jY^ö. 3-33

STORED-TOBACCO

INSECTS

Biology

and

Control

Agriculture

Handbook No. 233

UNITED STATES DEPARTMENT OF AGRICULTURE

Agricultural Marketing Service
CONTENTS

Paga

Introduction 5

The cigarette beetle 6

Description and life history 6

Seasonal occurrence 7

Habits 8

The tobacco moth 9

Description and life history 9

Seasonal occurrence 10

Habits 11

Other pests of tobacco 12

Source of insect infestations in

tobacco 13

Cigarette tobaccos in farmers'

packhouses 13

Cigarette tobaccos in storage

warehouses 13

Cigar tobaccos 13

Manufactured tobacco products 14

Control on the farm 14

Sanitation 14

Residual sprays 15

Space treatments or mists 15

Page

Control in storage warehouses. _ 15

Open-type warehouses 17

Semiclosed warehouses 19

Closed-type warehouses 23

Tarpaulin fumigation 30

An insect-control program in

tobacco warehouses 1 30

Control by chamber fumigation. 31

Atmospheric chamber 31

Vacuum chamber 32

Control in tobacco factories 34

Preventing infestation 34

Fan-guarded doors 35

Insect traps 36

Fumigation of manufactured

tobacco 36

High- and low-temperature

treatments 36

Other treatments 37

Cost of insect control 37

Safeguards in fumigation 38

Literature cited 38

Washiagton, D.C. October 1962
STORED-TOBACCO INSECTS

Biology and Control ^

Prepared by the Stored-Product Insects Branch, Market Quality Research

Division, Agricultural Marketing Service

INTRODUCTION

One of the oldest and largest industries in the United States comprises the curing, storing, processing, and manufacturing of tobacco.

Most tobaccos are held in storage for 2 years or more for natural

^W\%' j ""g ^^^^ * ß the cigarette beetle {Lasioderma serricome

} '' ^^ '^^ tobacco moth [Ephestia eluteUa (Hbn.)) cause heavy

lo^. rhe cigarette beetle is also a pest of tobacco products.

In this country most of the tobacco held for aging is stored near

the manufacturing centers. Storage of cigarette-type tobacco is concentrated largely m North Carolina and Virginia; much of this

*<' '^^° F export IS stored near Norfolk, Va., and at Morehead City

and Wilmington, N.C. Large quantities of cigar tobacco are stored

New York, Pennsylvania, Connecticut, and Florida.

Manufacturers prefer to maintain large stocks of tobacco at all

tones. Total stocks of tobacco on hand in the united States and

Puerto Rico m October 1960 were estimated at about 4i^ billion

pounds farm sales weight. Tobacco dealers and manufacturers take

many precautions to eliminate insects from their warehouses and

factories and make a constant effort to keep their stocks free from

insect infestation.

Insect damage to stored tobacco and to tobacco products was estimated in 1941 to be more than $11 million. About 1950, it was

believed to be between $5 and $10 million. Since 1950, new and improved preventive and control measures have been developed. However, stocks of tobacco have increased, and the value of these stocks

has increased greatly. It is difficult to estimate the amount of insect

damage, but annual losses from insects probably are more than

$10 million. Much of these losses could be prevented by more energetic application of the measures discussed in this bulletin.

Losses to cured tobacco caused by insects are of five kinds: (a)

Loss in quantity and quality of leaf tobacco; (b) loss in value of

manufactured tobacco, such as the cigarettes and cigars that become

infested at the factory or in wholesale or retail establishments; (c)

loss on exported tobaccos due to refusal of customers to accept infested tobacco, at least unless discounts are granted ; (d) discrimina-

' This publication supersedes U.S. Department of Agriculture Circular No. 869,

Control of Insects in Stored and Manufactured Tobacco, by Joseph N. Tenhet

and C. O. Bare.
tion in other countries against infested American tobaccos; and (e)

loss of good will, as when a customer turns away from a particular

brand after buying an infested product.

Tobacco production in other countries had greatly increased by

1962. This tobacco competes with American tobacco for the foreign

market. Because American tobacco is higher priced and of premium

quality, foreign customers are highly critical of insect damage. This

attitude of foreign buyers has made the American exporters more

alert to insect damage. Moreover, in order to ship tobacco to some

countries, the exporter must certify that the product is free from

infestation by the tobacco moth, or show certificat'^n of fumigation. Inspection or fumigation at port is expensive.

