The governor of California alienated both environmentalists and farmers when he belatedly ordered agricultural spraying of the insecticide malathion.
More than halfway through his second term in office, California governor Jerry Brown made the decision to proceed with extensive malathion spraying to combat an infestation of the Mediterranean fruit fly. In part because of governmental vacillation, the fruit fly’s numbers had grown far beyond its initial small population.
The climate of Southern California is nearly perfect for the Mediterranean fruit fly, Ceratitis capitata,
Adult Medflies have yellow-and-black bodies and banded, transparent wings. An adult female fly lays her eggs in groups up to six hundred in her lifetime. Using her ovipositor, she pierces the skin of the fruit, and the eggs develop in the pulp. The white-to-yellow maggots bore through the pulp of the fruit. The fly larvae grow through three stages during their ten to fourteen days inside the fruit. When fully grown, the maggots are about one centimeter long. By this time, the rotten fruit in the wild has usually fallen to the ground. The mature maggot then crawls out and forms a pupa in the soil for two weeks before it emerges as an adult fly. The total life cycle from egg to adult can occur in less than three weeks, or can last for more than three months, depending on climate. In warm regions, fly breeding is continuous throughout the year; otherwise, the pupal stage carries the fly through cooler weather.
The Central Valley region of California is the most productive agricultural region in the world. California ships about one-fourth of its $18 billion harvest abroad. If the Medfly became established in California orchards and fields, many other nations and American states would stop importing produce or demand inspection and treatment to effectively eliminate the risk of importing the Medfly. Such treatments and inspections would cost an estimated $1 billion. An embargo on California produce affected by Medfly concerns would cost an estimated $6.2 billion. In addition, if foreign countries, especially Japan, were to switch to other markets, it would be difficult for California to regain its market after eradication was achieved. Loss of the Japanese market alone would cost California more than six thousand jobs, and if other vulnerable foreign countries followed suit, the market would drop and more than thirty-five thousand jobs would be lost. While Japan and other major Asian countries have not yet embargoed produce from California, China has quarantined California produce because of the Medfly.
Because of the extent of potential damage, traps are used to constantly monitor for the first signs of newly arrived Medflies. If these flies are found, traps are dispersed to determine the exact areas infested and are continually monitored to assess efforts to eradicate the fly. The name of the insect food lure for the Medfly is Trimedlure. Its chemical formula is precisely known: t-Butyl 2-methyl-4-chlorocyclohexanecarboxylate.
Quarantines are imposed immediately when the Medfly is found. Fruit cannot be moved out of infested areas, thus protecting the ability of other areas to export fruit and slowing the spread of the pest to neighboring areas.
The insecticide used to kill the Medfly adults before they lay eggs is malathion. Unlike its more potent organophosphorus-compound relatives, malathion is a weak insecticide with much reduced toxicity for mammals. The control of muscles by nerves requires that a chemical transmitter (acetylcholine) be recycled by an enzyme (cholinesterase). The organophosphorus insecticides block this enzyme from recycling the transmitter, and the interference of the continuous signals to muscles eventually prevents vital organs from functioning; this soon causes death. This is a simplified explanation of why insects sprayed with an insecticide often “tremble to death.” Malathion is considered to be about as safe as any chemical pesticide in this class, requiring a 3,200 times higher oral dosage to produce the same toxicity as tetraethyl pyrophosphate (TEPP), a potent organophosphorus pesticide. Malathion is relatively unstable and soon breaks down rather than persisting in the environment.
Malathion is often mixed with a syrup bait or a yeast protein that attracts the fly. The Medfly is truly a fruit fly that is attracted to sugars and fermentation products. By mixing malathion with such baits, the fly is brought directly to the poison droplet, and overall malathion levels in the environment can be kept even lower. The 1981 campaign in California involved malathion applied at levels of 1.2 pounds of toxicant per acre. Helicopter spraying is generally used to assure complete coverage of the area. While the dosage is well below the allowed level and California has the most stringent pesticide regulations of all states this spraying is nevertheless very visible to suburbanites.
The Mediterranean fruit fly, or Medfly, is a worldwide agricultural pest. In 1981, California governor Jerry Brown ordered the spraying of malathion insecticide to combat the infestation.
New infestations often center in Los Angeles and Orange counties. A portion of the population of California in these areas, however, is opposed to the use of pesticides and in particular the malathion sprayings that are used to depress the Medfly populations and hold the line until sterile release can be used to eradicate the fly. Objections come from many sectors. Some opponents are concerned that the health effects of malathion are not yet well known and may pose a danger to both humans and pets. Because the Medfly repeatedly reinfests the area, some contend that the pest is a permanent resident and should be controlled with natural parasites and beneficial insect predators. Some people contend that the Medfly could not survive in the adjacent Central Valley. Entomologists and government officials, however, are far less certain that the fly could be contained, and they note that California produce would most definitely be quarantined both by other states that are not infested and by foreign importers, particularly Japan.
In the cases in which local officials and city councils have fought the spraying efforts, the governor has declared a state of emergency for infested areas, allowing the California Department of Food and Agriculture to ignore the local restrictions.
U.S. customs inspectors had long recognized the danger of importing this damaging fruit fly. The first infestation to gain a foothold in the United States was discovered in Florida in 1929. It was rapidly exterminated, and it was not until 1956 that another infestation was discovered near Miami. Increases in international travel and shipments have accelerated the risk of reintroductions.
The first Medfly infestation in Southern California was discovered in 1975. The extensive 1980 to 1982 infestation was eradicated, and California was essentially free from the pest for five years. The Medfly showed up again, however, in 1987 and in many of the years since then.
