The more entomologists study DDT, the new wonder insecticide, the more convinced they are that it may be a two-edged sword that harms as well as helps. To find out, they have lately taken to spraying entire islands and other large areas with it. The city of Toronto has now given a detailed report on one such test.
The scene was Toronto's Algonquin Park, heavily infested with budworm moths. City officials first gave the park a thorough DDT spraying by autogiro, then counted the survivors. Results: the deadly chemical killed not only the moths and other insects, but practically all invertebrates, especially crayfish; many minnows; some trout (those that ate poisoned insects); more than half of the snakes and frogs. It also damaged a few broad-leaved trees. But the census takers noted, with pleased surprise, that birds, chipmunks, mice, beaver and deer in the park were apparently unharmed.
The chemical is sometimes, however, destructive of some of man's best friends. At the University of California, when walnut trees were sprayed to kill the destructive codling moth, the beneficent ladybird beetles were killed too. Result: a horde of walnut aphids, normally eaten by the ladybirds, fell on the defenseless trees and stripped their foliage.
The California entomologists have found that in too heavy or improperly timed doses DDT may be harmful to plants (especially tomatoes), animals and people (if they eat heavily sprayed fruit or vegetables). But they have also learned that with care most of DDT's dangers can be avoided: e.g., bees, which are vulnerable to DDT, can be protected against poisoning by spraying fruit trees before they blossom.
The U.S. Department of Agriculture, summing up two years of intensive, nationwide testing, last fortnight reported: 1) DDT is unquestionably the most promising insecticide ever developed; but 2) it is not yet safe for general use.