The loss of good will to a manufacturer wb i a purchaser buys

insect-infested merchandise is an intangible i,hing and difficult to

eva,luate. It can seriously hurt a dealer s business before he is aware

of it, and the very thought of this kinc' of loss seriously disturbs any

tobacco dealer or manufacturer.

This publication offers 'nformation on insect pests of stored and

manufactured tobacco ana the most modem, effective, and economical

methods for the prevention and control of infestations.

THE CIGARETTE BEETLE

The cigarette beetle is cosmopohtan in distribution, having been

carried over the world by commerce in tobacco and other materials.

Specimens have been described from Tutankhamen's tomb in Egypt,

which seems to indicate an African or Asiatic origin for the species.

At least it was present in Egypt {!)'' more than 3,500 years ago. It

was recorded as a pest of cured tobacco in North Carolina as early as

1886 (g).

Description and Life History

The adult cigarette beetle is dark brown and less than % inch long.

The head is drawn under the body when the beetle is at rest and

usually when it is dead. The egg is pearly white, elongate-ovoid,

and about %o inch long. It is fragile, but has a waxy shell that is

very resistant to drying. The larva, or grub, is tiny (almost microscopic) when first hatched, but it grows to a length of about %g inch.

It IS creamy or grayish white and covered thickly with fine hairs,

which appear to be light brown on mature larvae. When fully grown,

the larva forms a tliin cell or cocoon, in which it transforms into the

inactive pupa, and from which the adult beetle emerges.

The adult beetle lives for 2 to 4 weeks—longer in cool weather—

and each female lays from 40 to more than 100 eggs. The average

number of eggs deposited, as determined by different scientists, has

ranged from 40 to 76, but studies in Nortli Carolina under warehouse

conditions gave an average of 42. Most of the eggs were laid during

the first 10 days after the adult emerged, but the largest niunbers of

eggs were laid on the fourth, fifth, and sixth days. About 80 percent

of the eggs were deposited from the third to the ninth day and more

than 90 percent after the second day (9). The egg hatches in 6 to 10

days, and the larva matures in about 30 to 50 days. In the summer

in North Carolina and Virginia, the average incubation period is about

7 days, the larval stage 40 days, the pupal stage 5 days, the pre-emer-

^ Italic numbers in parentheses refer to literature cited, page 38.
BN-16196

Figure 1.—Stages ef the cigarette beetie (left to riglitl: Egg; fuil-grown larva; pupa; and

adult. Greatly enlarged.

gence period 3 to 6 days, and the total life cycle about 56 days.^ The

four stages of this insect are shown in figure 1.

Seasonal Occurrence

The seasonal occurrence of the cigarette beetle varies with the conditions under which tobacco is stored and manufactured. In heated

buildings or in the subtropical climate of Florida, there may be no

well-defined hibernation period but a slowing of development during

the winter. In Puerto Rico and throughout the tropics, the beetle is

active during the entire year. Under such conditions all stages of the

insect may be found at almost any time. In North Carolina and Virginia and farther north, the beetle passes the winter in the larval stage

in tobacco or other hosts. The mortality of immature larvae is usually

heavy and in severe winters the population of mature larvae may be

materially reduced. If the tobacco temperature remains below 36° F.

for 16 consecutive days, all larvae are killed (7), and such low temperatures occur frequently in Virginia. In brick warehouses and

factories, however, infestations nearly always survive.

In the Richmond, Va., area the larvae begin to pupate late in the

spring, and usually the first adults of the spring brood emerge late

in May. Near Charleston, S.C., or Wilmington, N.C.j emergence may

start as early as the last week of March. The generations overlap, but

peaks of emergence of different broods are rather sharply defined.

At Richmond the spring peak is reached usually about the middle of

June. Since most individuals of a generation complete development

m 50 to 60 days, there are ordinarily two generations and part of a

third generation each year in North Carolina and Virginia. This

seasonal occurrence is shown in figure 2. At Richmond, there is usually

a peak emergence in June, another in August, and a third in October.

The third generation is usually smaller than the others, but in mild

weather it may be large. A large number of the second-generation

larvae and all of the third-generation larvae pass the winter in this

stage.

