D April 1947 E-717 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine PYRETHRUM-OIL SPRAYS IN OPEN-TYPE TOBACCO WAREHOUSES By Joseph N. Tenhet 1 / Division of Truck Crop and Garden Insect Investigations -/ Large stocks of flue-cured tobacco are normally held in stor- age for 2 to 4 years. This tobacco is attacked by two major in- sect pests, the tobacco moth (Ephestia elutella (Hon.)) and the cigarette beetle (Lasioderma serricorne (F»J). Much tobacco is stored in open- type warehouses, which cannot be readily fumigated. In these warehouses the tobacco moth is the most important pest. The most commo^i control measure has been dusting with pyrethrum powder. This treatment is fairly effective against the tobacco moth, but is of little value against the cigarette beetle. It is not so effective against the tobacco moth as is desired, and the powder leaves an objectionable deposit of spent dust. The tobacco moth and the cigarette beetle lay eggs on or near the tobacco. The eggs hatch into tiny worms, which feed in the tobacco. Sometimes the mass of tobacco in a hogshead is damaged to a depth of 6 or 8 inches, so that serious loss results. The adult insects do not feed on tobacco. It has been estimated that the average annual damage to flue-cured tobacco in storage caused by insects amounts to $5 per 1000 pounds. This represents a loss of $5,000 to f 15, 000 per warehouse. The tobacoo moth and the cigarette beetle pass the winter in the worm, or larval, stage* The first brood of adults appears in April, May, and June, the cigarette beetle usually 2 to 4 weeks la-er than the tobacco moth. The adult insects live for 1 to 2 weeks. In summer the life cycle of both speoies requires about 50 to 60 days, so that a second brood of adults (the main brood) ap- pears in July or August. Sometimes a partial third brood appears in October. The tobacco moth emerges from the tobacco to mate, but the cigarette beetle may mate in close confinement. There is a period in the beetle's life cycle when it emerges and is found in flight 1/ W. D. Reed (resigned June 13, 1946) supervised this work during its early stages, and the American Tobacco Company and the R. J. Keynolds Tobacco Company cooperated and gave active assis- tance in this project. APR 1 7 1947 -2- in large numbers. During this flight period, or period of activi- ty outside the tobacco containers, they are subject to control with insecticides. If insecticides can be applied systematically and frequently enough to prevent heavy egg deposition, an infes- tation can be controlled. An effort to find a more effective control measure for the tobacco moth in open warehouses has led to the development of a concentrated pyrethrum-oil spray. This spray is more effective and cheaper than pyrethrum powder, and leaves no undesirable resi- due. Extensive tests over a 6-year period have shown that it is safe to use on cigarette tobaccos. More than 120 million pounds of flue-cured tobacco in hogsheads have been sprayed with no injurious effects. Numerous tests have shown that there is no effect upon the taste, aroma, texture, or aging of the tobacco* Various fire- insurance underwriters have approved the spray for use in tobacco warehouses if reasonable precautions are used. SPARK-PROOF MOTORS AND SWITCHES SHOULD BE USED ON POWER SPRAYERS, AND SINCE ANY OIL IS FLAMMABLE, IT IS NECESSARY TO OBSERVE THE PRECAUTIONS RECOM- MENDED BY THE FIRE-INSURANCE UNDERWRITERS FOR HANDLING SUCH MATER- IALS. However, it is believed that the use of pyrethrum-oil spray offers no more fire hazard than does the pyrethrum powder, whioh has been in general use for 10 years. Tobacco takes up moisture readily, and excessive moisture induces molds and rots. Therefore, the diluent used in this spray was a light, highly refined, very volatile oil of the fly-spray base type. Manufacturer's specifications for this oil are as fol- lows: Max. sp. gr. at 60°F. 0,797, flash point 175°F., color- less, una no kerosene odor* This material is so volatile that all traces vanish within a few hours after spraying* The spray is a space «pray designed to kill the insects in the air. It does not penetrate the hogshead and will not kill the young stages of insects in the tobacco. Since the insecticide can kill only those insects it hits, thorough coverage is essential. Care must