Regulatory control

Mediterranean fruit fly

Mediterranean fruit fly on coffee berry.

The Mediterranean fruit fly, also known as the medfly, Ceratitis capitata (Wiedemann), is a destructive fruit pest widespread throughout Africa, southern Europe, the Middle East, Australia, and Central and South America. So far it is not known to be established in the United States except in Hawaii. It attacks over 250 species of plants and is potentially a serious commercial threat to apricots, avocados, grapefruit, nectarines, oranges, peaches, and cherries in the US. To protect US agriculture, APHIS/PPQ, in collaboration with various state departments of agriculture, maintains a rigid quarantine/eradication program based on a three-pronged approach: regulation, survey, and control.

Despite the quarantine, there have been numerous introductions of the medfly onto the US mainland. The first known infestation occurred in Florida in 1929. This outbreak was declared eradicated one year later. Subsequently there have been medfly introductions into Florida in 1956, 1962, 1963, 1981, 1983-1991, and 1997-1998, all of which were eradicated. In 1966 Texas had an introduction that was successfully eradicated, and California has had introductions in 1975, 1980, and 1987, all of which were declared eradicated. Medflies have appeared in the monitoring traps in California yearly since 1987, suggesting that the pest had become established rather than being reintroduced independently each year. However, data on microsatellite and mitochodrial DNA variability (Molecular Ecology (2002) 11, 891–899) confirm that many of the introductions have been small, localized, sporadic, and unrelated, probably the result of infested fruit smuggled in by travelers or sent through the the mails. A few have been near-simultaneous, multiple outbreaks over a wide area, more likely introduced on infested fruit in a commercial shipment distributed through various wholesale and retail outlets.

The improved version of the McPhail trap uses a combination of three chemicals to attract male and female fruit flies.

Medfly detection. Unlike the monitoring methods for the golden nematode (where you must have 10⁷ cysts/acre before you have a 50% chance of detecting it), the monitoring methods for the Mediterranean fruit fly are sensitive to low populations, making early detection of new introductions possible. Early detection and rapid mobilization of the eradication campaign have been the keys to the success of the Medfly eradication efforts in California, Florida, and Texas.

Eradication techniques. Also unlike the golden nematode case (where the eradication methods available simply reduce the nematode populations below the detection threshold), the methods used for Mediterranean fruit fly eradication are actually capable of driving populations to local extinction. The keystone of the medfly control program is sterile insect release, in which enormous numbers of male Medflies are reared in captivity, sterilized with radiation, and released to compete with the wild males in mating with the wild females. To make the sterile insect release more efficient, the outbreak populations of Medflies are first reduced with insecticide-laced bait, either a protein hydroysate plus malathion or a mixture of sugars and attractants plus spinosad. In infested orchards, the fruit is stripped from the trees and destroyed or buried, and a soil drench of diazinon is applied within the dripline of the trees to kill any pupae in the soil.

Half the cost of quarantine and eradication program is borne by the federal government, with matching funds provided by state and local governments. The cost is high, but it is still a small fraction of the societal cost if the Medfly were to become established. First there would be a loss of foreign markets for fresh fruits and vegetables because of their own quarantine laws. This would affect not only the producers themselves but also all the support industries associated with fruit and vegetable production. Secondly the production costs on the affected farms would rise, and the additional insecticides used to control the Medfly would impose a higher cost in the form of environmental pollution. The packing facilities would have to be modified to exclude the flies, and additional postharvest treatments would be required. The higher production costs would be passed on to the consumer in the form of higher prices for fruits and vegetables. Weighing the relative costs, state legislatures have voted year after year to provide the funds to help protect their local agriculture.

References

California Department of Food and Agriculture. 2003. Preventing Biological Pollution: The Mediterranean Fruit Fly Exclusion Program. http://www.cdfa.ca.gov/phpps/pdfs/Medfly_LegisRpt03.pdf