Frontiers of Science:

Keeping Tabs on Insects

By Dr. Sherwood B. Idso

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    When you’re looking for something tiny in a large area, you often say it’s like “looking for a needle in a haystack.” That same saying pretty well describes what some scientists are doing these days: using special radar equipment to detect and track individual airborne insects. Some of the larger flying insects can be detected out to distances of fifty miles or more. And, incredible as it may sound, the radars can also measure the rapidity with which an insect’s wings flap. On that basis scientists can determine what type of insect is being observed—and even whether the insect is male or female!

    But why would anyone ever want to find out such information? Primarily, scientists want to keep track of insect migrations. Each year insects destroy great quantities of food before it can be harvested. In the United States alone this loss amounts to over seven billion dollars annually. And since the great unknown in the fight against insects is how they move from place to place, scientists hope that the ability of radar to track insect flight patterns can help in their attempts to reduce insect pest damage.

    The story of scientists’ ability to track insects by radar began many years ago, when aircraft controllers noticed unexplained signals on their radar screens. Studies of these incidents led to the discovery that birds, and sometimes swarms of insects, were being observed. Scientists then began to wonder if individual insects could be detected. They thought they could do it, but how could they be sure that it was a single insect that they were observing?

    One approach used was to suspend individual insects from large balloons by fine strings that kept them in a known position while the necessary studies were conducted. Perhaps the most interesting experiment of this nature, however, involved a radar locked onto an aircraft flying at 8,000 feet for a distance of eight miles. When the aircraft signal was well established on the radar screen, the air crew was instructed to release a single moth measuring about three-quarters of an inch long. The radar was then held stationary; and as the aircraft signal moved off the screen, the signal from the moth was observed to begin from the position previously occupied by the aircraft.

    After very precise and detailed studies such as these had established that radar could indeed detect and track insects, some actual field experiments were attempted. One of the first of these experiments was performed in India, where in July of 1962 a great locust plague was in progress. Ground-based observers estimated that there were perhaps as many as fifty billion locusts within a 65-mile radius of New Delhi, but radar indicated that there were over twice that many. Radar also located huge swarms taking off night after night over large areas of the Sahara that were completely missed by observers on the ground. Consequently, proposals were made to construct a network of inexpensive radars to keep a constant watch over important breeding and swarming areas and to act as a means of directing aircraft spraying operations to control the locust populations.

    Another problem that has been solved by radar has to do with the activities of the cotton bollworm in the Sudan. Farmers there were always perplexed by the appearance of the crop-destroying larvae in their fields. How did the larvae get there? Where did they come from?

    By using radar, scientists discovered that every night during their active season, bollworm moths took to the air out of fields of groundnuts, where they spent their days. The moths would fly for about an hour and a half, covering a distance of 15 to 25 miles. Then they would alight in the farmers’ cotton fields, where they would lay their eggs that would shortly hatch into the leaf-devouring larvae. Armed with this knowledge, the farmers could combat the insects at their source before their cotton fields were infested.

    There are many other examples that could be cited, such as control of the spruce budworm that was once public enemy number one in several parts of Canada or the fall armyworm that each year does about 500 million dollars’ worth of damage as it migrates northward in the United States.

    By increasing our knowledge of insect behavior through radar studies, we become better equipped to cope with those species that destroy precious crops, desperately needed by so many of the people in the world for their survival. It’s a job well worth doing, and worth doing well.

    Illustrated by Shauna Mooney