CONTROL OF INSECTS IN TOBACCO 17 



walls of such warehouses are usually covered with hardware cloth or 

 wire screen. Hardware cloth of 4 to 8 meshes to the inch, often called 

 rat wire, Avas almost invariably used prior to 1939. Such wire, of 

 course, did not exclude insects. Storages of this type vary in size, but 

 most of them exceed 100 by 150 feet by about 16 to 18 feet. The ca- 

 pacity of a single section may range from 800 to more than 3,000 hogs- 

 heads. Few of the more modern warehouses have a capacity of less 

 than 1,500 hogsheads. 



Since World War II some manufacturers have eliminated the 

 louvres from their open-type warehouses. Such warehouses, usually 

 constructed of corrugated iron, have some of the advantages and some 

 of the disadvantages of both open and closed buildings. They cannot 

 be fumigated, but they can be more efficiently sprayed. 



Almost half the cigarette tobacco stored in the United States — most 

 of the flue-cured tobacco held for domestic manufacture — is stored in 

 open- or semiop'en-type warehouses. This tobacco is attacked by both 

 the tobacco moth and the cigarette beetle, but generally the tobacco 

 moth is the more important pest. In these buildings insect control is 

 a serious problem. Fumigation is impractical, and dusting with pyre- 

 thrum powder, the only control measure widely practiced in the past, 

 is not so effective as desired. This powder is also unpleasant to apply, 

 and leaves an objectionable residue. 



Tobacco absorbs odors readily. Furthermore, it rapidly absorbs 

 moisture, and the least excess of moisture may cause mold and rots 

 to develop. An insecticide for use in tobacco warehouses must meet 

 several requirements. Besides being an effective insecticide, the ma- 

 terial should be volatile but leave no objectionable odor; it should 

 not leave harmful or objectionable residues; it should not impose 

 any serious fire or explosion hazard; and it should be easy and safe 

 to apply. 



Pyrethrum-oil spray fits these specifications. Pyrethrum is a good 

 contact insecticide, and one of the least poisonous. The spray is 

 highly volatile, losing its effectiveness in a few hours. It leaves no 

 permanent odor or objectionable residue. The oil used in this spray 

 is of a light volatile type. The manufacturers' specifications for 

 such an oil are given on page 13. Pyrethrum-oil spray can kill in- 

 sects only by directly hitting them. It does not penetrate the hogs- 

 heads or bales of tobacco and cannot reach the young stages of insects 

 in the tobacco. 



Spraying should be started when the weekly trap catch reaches 10 

 tobacco moths or 10 cigarette beetles. It should be continued until 

 insect activity is checked by fall temperatures. The object of spray- 

 ing is to kill the adult insects before they have laid many eggs. 

 Sprays should be applied weekly, preferably on the same day each 

 week, and care should be taken to see that all parts of the warehouse 

 are reached. The dosage should be approximately 3 fluid ounces of 

 the pyrethrum-oil mixture per 1,000 cubic feet of air space. (The 

 air space of a warehouse is the volume of the building less the volume 

 of space occupied by tobacco.) 



To control the tobacco moth, the spray should contain 0.2 percent 

 of pyrethrins. The cigarette beetle is more resistant to insecticides, 

 and for use against this insect the spray should contain 1 percent of 

 pyrethrins. 



