The Bug That Saved California | Science

Orange and lemon groves as well as the residence of the citrus pioneer William Wolfskill, c. 1882.
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In the early 1870s, ambitious farmers were cultivating the first seedless navel and sweet Valencia oranges amid the bountiful sunshine of California’s citrus groves. Soon these groves would become the proving grounds for the new science of biological pest control, pitting a rare species of ladybugs against an invading horde of pests in a battle for the future of citrus agriculture in California—and the world.

Commercial agriculture drove the largest economic expansion in California since the discovery of gold at Sutter’s Mill. And oranges, initially brought there by Spanish missionaries, had become California’s most valuable commodity. The number of acres under citrus cultivation in Southern California increased sevenfold between 1877 and 1890, while the number of railroad boxcars exporting these juicy treasures doubled to nearly 6,000 a year, spurred on by the Southern Pacific railroad line, which reached Los Angeles in 1876, and by the Southern Pacific’s use of train compartments cooled by huge blocks of ice beginning in 1888. Fruit traveling east was now worth $20 million annually, having increased by a factor of ten in as many years. Nothing, it seemed, could stop what many were calling a second gold rush. Then a fuzzy white bug suddenly appeared, touching off an environmental crisis.

An adult Novius ladybug devours an Icerya in the Galápagos Islands.

Courtesy UC Riverside

How the cottony cushion scale, a virulent tree pest native to Australia, was unleashed upon the citrus trees of the world is a bit of a mystery. Its populations exploded in New Zealand in 1878; entomologists there identified it as the new species Icerya purchasi. By the early 1880s, it was ravaging San Francisco’s trees and quickly migrating south, its tiny red larvae hitching rides on anything that moved, even the wind.

In 1884, Icerya reached Los Angeles, assembling most aggressively on the south side of William Wolfskill’s ranch—the first commercial citrus orchard in the state, one of the largest. The ranch had seen various infestations before, but nothing like this. No matter what they tried—washing the trees with whale oil, heating them with sheet-iron stoves and blistering steam, cutting off and burning infected limbs—the waxy, mold-riddled scales excreted by Icerya, which one horrified grower likened to a “hideous leprosy,” continued to infect more and more trees. In desperation, they even tried gunpowder blasts, but the concussive vibrations had no effect.

John C. Wolfskill, brother of William, surveys the orange grove at Wolfskill Ranch, c. 1895. The property covered roughly 165 acres in Pasadena.

Los Angeles Public Library

The densest clusters of Icerya lurked on the tender underside of leaves, where they attached themselves with cottony fibers and extracted sap with their sharp beaks, causing leaves to wilt. Some 600,000 orange trees were growing in California, and the number that succumbed to Icerya is unknown, but it must have been high: In 1887, the state’s citrus export filled 2,000 boxcars, but only 400 the following year.

Throughout Southern California, ruggedly independent growers reacted to the insects’ assault by organizing themselves, in 1885, into the state’s first fruit cooperative, later calling itself Sunkist. Concoctions of kerosene, acids and other chemicals didn’t stop Icerya’s expansion. Fueled by an endless supply of trees to feast on, the pests spread rampantly. New laws required growers to dig up and burn affected orange trees. Real estate values that had risen 600 percent since 1877 cratered by 1888.

In 1886, the deepening crisis prompted Charles Valentine Riley, then 43 and chief of the U.S. Department of Agriculture’s Division of Entomology, to dispatch two federal entomologists, Daniel Coquillett and the German-born Albert Koebele, to Wolfskill. Their hundreds of pesticide experiments proved that no combination of ingredients could both exterminate Icerya and leave the trees unharmed. Coquillett marveled at Icerya’s “extreme tenacity of life,” observing that “an adult female…when sprayed with a solution so caustic that her back was burned black and hard and wrinkled, still retained use of all her organs.”

Riley mused publicly about discovering Icerya’s “natural enemies.” Biological control of agricultural pests wasn’t a new concept—as early as 1762, the French East India Company imported mynah birds from India to control locusts on the island of Mauritius—but it had never been tried on such a scale, or when the economic stakes were so high. Riley’s eventual success launched the field of applied entomology—using bugs to protect crops—and secured his legacy as its founder. Today, conscientious farmers use integrated pest management plans that blend biocontrol with the judicious use of pesticides.

Riley wished to send a field agent to Australia, where local entomologist Fraser Crawford had recently discovered the only known enemy of Icerya: a parasitic fly, Cryptochaetum icerya. In August 1888, Koebele sailed for Australia.