Unlike pesticides that may miss pockets of infestation and that may lead to survival of resistance strains of pests, sterile release is a proven technique that has the potential to drive certain insect populations into local extinction. Fruit flies are good candidates for eradication by sterile release, because they can be raised in large numbers in the laboratory and be subjected to high dosages of radiation. This produces seemingly normal but sterile fruit fly adults that are incapable of successfully fertilizing wild flies when released. Sterile flies must be released in numbers that swamp the wild fly population so that most fertile wild flies mate with sterile flies and lay infertile eggs. When this process is repeated for several generations, the wild fly population drops until the few remaining female flies all mate with sterile males and the population goes extinct locally.
Early experiments with sterilized Medflies in Hawaii in 1959 and in Costa Rica in 1963 showed success despite being held in regions where constant reinfestation kept the pest from being eradicated. Some insects, such as screwworm flies that mate only once and are easily sterilized by radiation without affecting mating behavior, are easily driven to local extinction with the technique. The technique is not effective on other insects such as mosquitoes, because they mate many times, are weakened by irradiation, or have other biological complications. The Medfly appears very vulnerable to sterile release, and the technique has been repeatedly successful in wiping out infestations in Florida. In at least one instance, however, the California Medfly sterile-release program may have suffered a setback when fertile male flies contaminated the sterilized factory flies being released.
The technique cannot work if Medfly populations soar to high levels and the natural fertile flies vastly outnumber the sterile flies scientists introduce. Generally, the ratio of sterile-to-wild flies must be between 10-to-1 and 100-to-1. Therefore, to assure a heavy supply of sterile flies, the sterile-release effort has to be coordinated with the laboratories located in Hawaii and Mexico that raise and sterilize the flies. If the infestation is allowed to spread over a larger area, far more sterile flies are needed. This is where malathion spraying comes in. When an infestation has just started and is isolated in a small area, the state agriculture department can usually use one malathion spraying to knock it down to a small level and finish the population off with sterile release. The California outbreaks, however, have often been unusually extensive by the time they are detected; multiple sprayings in such cases are necessary. Shortages of sterile flies have extended California spraying to several months. The best mode of application has proven to be nighttime aerial spraying from helicopters flying at an altitude of about five hundred feet. Not only is the dispersal of spray more effective from the air, the nighttime schedule assures that far fewer people will be covered by the dilute spray.
California is not the only U.S. port of entry for the Medfly. As a citrus state, Florida also has a tropical climate and carefully monitors for the pest. When one fly was found near Miami International Airport in 1990, Florida spent about $1.5 million to spray and eliminate the fly from a twenty-square-mile area. Control in California, however, has been much more problematic. The infestations between 1980 and 1982 cost the state and federal government $100 million for control, and farmers suffered another $100 million in crop losses. Spraying was required over a region of some five hundred square miles, spanning dozens of local communities and resulting in several hundred damage claims or lawsuits. California maintains a State Medfly Science Advisory Panel for science input to the state problem; a recent chairperson of this panel stated that, in both 1980 and 1989, the state waited too long to begin the eradication program.
The environmental sector consistently is on the lookout for biological control agents to combat the Medfly and has been overly optimistic in promoting these safe miracle cures. Some biological agents, such as the nematode parasite called the Mexican roundworm, have impressive records of depressing Medfly populations in some tests. The roundworm, however, only attacks larval Medflies and does not affect pupae. The populations of parasites cycle with the abundance of hosts. Because the Medfly is so devastating to agriculture, there is essentially a zero-tolerance level: Any survival of the pest would allow its exportation with produce and would have disastrous consequences for other regions.
The ongoing Medfly dilemma contributed to the withdrawal of some political support for Brown. As California governor, Brown had tightened air-quality standards and had reduced air pollution by 25 percent, had created an energy commission that blocked construction of nuclear power plants, and had established a California Conservation Corps. In spite of his substantial environmental record, the Medfly dilemma that occurred late in his second term as governor placed Brown in the middle of a dispute between environmental extremists who considered any pesticide spraying to be dangerous, and farmers who were facing economic disaster.
From both scientific and political perspectives, Brown delayed aerial spraying too long. By the time Brown authorized the necessary spraying, he had lost support from both camps. In spite of a drop in his popularity with voters, which involved other issues as well, such as school and highway finance, Brown ran against Pete Wilson in 1982 for a seat in the U.S. Senate and lost. Succeeding California governors George Deukmejian and Pete Wilson both had the advantage of seeing the consequences of Jerry Brown’s ambivalence when immediate spraying campaigns were needed. As long as wild populations of the Mediterranean fruit fly exist, however, the continued import of illegal fruits and vegetables, mostly in airline passengers’ travel luggage, will doubtless continue to pose the threat of new outbreaks.
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Davidson, Ralph H., and William F. Lyon. Insect Pests of Farm, Garden, and Orchard. 8th ed. New York: John Wiley & Sons, 1987. Continuous updates of this standard reference provide reliable background introduction to many pest species, their history, and control. -
Hill, Dennis S. Agricultural Insect Pests of the Tropics and Their Control. New York: Cambridge University Press, 1975. Details the range, damage, and life history of the Mediterranean fruit fly. -
Kilgore, Wendell W., and Richard L. Doutt. Pest Control: Biological, Physical, and Selected Chemical Methods. New York: Academic Press, 1967. Describes the field trials that extended the sterile-release technique to the Mediterranean fruit fly on Hawaii in 1959 and 1960 and Costa Rica in 1963. -
Metcalf, Robert L., and William H. Luckmann. Introduction to Insect Pest Management. 3d ed. New York: John Wiley & Sons, 1994. Standard reference to solid biological data on insect pests and practical aspects of their control.
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