Traps Have Some Value

Howard Baker, T. E. Hienton.

The habits of insects that cause them to hide in sheltered places, that cause them to travel on foot over open spaces toward sources of food, that make them to fold up and drop when disturbed, that attract them to favored food plants, colors, odors, and lamps suggest the use of traps to reduce their numbers and bring them under control.

Traps are devices by which to catch insects unawares. Their possible value in insect control has long been recognized. They used to be the main way to control many pests.

Most traps are only partly effective and continue in use only until more effective treatments are devised or to supplement other methods, but they have contributed greatly to our knowledge of insects. They are a useful tool of research and extension entomologists and often are invaluable in conducting and evaluating the results of large-scale control programs.

Insect traps may be small or large and simple or complex, take any one of a variety of forms, and operate on one of several principles. Most of them combine means or materials that force or draw insects into a receptacle that prevents their escape or holds them long enough to permit destruction. Popular interest in them is great, and research continues to improve them and expand their use.

Traps may be as simple as boards on the ground near plants, a furrow around a field, or a lantern over a tub of water. Or they may be a specific lure, such as an aromatic chemical or lamp, plus a suitable device for capturing or destroying the insects.

Trapping insects under chips, stones, boards, and other materials in appropriate places was an early recommendation for getting rid of insects that naturally hide in such situations. The method recommended about 1840 for the plum curculio required that the trash be cleared a couple of feet from the base of the trees and bark chips, stones, and other similar materials be put in the cleared place as hiding places for the adult curculios, which were then collected and destroyed at regular intervals. The method was less effective than others and was soon dropped.

A somewhat similar way to control cutworms was recorded as early as 1838: Compact handfuls of elder sprouts, milkweed, clover, mullein, or almost any green vegetable were placed in every fifth row and sixth hill, and pressed down with the foot. Regular visits and examinations would expose the worms, which could be killed with a sharp instrument.

Poison was added later to the trap material so that the routine examinations could be dispensed with. Wire-worms have also been lured under board traps and killed. Corn was protected from them in the late 1800's by placing small bunches of cut clover poisoned with Paris green in water under bits of board at intervals through a cornfield. Large numbers of the parent beetles were killed in this way. Squash bugs, too, hide under such things as trash and boards. They have long been partially controlled in home gardens by trapping the adults under small pieces of board put near the plants. The trapped bugs must be collected and killed each morning.

Joseph Burrelle in 1840 suggested winding something around the trunks of apple trees or placing a cloth in the crotch and then destroying in a hot oven the trapped codling moth larvae. The larvae leave the apples when full-grown and spin their cocoons in protected places on the trees. Before long, others found that more worms could be trapped if the rough bark was scraped from the trees and the ground beneath them cleared of weeds and trash. Thus a larger proportion of the worms was forced to the bands.

Banding materials vary considerably. A hay rope was popular in the 1860's. Heavy wrapping paper, building paper, crepe paper, corrugated paper, flannel cloth, canvas, and burlap came into use later. The bands had to be removed and the worms in them destroyed every 10 days or so during the period they were leaving the fruit. An improvement that came in the 1920's was a band, usually of corrugated pa- per and coated with beta naphthol in oil, which killed the worms cocooning in them. Under favorable conditions such chemically treated bands often capture 50 percent or more of the worms that develop in the fruit.

Screening or otherwise enclosing packing sheds to trap codling moths that emerge in spring also takes advantage of the habit of codling moth larvae of cocooning in protected places. Worms maturing in apples after they are picked may cocoon in whatever container they happen to be in at the time or in a protected place in the packing shed. If harvesting equipment is stored in the packing shed, one can trap moths as they emerge and keep them from the orchard. Moths so confined are attracted to an incandescent lamp at night and can be killed by an electric-grid trap.

Some insects among them the plum curculio and pecan weevil fold up, drop to the ground, and play dead when they are disturbed. For years injury of the plum curculio was reduced simply by jarring the trunk and larger branches of infested trees to dislodge the adult curculios onto a sheet spread beneath the tree. The sheet was a trap from which the beetles were collected and destroyed. For a long time that was the only recommended way to fight the pecan weevil, a serious pest of pecans. It is about 50 percent effective.

