Hornworms are the most widely distributed and destructive. Lead arsenate was used extensively for many years although it had several objectionable features. Scientists have tried to find a substitute that will control the pests without leaving a poisonous residue, will not injure the plants, and will not lower the quality of the cured tobacco.

They found that paris green is fairly effective although it injures tobacco under some conditions and contains arsenic. Cryolite is also fairly effective and has been used by some growers. DDT is effective against the tomato hornworm on tobacco but not against a closely related species, the tobacco hornworm, which is the predominant species in the South. Encouraging results have recently been obtained in controlling both species by applying dust mixtures or sprays that contain TDE.

Tobacco thrips.

Considerable research has been devoted to methods for luring, trapping, and poisoning the parent moths of the hornworms. Used alone, that practice is not completely satisfactory, but it has some value as a supplement to other methods, such as hand-picking or using insecticides.

The tobacco budworm is widespread and destructive in the South. In early days growers used the "little boy-big boy" team to fight it the little boy placed in the growing bud of each infested tobacco plant a small handful of warm surface soil; it caused the bud-worm to leave its place of concealment in the folds of the expanding leaves of the plant. The big boy followed closely and killed the budworm before it could move out of danger. In later years, the budworm could be thwarted by applying a pinch of cornmeal and lead arsenate to the growing bud an effective method that left only a little poison on the harvested product. But it took too much time and labor. Now growers use a dust mixture containing DDT, which is as effective as the poisoned bait and can be applied without too great an outlay for labor. DDT can be used on maturing plants or the seed-heads of tobacco plants, when the poisoned bait cannot be used.

Since 1946 tobacco in most of the producing regions has been subjected to an outbreak of aphids, principally the green peach aphid. They have reduced the yield and quality of the tobacco by sucking the juices from the plants and have contaminated the product with insect remains and a sticky material known as honeydew, which they secrete and which cannot be removed from the harvested tobacco without injuring the product for market. Extensive research on the habits of the aphids and methods of control and tests of the newer insecticides disclosed that a satisfactory control may be achieved by the timely use of dusts or sprays containing parathion or tetraethyl pyrophosphate. Many growers have used those materials, but further research is needed to determine their ultimate effect on the tobacco plant and the extent of their toxicity.

Although flea beetles are controlled successfully in the plant bed and on the newly set plants, heavy infestations are sometimes encountered on plants in the field. The infestations are occasionally severe near harvest and require the application of insecticides, particularly on the types of tobacco grown for cigar wrappers, since a few holes made by the beetles ruin tobacco leaves for cigar making. Rotenone was found to be an excellent remedy. More recently, dusts or sprays containing DDT were shown to be effective against flea beetles and useful against other species of leaf feeders, including the tobacco budworm, which sometimes injures the plants during the same period. Dusts or sprays containing cryolite are fairly effective.

Tobacco thrips mar leaves used for cigar wrappers. Often they are associated with flea beetles. A dust mixture containing pyrethrum and rotenone will control thrips on tobacco leaves and reduce damage by flea beetles.

Mole cricket.

The suckfly attacks tobacco grown for flue-curing in many parts of the South. Periodically it becomes abundant enough to cause serious damage in fields of late-planted tobacco. In growing tobacco shortly before harvest, its feeding may reduce the weight and thickness of the cured leaves. Unsightly specks of excrement on the under surfaces of the leaves and an abnormal change in their condition prevent proper coloration and curing and a consequent loss in quality. A dust mixture containing parathion or sprays containing parathion or tetraethyl pyrophosphate are effective against the suckfly.

Several species of the grasshoppers sometimes despoil the growing tobacco crop, particularly along the margins of fields. The pests can be checked under field conditions by the poisoned baits which I mentioned for use against them in plant beds or by a dust mixture containing toxaphene applied to the weeds growing along the margins of tobacco fields which normally harbor the grasshoppers before they invade the tobacco.

INSECTS INFESTING stored tobacco and tobacco products affect a large industry concerned with the curing, fermentation, and manufacture of those products in the United States. The insect enemies take a large toll each year, but it should not be inferred that tobacco products from the factories of American manufacturers are likely to be insect-infested or that they were made from infested tobacco. Precautions are taken to eliminate insects from tobacco warehouses and factories. The industry makes a constant effort to keep its stocks free of insects. Most tobacco must be held in storage for 2 years or longer so that it will slowly ferment or age under natural conditions of temperature and moisture. Therefore manufacturers must carry large stocks of tobacco in storage to fill trade and manufacturing requirements. In August 1950, for example, 3,155,000 million pounds of unmanufactured leaf tobacco were in storage in the United States and Puerto Rico.

Years ago the cigarette beetle was the principal pest affecting stored tobacco, but beginning in 1930 the tobacco moth assumed importance as a pest of flue-cured and imported Turkish tobaccos used for cigarettes in some parts of this country. Specimens of the cigarette beetle were found in alabaster vases in the tomb of Tutankhamen, indicating that the species was present in Egypt at least 3,500 years ago. Research in the second decade of this century demonstrated that fumigation of tobacco with hydrogen cyanide gas would control the cigarette beetle in closed tobacco warehouses as well as in vaults and in vacuum chambers. Continued experience of the industry showed, however, that hydrogen cyanide gas, directed against both the cigarette beetle and the tobacco moth, was not effective under practical conditions in some closed warehouses, because of the leakage of the fumigant from inadequately sealed structures. Further research developed methods for sealing ventilators in the walls of such warehouses with suitable paper and glue, for sealing sliding doors with a dough made of asbestos, calcium chloride, and water, and for sealing cracks or crevices in the walls and around the eaves with elastic roofing cement applied with a pressure gun. These methods of sealing warehouses before fumigation were successful and were widely adopted by the tobacco industry in this country and abroad and also by other industries.

The efficiency of such fumigation was further improved by the development of a suction light trap, which attracted and captured the adult insects and thus indicated the most efficient time of fumigation by providing a continuous index of insect abundance and activity. One of these traps is installed for each 75,000 to 100,000 cubic feet of space in a tobacco warehouse. The traps are operated during the part of the year when insects affecting stored tobacco are active in the latitude of eastern South Carolina from about April 1 to December 1. As soon as the average catch in each of the suction light traps rises above an established danger point usually 50 cigarette beetles or tobacco moth adults a week the warehouse should be fumigated. Visual inspection cannot be depended upon for detecting the need for fumigation, because the feeding activity of the insects in the tobacco within hogsheads and bales often proceeds to a danger point before external indications of injury are noticeable.