How a Ladybug Saved Citrus Trees. Biological pest control celebrates 100 years of success. AUSTRALIAN IMMIGRANT TO THE RESCUE

PAUL DEBACH, America's foremost chronicler of biological pest control, likens the event to a ``shot heard round the world.'' Exactly 100 years ago, a tiny Australian immigrant, a dainty ladybug known as the vedalia beetle, rescued the California citrus industry from possible oblivion.

It did so with a speed that seemed almost miraculous and sparked the start of serious research into biological pest control in the West.

Just two years earlier, in 1887, the Golden State's citrus farmers had shipped some 2,000 boxcars of oranges, grapefruit, mandarins, and related exotics to eager buyers elsewhere in the country. The Northeast, in particular, had developed an almost insatiable appetite for citrus fruit, and the future for the young and vigorous industry appeared expansive.

Then came the crash. The groves were almost destroyed by the cottony cushion scale, a small woolly pest, and production plummeted. In 1888 a mere 400 boxcars of fruit left the state, and the price of oranges soared in New York and Boston.

More alarming was the fact that the infestation was increasing at a rate that would almost certainly drop shipments to zero the following season and perhaps eliminate citrus growing as a California industry altogether.

Then in the spring of '89, a program that had been as hotly debated outside the scientific community as it was inside was put into effect. Hundreds of thousands of the voracious little ladybugs were released into the citrus groves.

Reports said that the trees were white with the scale from one end of the region to the other, yet by midsummer they were clean. By year's end, teams of inspectors walking through the groves found no visible evidence of the pest, though it was presumed that a scattered remnant had survived. The cottony cushion scale and the ladybug have kept each other in balance ever since.

THE vedalia beetle must share at least some of the praise now being heaped on it with a fellow Australian, a parasitic fly that was introduced at the same time. Many feel that the vedalia beetle was the more effective of the two, but William Olkowski, an editor of IPM Practitioner of Berkeley, Calif., wonders if this isn't partly the result of the cute little ladybug, or ladybird as the English and Australians call it, getting ``better public relations.''

Writing in the January issue of the IPM Practitioner, Mr. Olkowski says the story surrounding the introduction of biological control to California's citrus orchards is ``worthy of a novelette or PBS production akin to those depicting Darwin's voyage on the Beagle.'' The story has ``drama, excitement, discovery, incompetence, and even some professional jealousy.''

When outbreaks of the cottony cushion scale began to occur, California growers quickly found that known methods of pest control were ineffective.

In desperation some threw tents over individual trees and applied cyanide gas without any effect, though, as Sheila Daar of the Bio-Integral Resource Center in Berkeley put it in a recent address to the Massachusetts Horticultural Society, ``a minor accident and the applicators might easily have eradicated themselves.''

At the time some astute entomologists, among them C.V. Riley, head of the US Department of Agriculture's division of entomology, which has been recently established, and his assistant, Albert Koebele, attacked the problem with logic.

They reasoned that since the scale was not a devastating pest in Australia, effective natural enemies must exist there.

Natural balance is now the basic tenet of classical biological pest control. But a hundred years ago, some scorned the concept. Many people were convinced that the entomologists were simply looking for a free trip to Australia at the taxpayers' expense.

EVENTUALLY reason won out and Mr. Koebele went to Australia to collect the parasitic fly, Cryptochaetum iceryae, previously identified as an enemy of the pest. Koebele also found the vedalia beetle Rodolia cardinalis to be an effective predator and shipped 524 of them back to the United States, along with the flies.

Tests soon showed these insects to be effective control agents and no threat to the California environment. Thousands were bred for general release the following spring, with the now-celebrated results.

In the past 100 years no major outbreak of cottony cushion scale has occurred in California.

But, where minor infestations have broken out, investigation has always revealed one of two causes, according to Mrs. Daar: Either previous pesticide spraying (for some totally different reason) had eliminated the natural enemies, or unusually cold weather had done the same thing. On these occasions the natural enemies are quickly reintroduced so that the balance is restored.

The centennial of this ecological event will be celebrated this spring with two symposiums: ``The International Vedalia Symposium on Biological Control: A Century of Success'' in Riverside, Calif., March 27 to 30, and in McAllen, Texas, April 4 to 6.