Insects Feel the Electricity in Possible MeBr Alternative

Microbursts of high-voltage electricity could provide a new avenue of research for postharvest control of insects on citrus and other fruit, according to Agricultural Research Service and Ohio State University scientists.

Pulsed electric fields (PEF), as such jolts are called, have been recently studied to inactivate microorganisms such as E. coli in food. PEF is used on liquids such as apple juice in a cold pasteurization process to avoid the changes in color, flavor, texture, and nutrients that the heat of thermal pasteurization can cause.

Reading a technical report on the subject by Q. Howard Zhang, who is with the Ohio State University Department of Food Science and Technology , gave ARS entomologist Guy J. Hallman the idea of seeing if such pulses could take care of insects inside of fruit without damaging the produce.

"I figured if microsecond bursts of 25,000 volts killed E. coli, much lower voltages would disrupt fruit flies because they are much more complex organisms," said Hallman, who is with the ARS Crop Quality and Fruit Insects Research Unit in Weslaco, Texas.

The two scientists found that ten 50-microsecond pulses of 9,000 volts were enough to kill all but three percent of Mexican fruit fly eggs in a small chamber. Of the few eggs that did hatch, none survived to become large larvae. Each pulse was only 1/20,000 of a second long.

Larvae exposed to even smaller, 2,000-volt pulses, while not killed outright, became very sluggish or paralyzed, and began dying a few days later. None of the exposed larvae developed into pupae.

"It is very similar to the effect of irradiation in the sense that, instead of immediately killing an insect, PEF disrupts the insect's ability to mature or reproduce," Hallman explained.

The comparatively low level of electricity and especially the very short durations of the pulses also require only a small total amount of energy and generate very little heat, so treated fruit are not likely to be harmed by the process, Hallman added.

But at this point, Hallman and Zhang have tried the micropulses only on free fly eggs and larvae; they have not tried controlling fruit flies directly in fruit because they lack the necessary equipment. Many additional steps must be taken to prove PEF can completely control fruit flies and that the citrus quality remains the same after treatment.

"We've only opened an interesting door at this point, but it is worth taking a longer look at PEF. We need to see if this is practical on a commercial scale, scientifically and economically," Hallman said.

The problem is no one is building commercial PEF machinery right now. Zhang and Hallman are working with an old PEF generator that had been shelved by the National Aeronautic and Space Administration after it was used to test communications microwave tubes in a Strategic Defense ("Star Wars") Initiative.

ARS is currently seeking an industrial partner to further explore PEF's possibilities. "I'm not ready to be either optimistic or pessimistic about pulsed electric fields as an alternative to methyl bromide for postharvest control of insects like fruit flies on citrus, but it is an idea worth more research," Hallman said.

Last Updated: April 9, 1999