Taking the Bait
Synthetic pheromone cocktails attract more than apple moths.
Thursday, January 24, 2008
Think of a group of barflies thirsty for Cuba libres: rum, cola and lime juice. Chances are good they’ll accept an offering of plain old rum and Coke.
Now imagine a larger crowd of boozers with a variety of preferred drinks—daiquiris, mojitos, Long Island iced teas—with some of the same ingredients. Plunk a pitcher of rum and Coke in the middle of the room, and some of them will gravitate toward it.
Apply that sloppy metaphor to insect pheromones, and you’ll have an idea why the products designed to lure invasive light brown apple moths (LBAMs) also attract some members of related species.
In response to public concerns about the aerial spraying of synthetic pheromone products over Monterey and Santa Cruz counties last fall, the California Department of Food and Agriculture has stated that that the products used, CheckMate OLR-F and CheckMate LBAM-F, are “highly specific” and won’t affect monarch butterflies.
But they appear to attract at least five other “leafroller” moths of the tortricid family, whose larvae form nests by rolling leaves and tying them with silk, and at least one moth from another family.
The state’s more than 45,500 pheromone-baited traps, placed in 51 counties, caught almost 12,200 LBAMs, according to a CDFA report. The traps also commonly lured at least six other kinds of insects, some native to California, according to CDFA insect biosystematist Marc Epstein and University of California Cooperative Extension entomologist W.K. Frankie Lam.
Female moths emit unique sex odors that drive only their own males wild, Lam explains. But each trademark pheromone is composed of multiple chemicals in different proportions. In order to synthesize a smell that will dupe males of a target species, scientists isolate one or two chemical ingredients in the female’s pheromone and re-create them in a lab. The resulting product smells almost like a lusty lady of the species.
While the two active chemicals in Suterra LLC’s CheckMate LBAM-F product are believed to be key ingredients in the female LBAM’s sex odor, they may also be present in other pheromone cocktails—particularly those of LBAM’s moth relatives.
That may explain why the state’s CheckMate-baited sticky traps caught not only LBAMs, but also garden and orange torticids, Clepsis fucana and other leafrollers. A moth from the Pyralid family, Archyra sp., also regularly took the bait. At least two of the non-LBAM species caught in the traps are considered invasive pests, but most are believed to be native.
“These pheromones are not as specific as people thought,” Lam says. “Families related to the leafroller family may use the same chemical.”
Top entomologists have publicly doubted that aerial pheromone spraying alone can successfully wipe out invasive LBAMs. The CDFA’s revised plan, released Jan. 22, pushes the next aerial spraying—originally planned for early spring—to late spring or early summer, with hopes of using longer-lasting alternatives to CheckMate pheromones. In the meantime, officials plan to begin ground treatments with pheromone-spiked twist ties, insecticidal bacteria, moth-egg-eating wasps and an “attract and kill” goo containing both pheromones and pesticides.