The Saga of the Mediterranean Fruit Fly, Part II: 1950 to Present
March 26, 2013
The Mediterranean fruit fly is one of the most destructive agricultural pests in the world. First detected in Florida in 1929, the Medfly attacks more than 260 kinds of fruits, flowers, vegetables and nuts and can be especially damaging to citrus, peaches, pears, apples, peppers, tomatoes and figs. Agriculture officials declared the Medfly eradicated from Florida in 1930 after an intensive campaign in 20 counties that resulted in a number of innovative techniques including trapping, scouting, bait sprays, dividing the state into infested and protective zones and putting controls into place on groves and in packing houses.
(See Part I of this post here.)
Florida’s second Mediterranean fruit fly invasion began in 1956 with the detection of larvae in grapefruit at Miami Shores. Within a week, 23 adult flies had been detected. Eventually, the fly would be found in 28 counties extending from Seminole County south to Key West.
This time, instead of stripping all host plants of fruit and produce to eliminate breeding spots, regulators used fumigation and certification to minimize loss to producers and farmers. Another innovation, airborne spraying, made mass applications of pesticides possible, often within minutes of detection.
At the height of the infestation there were 27 planes in operation daily. Aircraft ranged from World War II B-17s to single-engine Piper Cubs. During the campaign, insecticides were applied to almost 7 million acres.
The spread of the Medfly followed the state’s major highways and as in the 1929 infestation, the National Guard was called in to man roadblocks. Federal quarantines regulated movement of possible hosts out of Florida.
At the peak of the program, 54,000 traps were in use from Pencacola to the Keys. An astonishing 11,932 Medflies were trapped during the successful 18-month eradication campaign that cost $11 million.
The 1980s and 90s: Medfly, Medfly and more Medfly
A series of serious Medfly infestations occurred in the Miami area in 1985 (in the midst of a citrus canker crisis!), in 1987 and again in 1990. A new control measure was introduced to Florida in 1985: Sterile Insect Technology (SIT). Sterile male Medflies were released in combination with traditional aerial treatments. Sterile flies were used again in 1987, following aerial spray treatments.
Sterile male flies are released at a target ratio of 100 sterile flies to one wild female (the overflooding ratio), making the likelihood of a female mating with a wild male low. Mating with sterile males prevents females from reproducing, because their eggs are unfertilized.
Currently sterile flies are reared in Florida from sterile pupae shipped from Guatemala, and routinely released to prevent Medfly infestations. The sterile flies are marked with a dye so inspectors can identify them when they end up in traps.
The 1990 eradication program was the first to encounter mild opposition from the urban public. Some members of the public complained about the aerial spraying that began after 23 flies were found in three residential areas adjacent to Miami International Airport. This time, releasing sterile flies, generally more acceptable to urban residents than aerial spray, was not an option. California was also in the midst of a Medfly eradication program; quality control testing indicated the sterile flies Florida was obtaining were of low quality. Basically, these sterile flies would not mate, and mating, of course, is the whole point of sterile release.
Severe infestation in late 1990s
The most severe Medfly infestations in four decades occurred in the late 1990s. In 1997, the first fly was found in Hillsborough County. By the end of the eradciation program there, 749 flies had been detected in portions of five counties.
The Hillsborough County outbreak spread over an area of about 400 square miles. The program began night-time aerial spraying using three DC-3 aircraft. This time the aerial spraying triggered vocal public opposition. Following aerial treatments, the program released 14 billion sterile flies over a 313 square mile area west of I-75. The USDA removed Hillsborough County from the list of quarantined areas in April 1998.
Later in 1998, the FDACS Division of Plant Industry faced four separate Medfly infestations. Flies were detected in Miami and Umatilla in April, Bradenton/Palmetto in May and Sebring in July. Miami Springs, where only two Medflies were detected, underwent four ground baitspray treatments. In highly agricultural Umatilla, where a total of 1,315 flies were detected, residents requested and received seven aerial treatments by helicopter. In the predominantly urban Bradenton/Palmetto area, 553 flies were detected. Initially, ground treatments were applied, but after the affected area grew to nearly 40 square miles, DC-3 aircraft delivered aerial treatments. In Sebring, 134 flies were found and eight aerial treatments were delivered using helicopters.
In each of these areas, baitspray treatments were followed by sterile fly releases.
The continuing role of sterile release
Following eradication, a preventive sterile release program began in May 1998 over a 700-square-mile corridor of Hillsborough, Manatee and Sarasota counties west of I-75. In October 1999, this area was reduced to about 370 square miles, and in march 1999 the program began dropping about 20 million flies per week over a 100-square-mile area in Miami-Dade County. Officials credit the preventive sterile release program, which continues today, for reducing the incidence of the Medfly in Florida. A new FDACS/USDA sterile insect rearing and release facility opened in Sarasota in February 2002. Presently, approximately 80 million flies are being released weekly.
During 2013, this blog will focus on some plants that, for better or worse, have helped form the history of our state. We will be drawing on expertise of our DPI scientists and we invite everyone to participate. We welcome your questions and comments.