River of Insecticide

Brazil's Rio Negro, one of the Amazon's main tributaries, is truly black.

So black, in fact, that light penetrating to a depth of 1 ft. is only one-tenth as bright as light on its surface. At 2 ft., it is only one-hundredth as bright; at 6 ft., there is no light at all. Reason: unlike the Amazon's clear-water tributaries, the river does not originate primarily in mountains and course through relatively narrow channels, but flows sluggishly across flatland. jungle and swamp areas. Each year at flood stage the Rio Negro overflows its banks, while draining some 253,000 sq. mi. -- an area almost as vast as Texas. In the process, its waters dissolve untold quantities of plant juices and tree sap. Now scientists have discovered that the Rio Negro's botanically infused waters may be a simple, untapped and essentially unlimited supply of a new and fool proof insecticide.

Leader of the expedition that stum bled on the river of insecticide was Harvard Biologist Carroll M. Williams, 50. Recently Williams has been work ing with hormones that are secreted by insects to permit and regulate growth and maturation from egg to larva to pupa to adult. If insect juvenile hor mone comes in contact with larvae at the wrong stage of development, the in sects will not mature. When insects at later stages are treated with growth hor mone, they are killed by developing at too rapid a rate. Moreover, Williams .and other researchers have discovered that lethal equivalents of these sub stances have been manufactured naturally as a protectant by trees and plants lor millions of years.

His pioneering work fresh in his mind, Williams flew to Manaus, Brazil, last month to fulfill a longstanding six-week commitment to serve as senior scientist aboard the Alpha Helix, a sophisticated research vessel operated by California's Scripps Institution of Oceanography. From Manaus, Williams headed the Alpha Helix upstream for the expedition's shore camp at the confluence of the Rio Negro and the Rio Branco. The Negro, at high-water level during this time of year, "looked like Chesapeake Bay," says Williams. Along the shore, trees and plants were steeped in 30 ft. of the river's opaque water. As the Alpha Helix moved along looking for a landing site, Williams noticed that there were astonishingly few insects, though they are maddeningly plentiful along the Amazon's clear, mountain-bred tributaries.

Williams quickly hypothesized tint the Rio Negro might in effect be an immense tea, pontaining infusions of plant and tree substances similar to the insect hormones. Scooping up the dark river water, Williams and his colleagues, Professors Fotis Kafatos of Harvard and David Prescott of the University of Colorado, freeze-dried and boiled the water to concentrate the chemicals in it, extracted them with solvents, then injected the resulting solution into immature cockroaches. Sure enough, the roaches all died without reaching sexual maturity.

Since many insects have become immune to sophisticated chemical insecticides, Williams' discovery may well provide a crucial weapon in man's interminable war with disease-carrying and crop-ruining insects. But there are problems yet to be solved. So effective are the hormones and their plant-made equivalents, that sprays or dusts containing even minute amounts will kill any insect, including those helpful to man and essential to the functions of nature. The reason that all insects are not wiped out in the Rio Negro area is that not all of them come into contact with the insecticide-laden river. Back at work in his Harvard lab, Williams is now studying the river concentrates to learn what chemicals they contain, and how these lethal substances can be extracted separately for discriminate use against particular pests.

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