SOME OF THE INSECTS

C. M. Packard

AN INCREDIBLE number and variety of insects live on grasses and legumes. Under favorable conditions many species compete successfully with domestic animals as consumers of these crops, as any farmer knows who has seen an outbreak of grasshoppers or armyworms ruin a good stand of grass or grain almost overnight or a whole cutting of alfalfa lost to the alfalfa aphid.

Often the number of insects runs Into many millions to an acre and their large appetites more than make up for their small size. Hundreds of species are pests of grasses, legumes, and other forage plants. Herbert Osborn has written a book, Meadow and Pasture Insects, about them; only a few of the most important ones can be discussed in this article. Only brief mention can be made of the control methods used against them. Readers should consult their county agricultural agents or State experiment stations when specific instructions are needed.

Grasshoppers are among the most widely prevalent pests of pasture and hay crops. Some species favor the uncultivated ranges; others like the cultivated grasses and legumes. In both environments their abundance and control may mean the success or failure of a year's farm operations.

Fortunately, effective means have been developed for controlling them. For many years the application of a poisoned bran or bran-sawdust bait broadcast thinly in the infested fields has been a standard, cheap, and, under most conditions, effective method of control. When bait is properly handled and applied there is no danger to livestock pastured in the treated areas. The substitution of sodium fluosilicate for the arsenical poisons formerly used in baits has practically eliminated the danger of stock poisoning.

Although much bait is still spread by hand, highly efficient power equipment for spreading it from the ground and from airplanes has been developed and is widely used. During the bad grasshopper year, 1938, United States farmers spread about 136,000 tons (dry weight) of grasshopper bait, supplied them by Government and State agencies, on 30,895,000 acres, and thereby saved crops valued at more than $175,000,000.

Baits are often rather ineffective in thick, succulent crops like alfalfa. Investigators have therefore been working hard to find a better method for use in the protection of such crops. Their experiments have shown that several of the new insecticides, particularly Chlordane, benzene hexachloride, and a chlorinated camphene, commonly called Toxaphene, directly applied in a spray or dust, with ground equipment or airplanes, are effective against grasshoppers. Proper use of these insecticides, it is found, is a practical supplement or substitute where poor control is obtained with bait. Until more is known about the residue hazards involved, however, these insecticides should be applied only to the early growth just after cutting if the crops are to be used for hay or feed, and to field margins, fence rows, roadsides, and idle lands in which the hoppers congregate and which are not to be pastured or cut for hay. Treated crops should not be fed to dairy animals or to meat animals that are being finished for slaughter.

The Mormon Cricket

The Mormons were the first ones to lose range forage and crops to the Mormon cricket, hence its common name. They encountered it soon after they first settled in Utah, about 1848. In the northern Rocky Mountain and Pacific Coast States the Mormon cricket often damages large areas of range forage severely. When very abundant, it depletes the forage supply in these areas and migrates to new pastures on foot in bands sometimes miles in extent. These bands will also attack cultivated grass, grain, forage, and garden crops athwart their path. They look like big, black, long-legged crickets, but they are really wingless grasshoppers. A closely related species, the coulee cricket, also occurs in some areas in the Northwest and has similar habits.

The early Mormon settlers knew no satisfactory way of fighting the Mormon cricket, but their crops are said to have been saved from destruction by an influx of sea gulls that appeared in answer to their prayers and ate up the crickets. A monument to the gulls has been placed near the Mormon Tabernacle in Salt Lake City.

Recently it was found that these crickets can be cheaply and quickly controlled by means of a poisoned bran or bran-sawdust bait. Although the crickets do not like a bait containing an arsenical, investigators finally discovered that they will readily eat one containing enough sodium fluosilicate to kill them. Baits containing this poison, broadcast by hand, power spreaders, and airplanes, have been widely and successfully used.

Cutworms and Armyworms

In an unpublished paper on the cutworms and armyworms of the central Great Plains, H. H. Walkden reports the observation of 54 species in cereal and forage crops, pasture grasses, and wastelands. Six of these species are known to be of major economic importance, the pale western cutworm, army cutworm, variegated cutworm, army-worm, fall armyworm, and corn ear-worm. Lawns as well as farm crops are sometimes attacked.

A few of the cutworms, like the pale western cutworm, work mostly under ground, whereas others bore within the stems of their host plants.

The only methods of control yet known for these species are cultural measures such as rotation of crops and properly timed summer fallowing.

Armyworms are really cutworms that occur in great numbers under favorable conditions and migrate in droves on foot in search of food as they deplete the supply in the infested fields. Most cutworms and armyworms feed on the above-ground parts of the plants and hide under the surface litter and soil during the day. Because of this habit they usually can be easily killed with poison bran or bran-sawdust bait broadcast in the infested fields late in the afternoon so that it is fresh and attractive to them as they emerge hungry in the evening. The bait may be applied by hand or with power or airplane equipment.

Another method of control sometimes used against armyworms is barrier furrows plowed along the side of the field being invaded. In plowing a barrier furrow, the dirt is thrown toward the crop to be protected. A log is then drawn back and forth in the furrow to work up a loose dust, which helps to keep them from climbing out, and kills them as they accumulate in the furrow. Sometimes instead of using a log, the furrow is left smooth and hard and post holes are dug in the bottom of it every 20 feet or so. The worms crawl along the furrow and tumble into the holes, where they may be killed by crushing or by the application of coal oil or crankcase oil.

Still another method is the application of an insecticidal dust or spray to the infested crop. Lead arsenate, calcium arsenate, and some of the new insecticides such as DDT have been found effective against certain species. Because of the residue hazards involved, however, their use on forage crops or pastures is inadvisable, except Perhaps when several months of lush Plant growth and heavy rains occur between treatment and harvest.

Range Caterpillar

A large spiny worm commonly called the range caterpillar has at times caused extensive losses of range forage in eastern New Mexico. Although it feeds on at least 40 different species of plants, including cultivated grain and forage crops, it is primarily a pest of the range grasses common to that region. It injures them in two ways : First, by eating them down to the roots over large areas; and second, by leaving on the plants the poisonous spines which it sheds as it crawls around or when it molts. Control measures such as burning over the range, the use of heavy corrugated iron rollers, and brush dragging have not been successful.

They can be killed with a lead arsenate spray if the value of the crop to be protected would warrant the cost. It is possible that cryolite or one of the new insecticides such as DDT might also be effective, though none of these have actually been tried against them. If one of them were to be applied, the same precautions concerning the attendant residue hazards should be observed as have already been mentioned in connection with the use of sprays and dusts against cutworms. Apparently poison bran baits have never been tested against the range caterpillar and might well be given a trial.