Fruit fly pest identified in wine grapes

Drosophila suzukii male Photo: G. Arakelian, Los Angeles County Agricultural Commissioner/Weights & Measures DepartmentA newly recognised 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."

Losses to fruit crops have been significant in some places this year, according to OSU entomologist Vaughn Walton, who is working with Dreves and others on strategies to combat this invasive fruit fly. California lost about one-third of its cherry crop from Davis to Modesto. Willamette Valley peach growers were hit hard, especially in the late season, with losses up to 80 per cent in some orchards. Crop losses up to 20 per cent were seen in Oregon raspberries.

In early October, two blueberry fields were sampled, and one showed no damage at all while another had approximately 20 per cent infestation (sampled and dissected approximately 400 berries at each site). "We have frozen samples from an infected blueberry field," Walton explained. "The berries were picked at different times, and we can dissect them to help determine times of the first infestations this season in Benton County."

New reports of its occurrence have been confirmed almost every week since OSU researchers first identified the fly in a sample of Oregon blueberries in August.

Dreves and Walton are now reporting that adult Spotted Wing Drosophila had emerged from wine grapes that had been collected in the northern Willamette Valley two weeks earlier. Also confirmed by the Oregon Department of Agriculture were flies emerging from infested red table grapes collected from the Willamette Valley.

At this stage, growers have not seen noticeable damage to harvested grapes, Dreves said, and the harvest of grapes is nearly complete in the Willamette Valley without signs of Spotted Winged Drosophila impact.

Dreves and Walton are part of a team of researchers from OSU, U.S. Department of Agriculture, and Oregon Department of Agriculture working to uncover the extent of infestation and to test methods for controlling its spread.

Their work is one part science, one part Extension, and one part detective work.
Native to Japan and parts of Southeast Asia, D. suzukii had been introduced into Hawaii in the 1980s and was first confirmed in Florida and California last year. Since August 2009, the fly has been reported throughout California, from Vancouver, Wash., to Abbotsford in British Columbia, and in 12 counties in Oregon.

"That's because we're looking for it now and this year's environmental conditions were right," said Dreves. Because the Drosophila fly larvae are small, shapeless and pale, Dreves and her colleague, OSU entomologist Vaughn Walton, culture suspicious larvae from sampled fruit to confirm the identity of the insect in adulthood.

Other research partners, in recent reports, suspect the fly has been found on pears in Oregon, Dreves said. What might be good news for Oregon is that D. suzukii, at least in Japan, only lays eggs in apples that are already damaged; apples seem not to be a primary host.

The Spotted Wing Drosophila is a close relative of the so-called "fruit or vinegar fly" associated with overripe bananas. That fly, Drosophila melanogaster, feeds on spoiled and rotting fruit and is the star attraction in high school biology classes when students learn about genetics and mutations. The spotted wing Drosophila fly, in contrast, infests fresh fruit, which presents a significant economic threat to fruit growers.

Discovery of the Spotted Wing Drosophila in wild Himalayan blackberries has the researchers worried. Despite the efforts growers will put toward cleaning their orchards of all left-over fruit, these feral areas could offer a refuge for overwintering populations of flies, according to Dreves. "We just don't know."

There's a lot that researchers don't know about this new invader, but they are learning fast. Dreves is scouring the scientific literature, going back to Japanese monographs from the 1930s to learn everything that is known about D.suzukii.

"In Japan, these flies are reported to reproduce up to 13 times in one season," she said, which suggests that the population could explode toward the end of the season, as seems to have happened this year.

According to reports, these flies thrive in cooler areas and are most active at temperatures of 68 degrees. Activity, longevity and egg-laying are said to decrease at temperatures above 86 degrees, although infestations have been found in warm parts of California and Florida.

Much of western Oregon's growing season would seem to favor conditions favored by these flies, which means that most of Oregon's berry crops could be at-risk during the growing season, according to Dreves. And because Oregon has a variety of crops that ripen at different times during the season, the spotted wing Drosophila fly could move from one crop to another as the season progresses, and populations could build up to high numbers in many crops.

On the other hand, the fly might be gone by next season, Walton said, pointing out the uncertainty associated with a new invasive species.

