An entomology undergrad combats the worm in the apple
When they hatch, they’re so tiny you can barely see them. Then they eat. They bore their way inside an apple and consume it from within. After two weeks, they’re half an inch long, pinkish orange, and engorged, with tiny dark heads. They’re also translucent, so if you look closely, you can see their food moving along their digestive tracts.
They’re codling moth larvae, the number one adversary of Washington apple orchard growers and the subject of her fascinating summer of research at the Washington State University Tri-Cities’ Food and Environmental Quality Lab. With faculty members Allan Felsot and Vincent Hebert, Henderson came to know much about the diminutive despoiler-and the best way to kill it. She loved almost every minute of her work.
From mid-May to mid-August, Henderson ran bioassays on the larvae as part of research on sprayer technology for pesticide application in orchards. Felsot, Hebert, and the students used two different types of sprayers, the industry standard Airblast and the newer Proptec. The researchers also used two different pesticides, the most commonly applied Guthion, slated for phaseout by 2005, and its replacement, Intrepid.
Guthion is being replaced because of its dangers to human health, Henderson says. The neurotoxin binds to a certain neurotransmitter in the synapse so it can’t be broken down. Its buildup can cause seizures, and death.
Henderson learned just how effective Guthion is on larvae during the course of the summer. For each bioassay, leaf samples were collected from various sites in the lab’s orchard. The sites were treated differently: with the two sprayers, the two pesticides, and two concentrations. Henderson took small leaf samples from each plot, put them in a petri dish, and placed five larvae on the samples. She checked all samples at different time intervals to see how many had died.
“Shortly after application, with the full rate and the half rate, all five larvae would be dead in two hours,” she said. “Guthion is used wherever there are apple orchards. It’s really the best thing for killing codling moth larvae.”
Intrepid is an insect growth regulator that restricts the larva’s ability to go through a normal molting cycle.
“With Intrepid, we would get mortality, but it wouldn’t be until 24 to 48 hours later, and it wasn’t always 100 percent mortality,” Henderson says. The problem is that codling moth larvae move very quickly, and it takes them less than 24 hours to chew into an apple. Once a larva gets inside, the fruit isn’t marketable anymore.
“It kind of comes down to choosing human safety or effectiveness,” she says. “But what they’re hoping to do in the lab is reduce worker exposure through the safer sprayer technology, therefore enabling the orchards to continue to use Guthion.”
Before last summer, the Kennewick native’s only work in a research laboratory involved washing glassware in Clark Hall during the school year, a job she inherited from her older brother, Fred, a WSU electrical engineering senior. But John Brown, chair of the WSU entomology department, asked her if she needed a summer job. He sent her resume to entomology-related labs near the Tri-Cities, and Felsot called her home during spring break.
Once at the lab, the researchers taught Henderson how to set up bioassays, record data, label and store samples, and take care of codling moth larvae until they were used in the bioassays. That’s how she got to know the ugly buggers so well. Moth eggs were shipped weekly to the lab, Henderson put the eggs on untreated leaves and placed them in an incubator until they hatched two days later. She became so familiar with the lab’s work that in early July, she presented findings from her part in the bioassays to two visiting groups.
“What most impressed me about the job was I would actually be working with the research, especially since it related to my major,” she says. “I didn’t really expect to be participating so much. I just figured I’d be washing more glassware. It was very satisfying to go to my summer job and do something that meant something to the world.”