Because caffeine has never been federally approved as a pesticide, the State of Hawaii had to petition the Environmental Protection Agency for permission to experiment outdoors with the antifrog stimulant. The agency granted the state permission to try a 2-percent-caffeine solution as an experimental pesticide spray for 1 year. Pitt says that tests on small plots of infested greenery proved that the spray is indeed "an effective frogicide, if you will." Best of all, he says, caffeine exhibited "very few impacts on other, nontarget organisms." For instance, insect populations in sprayed plots declined a bit, but within a week had returned to normal. The tests turned up another potential benefit. Garden slugs, the bane of the orchid industry, rose to the surface of treated soils and died (see http://sciencenews.org/20020629/food.asp). In September, the temporary EPA permission for testing expired. USDA has now applied for a 3-year extension to conduct further research that might eventually lead to caffeine's federal approval as a frog-control agent. "But we don't want to limit ourselves to one tool," Pitt says, so his laboratory has continued testing other unusual candidate frogicides. It recently uncovered one that's so safe a food product that EPA doesn't regulate it. It's citric acid, the primary constituent of lemon juice. Preliminary tests, begun in August, used a citric-acid formulation roughly comparable to double-strength lemon juice. The spray isn't quite as potent as caffeine for killing frogs, Pitt told Science News. Nevertheless, early data on citric acid "look very promising," he says, "and we see very little impact on plants." In July, the Honolulu Star Bulletin reported that the Hawaii Department of Agriculture had found that hydrated lime, the powder used to reduce the acidity of soil, also kills frogs. Ohashi confirms this, but he points out that hydrated lime couldn't legally be used against frogs unless it were to receive federal approval as a pesticide. And that's unlikely, he adds. Manufacturers don't view as worthwhile the prospect of carrying out the necessary safety and efficacy testing, he explains, "because they make enough money selling it for its currently labeled use." Pitt says that plant growers might also resist lime because it can leave a white residue on treated plants. "If you're an orchid grower selling $200 or $300 plants, a little leaf spotting may not be acceptable," he says. Finally, several research centers are investigating an experimental nursery technique to prevent the spread of frogs in potted plants. Ed Brodie of Hawaii's Division of Forestry and Wildlife in Hilo, for instance, has fine-tuned an $11,000 computer-controlled device that sprays hot water onto a few potted plants at a time to kill pests. A 3-minute spray of 46.5°C (116°F) water kills any coquies and greenhouse frogs present. As a bonus, he says, the treatment kills geckos, centipedes, and about everything else in the soil except ants. Brodie's lab includes a nursery for endangered and native plants. Over the past 3 years, workers there have treated up to 1,000 plants a day with the hot-water spray. The only downside so far is that orchid blooms wilt, but the rest of the plant remains healthy. Source: http://www.sciencenews.org/