Good Mosquito

When nine inches of rain pounded New Orleans in one day early last month, the downpour left behind containers and pools of stagnating water that were perfect breeding grounds for mosquitoes. That was a bonus for the U.S. Department of Agriculture, which had already picked New Orleans as the site for the first extensive test of mosquito control not by chemical or hormonal means but by another kind of mosquito.

The predator mosquito that has raised the hopes of USDA scientists is a creature with the formidable name of Toxorhynchites rutilus rutilus. During its larval stage in stagnant water, the mosquito feeds on the larvae of more common, biting and disease-carrying cousins, like the Aedes aegypti, which also breeds in pools and water-filled containers. Although the Tx. rutilus is found from Florida to Canada and as far west as Texas, it is not very prolific by insect standards and does not exist naturally in numbers large enough to control the population of other mosquitoes. That deficiency presents no problem to USDA Entomologist Dana Focks, who has learned to mass-produce the creature in his Gainesville, Fla., laboratory. Says Focks: "Toxorhynchites are found everywhere and are feasible to use in mosquito control everywhere. But we need to know how many are required and how much it will cost."

To find the answers, Focks will set up in New Orleans two 40-hectare (100-acre) sites, one as a control and one for experimentation. During this summer, he will release in the test area about 1,000 female Toxorhynchites, which will lay eggs that hatch into predatory larvae. Because the New Orleans mosquito control board has kept records on the Aedes aegypti for four years, any significant decrease in its numbers will be apparent. "We know the Toxorhynchites will be effective," declares Focks, "and the cost could be only pennies per acre."

But what happens after Tx. rutilus does in large numbers of the prey mosquitoes? Does it turn, in its adult stage, to bigger meals--like man? Fortunately, the bug's proboscis cannot penetrate the skin of animal or human, and the adult depends for food only on flower nectar and plant detritus. Thus for mosquito control, as Focks puts it, "the Toxorhynchites is a neat package."

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