Word: larva
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Dates: during 1960-1969
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Scientists anxious to find a safe but powerful pesticide have long been fascinated by the juvenile hormone that is secreted by insects. At certain stages of an insect's life cycle, the hormone must be present to regulate growth and control the transformation from larva to pupa. At other times the hormone must be absent, or the insect will develop abnormally and never reach sexual maturity. If a sufficient dose is given to a mature female, it can make her sterile for life thus eliminating future generations. The trouble is that the hormone, synthesized in commercial quantities and sprayed...
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...
Chemist Clever soon had his answer. Within 20 minutes after a larva got an injection of ecdysone, its chromosomes grew puffs. Shortly after that, the larva turned into a pupa...
...nature reads its own code. The great store of hereditary information that DNA contains, says Karlson, is not needed all at once. It comes into play gradually, as if it were being looked up, item by item, in a book of instructions. When the time comes for a larva to turn into a pupa, ecdysone secreted by its glands circulates among the cells and comes in contact with the long, ropelike molecules of the DNA in the chromosomes. The hormone affects only those parts of the DNA molecule that contain a few items of chemical instructions needed for metamorphosis...
...kill a pest may attack friendly insects or even humans. Berg does not believe that the marsh fly-either in its hungry larval stage or as a weak-winged grey or brown adult -poses any threat at all. Unlike the disease-spreading housefly, the sciomyzid avoids human company; its larva is hooked on snails to the exclusion of other food supplies. Says Berg: "Anything which is so highly specialized is not going to change its eating habits and start attacking babies...