Planning for the worst, the OSU team is working with colleagues in the USDA Agricultural Research Service and ODA to develop management plans for this new pest in Oregon. They are sampling fruits at farmers' markets and receiving samples from growers and OSU Extension agents in the field to map the extent of the infestation. And they are testing baits to monitor population levels this fall. In small areas, it may be a possibility to lure flies away from vulnerable fruit by setting up traps.

For now, Dreves said, two principles are at the heart of controlling the fly regardless of crop. First, reduce the fly's breeding sites by immediately removing and disposing of the source – infested fruit. And monitor for the presence of adult flies before they lay eggs.

The spread of invasive species

These red flour beetles are pictured on the wheat they eat and are often found near. Photo: USDAUnknowns may place more species at risk in a changing climate

Whether for introduced muskrats in Europe or oak trees in the United Kingdom, zebra mussels in United States lakes or agricultural pests around the world, scientists have tried to find new ways of controlling invasive species by learning how these animals and plants take over in new environs.

In a paper published in this week's issue of the journal Science, biologists Brett Melbourne of the University of Colorado and Alan Hastings of the University of California at Davis report a previously unknown high variability in the rates of invasive species spread.

To reach their conclusions, they studied red flour beetles – beetles attracted to wheat flour – in experimental, enclosed landscapes with patches of habitat linked together.

They collected data from 30 landscapes composed of identical patches of land, all maintained under the same conditions, each initially home to 20 red flour beetles.

Although the landscapes were identical, there were considerable differences in how the beetles spread. By the end of the 13-beetle-generation experiment, the distance the beetles ranged spanned 10 to 31 "landscape patches."

"Scientists have struggled to understand why some species spread rapidly, while others don't," says Saran Twombly, acting deputy division director of the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research. "Once ecologists identified the key factors, it was thought, they could predict species spread with some certainty.

"Melbourne and Hastings have showed the opposite: intrinsic variability that could be random or have a genetic basis appears to have a large influence on species' spread. Researchers must now incorporate uncertainty in future approaches to 'ecological forecasting.'"

Everyone's familiar with uncertainty in weather forecasts, says Melbourne. "How often have we heard, 'there is a 75 per cent chance of rain today’?”

As in weather systems, there's a degree of unpredictability in ecological systems.

The uncertainty arises because of randomness in both environmental and biological processes. "Ecologists have rarely measured it, however, so we haven't known how big it is," states Melbourne.

"We need to know more about how this affects the specific case of biological invasions," says Melbourne, "and how it changes ecosystem responses generally."

Ecologists will increasingly be called on to make the biological equivalent of weather forecasts: how will ecological systems respond to climate change, habitat destruction and loss of biodiversity?

Will species be able to migrate fast enough to keep pace with climate change?
Although more research is needed, the uncertainty Melbourne and Hastings found may place more species at risk in a changing climate: flora and fauna may not be able to march one step ahead of the pace of global warming.

Experimenting weevil control

Photo: Scot Nelson et. al./University of Hawaii at ManoaYou may have never encountered the New Guinea sugarcane weevil Rhabdoscelus obscures, but this naughty little weevil may be enjoying life in your coconut, betel nut or other palms. The larvae bore into living tissue of palm branches, producing tunnels that weaken affected parts of the host plant and permit the invasion of fungal and bacterial pathogens.

In coconut palms they bore into the base of the trunk and can weaken the tree until it is blown down in high winds. In betel nut palms they frequently bore into areas near the growing tip of the tree and the end result may be death.

Dr. Gadi V. P. Reddy of the Western Pacific Tropical Research Centre, UOG has been awarded a USD75,000 USDA Natural Resources Conservation Service grant to address the weevil threat to palms in the region. This miniature menace is especially troubling for nursery owners.

In collaboration with the Northern Marianas College, Dr. Reddy and his research team will develop environmentally friendly control tactics designed to reduce the use of insecticides currently employed to control the New Guinea sugarcane weevil. This integrated pest management (IPM) approach will safeguard the environment and keep palm trees healthy.

USDA grant funding will support the design of an efficient pheromone trap for catching weevils in field conditions, and experiments with Petri dish traps containing fungal spores (Beauveria bassiana and Metarhizium anisopliae) for auto dissemination through trapped weevils.

