Regrouping in battle against bugs

* Double-dipping papayas in baths of hot water. * Zapping fruit with gamma rays. * ''Fly-free zones'' littered with booby traps and small armies of sterile flies.

These are among a host of new weapons being considered by farmers and researchers for dealing with one of agriculture's enduring dilemmas: controlling insects and preserving food.

The problem of pest control has been highlighted in the wake of the regulations on the pesticide EDB (ethylene dibromide) as a fumigant for grain, fruits, and vegetables.

It is a problem that has been around since seeds were first put in soil. It will be a predominant theme over the next few decades, as the pressure to produce more food and public anxiety about theuse of agricultural chemicals mounts.

This concern is spurring the hunt for more benign brews and nonchemical alternatives to rid food of irksome insects. The search won't be easy, however. Already, some of the ideas -- both new and old -- being looked at to replace EDB , a pesticide linked to cancer in laboratory animals, are stirring deep-seated political debate.

Nor are there any simple technological solutions. Health concerns aside, EDB and other fumigants are low-cost, verstile pest killers: EDB will eliminate a fruit fly on papaya as well as a moth in a grain silo. With most fumigants, a different treatment is needed for every kind of pest on every type of food.

The upshot is that agriculture is going to have to stock more arrows in its pest-control quiver. ''In the past, agricultural chemicals could do no wrong,'' says Dr. Robert Metcalf, a University of Illinois entomology expert. ''We are moving to a more balanced approach.''

Among some of the alternatives to EDB -- and their shortcomings:

* Other chemicals. In the short run, another pesticide, methyl bromide, is expexted to be used more to treat grains and some citrus fruits. It has long been used for both. As a fumigant, it penetrates deeply into foods and dissipates quickly, usually within a few days. The snag is that the chemical is a gas (EDB is a liquid at room temperature), and thus can be more dangerous to workers who apply it.

A recent laboratory-animal study has alos indicated that it is carcinogenic, as many scientists had suspected. Many observers believe its use will be restricted within a year or two. Two other likely substitutes are carbon tetrachloride and phosphine. Carbon ''tet'' is under attack as a health threat, too.

* Cold storage. This is considered a good, if expensive, alternative for treating some fruits and vegetables, particularly those shipped overseas. The reason is time: Freezing larvae in the fruit requires 13 to 22 days in a warehouse cooler 00 roughly the time it takes a refrigerated ship to make it from Florida to Japan (the state's biggest export customer).

For sterlizing domestically shipped produce, however, it would be too time-consuming a process -- and too costly to build enough coolers. One added problem: To avoid cold damage, some citrus, such as grapefruit, have to be chilled a week before being put in the near-freezing refrigerators, requiring an even longer treatment process.

* Irradiation. Using low levels of radiation for pest control recently gained prominence when Margaret Heckler, US secretary of health and human services, proposed it as an alternative to toxic chemicals like EDB. The process is now prohibited in the United States, except for treating minor items like spices and space food. The Food and Drug Administration should decide by year's end whether to expand its use. The chief objections to it are concern about whether the treatment causes chemical changes in food, and, most important, public suspicion about using anthing nuclear.

The technique, around for some 30 years, has several pluses: it kills pests and bugs without leaving chemical or radioactive residues. It also retards spoilage and increases the shelf life of many foods, ranging from lettuce to precooked meats. There are practical considerations, though. ''You just can't irradiate a silo of grain,'' says Dr. John Osmun, a pesticide expert at Purdue University.

* ''Fly-free zones.'' These are areas kept bug-free, most often through natural land management and biological techniques. Florida is experimenting with the idea to control the dreaded Caribbean fruit fly. First, an orchard is cleared of the main foods that attract the fly (Suriname cheries, for instance). Then, bird-feeder-like traps are usually hung on trees to nab what intruders are left.

To further control pest populations, sterile flies can be released in the orchard: These mate with the normal bugs and produce steile offspring, eventually reducing the population. This approach has worked well with such insects as the screwworm, which attacks cattle. Texas has had some success with fly-free zones. Florida is now testing the idea on 2,500 acres of grapefruit. The state is also considering building a sterile insect-rearing facility.

Snags with fly-free zones: They often work only in areas where there are low bug populations to begin with (rural areas in Florida). Clearing ''host trees can be costly. Just a few bugs can spoil the effectiveness of this method.

Other approaches, however, might work for specific fruits and vegetables.

Researchers can rid papayas of insect larvae by picking the fruit when it is one-quarter ripe and then dipping it twice in hot water. But more study is needed to make it practical for growers to twll exactly when the melonlike fruit is one-quarter ripe.

''In the future we are going to have to have as many tools to control pests as possible,'' says Dr. Milton Ouye, a scientist at the US Department of Africulature research center in Beltsville, Md.