
The meeting will be an important opportunity to hear the latest research by Santa Cruz County UCCE Farm Advisor Mark Bolda, the lead writer of an important paper on the fruit fly pest published in early August, A New Pest In California: Spotted Wing Drosophila. It is an eye-opening read.
I contacted Mark Bolda with a series of questions.
Admin How long has this species been known to exist in California?
Mark Bolda Probably since 2006.
What might have been its origin?
MB SE Asia, common to Korea, Japan and Hawaii.
Is its appearance possibly associated with climate change?
MB I doubt it, it was brought in on produce, something that got around the various checks at ports of entry to California. It is best suited to the cool, moist climate of the west coast apparently.
Have there been any reports of damage to vitus vinifera, wine grapes?
MB There are some rumors, apparently the very first unconfirmed hit was on a wine grape out of Paso Robles in 2006. Martin Hauser I believe will discuss this when he comes to talk on Wednesday. No specimens were kept out of the Paso hit, however, so we didn’t pick them up again until a major infestation in berries here in Watsonville in the summer of 2008.
Along with producing multiple generations, how many eggs does it lay per fruit?
MB 1-2 eggs per fruit, 200-300 per female. Lots of traveling around. Multiple females will lay in the same fruit, so you can get infestations of up to 40 in a raspberry.
Can you point me to additional research?
MB Come to the meeting, and look at my blog (not the fancy title like yours, but nonetheless should be pretty informative).
Spotted Wing Drosophila Meeting
Reunión de Drosofila de Alas Manchadas
August 26, 2009/ 26 de agosto, 2009
University of California Cooperative Extension
1432 Freedom Blvd., Watsonville, CA, 95076
9:00 Introduction/ Introducción
9:10 History and Management of Spotted Wing Drosophila in Santa Cruz County/
Historia y Manejo de Drosofila de Alas Manchadas en el Condado de Santa Cruz
Mark Bolda, UCCE, Santa Cruz County
10:00 Biology of Spotted Wing Drosophila/ Biología de Drosofila de Alas Manchadas
Dr. Martin Hauser, Diptera Specialist, CDFA
10:30 Close of Meeting
Because of the short lead time for this meeting, no continuing education hours will be available. For more information, contact Mark Bolda (831)-763-8040; 1432 Freedom Blvd., Watsonville, CA, 95076.
Please call ahead for arrangements of special needs; every effort will be made to accommodate full participation.
Spanish translation will be available.
END
For additional information also please see Another Exotic New Pest Threatens Variety of Crops published by the Cal. Farm Bureau Federation.
As I will be in attendance, I will post what is announced.
–8/30 Update has been posted.
10/13 Update has been posted.
Admin
Firstly, for critical background on the original pioneering field work of Mark Bolda, farm advisor from of the University of California Cooperative Extension, and the historical and cultural dimension from Martin Hauser, Associate Insect Biosystematist with the Plant Pest Diagnostics Lab, California Department of Food & Agriculture (CDFA), Sacramento, please see my Spotted Wing Drosophila Emergency Meeting Results.
From the California Food and Agriculture’s Plant Pest Diagnostic Center–Entomology Laboratory may be read Martin Hauser’s just posted summation of SWD’s preferred hosts here in California and in Japan.