Dr. Reddy will conduct sugarcane weevil control experiments at several major ornamental nurseries throughout Guam, which will allow growers and nursery owners to participate in all phases of the project and learn integrated control tactics and environmentally friendly best pest management practices. This project will provide basic, applied, and practical information on the control of R. obscurus in the Mariana Islands.

Biological clock in pest control

This image shows a 0.1 x 0.03 inch (2.5 x 0.8 mm) small Drosophila melanogaster fly. Photo: André Karwath/Wikemedia CommonsResearchers at Oregon State University have discovered that the circadian rhythms or biological "clocks" in some insects can make them far more susceptible to pesticides at some times of the day instead of others.

With further research, the scientists said, it may be possible to tap into this genetic characteristic, identify the times that a target insect is most vulnerable to a specific pesticide, and use that information to increase the effectiveness, reduce costs and decrease the amounts of pesticide necessary for insect control.

Approaches such as this may also be highly useful in programs of "integrated pest management," the researchers said, which aim to minimise pesticide use, prevent development of resistance to pesticides, and use a broad range of physical or chemical control measures to enhance the long-term effectiveness of an insect control program in crop agriculture.

The findings were just published in PLoS ONE, a professional journal, in work supported by the U.S. Department of Agriculture, National Institutes of Health and National Science Foundation.

"We found that it took triple the dose of one pesticide to have the same lethal effect on fruit flies at the time of day their defenses were strongest, compared to when they were weakest," said Louisa Hooven, a postdoctoral fellow in the OSU Department of Zoology and lead author on the study. "A different pesticide took twice the dose. This makes it pretty clear that the time of day of an exposure to a pesticide can make a huge difference in its effectiveness."

In recent years, researchers have found that the genes which are sensitive to the natural rhythms of day and night can have a wide range of biological effects, on everything from fertility to feeding patterns, sleep, hormone production, stress, productivity, medication effectiveness and many other functions. And they operate in multiple cells in many or most plant and animal species, including humans.

In the newest work, circadian rhythms appear to coordinate "xenobiotic metabolising" genes, or the genes responsible for breaking down and detoxifying various poisons, such as pesticides. Besides that, it's possible that circadian clocks may also affect absorption, distribution, excretion, and molecular targets of toxicity.

"This rhythmic defense mechanism may have evolved in order to disarm the noxious compounds that plants produce to avoid being eaten by an insect," said Jadwiga Giebultowicz, a professor of zoology at OSU. Other co-authors on this work included OSU undergraduate students Katherine Sherman and Shawn Butcher.

The OSU study found that insect defenses against two commonly used pesticides, propoxur and fipronil, were strongest during mid-day, and weakest around dawn, dusk or the middle of the night. The effectiveness of two other pesticides studied – deltamethrin and malathion – did not seem to be so strongly associated with time of day, at least with fruit flies.

"For this approach to be useful in agriculture or other places pesticides are used, we will need to test specific insects against specific pesticides, and we will probably find differences in time of maximum effectiveness for various pest-pesticide configurations," Giebultowicz said. "In some cases we may be able to greatly improve the effectiveness of pesticides or allow the use of reduced doses."

Although many pesticides have a residual effect, the researchers said, the timing of the first exposure can be critical. Many pesticides are repellent to insects, and if they are not killed immediately they may simply avoid the residue, or in some cases develop resistance to the pesticide – a critical and costly problem in modern agriculture. Pesticide resistance has been a driving force behind the evolution of the field of integrated pest management, as growers realised that sustainable pest control is not as simple as using the same pesticide, year after year, which often becomes increasingly ineffective and more expensive.

The new findings, the OSU researchers said, are also another example of how circadian rhythms are important in other detoxification systems in biology. In human medicine, a field called "chronopharmacology" is already developing, based on the observation that some medications are far more effective if administered at one time of the day instead of another.

Research into the molecular mechanisms underlying circadian rhythms was pioneered in fruit flies, but the OSU researchers hope their future research will shed light on how the biological clock influences responses to chemicals in humans.

"A fundamental understanding of the functional significance of circadian rhythms in chemical exposures may facilitate strategies to reduce adverse events in humans, promote control of pest species and reduce pesticide use," the researchers wrote in their report.

"Our study strongly suggest that time of day should be included in insect control strategies and human risk assessment of chemical exposures, including pesticides," they said. "In some cases, the clock, together with the dose, may make the poison."