SOME TRAPS ARE DESIGNED to catch the insects that hop or jump when disturbed. A hopperdozer is one of the best known. It is merely a long, narrow, shallow trough of boards or metal and mounted on runners that can be drawn across a field to catch grasshoppers. A vertical shield, about 3 feet high, at the back of the trough is filled partly with water. Sometimes enough kerosene is added to cover the water with a thin film. The grasshoppers fly up to avoid the hopperdozer, strike the vertical shield, and fall into the kerosene-coated water. One model merely traps the grasshoppers in a screen box and does not require the kerosene-coated water. Up to 8 bushels of grasshoppers an acre have been caught with the machines. Sometimes the back and sides are coated with a sticky material. Such a device catches many leafhoppers when it is run over clover and alfalfa fields. A modified hopperdozer, merely a sticky shield or a box with the inner walls coated with a sticky material, can be used for flea beetles in vegetable gardens.

CRAWLING INSECTS are easy to trap, especially with traps made with a barrier. When chinch bugs, armyworms, wingless May beetles, and such are moving from one field to another they can be halted by deep, dusty-sided furrows plowed across their path. The loose dirt keeps them from escaping. The insects will fall into post holes dug at intervals along the bottom of the furrow. They can be destroyed with kerosene or crushed with a heavy stick. Irrigation ditches sometimes prevent movement of Mormon crickets from range land to irrigated fields. Sticky bands can be used to bar the progress of crawling insects (the fall and spring cankerworms on apple, elm, and other fruit and shade trees, the white-fringed beetle on pecan and other trees, and climbing cutworms on a number of host crops). Also used are chemicals, such as creosote or calcium cyanide, spread or poured along the line of march of chinch bugs and supplemented by a series of post holes on the outer side to capture the repelled bugs.

Small insects that fly or are carried by wind often are caught by a simple trap made by coating with a sticky material a piece of paper, board, wire screening, or the inside of an open-faced box, cylinder, or cone. Sticky flypaper is an example. Sticky traps are useful for studying the flight habits and dispersion of leafhoppers, aphids, psyllids, scale insects, and other insects. For that purpose the traps may be hung on standards in yards, fields, or orchards, in trees, or mounted on a moving vehicle. The color of the coated material may affect the number of insects caught when the trap is stationary. Yellow and other colors to a lesser extent seem to increase the attractiveness of traps to insects during hours of daylight.

Light has been used for a long time to attract night-flying insects to traps. Open flames and lanterns have been superseded by electric lamps. Several hundred kinds of insects are attracted to light at night, among them the codling moth, European corn borer, tobacco and tomato hornworm moths, corn earworm, and cigarette beetle.

Factors like wavelength and intensity of radiation of lamps affect the responses of insects. Ultraviolet, blue, and green generally are more attractive than yellow, red, and infrared. The near ultraviolet, or black-light, region, is very attractive to the European corn borer and the hornworm moth. Attraction of night-flying insects increases with an increase in intensity, although not in the same ratio, up to about one-fourth that of bright sunlight.

In places where night-flying insects are bothersome, yellow and red lights or lamps, which are less attractive to insects, should be chosen in preference to white or blue lamps.

THREE TYPES of electric insect traps are the grid, suction, and mechanical. A lamp usually is used as the attractant with all three types, although baits may also be used effectively with the grid and suction types.

Eighty-five pounds of Clear Lake gnats, attracted by an electric lamp, were caught in a single night in a suction-type trap. Each pound contained about I million insects. House and stable flies attracted to a bait in an electric-grid box trap have been destroyed at the rate of 100,000 a day. More than 500 hornworm moths were attracted and captured in I night with a mechanical trap.

The grid type is made in several shapes and sizes. The grid itself consists of parallel wires, which are connected alternately to the terminals of a high-voltage, low-amperage circuit. An insect that tries to pass between any pair of wires completes the circuit between them and is electrocuted. A transformer is required to step up the supply-circuit voltage from 110 to 3,500 or more volts on the grid. A flat rectangular lar type, with vertical or horizontal grid wires, was developed originally for use on window or door screens in restaurants, bakeries, and dairy farms to control flies. It is used in field installations with an appropriate lamp to check time of emergence and heaviness of flight of such insects as the European corn borer and codling moth. Another type for field installations is circular and has a grid that encloses the lamp. A box type of grid trap, rectangular in shape and several inches deep, has a grid on the top of the box and is used principally for fly control where freedom from flies is essential for sanitary reasons.