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Males-only Medflies Best for Foiling Invasions

To squelch invasions of the notorious Mediterranean fruit fly, warm-weather states like Florida and California turn loose millions of laboratory-reared, infertile medflies. When these sterile medflies find and mate with wild females, no fertile offspring result, so the wild population soon crashes.

Laboratories in Guatemala and Hawaii that produce sterile medflies for use in these anti- medfly campaigns on the mainland United States may soon shift to producing special, males- only strains known as Temperature-Sensitive Lethal medflies. That’s due in part to investigations by Agricultural Research Service scientist Donald O. McInnis and colleagues with the Animal and Plant Health Inspection Service. McInnis is based at the U.S. Pacific Basin Agricultural Research Center, Honolulu.

Medfly is one of the worst insect pests of agriculture worldwide because it can attack more than 250 different kinds of crops.

According to McInnis, tests that he helped conduct during the past 6 years in Guatemalan coffee fields indicate that what’s known as the Toliman strain of Temperature-Sensitive Lethal (TSL) medflies may be three to five times more effective in quelling invasions than are today’s conventional, mixed-sex strains of laboratory-reared sterile medflies.

TSL medflies get their name from a genetic quirk that makes eggs containing female embryos sensitive to heat. That trait simplifies production of males-only batches. The advantage? Only sterile males are needed for outdoor campaigns.

At medfly-rearing facilities, workers bathe medfly eggs in 97 degrees Fahrenheit water for 12 to 24 hours. That kills eggs with female embryos but doesn’t harm those with medfly males inside. Later, irradiating the male medflies renders them sexually sterile.

Researchers in Austria developed the Toliman TSLs. The ARS and APHIS studies were the largest-ever outdoor tests of the TSL insects. For details, see the June issue of Agricultural Research magazine at:

ARS is USDA’s chief research wing.

Scientific contact: Donald O. McInnis, ARS U.S. Pacific Basin Agricultural Research Center, Honolulu, Hawaii; phone (808) 988-8232, fax (808) 988-7290, dmcinnis@pbarc.ars.usda.gov.