New Lure May Help Conserve Helpful, Sterile Medflies

By Tara Weaver
July 31, 1997

GAINESVILLE, Fla., July 31--The newest Mediterranean fruit fly lure being field-tested in the Tampa, Fla., area may have an additional advantage over conventional lures in medfly traps, said the U.S. Department of Agriculture scientists who developed it.

"Ideally, we only want to trap egg-laying female medflies, and our new lure does this better than other lures tested," said chemist Bob Heath with USDA's Agricultural Research Service in Gainesville, Fla. "The new lure also could prove less appealing to sterile male fruit flies."

That would help the Florida Department of Agriculture, which began releasing millions of sterile medflies July 25. The sterile flies' job is to mate with any wild females that survived the recent malathion sprays. Since none of the offspring of these matings survive to maturity, the sterile-release tactic disrupts the pests' reproductive cycle, Heath noted.

He said traps using the new ARS lure could be placed in sterile-release areas within a couple of weeks. "Our newest lure is relatively unappealing to the steriles because it smells like protein. Sterile male flies, unlike fertile females, don't need protein," Heath said. He and ARS entomologist Nancy Epsky co-developed the new lure at ARS' Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, Fla.

"We placed 50 traps with our attractant in the Tampa Bay area for a demonstration project, to test it during an actual medfly outbreak," Heath said. "We caught about 150 medflies in six days. The several hundred other traps in the Tampa area caught 200 medflies in three weeks. Our traps accounted for 80 percent of all the females caught in all the traps."

A potent synthetic attractant for female medflies has been a major hurdle in designing medfly lures. But "in our traps, 50 to 90 percent of the medflies captured are females," Heath said.

That's because the new lure mimics a high protein source, said Epsky. "The females are attracted because they are developing eggs and have very high food needs compared to the males," she said.

The newest lure has three components--ammonium acetate, putrescine and trimethylamine. The researchers' previous lure had only the first two. The trimethylamine greatly improves female capture, Epsky said.

All three chemicals are emitted from the medfly's natural food sites such as citrus trees, Heath noted.

For the new three-component lure, the Tampa-area test is the largest to date in the United States, Heath said. "California is testing some traps baited with the three-component attractant to detect medflies. There has been no widespread use of our lures in the United States. But Portugal, Spain, Greece, Israel and Guatemala have used them in detection and eradication programs for several years."

California, Texas and Florida use large numbers of trimedlure-baited Jackson traps to detect male flies and protein-baited McPhail traps for male and female flies. Both trap systems have problems.

The glass McPhail traps attract both male and females, but are fragile, cumbersome and difficult to service. Each week, they have to be removed and cleaned, and the baits have to be replaced. They also capture many non-target insects.

Trimedlure, the main lure in Jackson traps, is very attractive to male medflies. But it only weakly attracts females, which are crucial targets because their eggs represent the makings of a wider medfly infestation. Trimedlure baited traps also capture large numbers of sterile male flies.

"Our synthetic food lure captures both females and males, but attracts fewer non-target insects than the protein-baited traps," Heath said.

The researchers' newest attractant is used in a cylindrical plastic trap that protects it from the environment. Each of the three lures comes in its own sealed package and can be placed in a trap without removing it from a site. The trap can be used with or without water, and the lures last 6 to 8 weeks.