The population of cigarette beetles fluctuates widely, but there is

some indication of cycles of abundance. Beetles appear to be more

abundant every other year, and perhaps there is a longer cycle, but the

picture is somewhat obscured. In any storage warehouse the most

important factors influencing population are temperature, relative

humidity, and types, grades, age, and quantity of tobacco present.

At times, parasitism may also be of some importance.

' In the insectary with the temperature constant at 80° F., and the relative

humidity at 70 percent, the total life cycle is about 45 days.
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BN-16194

Figure 2.—Seasonal occurrence of the cigarette beetle in Virginia and North Cat«lina.

Habits

Practically all injury to tobacco by the cigarette beetle is caused by

the feeding of the larvae. The adults do not feed. The only damage

they cause is by cutting exit holes to escape from the tobacco or package in which they pupated. Most of the adults attempt to leave the

tobacco. However, these insects can mate and lay eggs in close confinement, and some of the adults do.

This insect attacks the principal types of cigarette, cigar, chewing,

and snuff tobaccos, as well as most forms of manufactured tobacco.

Burley and Maryland tobaccos are rarely attacked, however, and these

types have never been known to be damaged economically.

BN-16193

Figure 3.—A hanci or bundie of flue-cured tobacco, showing typical injury by the cigorette

beetle. About one-third natural size.
The larva burrows through the tobacco, making rather clean-cut

holes, and leaving behind a fine powder of excrement. Cigars and

cigarettes are made unfit for smoking by the holes in the wrapper or

paper, which prevent a satisfactory draught. Infested smokmg or

chewing tobacco or infested snufl is objectionable to the consumer from

the aesthetic standpoint as well as in taste. However, the greatest

losses caused by the cigarette beetle occur in leaf tobacco in storage.

Injury to leaf tobacco is shown in figure 3.

The cigarette beetle has a very wide range of host foods; it is one

of the most omnivorous of the storage pests. It has been recorded

as infesting cottonseed meal, cottonseed, dry yeast, chili powder, curry

powder, ginger, cayenne pepper, paprika, turmeric, saffron, nutmeg,

mixed spices, licorice roots, pyrethrum powder, dried pyrethrum

ñowers, opium, belladonna, dates, raisins, dried figs, cereals, rice, bran,

dried citrus pulp, leather, woolen cloth, bamboo, broomcom, aniseed,

areca nuts, copra, cassava, coffee beans, cacao beans, peanuts, dried

vegetables, dried herbs, flax tow, dried Spanish moss (tow), dried

insects, fish meal, meat meal, and other materials (5 and 7). It has

been reported as damaging paper and also nylon cord used in the

manufacture of automobile tires.

THE TOBACCO MOTH

The tobacco moth is widely distributed in the temperate and tropical

climates of the world. It was first reported as a pest of American

tobacco in 1930 (S), and now it is one of the important pests of fluecured and oriental types of tobacco in the United States. It has never

been recorded as attacking air-cured, fire-cured, or cigar types of

tobacco. In 1937^0 an outbreak of this insect occurred in farmers'

packhouses in North Carolina and Virginia. Farmers suffered heavy

losses between the time their flue-cured tobacco was harvested and the

time it was sold. Slight damage was reported from some farmsin 1948

and 1949 and almost every year thereafter.

Description and Life History

The adult tobacco moth is a small gray or brownish-gray moth. It

measures about % inch from head to tips of folded wings and has a

wingspread of about % inch (6). The eggs are laid singly or in loose

groups on or near tobacco. They are sandy white when laid, and

gradually they turn darker. They are slightly elongate and about

1/45 inch long. The shell is very tough. The eggs are only loosely

attached to the tobacco. The larva is tiny when first hatched, but it

grows to % to 1/2 inch long. It is pinkish white and has a few fine

hairs. The head is reddish brown, and the body has small brown spots

along the back. When full grown the larva spins a weblike cocoon in

which it transforms to a pupa. Adult moths emerge from the pupae.

