Mediterranean fruit fly

The Mediterranean fruit fly (referred to as Med fly, or Moscamed in Spanish), Ceratitis capitata, is one of the most destructive fruit pests in the world. The United State has suffered infestations of Med fly in California, Texas, and Florida, but with aggressive detection and eradication programs, the Med fly has not yet become established in the United States. However, eradication efforts are difficult and expensive. There is a loss of crop yield associated with the infestation, control measures are costly, and both fresh and processed fruit and vegetables must be sorted. Some countries maintain quarantines against the Med fly, which eliminates potential markets when Med fly becomes established in an area.

The Med fly, which originated in Africa, is widely distributed throughout the world, as it has a wide range of hosts and is able to tolerate colder climates better than most other species of fruit flies. It has caused infestations in over 85 countries in tropical and subtropical regions. Since 1929, the United States has been involved in several outbreak and eradication programs. The Med fly became established in Hawaii in 1910. Hawaii remains infested, and there is no eradication program currently under way.

Med fly larvae can develop and feed on most deciduous, subtropical, and tropical fruits and some vegetables. It has been shown to attack more than 260 different fruits, flowers, vegetables, and nuts. The Med fly prefers thinskinned, ripe succulent fruits such as deciduous fruits (for example, pear, peach, and apple) more than citrus fruits. The larvae feed on the pulp of fruits, tunneling through it, and reducing the fruit to an inedible juicy mass. In the Mediterranean countries, often only the earlier maturing fruits are grown, because later maturing fruits would be too heavily infested to be marketable. Harvesting before complete maturity is also practiced in Mediterranean areas with Med fly infestations.

The adult Med fly is slightly smaller than a common housefly. It is colorful, with dark blue eyes, shiny black thorax (back), and a yellowish abdomen with silvery cross bands. Its droopy wings are covered with yellow, brown, and black blotchy spots and bands.

The life cycle of the Med fly has fives phases: (1) the adult female pierces the skin of a fruit or vegetable with a needle-like ovipositor and deposits one to 10 eggs (other Med flies may deposit in the same puncture); (2) eggs hatch into maggots (worm-like, legless larvae); (3) larvae feed upon the pulp of the fruit or vegetable before dropping to the ground; (4) the larvae transform into pupae into the soil ; and (5) the pupae mature into adults and emerge from the soil. The life cycle is completed in 21–30 days under tropical summer weather conditions.

An eradication program consists of three areas of action: survey, regulation, and control.

The Animal and Plant Health Inspection Service (APHIS) of the U.S. Department of Agriculture in cooperation with state departments of agriculture survey high-risk areas of states susceptible to Med fly infestations by conducting trapping programs. If one or more Med flies is collected in a trap, APHIS and state officials implement a survey to determine if there is an infestation and if so, to define the limits of the infested area. Using the original detection site as the focal point, additional traps are placed and monitored.

If an infestation is identified, then federal and state regulations dictate that a quarantine must be imposed to prevent the spread of the Med fly. Federal quarantine laws prevent the interstate movement of any article that might harbor the fly. State regulations control the movement of these articles going to uninfested areas within the same state. The regulated articles include all of the fruits and vegetables within the area that could serve as a Med fly host. Open-air vegetable and fruit stands are required to cover produce to prevent infestation. All commercial and home-grown produce may not be transported without inspection and treatment.

To eradicate a Med fly infestation, three kinds of treatment are used alone or in combination. An aerial and ground bait spray can be used that contains a protein/sugar bait to attract the fly and an insecticide in minimal amounts to kill the flies.

In the Sterile Insect Technique (SIT), Med flies are raised in large numbers, sterilized with a non-lethal dose of irradiation, and released into infested areas, where they mate with the wild Med flies. As these matings do not produce offspring, the wild population is eliminated through attrition. This technique is most effective in areas with low Med fly populations where a high proportion of sterile to wild Med flies can be achieved. Before the use of SIT, bait spray can be applied to decrease local populations down to lower densities.

The third method is to apply insecticide to the soil under host trees, where the insecticide kills some larvae as the enter the soil to pupate but most of the adults as they emerge from the ground. Application of insecticide to the soil is used only when larvae are detected. The preferred method of eradication control is an integrated approach, using all three treatments, with the use of SIT emphasized.

To prevent Med flies from being brought into the United States, APHIS administers agricultural quarantine laws to keep foreign plant pests and diseases from being brought into the country. Travelers coming to the continental United States from Hawaii or a foreign country are not allowed to bring into the country fresh fruits, meats, plants, birds, and plant and animal products. In fiscal year 1998, when 400,000 aircraft were cleared to bring travelers and cargo into the United States, APHIS officers intercepted more than 1.8 million illegal plants, animals, or plant and animal byproducts. More than 52,000 plant pests and diseases known to be dangerous to the U.S. agricultural industry were also intercepted.

If Med fly were to become established in the United States, prices of fruits and vegetables would increase, and produce would become less available. Both commercial production areas and backyard gardens would require the application of more pesticides on a regular basis. In 1993, APHIS estimated that annual losses due to Med fly infestations would be about $1.5 billion annually, if Med fly were to become established in the United States. These losses would be due to export sanctions, lost markets, treatment costs, reduced crop yields, and premature fruit drop.

[Judith L. Sims ]