be taken to see that the spray reaches all parts of the warehouse. A mobile power sprayer (l) especially designed to blow the spray over the tops of the racked" hogsheads has been found to be most satisfactory for applying the spray. A dosage of 100 ml., or approximately 3 fluid ounces, per 1000 cubic feet of air spaoe is desirable* A lesser amount failed to give adequate coverage, and more was unneeded. For control of the tobacco moth a spray containing 0.2 per oent of pyrethrins is recommended. It will kill all tobacco moths hit -3- by the spray. This spray is not strong enough to control the cigarette beetle, which is more resistant to pyrethrum. The ciga- rette beetle can be controlled with a spray containing 1 per cent of pyrethrins. This stronger spray, of course, is more expensive and should not be used unless necessary. Suction light traps should be operated in all tobacco ware- houses. A weekly catch in such a trap of 50 tobacco moths or cigarette beetles is considered dangerous. As soon in the spring as the tobacco moth infestation reaches that point spraying should be started. Spray should be applied weekly throughout the summer and until insect activity is stopped by cold weather. Usually 20 to 24 applications will be needed in a season. An example of con- trol of the tobacco moth obtained by weekly applications of pyre- thrum-oil spray is shown in table 1. In this experiment 24 large warehouses were used, each containing approximately 2500 hogsheads of flue-cured tobacco. -A- Table 1.— Tobacco moths caught in suction light traps in screened, open-type tobacco warehouses, 8 sprayed with pyrethrum- oil (0,2 per cent pyrethrins), 8 dusted with pyrethrum powder (0.8 per cent pyrethrins), and 8 untreated. Richmond, Va. 1945 Trapping period, week ending*^- Sprayed .Dusted Untreated Ifcy 31 12521/ 15241/ 9952/ June 7 122 317 1184 14 14 169 989 21 11 85 371 28 7 61 305 July 5 9 21 96 12 33 89 193 19 7 44 202 26 7 57 756 August 2 27 178 2556 9 84 165 2811 16 104 161 3025 23 28 42 1644 30 41 173 2287 September 6 109 456 2681 13 19 71 1712 20 28 148 1200 27 7 49 512 Ootober 4 10 12 581 11 37 87 461 18 48 112 256 Average weekly catc :h 37.6 124.9 1191.1 i/ Catch for the week prior to first application on May 31; figure not included in the average. -5- In spraying a warehouse the power sprayer should be moved along the aisle very slowly, and brought to a complete stop every 15 to 20 feet, in order to give the blower time to roll the fog of spray to the rear of the building. A minimum of 20 minutes should be used in spraying a medium-sized warehouse. If the spray*. er is moved too rapidly, many insects will escape the spray. Care should be taken to direct the spray down the aisle, paying especial attention to the area around the doors, as well as over and between the racked hogsheads. To obtain best results from spraying, it is necessary to screen the warehouse thoroughly with fine-mesh wire gauze. This gauze may be either 18 or 20 mesh (preferably 20), but the openings should be less than 0.0596 inch in width* An 18-mesh gauze made of wire 0.02 inch in diameter is satisfactory (2). In unscreened warehouses, even though all the insects are killed by spraying, reinfestation may occur within an hour. Pyrethrum-oil may be purchased ready mixed in the desired strength-^- 0.2 per cent of pyrethrins for use against the tobacco moth, and 1 per cent of pyrethrins against the cigarette beetle— or the warehouseman may mix his own spray. Pyrethrum concentrate may be purchased in various strengths of pyrethrins, such as 2, 10, or 20 per cent. To obtain a finished 6pray, it is only necessary to dilute the concentrate with a fly-spray base oil; a small a- mount of agitation is sufficient. It is usually a little mere eco- nomical for a warehouseman to mix his own spray. However, a man with only one or two warehouses may find that the convenience of having a ready-to-use spray will offset the slight additional coat* LITERATURE CITED (1) Tenhet, Joseph N. 1946. A power sprayer for applying concentrated in- secticides. U.S. Bur. Bnt. and Plant Quar. ET-231, 4 pp. illus. fiprocessedJJ (2) Vinsant, J. P., and Reed, W. D» 1941. Type of wire screen required for excluding cigarette beetles and tobacco moths from ware- houses. Jour. Econ. Ent. 34 (6)x 724. UNIVERSITY OP 3 1262 09239 1449