DDT Down, 2,4-D Up

The U.S. Department of Agriculture had a mournful announcement to make: DDT, the wonderful insecticide that debugged World War II, is losing its effect against mosquitoes.

The first bad news had come from the Air Force, which for four years has been DDTing the marshes near Cocoa, Fla. with signal success. But this year, massed mosquito formations roared out of the swamps once again to puncture young & old. The Air Force fought back with more DDT, but it could not regain command of the air. The Department of Agriculture discovered that the Air Force defeat was due to a new, tough breed of mosquitoes.

Two salt-marsh species so thoroughly adapted themselves to life with DDT that it took ten times the regular dose to kill their wiggler offspring. The discovery justified an uneasy suspicion held by entomologists: when the weaker members of the tribe are killed off, the survivors, mating together, gradually produce a strain that can ignore DDT.

The DOA fears that other mosquito species, including those that carry malaria and yellow fever, may adapt themselves too, as house flies in some places already have. But the department is not discouraged. Other powerful insecticides (e.g., the gamma isomer of benzene hexachloride) can probably take over the job of defeated DDT -- at least for a while.

In the war against nature's banes, scientists also had a victory to report.

One of the worst pests of the southwestern cattle ranges is sagebrush, which romanticists admire but which cattle will not eat. In many places it makes the range almost worthless. Mowing it down mechanically is a slow, costly job.

At the Southern Great Plains Experimental Range at Woodward, Okla., state and federal experimenters found that airplane-sprayed 2,4-D, the chemical that kills "broad-leaved" plants while leaving grasses unharmed, did a fine job of killing sagebrush. The treatment costs a little more than $2 an acre and destroys as much as 90% of the pest. On de-brushed range, cattle gain 75% more weight per acre, and sell for twice as much as if they had to hunt grass among sagebrush.

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