Operation Bug Off
Oregon State University’s entomology lab in Hermiston is the command center for several battles against crop-damaging insects. Equipped with microscopes and temperature-controlled chambers, the facility is deploying chemical and biological warfare to defeat winged and wormy enemies.
[caption caption="Sweep Net Technique for Collecting Specimens"]
On one front, it’s battling the destructive, sap-sucking potato psyllid, a type of jumping plant lice. With its needle-like mouthparts, the pest injects potato plants with a lethal bacterium that causes zebra chip disease, named for the discoloration that occurs inside the spuds. The pathogen also reduces yields and makes the tubers taste bad.
“Since 2011, this has been the ‘it’ pest in the Columbia Basin,” said Silvia Rondon, who heads the lab at OSU’s Hermiston Agricultural Research and Extension Center. “All growers went on red alert. They came to us to ask for advice. This was new to us. We had a steep learning curve.”
So Rondon’s lab-coat-wearing special-forces team began conducting reconnaissance by setting traps around Oregon, which it continues to do in Baker, Morrow, Umatilla, and Union counties. Every Friday, the lab emails updates to growers on the location, types, and number of insects the crew has trapped that week. Rondon also teaches growers how to identify the potato psyllid and catch them using vacuums and yellow sticky cards. The farmers then send the insects to the center to see if they are infected with the bacterium.
In 2012, hundreds of boxed sticky cards arrived each week at the entomology lab. “One day I arrived in my lab and there was no space to sit or put stuff on the counter because there were sticky cards up to the roof,” said Rondon, who is also an entomologist with the OSU Extension Service. Her research assistants then carefully plucked off the potato psyllids with tweezers, placed them in vials, and handed them over to the center’s plant pathology lab for testing. Lab technicians found that even though the number of psyllids was high, less than one percent carried the bacterium. The pest is still a problem, however, because if growers don’t control even that one percent, they can lose their crop, Rondon said.
Sticky cards work when the psyllid first arrives in a field and gets stuck on them while looking for a place to dine. Once in a field, however, the insect tends to stay put, so if it hasn’t run into a trap by then, chances are it won’t, Rondon said. So Erik Echegaray, an entomologist in her lab, is studying how it arrives at fields and which trapping techniques work best. He’s exploring the use of vacuums (which look like leaf blowers) to suck up the bug along the edges of fields.
So far, using chemicals has been the standard operating procedure for controlling the potato psyllid, Rondon said. So her lab has tested which ones work best and how many times growers need to apply them. Rondon also co-authored an OSU Extension factsheet on how to manage the insect.
Her lab discovered something disturbing. The potato psyllid can survive the Columbia Basin winter by seeking shelter in a weed known as bittersweet nightshade. Previously, researchers thought it couldn’t live through the cold temperatures and that it migrated north from California in the summer.
On another front, the lab is fighting the brown marmorated stink bug, which noshes on a variety of crops, including corn, wine grapes, hazelnuts, pears, apples, and sweet cherries. A global hitchhiker, the non-native, shield-shaped pest was found in Portland in 2004 and has since shown up in more than a dozen Oregon counties, including Union in northeastern Oregon.
Nik Wiman, an entomologist affiliated with the Hermiston lab, is gathering intelligence on the bug around the state, forecasting its population, and trying to put a dollar amount on the damage it could do to crops. Along with Rondon and others, he also co-authored an OSU Extension flyer on how to distinguish the pest from look-alikes. Additionally, he’s studying how far, fast, and frequently it flies and whether its flights affect reproduction. He glues the insect to a carousel-like device and watches it circle around a pivot like a flying chair ride at an amusement park. Each rotation is logged by a computer.
The lab has also launched an assault on the beet leafhopper, which transmits a bacterium via its saliva that can kill potato plants within weeks. Alexzandra Murphy, an entomologist in Rondon’s lab, has determined that Columbia Basin potato plants are most susceptible between April and June. She also found that three to five leafhoppers per plant can reduce a plant’s yield by at least a quarter.
Murphy also has aphids in her crosshairs. She’s surveying potato and wheat growers around the state to see which species they’re finding and where. In the past, farmers in Oregon and Washington successfully used parasitic wasps to control the aphids, which transmit viruses to these two crops. But for the last three years, outbreaks have been reported on wheat. Murphy suspects the aphids may be helped along by weeds, which they live in during the winter. She’s examining the weeds to see if they’re infected by the viruses, and she’s studying how the aphids migrate from them into neighboring crops during the spring. If the weeds test positive, then growers would know that they need to spray them to control the aphids.
Another foe, the potato-burrowing tuberworm, has been on Rondon’s radar since her first day on the job with OSU in 2005. At the time, the insect was wreaking havoc in Oregon and Washington. So, Rondon set about trying to comprehend the bug. She and colleagues from OSU and other states trapped and counted them, doused them with water, buried them under soil, eyeballed them under microscopes, and gathered their DNA. They identified resistant potato germplasm, tested hundreds of chemicals, and even hunted down an old specimen housed in OSU’s insect collection.
They discovered that the tuberworms in Oregon and Washington were genetically different from those in the central and eastern parts of the United States. Ominously, that means the insect has adapted to cold Northwest winters and may be here to stay. In her lab, Rondon incubated speck-size tuberworm eggs and determined that young tuberworms can survive temperatures as low as 41 degrees. In field trials, she found that pupae can endure more than 90 days of exposure to extreme winter conditions.
To combat tuberworms and other invaders, Rondon plans to expand her arsenal to include a technique she learned on sabbatical in France in 2013. It involves using chemicals that plants secrete. When an insect nibbles on a plant, the plant releases substances that repel or kill the pest or attract “good” bugs that kill the undesired insects. Rondon aims to find out what chemicals potato plants produce to attract these beneficial bugs. The results of her research would benefit the environment and could save growers money because they could curtail their use of pesticides, she said.
The battle against bugs is an old one that’s always changing. Just as scientists think they have one species under control, another comes along. Or an insect develops immunity to a pesticide that once worked. Or favorable weather conditions cause an outbreak. It’s a constant fight that requires scientific know-how, surveillance, and a proactive strategy. Because, as Rondon knows, the best defense is a good offense.