Gaga for Gum: Study Shows Sticky Mixture Distracts Fruit Fly Pest
By Edward Ricciuti
Many research papers in scientific journals have scholarly—face it, for the lay person, boring or complicated—titles, but one published in April in the Journal of Economic Entomology contains an unusual touch of wit: “Gumming Up The Works: Field Tests of a New Food-Grade Gum as Behavioral Disruptor for Drosophila suzukii.”
For the record, the colloquial phase “gum up the works” refers to the sweet sap of the redgum tree. Pioneer kids chewed it like today’s youngsters chomp bubble gum. The backwoods kids may have loved it, but their parents probably didn’t because it was almost impossible to get out of hair and off clothing. And when the logs from gum trees were dressed for their high-quality lumber, sap all too often made a gooey mess that gummed up milling machinery, thus the origin of the phrase. And so, as the title of the research paper mentioned above suggests, trials of an experimental, fruity smelling gum does the same to the reproduction of a notorious invasive agricultural pest, the tiny fly known as the spotted-winged drosophila (Drosophila suzukii), or SWD.
What looks like a gob of gooey black gunk drained from a gear box could be the answer to curbing this invader from Southeast Asia, whose tiny size—at most 3 millimeters long—belies the immense damage it does to U.S. agriculture from coast to coast. Its assault on small fruits such as cherries, grapes, and berries, costs growers more than $700 million annually. Since 2008, when found in California, it has destroyed up to 100 percent of berry crops in some areas.
Unlike some of its relatives, which damage already rotting and otherwise damaged fruits, the female SWD cuts into intact, ripe fruit with its saw-like ovipositor to inject eggs under the skin. Not only do the larvae damage fruit after hatching but the wound caused by the ovipositor can lead to rot and fungal disease.
Although more than a decade has passed since SWD was first detected in the U.S., no robust integrated pest management program has been designed against it. There is a considerable downside to the most effective way so far to control SWD, which is chemically, with insecticides. It poses potential risk to pollinators and insects that are natural enemies of the fly, as well as to the environment, through consequences such as runoff. Traps with scented baits, according to the paper, attract large numbers of SWD, but often so successfully that fruit damage increases.
The new gum, surprisingly, is not a trap; the fly does not get stuck like Br’er Rabbit on the tar baby. Instead, it gums up the way the SWD’s reproductive process operates.
“The way the gum works,” says lead author M. V. Rossi Stacconi, Ph.D., of Oregon State University, “is not the same as of a standard trapping device. The odors—volatile organic compounds, or VOCs—emitted by the gum disrupt the behavior of the flies, so that they spend a significant amount of their time probing, or tasting, the gum or flying in its close proximity instead of attacking on the crop. The flies are not physically trapped by the gum; however, their behavior is altered and they lose interest in laying eggs in the fruit.”
The gum is an odoriferous concoction of a food-grade, plant-based powder, containing materials such as agar gel, cellulose, pectins, and fructose and glucose sugars, mixed with water into a jelly.
“In order to apply the gum in the field, we created a delivery device,” says Stacconi. They smeared the gum on microfiber cloth, hanging it up, and activating and keeping it moist with water from a drip irrigation system. It was effective that way for more than three weeks. Since the paper was written, he says, the researchers have come up with an even more effective method, akin to spreading jelly on a piece of bread, except that the “bread” is a biodegradable pad of hemp fiber. “It can be easily deployed by growers at the base of the plants, in contact with the drip irrigation system,” says Stacconi, at an optimal ratio of 50 pads per acre.
“We tested the gum on all the main crops attacked by the SWD, and we obtained control levels comparable to those achieved with conventional insecticides. Providing growers with an alternative control tool for SWD is critical, especially considering recent studies showing that the pest is building up resistance against pesticides. We are currently working of the gum to improve its efficacy and to make it easy to use for growers,” he says.
Journal of Economic Entomology
Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.