Scientists Pit Fungus against Apple Pest

A cocktail of gaseous compounds emitted by a beneficial fungus may offer a way to biologically fumigate stored apples, ridding them of codling moth larvae.

That's the implication of studies conducted by entomologist Lerry Lacey and others at the Agricultural Research Service's (ARS) Yakima Agricultural Research Laboratory in Wapato, Wash. In earlier studies, they showed that a blend of alcohols, esters and other gases released by the fungus Muscodor albus killed adult potato tuber moths and larvae, costly pests of stored tubers. The ARS researchers' work is part of a cooperative agreement with AgraQuest, Inc., of Davis, California.

In the Pacific Northwest, codling moths (Cydia pomonella) are problematic for both growers and distributors. Stored apples are often fumigated with broad-spectrum chemicals when the fruit is destined for foreign markets. However, biobased treatments may provide options for codling-moth control with economic and environmental advantages over standard chemical fumigation.

The Wapato team's investigation of M. albus falls under a larger program to diminish reliance on synthetic chemical controls by using biocontrol agents in an integrated pest management approach.

In laboratory trials, Lacey placed adult codling moths inside special fumigation chambers and exposed them for three days to fungal fumes that killed 83 percent of the insects. Similarly exposing the larvae killed up to 87 percent, depending on their developmental stage. The fungal gases even reached larvae that burrowed inside apples, killing 73 percent of the pests.

Although the initial short-exposure tests didn't yield results comparable to broad-spectrum chemicals, biofumigation's full potential has yet to be evaluated within apple cartons, where the pests will be exposed to fungal fumes for prolonged periods of time. For example, 14-day exposures of the moth's overwintering stage--cocooned larvae, which are the hardest to control--resulted in 100% mortality.

Research by AgraQuest and others has also shown Muscodor's potential to kill other fungi and bacteria harmful to stored fruit and vegetables and to humans.

ARS is a scientific research agency of the U.S. Department of Agriculture.