United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
PYRETHRUM-OIL SPRAYS IN OPEN-TYPE TOBACCO WAREHOUSES
By Joseph No Tenhet
Division of Truck Crop and Garden Insect Investipetions
Large stocks of flue-cured tobacco ars 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 (Hbna)) and the
cigarette beetle (Lasioderma serr nJcorn T Fj)a 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 common 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 des'ited, 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 $15,000 per warehouse.
The tobacco moth and the cigarette beetle pass the winter in
the worm, or larval, stage. The first brood of adults appeals 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 species r.iq.cires about 50
to 60 days, so that a second brood of adults (the main brood) a
pears in July or August. Sometimes a partial third brood appears
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
I/W. D. Reed (resigned June 13, 1946) supervise "v.s vor
during its early stages, and the American Tobacco CompL-rn, and th
R. J. Reynolds Tobacco Ccrpany cooperated and gave active assis-
tance in this project.
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 hs 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 SINCM ANY OIL
IS FLAMMABLE, IT IS NECESSARY TO OBSERVE THE PRECAUTIONS RECOM-
MENDED BY THE FIRE-INSURANCE UNDERWRITERS FOR HANDLING SUCH MATER-
ILALS. However, it is believed that the use of pyrethrum-oil spray
offers no more fire hazard than does the pyrethrum powder, which
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 60F. 0.797, flash point 175F., color-
less, anu no kerosene odor. This material is so volatile that all
traces vanish within a few hours after spraying.
The spray is a space spray 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 (1) especially designed to blow
the spray over the tops of the racke& 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 space 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 cent
of pyrethrins is recommended. It will kill all tobacco moths hit
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.
Table I.-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
week ending..- Sprayed .Dusted Untreated
May 31 1252Y 1524:/ 995./
June 7 122 517 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
October 4 10 12 581
11 37 87 461
18 48 112 256
Average weekly catch 37.6 124.9 1191.1
SCatch for the week prior to first application on May
figure not included in the average.
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 &i3le, payii 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 0.0396 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 spray, 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 moacre eco-
nomical for a warehouseman to mix his own spray. However, a man
with only one or two warehouses may find that thie convenience of
having a ready-to-use spray will offset the slight additional oost.
(1) Tenhet, Joseph N.
1946. A power sprayer for applying concentrated in-
secticides. U.S. Bur. Int. and Plant Quar.
ET-231, 4 pp. illus. [processed.]
(2) Vinzant, 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): 724.
UNIVERSITY OF PLOR DA
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