Mating and egg laying usually begin within 24 hours after emergence. The average female probably lays more than 100 eggs, and

as many as 279 have been recorded. The eggs hatch in 3 to 17 days,

and the larvae reach maturity in 25 to 128 days. The pupal stage

requires from 5 to 25 days. Under summer conditions the life cycle

.from egg to egg averages about 50 days—5 days for incubation, 35

days for larval development, and 10 days for pupation. The adult

9

644464 O—82 2
Figure 4.—Stages of the tobacco moth; A, large larva; B, pupa; C, adult; and D, eggs (

young larva on section of tobacco leaf. About seven times actual size.

moths may live as long as 7 or 8 days—longer in cool weather. The

four stages of this insect are shown in figure 4.

Seasonal Occurrence

The tobacco moth passes the winter as a larva. In the fall most of

the mature larvae leave the tobacco and migrate to cracks and crevices

about the building, where they spin the loose cocoons of silk in which

they hibernate. Some larvae may spin cocoons on or near the surface

of the tobacco. Immature larvae may remain in the tobacco in an

inactive state, and probably many of them fail to survive the winter.

However, relatively few immature larvae enter the winter. Once

hibernation has begun, the mature larvae seem able to withstand low

temperatures for long periods. Larvae have been reported to survive

the winter in unheated buildings in Canada at a temperature of —30°

F. In Forth Carolina and Virginia, larvae have been known to

survive exposure to near-zero temperatures for periods of 2 to 3 weeks.

n^ ä 15 31 15 30 15 31 15

FEB. I MtR, I APR. I MAY | JUNE

Figure 5.-

BN-ieZ81

-Seasonal occurrence of the tobacco moth in Virginia and North Carolina.

10
At Richmond, Va., pupation usually begins in April. Emergence

of moths of the overwintered brood generally starts in May. At

Charleston, S.C, and Wilmington, N.(S, moths may emerge as early

as the last week of March.

The peaks of emergence of the broods of the tobacco moth are a

little more sharply defined than those of the cigarette beetle. In the

Richmond area, emergence of the spring brood is usually at a peak

in the last 2 weeks of May. The population of moths in a warehouse

then declines, reaching a very low ebb early in July. A second peak of

emergence occurs in August, and a third and usually much smaller

peak is often noted late in September or in October (fig. 5). In 1948

and 1949 a full third brood occurred, and at Norfolk, Va., active moths

were noted as late as the middle of December.

Habits

Only the larva of the tobacco moth feeds on tobacco. This insect

does not attack manufactured tobacco products. It feeds only on leaf

tobacco of the flue-cured and Turkish types, preferably of the better

grades—those high in sugar and low in nicotine. Tobacco with a sugar

content (dextrose before inversion) of more than 10 percent (much

flue-cured tobacco contains 20 percent or more of sugar) and a nicotine

content of less than 2 percent seems particularly attractive to the

tobacco moth.

This insect is a heavier feeder than the cigarette beetle ; in a severe

infestation it devours many leaves completely except for the midrib

and larger veins (fig. 6). In crawling, the larva leaves behind a

Figure 6. Damage to leaves of flue-cured tobacco by larvae of the tobacco moth. About

one-flfth natural size.

11
silken thread that forms a webbing and catches pellets of excrement.

Such accumulations of webbing and excrement are unsightly and

objectionable to buyers and manufacturers.

Mature larvae move out of the tobacco, or at least to the surface—

a necessary migration, because the soft, fragile adult moth could not

cut its way out of confinement. It is often trapped while trying to

crawl through very tiny openings. The moth apparently does not

mate in close confinement ; therefore, it must emerge before fertile eggs

can be laid.

The tobacco moth feeds on many stored products besides tobacco.

In the United States it has been found in almost all grains, as well

as in peas, beans, cornmeal, wheat flour, rolled oats, peanut meal,

poultry laying mash, stock feed, and various cereal products. It has

also been reported as infesting cacao beans, shelled nuts, linseed meal,

coffee, chicory, ship's biscuits, cottonseed cake, cayenne pepper, rice,

pearl barley, other seeds, peanuts, and dried citrus pulp (7).

OTHER PESTS OF TOBACCO

Several insects other than the cigarette beetle and the tobacco moth

also feed on tobacco and may occasionally cause some injury.

The larger tobacco beetle (Oatorama tahaoi Guer.) is primarily

a tropical species, but it has been reported in Florida and Puerto

Rico. It attacks cured tobacco in much the same way as does the

cigarette beetle. It resembles the cigarette beetle, but is larger and

is black instead of brown.

