Butterfly population declines due to use of insecticides
Graceful, scintillating butterflies along with their drab, fat-body cousins, the moths, are fast losing the numbers game.Skip to next paragraph
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Are they vanishing? Probably not, but their population figure is way down compared with earlier times - before insecticides.
This is the report of Perry A. Glick, a former entomologist with the United States Department of Agriculture, who recently became a fellow of the Explorers Club of New York.
In years gone by, Mr. Glick did some ground-breaking flying for the Department of Agriculture, collecting insects by plane. A world traveler and author of 30 papers in his research field, he spent much of his active life collecting butterflies, moths, and skippers.
Recently he transferred a collection of 5,000 specimens to Texas A & I University at Kingsville, Texas - and then got busy on another collection. He lives in Brownsville, Texas. Collecting specimens is not as easy as it used to be, however.
''In the early 1950s I collected in one hour in the Rio Grande Valley as many butterflies as it takes me two or three years to collect here now,'' Glick explained.
This statement might well be repeated in many areas of the United States. The situation is due mostly to the use of insecticides, to which farmers of South Texas owe so much of their phenomenal success in raising crops.
''It has become hard to collect in places like Maine, Minnesota, Texas, or California because of the dusting of vegetation,'' Glick said. ''Biological control has helped an awful lot, but insects were killed off in such numbers that even biological control has become limited in its effectiveness.''
Chemists are now at work on insecticides ''with which they hope to kill off harmful insects and leave those that are harmless or beneficial, such as butterflies.''
For the collector and art fancier there is another circumstance cutting down on the trade in the most valuable butterflies. Governments in various foreign nations are imposing restrictions to preserve lepidoptera.
Mexico, for instance, though it remains a haven for vast numbers of butterflies, including an enormous colony of wintering monarchs, takes a severely restrictive view of netters. One can no longer collect in Mexico without a permit.
The Texas entomologist, who has collected extensively in parts of South Africa, Kenya, and Tanzania, where insecticides have not made as much inroads on lepidoptera, finds that these areas too are beginning to curb netting.
The choice foreign spots in the Western world other than Mexico have been in Ecuador, Bolivia, Colombia, Peru, and Brazil. Hunting with a net has been particularly good in the Amazon River area where roads, at least until recently, had not penetrated. ''One could fly for miles and see nothing below but wilderness and forests,'' Glick recalls. How long such ''good hunting'' will last in these areas is problematical.
Of what ''use'' are butterflies?
They interest collectors because of their beauty, their rarity, and the variety of specimens you can collect from many countries. Certain species can be destructive, such as the cabbage butterfly, whose larvae (the pre-adult stage of butterflies and moths) eat the cabbage. These are sometimes confused with moths, but they are butterflies. Also there is a butterfly that eats alfalfa and clover.
''It's in their caterpillar stage that these species are so destructive. The adult (winged) stage is harmless,'' Glick explained. ''Exception: there are moths in the adult stage that are destructive, such as one that feeds only on cotton or very closely related plants.
''One of these varieties (cotton leaf moth, the Alabama argillacea) is carried up into Canada, where the adults become strangely destructive because they pierce peaches and grapes for juice. This does a great deal of damage. They originate in the southern cotton region, eating their way northward until they run out of cotton. Then they are carried north into Canada, where there is no cotton.''
Some of the lepidoptera play a role in pollinization of plants. They contribute much to the fertilization of flowers. Some butterflies feed on the nectar of plant blooms. They don't actually cause the plants to develop and, of course, bees and other insects make the major contribution. But butterflies do have a share in this.
Some moths are essential to the development of certain plants. Take the yucca moth; without this insect the yucca plant, so distinctive in desert country, would soon die and become unknown. This moth is the only living thing that pollinates the plant for which it is named. There are not many of this type of moth.
Another striking aspect of butterflies is their ability to navigate, be it half the circumference of Earth. The strange thing about observed insect flights is that they occur in the same flyways as are used by birds. This was made more mysterious by the assumption that butterflies and moths had made themselves so repulsive to birds that they were rarely included in the bird food chain. But recent photos make it clear that birds do eat monarchs and other butterflies, Glick said.
In either case there's a dilemma here for naturalists: Which of these creatures, birds or butterflies, established the flyways in the first place?
''It's somewhat like the chicken or the egg controversy,'' Glick said. ''We may never know for sure.''