He arrived in Sydney on September 20, 1888. After a spell collecting Crypto flies, he spotted a different insect on October 15 that would change everything: a species of ladybug, now known as Novius cardinalis, eating a large Icerya. Neither he, nor Crawford, nor Riley, whom Koebele informed of the discovery by letter, recognized the force of nature Koebele had found. “We have much more to hope [for] from” the Crypto fly, Riley wrote in reply.

The Crypto flies that Koebele sent to Coquillett at Wolfskill via steamship—the first batch arrived on November 30, 1888—failed to establish themselves in Southern California. But he had also presciently included a cache of Novius, and two Novius larvae that had survived the journey proved their worth by hungrily attacking and killing an Icerya on an orange tree that Coquillett had enclosed in a tent. From October 1888 through January 1889, Koebele shipped Coquillett 164 Novius ladybugs, stored in freezers so they’d survive the 30-day trans-Pacific crossings. Once at Wolfskill, they exhibited an appetite for Icerya unlike that of any other insect in California–—including American ladybugs, which are more than twice the size of Novius.

“[It was] the world’s most successful experiment in biological control.”

Koebele studied Novius closely. Male and females copulated for days, then the females laid countless eggs as both sexes went on a feeding frenzy among the Iceryae. One female Novius ate the Icerya’s body “very quietly at first,” Koebele noted, then in a “lively, almost furious” manner, “tearing the scale off from its hold by the beak and turning it up and down in the air…leaving nothing but the empty skin”—after which she went back to thrusting her eggs between or under Iceryae.

Life-sized and enlarged images of Novius cardinalis (4 and 4a), and of pesky Icerya (5-7), shown most conspicuously on the branch.

Alamy

In California, the ladybugs Koebele had sent were devouring every Icerya on the orange tree Coquillett had enclosed inside the propagation tent, so in early April of 1889, Coquillett decided to open one side of the tent to release the swarming ladybugs. In mere weeks, they had restored every tree at Wolfskill Farm to its pre-infestation health without any negative side effects. Citrus growers throughout Southern California came to Wolfskill with Icerya-infested branches to take ladybug colonies of their own back home, where the new miracle bugs performed similarly. By the autumn of 1889, California growers were faced with a fresh and almost comical new challenge, suddenly scrambling to preserve enough Icerya to keep the ladybugs from cannibalizing themselves out of existence: Without Icerya to feed on, these cute but quietly ferocious bugs eat each other, including their own larvae, so growers had to devise methods to keep the two populations in balance.

The following spring, Koebele and his Novius ladybugs were being hailed as heroes by an adoring public. The fruit growers’ association gave him a gold watch and his wife diamond earrings—small tokens for his spectacular accomplishment, which has since produced incalculable returns worldwide. Today scientists refer to the episode as the first instance of modern biocontrol. In her 1962 classic Silent Spring, Rachel Carson calls the Novius’ work in California “the world’s most famous and successful experiment in biological control.” In the years since, even the most fortunate entomologists have struggled to match the stunning results enjoyed by Riley, Koebele and Coquillett. The introduction of the Novius ladybug to California remains the standard against which all biocontrol efforts are measured.

Riley retired from the Department of Agriculture in 1894. Before his untimely death in a bicycle accident in 1895, he donated his insect collection to the Smithsonian Institution’s division of entomology and became its first honorary curator; his beetle specimens are still an important part of the National Museum of Natural History’s Coleoptera collection. Coquillett became a global expert in flies but also died young, at 55. Koebele continued to hunt bugs across the world, primarily to combat sugarcane pests in Hawaii. He died in his native Germany in 1924, at 71. Over the next century, Icerya spread around the globe—to France, Italy, Eastern Europe, South Africa, India, Japan, Peru, Chile, the Galápagos Islands and elsewhere. Descendants of the original Novius ladybugs persist in their crucial work, rescuing citrus and other trees from destruction.

The advent of large-scale industrial pesticide use, born of chemical weapons developed in World War II, has made controlling Icerya more difficult: Wherever pesticide use destroys Novius populations, outbreaks of Icerya still occur, even in the orange groves of California. Not surprisingly, Icerya are stubbornly resistant to modern pesticides. These days, some orchardists pay up to a dollar per Novius ladybug whenever the ugly white fuzz returns.

You are not likely to see this exceptional species of ladybug on your windowsill or in your backyard. To find a Novius, you must first find Icerya. In such places, you might spy just one dancing on a leaf in the hot sun, blissfully unaware of its species’ importance to the fortunes of citrus agriculture and the future of biocontrol across the world.