The phycitid moth Tlmeala fmitella (Wlkr.) was taken from fluecured tobacco at Eichmond, Va., in 1932, and a few individuals have

been observed since that time.

The larva of an Aglossa moth, presumably caprealis (Hbn.), feeds

on moldy or partly decayed tobacco. It is sometimes observed in

warehouses and farmers' packhouses.

The following species are listed in approximately the order of

their prevalence :

TnboUv/m oonfiiswn Duv.

Tribolium castcmevm, (Hbst.)

Henoticus serrátil» (Gyll.)

Ahasversus advena (Waltl.)

Typkaea stercorea (L.)

Anthrenus verhasci (L.)

Lepisma saccharina L.

Ptinus hirtelhis Sturm.

Attagenus piceus (Oliv.)

Trogoderma omatum (Say)

Oryzaephihis surinamensis (L.)

Mezvwm americanwm Lap.

Dinoderus brevis Horn

Stegoiiv/m paniceymi (L.)

Sitophilus oryzae (L.)

Dermestes maculatus Deg.

Tenebño ohscurm F.

Tensbrio Tnolitor L.

Anthicus cervinus Laf.

Anthicus ßoralis (L.)

Many of these insects act as scavengers, eating dead bodies of the

cigarette beetle and the tobacco moth ; others probably use the tobacco

as a temporary shelter.

Since 1958 increasing numbers of a small black beetle, very similar

in size and appearance to the cigarette beetle, have been captured in

tobacco warehouses. This insect has been identified as Catorcmva confusum, Fall. Repeated attempts to rear this insect on tobacco have

failed, but, because it is commonly found in tobacco storages, it

warrants continued surveillance.

12
SOURCE OF INSECT INFESTATIONS IN TOBACCO

Cigarette Tobaccos in Farmers' Packheuses

The tobacco moth is sometimes a serious pest of flue-cured tobacco

on the farm. Infestation may begin even in the curing barn and

continue until the tobacco is marketed. Most damage occurs in the

packhouse, where the tobacco is bulked before grading. Infestation

may develop from moths flying from commercial storages or farms

nearby, or it may be already established on the farm and carried over

from year to year in scrap tobacco, peas or beans, stock feeds, or other

host foods {iS).

Cigarette Tobaccos in Storage Warehouses

The redrying of flue-cured leaf tobacco before it is packed in hogsheads for storage destroys all stages of the cigarette beetle and the

tobacco moth. Hence, leaf tobacco is free of insect infestation when

it is" prized into hogsheads. However, domestic cigarette manufacturers have been storing much tobacco as "strips" (the lamina of

the leaf, from which the midrib has been removed). Strips are

redried much more rapidly than leaf and at lower temperatures, and

this process does not always destroy all insect life. It is about 98 to

99 percent effective; a few larvae or pupae may survive. Moreover,

in the United States the crop of bright tobacco is redried from July

through December, most of it in late summer. At this season of the

year, insects are active, and almost all redrying plants and warehouses, as well as many trucks and railway freight cars in which

tobacco is shipped, are infested.

If newly packed tobacco is held for even a few hours in an infested

building or vehicle, it may become infested. Moths or beetles fly

about and lay eggs on the tobacco or in the cracks of the hogshead

or case. The larvae that hatch from these eggs immediately begin

feeding on the tobacco. Tobacco packed in July or August can

develop one generation of insects, and under certain conditions two

fenerations, before cold weather begins. Tobacco for export, packed

com July through September and held for even a few days in an

infested storage, is almost certain to develop an infestation. Therefore, tobacco should be fumigated before shipment. In its early

stages an insect infestation is not easily detected, and new-crop tobacco

exported late in the summer may be infested on arrival abroad.

Turkish tobaccos are usually infested before they are imported. The

tobacco moth and the cigarette beetle are common pests in Turkey,

Greece, and the Balkans, and little eifort at insect control is made in

those countries. Moreover, many ships' holds are infested by these

insects. Much imported tobacco is fumigated at the port of entry.

Warehouses that have been in use for several years may harbor an

infestation even though all old tobacco is moved out before a new crop

is received. Tobacco dust and scrap accumulate in cracks and crevices and under dunnage and false flooring. The tobacco moth's habit

of leaving tobacco in order to pupate may also help to spread infestations.

