Aphids are among the most serious insect problems in flower and vegetable gardens. They love warm weather and with rather consistent daily temperatures of 70 and over, they can be expected to appear in larger number.

Sucking sap from plants probably is the biggest source of damage by these plant lice. Plants lose vigor, their leaves become distorted, curled and discolored, buds harden and flowers become deformed. They spread many plant diseases, especially the viruses.

Aphids are slow-moving, soft-bodied, pear-shaped insects.They vary in length from about 1/8 to 1/4 inch, according to the species. Color may be black, brown, yellow, red, gray or green.

Perhaps the most impressive feature of aphids is their enormous reproductive ability. Take the melon aphid, for example. A single individual produces approximately 85 young in its lifetime. Each of the resulting young reaches maturity in two or three weeks and in turn gives birth. Thus, in a few months, 10 or more generations have resulted from the original aphid.

When aphids become crowded, winged individuals appear in large numbers and these leave the plant in search of new food sources and spread virus to other plants.

Unfortunately, insecticides have proved of little benefit in retarding virus spread, since the act of transmission by the aphid is usually so rapid that the virus is transmitted to plants before any poison applied to the plant can kill the insect.

There may be a fairly easy way to control flying aphids without spraying with insecticides. Aluminum foil placed on the soil around plants repels flying aphids and may provide adequate protection from those that spread diseases.

For those already on the plant, Virginia Tech specialists recommend spraying or dusting with malathion or diazinon (spectracide). Label directions for mix and application should be followed closely.

The aluminum foil strips provide an effective barrier by reflecting ultraviolet rays from the sky. This causes the flying insects to change their course.

Years ago, entomologists Floyd F. Smith and George V. Johnson, and plant pathologist Raymon E. Webb, of USDA's Agricultural Research Service, obtained dramatic increases in squash yields in plots protected with aluminum foil. Good results were obtained under growing conditions in both Long Island, N.Y., and Beltsville, Md., during two seasons.

Gladiolus flowers protected by the same material produced flowers averaging two inches taller than those grown in unprotected plots. Only 5 per cent of the flowers protected by aluminum repellant showed the discoloration typical of virus disease: however, 30 per cent of the unprotected flowers were diseased.

Smith and Johnson reported best results when 50 per cent of the ground area was covered by reflective material. The material also serves as a water-conserving mulch.

Despite the fact that uphids are born on green plants and mature on them, flying aphids will alight on yellow objects in preference to green ones, according to research done by Dr. James B. Kring, University Connecticut entomologist.

Since starved and diseased plant are more frequently yellow than thy ones, more aphidsalight on them.