San Diego Floral Association
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March/April 2011 Volume 102 No. 2
Biological Control: Finding the Right Parasite for the Right Pest
By John Blocker
No single achievement has more thoroughly, soundly, and significantly established a major pest control tactic than the vedalia project. All subsequent projects, programs, advances, and refinement in theory and practice of biological control have sprung from this single event.
– L. E. Caltagirone and R. L. Droutt in the 1989 Annual Review of Entomology writing about the importation of the Australian vedalia beetle 100 years earlier to control cottony cushion scale in California.
New plant pests hitchhike on the considerable amount of plant material arriving in San Diego County each year from around the globe, causing mayhem in our gardens and destruction to farm crops. “We are always inundated with new pests,” says Dr. David Kellum, Entomologist for San Diego County Department of Agriculture.
Since the introduction of the vidalia beetle in 1889 to control cottony cushion scale in California, biological control has proved a reliable method to combat these new pests in both garden and orchard settings. The Federal government, the State of California and the University of California now have divisions that promote pest control with their natural predators and parasites.
The control of the Eugenia psyllid and the giant whitefly provide two examples of this technique. Throughout the late 1980s, leaves of Eugenia plants throughout Southern California suddenly became disfigured. A psyllid, new to the area, proved to be the cause. Spraying, sometimes as often as once per week, was the only way to keep the insect in check and plants looking good.
The psyllid, dubbed the Eugenia psyllid, is native to Victoria and New South Wales, Australia. Found by a homeowner in Los Angeles in May 1988, the psyllid reached San Diego County by the end of that same year. University of California researchers began studying this pest immediately, and in 1992 they released throughout the state a parasitic wasp shipped from Australia. Damage to the leaves largely disappeared, but Dr. Kellum says because the cool spring in 2010 slowed the activity of the parasite, some disfigured leaves appeared again on Eugenia plants for a short time.
Then in 1992 giant whitefly, a pest of hibiscus from Mexico, appeared in San Diego. Scruffy, long white flocking coated the undersides of hibiscus leaves. When the leaves were disturbed, giant whiteflies floated in the air like ash. The University of California imported two species of wasps from Mexico to control the pest. Dr. Kellum believes this pest to be at least 80 percent controlled now.
Leaf damage caused by the Eugenia pysllid
during the winter. Photo: John Blocker
The development of biological control as a pest control method in citrus groves was a long and often painstaking process. In 1926, citrus mealybug invaded the citrus groves in the City of Fillmore as it had Chula Vista’s lemon orchards a few years earlier. The extent of the infestation is reflected in the headline from the Fillmore Herald: “Fillmore and Piru Citrus Growers to Rush Erection Here of Insectary Plant to Kill Citrophilus.”
On April 2, 1926 the Fillmore Citrus Protection District hired Howard Lorbeer, a recent graduate from Pomona College, to oversee the citrus mealybug control project. Immediately, he built an insectary for the 50-member cooperative to raise cryptolaemus, a ladybug known to control citrus mealybug.
Despite the release of the cryptolaemus, citrus mealybug continued to spread out of control in Fillmore and around the state. Recalling how cottony cushion scale and citrus mealybug were controlled by imported predators from Australia, growers urged the University of California to take action. They sent Harold Compere, an entomologist with the Citrus Experiment Station in Riverside, to Australia to look for more parasites and predators. He found two species of wasps in the Sydney area. Upon his return in 1929, he released them into the Fillmore orchards as well as other locations throughout California. As the vedalia beetle had overcome cottony cushion scale in 1889, these new wasps, along with the cryptolaemus already released into the groves, brought citrus mealybug under control in one year.
In the early 1950s, Howard Lorbeer still managed the Fillmore Citrus Protection District’s groves. Around this time he began combining the use of the newly discovered oregano-phosphate pesticides into the District’s pest management scheme. Red scale and red mite were two major pests in his groves. By 1960, the cost of spraying pesticides escalated to the point that the District decided that when pest populations grew too large, growers would have to pay to spray their own groves. The District would continue to release biological control agents for their members.
In 1960, the District released over 75,000 red scale parasites obtained from the University of California Citrus Experiment Station and Rincon-Vitova, a commercial insectary. By the next year, red scale was controlled on Fillmore ranches.
Growers expected to continue spraying pesticides to control other pests such as red mite. But red mite populations also declined when pesticides were not used. Lorbeer had predicted this result. He realized the pesticides destroyed natural enemies of the mites. Without the use of pesticides, the natural enemies now kept the red mite under control. Using parasitic insects for red scale control in the groves reduced total pest control costs by more than half.
Lorbeer demonstrated to researchers at the University of California that releasing parasites of mealybug and other citrus pests provided an effective overall method of pest control in groves and use of pesticides could be minimized. By 1974 when he retired after 47 years, the Fillmore Citrus Protective District, relying largely on biological control, was considered to have one of the most advanced pest management systems in the world. Each year people from colleges, universities, government agencies and foreign countries continue to visit the District to study their pest control methods.
A lemon tree in the landscape free of pests
Hisbiscus plants free of pests
Photos: John Blocker
Rise of a commercial insectary
Everett Dietrick, an entomologist at U.C. Riverside, started the first commercial insectary in California in 1950. He produced aphytis, a parasitic wasp, in his garage. Aphytis proved successful in controlling red scale in Riverside’s hot, dry climate. His only customer that first year was a Mr. Stover, director of a large citrus production company.
In 1951, Earnest and Douglas Green were rearing cryptolaemus beetles in an empty restaurant on Rincon Beach north of Ventura to sell to growers. This is the same predator produced by the San Diego County insectary in Chula Vista beginning prior to 1920, and later by the insectary in Fillmore. Fiscal cutbacks and possibly the touted successes of broad spectrum insecticides in controlling pests led to the closure of the county insectaries and an opportunity opened for a commercial venture.
Dietrick drove with his family from Riverside to Ventura on weekends to help his friends, the Green brothers, establish the insectary. He is still part owner. Today the Rincon-Vitova insectary produces a wide variety of predators and parasites and sells insects for use in commercial groves and residential settings.
According to Gary Bender, San Diego County Farm Adviser for Subtropical and Deciduous Fruit, pests in today’s citrus groves are largely controlled by predators and parasites found in the grove. Growers survey their trees every few weeks. If pest levels are too high, parasites or predators bought from insectaries such as Rincon-Vitova are released. “It is not unusual for citrus growers to spray their groves only once per year with light oil,” Dr. Bender says.
Dr. Bender had his own success story to tell concerning the use of biological control agents. Introduced into California in 1994, the glassy winged sharpshooter threatened to spread a devastating bacterial disease to grapes. Around 2000, Dr. Bender released a parasitic wasp into a heavy infestation of glassy winged sharpshooter on an acre of citrus in Pauma Valley. By the end of the season, the sharpshooter was completely controlled. “When you find the right parasite,” Dr. Bender said, “the results can be amazing.”
–John Blocker worked with the agricultural industry in San Diego for 31 years and has attended garden conferences and viewed gardens around the world during the past 20 years. From 1998 to 2008 he was on the board of the California Garden and Landscape History Society.
Proceedings, Fruit Growers and Farmers Convention, Issue 11, University of California.
Bulletin of the Entomological Society of America, 30: 4 (1984).
The Fillmore Protective District, UC IPM Pest Management Guidelines.
Rincon-Vitova Insectaries (www.riconvitova.com).
Mission: To promote the knowledge and appreciation of horticulture and floriculture in the San Diego region.