Wiggly, wormy insects that would like to hide inside nuts and dried fruits succumb to heat generated by radio waves. Researchers, in fact, have known this for decades. Now, however, Agricultural Research Service scientists and their university colleagues are taking a new look at using radio waves to clobber pesky insects in these crops at packinghouses and processing plants.

ARS research entomologist Judy A. Johnson, based at Parlier, Calif., and collaborators at the University of California at Davis and Washington State University at Pullman are evaluating the technology's potential use as a safe, effective substitute for methyl bromide fumigant. Methyl bromide is being phased out in the United States.

Johnson's studies at ARS' San Joaquin Valley Agricultural Sciences Center target navel orangeworm and Indianmeal moth. Those insects are among the worst enemies of walnuts, almonds and pistachios and of dried fruits such as figs and raisins. In addition, Johnson is scrutinizing another culprit, the red flour beetle.

Though a lesser pest of nut and fruit crops, the beetle is a major problem in flour mills and food-processing plants.

Drill test holes

In studies conducted over the past two years, the scientists have developed a preliminary picture of the troublesome insects' thermal tolerance — that is, their ability to endure heat generated by the radio waves. These laboratory experiments are the first to extensively detail the thermal tolerance of the navel orangeworm and Indianmeal moth.

For one test, Johnson and co-investigators drilled tiny holes in more than 500 in-the-shell walnuts, enticing the slender, whitish navel orangeworms to enter the shells. The scientists then plugged the holes and heated the walnuts with radio waves, hot air or both.

All the treatments killed 100 percent of the navel orangeworms. Also, tests led by Johnson's collaborators showed that the treatments didn't harm the quality of the walnuts.