Common baking ingredients may offer a way to bolster the effectiveness of Cydia pomonella granulovirus (CpGV), a natural insect pathogen that’s been commercially formulated to kill codling moth larvae—the proverbial worms in the apple (and pear, walnut and other orchard crops).
Studies by U.S. Department of Agriculture (USDA) entomologist Alan Knight and his Swedish colleague Peter Witzgall show that adding two feeding stimulants to the spray formulations—brewer’s yeast and brown sugar—can increase the pests’ ingestion of the lethal insect virus, sparing more fruit from harm.
The scientists’ investigations are part of a broader research effort to incorporate novel ingredients, or “adjuvants,” that will improve CpGV’s performance as a biobased alternative to broad-spectrum insecticides, which can be costly to apply and harmful to beneficial insects, including parasites or predators that keep secondary pests in check.
Currently, CpGV is used on more than 370,000 acres of apples worldwide. However, its effectiveness as a bioinsecticide can be diminished by exposure to ultraviolet light (UV) and the larvae’s tendency to burrow into fruit to feed shortly after hatching, according to Knight, who is with USDA’s Agricultural Research Service (ARS) in Wapato, Washington.
In 2 years of field trials, the addition of sugar and brewer’s yeast to sprays of CpGV killed more larvae (83 percent) than virus-only formulations (55 percent) and water-only controls (17 percent). The treatments also reduced feeding injury to the apples in 1 of the 2 test years, reports Knight, with the ARS Fruit and Vegetable Insect Research Unit (also known as the “Yakima Agricultural Research Laboratory”) in Wapato.
Besides sugar and brewer’s yeast, Knight and Witzgall are evaluating other natural adjuvants to make the virus more effective. These include feeding stimulants such as pear ester, unpasteurized corn steep liquor and certain wild yeast species.
Even with improvements, CpGV isn’t likely to become a stand-alone codling moth control for all growers in the industry, but rather a part of an integrated approach to managing the pests using a variety of measures, such as sex pheromone-based mating disruption.