Sex and the Single Fruit Fly

A decade ago, the California Department of Food and Agriculture was dropping malathion on us in order to kill medflies. Now they've changed their approach: They raise medflies and drop them on us.

This may seem mad, but there's method in it. The ingenuity of the program is that the flies that rain down on Los Angeles have been blasted into sterility with ionizing radiation. They're sexual decoys. It's a numbers game: If there are 100 sterile flies prowling around for every fertile wild one, the great majority of matings will produce no offspring. The dreaded damage medflies wreak on fruit occurs as a result of the flies' reproductive routine. It's the maggots, not the flies themselves, that spoil fruit: no eggs, no maggots.

White cardboard boxes travel by night from high-tech fly farms in Guatemala and Hawaii. They reach LAX at dawn. Couriers hurry them to the Eclosion Lab, located on several acres of the Armed Forces Reserve Center at Los Alamitos. There, in a trailer stained a lurid pink by fluorescent-dyed dust, white-coated, masked attendants slice open the boxes and lift out the garish "sausages" - plastic bags filled with dyed pupae that look like pink rice. Each bag carries a black label: irradiated.

Harrison Ford scowls down from an Air Force One poster on workers opening the bags and pouring out the pink grains. One scoops a cupful at a time into small brown paper bags, then staples the bags loosely at the top and arranges them, six at a time, in the bottom of gray plastic crates called PARC - for "Plastic Aerial Release Container." Others snap lids onto the crates and carry them to a dark, narrow, warm enclosure - the Incubation Trailer - where dozens of other PARC boxes are already stacked, receding into the gloom.

Two hours later, workers take down the stacked boxes, lay a transparent gelatinous slab of fly food on a screened window in the lid of each one, and restack them. They then close the door tightly on the warm, humid darkness.

After three days the door is opened again. By now an ominous buzzing fills the room, and its atmosphere is dense with a musty, stifling, indescribable odor. You hit it like a wall. It's pheromone: the B.O. of millions of sex-starved medflies.

Today - freedom! First, however, they must be immobilized. Workers carry the PARC boxes to a refrigerated trailer where the flies cool, in the space of half an hour, to 38 degrees Fahrenheit. Torpid, they are taken to the Knockdown Room, where the opened crates slide down a long stainless-steel counter and are slammed inverted over a wide funnel. A slowly squirming mass of logy flies tumbles into waiting trays. These in turn are emptied into a chilled stainless-steel hopper, a cube about 3 feet on a side.

The hopper is hefted into a van and driven to the airport ramp, where an old tail-wheel Beechcraft, modified with twin turboprop engines, awaits. The airplane's passenger cabin has been gutted. Bolted to the center of the floor is a metal structure with three troughs containing motorized white Teflon screws that turn slowly, driving whatever lies in the troughs toward a pair of chutes that stick out through the boom of the fuselage. From one side rises a pedestal sprouting cables and switches. The fly-filled carrier clamps onto the top of this apparatus. The pilot and first officer climb in, turn on the fly refrigeration system, and close the cabin door behind them. Soon, with a dull whine, propellers begin to turn.

The old twin Beech will fly to a specified area, and, under satellite guidance, it will weave back and forth precisely along preprogrammed parallel tracks. In half an hour the flies, augered into space at a rate of 62,500 per square mile, will be raining down like mercy on you and me, warming as they fall. Five airplanes, 14 pilots, seven days a week, rain or shine. Each week, every one of 2,155 square miles gets dumped on twice. Each year, 14 billion shivering flies fall down those chutes. "We've got McDonald's beat," one Agriculture official quips, probably for the thousandth time.

The program costs about $15 million a year. In order to ensure that those dollars are well spent, each day a sharp-eyed technician sexes flies, records infant mortality and mutation rates, and even assesses "mating propensity" to be sure that the insects bombing L.A. aren't duds. Meanwhile, fly geneticists are perfecting a modified strain in which heat is more lethal to the females than to the males. This will permit them to kill off most of the females, and drop males only - they're the ones that count in this business - in smaller numbers. That would bring costs down. The current program aims only at prevention; eradication would require greater saturation, and would cost twice as much.

The fly bombers can often be seen overhead; they cruise low, at 2,000 feet, and can be recognized by their unpainted metal skins, their oddly long noses and engine nacelles, and their old-fashioned double tails. But if you happen to look up the next time you hear a low-flying plane - remember to keep your mouth closed.