Mechanical traps include a lamp or another type of attractant. Below it might be a shallow pan that contains a liquid to capture the insects. A more complicated device has an enclosure that insects can enter easily but cannot leave because of baffles around the enclosure.

A trap of this type, developed by engineers in the division of farm electrification, Bureau of Plant Industry, Soils, and Agricultural Engineering, has shown some promise in the capture of hornworm moths. Five of these traps installed on a tobacco farm in Wake County, N. C., captured 12,874 moths in I week in September 1951.

Insects that feed on more than one crop may be trapped on one of them in order to protect another. When a few hills or rows of a favored host are planted in or around a main crop in time to attract a mutually injurious insect species, the main crop may not be seriously attacked as long as the trap crop remains attractive. The method is only partly effective at best and may have no value if the insects gathered on the trap crops are not destroyed before they leave it. The method has been suggested for protecting cantaloups and cucumbers from the pickleworm by planting bush squashes every 2 weeks in the cantaloup field; for protecting the seeded main crop from the onion maggot by planting rows of cull onions around the field and at intervals through the field to attract the egg-laying flies; for protecting host crops of the harlequin bug by planting as trap crops strips of mustard, kale, turnip, or radish early in the spring or late in the fall; for protecting peas from the pea weevil by planting border strips of peas in advance of the main crop; and for protecting corn from the Japanese beetle by planting a narrow strip of soybeans around the field of corn.

The trap-tree or trap-log method for trapping bark beetles in forested areas is a variant. Logs are felled to attract injurious bark beetles to a point where they can be destroyed easily. Long recommended in Europe, the method has not been found very effective in the United States.

The attractiveness of favored foods to insects can be utilized to trap many pests. Small paraffin-lined pill boxes or cans baited with sugar solutions or sir-ups, bacon rind, fat, or meat attract ants. The ants can be destroyed by dropping the container in a pail of boiling water or by adding a poison to the bait. Cylindrical, screen-wire cages baited with stale beer, a solution of one part of blackstrap molasses in three parts of water, milk, or fruit waste have long been used to catch flies. The standard screened cages are 12 to 18 inches in diameter and about 24 inches in height. They have an open-end, screen-wire cone inside that reaches nearly to the top. They are set on 1-inch legs over a shallow pan containing the bait. Similar fly traps baited with meat in water have reduced blow fly populations in large areas in Texas. Nicotine sulfate in the bait kills the flies as they are attracted to it. Flies are also killed on the grids of electric box traps to which they are attracted by a bait, or on electric window screens through which they may attempt to fly.

Fermenting solutions and aromatic and miscellaneous chemicals attract a wide variety of insects to traps. The trap for exposing the baits may be a glass jar, stew pan, tin can, or pail; a sticky-coated baffle or support may also be used. The lure may be a simple fermenting sugar or malt solution; an aromatic chemical such as geraniol, methyl eugenol, oil of sassafras, or terpinyl acetate; and protein material, such as powdered egg albumen, dried yeast powder, or casein; pine tar oil, linseed oil soap, or household ammonia; or a specialized material, such as the sex attractant, identified as gyptol, that is obtained from the terminal segments of female gypsy moths.

Traps based on lures for flying insects have received attention in recent years and some uses have been developed that have had wide acceptance. None, however, gives more than partial control.

In Japanese beetle infested areas in the East, bright-yellow traps hung on standards in sunny places have captured large numbers of the pest. A standard trap consists of an aromatic chemical (a combination of geraniol and eugenol) , and bait dispenser (a small bottle with a wick) for holding the bait, and a baffle for deflecting the beetles into a funnel below the baffle leading to a receptacle for retaining the captured beetles. If they are used on a community basis in areas of heavy infestation, such traps may capture bushels of beetles and lower the general level of infestation. Used on an individual basis, however, the usual result is more extensive damage on the property on which the trap is placed.

Apple growers are as familiar with bait traps for the codling moth as the average housewife is with sticky paper to trap flies. The codling moth is attracted to fermenting sugar or malt solutions in wide-mouth glass jars, stew pans, or tins hung in the trees. The traps are more effective when hung in the tops of the trees and when the bait solution is supplemented with an aromatic chemical such as oil of sassafras, bromo styrol, oil of mace, or pine tar oil. Such traps were estimated to have caught nearly 500,000 codling moths in 4 years in traps hung at the rate of one per tree over 35 acres in the Pacific Northwest. Nevertheless, there was just about as much wormy fruit in the baited as in a comparable unbaited area.

A GLASS TRAP, known as the McPhail trap and shaped like an ink bottle, has been popular for exposing baits to attract fruit flies, particularly tropical and subtropical species. Fruit flies gain access to the trap through the partly open concave bottom. Baited with protein lures, this type of trap is useful against several Central American species; baited with a linseed oil soap, it captures large numbers of melon flies; baited with methyl eugenol, it is effective for male oriental fruit flies; baited with a fermenting sugar solution, it is attractive to both sexes of oriental fruit flies.

A small metal cylinder, baited with an extract prepared from the last two abdominal segments of female gypsy moths, is highly attractive to male gypsy moths. The cylinder has a rim at each end to which is attached a screen cone in which there is a hole for the moths to enter. A sticky paper lining prevents their escape. The use of the extract from two tips per trap will catch male gypsy moths, but the extract from 15 tips is necessary to attract the maximum number. The extract is dispensed on a corrugated paper roll suspended by a wire inside the cylinder. The traps are not practical for control, but were used in surveys of approximately 7 million acres for the presence of the gypsy moth in New England, New York, New Jersey, and Pennsylvania in 1950 and again in 1951.

THE INTEREST in traps remains at a high level and efforts to improve their effectiveness and extend their range of usefulness continue. The day may come when traps will be devised that are greatly superior to those we now have; the effort to develop them will be worth while.

HOWARD BAKER is assistant leader of the division of fruit insect investigations, Bureau of Entomology and Plant Quarantine. He was graduated from the University of Massachusetts in 1923 and joined the Department immediately thereafter. After various field assignments on apple and pecan insects in the East, Middle West, and South, he was transferred to Washington in 1944.

T. E. HIENTON is in charge of the division of farm electrification, Bureau of Plant Industry, Soils, and Agricultural Engineering. Between 1925 and 1941 he was in charge of farm electrification investigations at Purdue University, where he conducted research on the development of farm electrical equipment. Dr. Hienton holds degrees from Ohio State University, Iowa State College, and Purdue University.