Males-only Medflies Best for
By Marcia Wood
June 26, 2000
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. Thats 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
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 whats known as the Toliman
strain of Temperature-Sensitive Lethal (TSL) medflies may be three to five
times more effective in quelling invasions than are todays 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
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
doesnt 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 USDAs chief research wing.
Scientific contact: Donald O. McInnis, ARS U.S. Pacific Basin
Agricultural Research Center, Honolulu, Hawaii; phone (808) 988-8232, fax (808)