Principal Investigators: Jennifer L. Sharp, research entomologist, and Jimmie King, support chemist, Subtropical Horticulture Research Station, USDA-ARS, Miami, FL 33158.

Methyl bromide will be banned for use in Canada and the United States in 2001 because the chemical has been reported to destroy the ozone layer of the stratosphere. Methyl bromide is a broad spectrum fumigant used to control a multitude of pests, including nematodes, snails and slugs, mites, insects, and microorganisms. The loss of methyl bromide will cost consumers and producers billions of dollars unless a successful replacement can be found.

Unlike methyl bromide, methyl iodide is not considered a threat to the ozone layer because it is rapidly destroyed by ultraviolet light. Methyl iodide, however, acts as a biocide similar to methyl bromide. Methyl iodide has been tested successfully and shown to control soil and weed pests. Tests were initiated at the Subtropical Horticulture Research Station in July 1997 to investigate methyl iodide as a toxic fumigant to control Caribbean fruit fly eggs and larvae and to evaluate its effect on the market quality of treated fruits and one vegetable.

Fumigation chambers used in the experiments were 1-cubic-foot vacuum chambers modified by the addition of a circulation fan and sampling ports. The chambers were mounted in a fume hood so that the toxic vapors of methyl iodide could be vented easily. Test materials were placed in the chamber and then methyl iodide was measured and dispensed into petri dishes by using a microliter syringe. Metal "c" clamps pressed the vacuum doors firmly against the seals. Only 190 microliters of liquid methyl iodide (2.28 grams per milliliter) were needed for a dose of 16 grams per cubic meter. Methyl iodide boils at 108.5 ^oF and rapidly vaporized inside the chambers.

Grapefruit, guava, papaya, and chayote were fumigated for 1, 2, and 3 hours at a dose of 16 grams per cubic meter and then stored at 55.4 ^oF for a week to determine if the treatment damaged the market quality of the produce. Only the fumigated chayote showed injury, which was stem-end rot and brown areas caused by prior rough handling and exacerbated by the treatment.

Guavas infested with Caribbean fruit fly eggs and larvae in the field initially were fumigated for 2 hours with doses of 16, 32, and 48 grams per cubic meter. Treated eggs and larvae did not survive the treatments. Next, similarly infested guavas exposed to 16 grams per cubic meter of methyl iodide for 20, 30, and 40 minutes resulted in 54, 62, and 64 percent control, respectively, of the natural infestation of eggs and larvae. Caribbean fruit fly eggs 24 hours old obtained from a laboratory colony exposed to 2, 4, and 8 grams per cubic meter for 30 minutes resulted in 24, 49, and 90 percent control, respectively. Exposure of laboratory-reared mature larvae 7 days old to concentrations of 2, 4, and 8 grams per cubic meter for 30 minutes resulted in 96, 96, and 99 percent control, respectively.

If registered, methyl iodide would appear to be an effective methyl bromide alternative to control eggs and larvae of Caribbean fruit fly. Additional tests are being conducted to establish minimum doses required to meet quarantine rules and regulations.