Cigar Tobaccos

Cigar tobaccos are attacked by the cigarette beetle only. This insect

is prevalent in almost every area where these tobaccos are stored. The

13
beetle is present in many warehouses and attacks the tobacco soon after

it enters storage. During the aging or sweating process some infestation is usually present. Much imported cigar tobacco is already infested \Yhen received. Much tobacco is imported from Cuba and

Puerto Rico, where the cigarette beetle is prevalent.

Manufacfured Tobacco Products

Practically all manufactured tobacco products are attacked by the

cigarette beetle. The beetle is a strong flier and has been known to fly

2 miles or more. In any manufacturing center beetles can and probably will fly through any open door or window. They frequently lay

eggs on packaged cigars, cigarettes, or other tobacco products in wholesale or retail establishments, as well as in manufacturing plants. A

package covered with paper, cardboard, foil, or cellophane and effectively sealed is protected from cigarette beetle attack. Unfortunately,

however, few packages in commercial use today are adequately sealed.

Eggs laid on a package hatch into tiny larvae, which oft«n crawl

aromid and through the folds of the wrapping, or penetrate almost

microscopic holes or cracks in the package to reach and infest the contents.

Cigars are often held in open trays or boxes for 4 or 5 weeks for

aging—an excellent opportunity for infestation.

In cigarette factories, leaf tobacco before manufacture is passed

through a thermal vacuum process, which destroys all stages of the

cigarette beetle and the tobacco moth. However, much of the tobacco

brought into a factory is infested, and this tobacco may remain in the

plant for several hours, or even days, before being processed. Beetles

emerge from this tobacco and readily fly about in the plant. In the

factory the shredded tobacco is treated with flavoring and allowed to

stand for several days for the flavoring to permeate the tobacco. Eggs

laid on the tobacco at this time usually do not hatch until the tobacco

has been made into cigarettes and packaged.

At a moderate temperature and high relative humidity the cigarette

beetle is active and breeds the year round. It thrives best at about 80°

F. and 70 percent relative humidity. Great care should be taken to

eliminate any accumulations of scrap tobacco and not to retain more

than a few days' supply of tobacco in the processing area of the factory.

CONTROL ON THE FARM

Sanitation

Once an infestation of the tobacco moth has developed in a farm

packhouse, the farmer's simplest course is to grade and market the

tobacco as quickly as possible. However, he can do a lot to prevent an

infestation. As soon as a crop is graded and sold, the packhouse and

grading room should be thoroughly cleaned, even the walls brushed

down. All scrap tobacco should be hauled away and scattered thinly

over the fields or destroyed. No seed, feed, or fertilizer should be

stored in the packhouse. In the spring when the moths emerge, they

will fly away in search of material in which to lay their eggs. The

young larvae from such eggs as may be laid in a clean packhouse will

die for lack of food. If grain or feed is stored in the packhouse, the

moth will breed in this material until the tobacco is harvested.

14
Residual Sprays

A thorough application of 5-percent DDT spray to the walls and

ceilings of the packhouse early in the spring (during March in South

Carolina or eastern North Carolina and during April in central North

Carolina and Virginia) can be beneficial. The most desirable formulation is DDT wettable powder in water. It should be applied as a

coarse, wet spray, and surfaces should be wet almost to the runoff

stage. The DDT residue will kill the moths that rest on a sprayed

surface for a sufficient time. It will continue to be effective for a

month or more {16).

Space Trealmenls or Mists

If an infestation develops and it is necessary to hold the tobacco for

more than 2 or 3 weeks, it may be desirable to treat the airspace inside

the packhouse with pyrethrum in oil once or twice a week. This mist

spray should contain 0.2 percent pyrethrins, with or without a Synergist, in a light volatile oil. Specifications for a suitable oil are as

follows (10).

Specific gravity at 60° F 0.77-0.80.

Flashpoint (Tag closed cup) 140° F. minimum.

160-170° F. preferable.

Initial boiling point 370° F. minimum.

Distillation end point 490° F. maximum.

Unsulfouated residue 97% minimum.

Color Water white.

Odor Neutral—no kerosene or naphtha odor, no

residual odor.

Such a formulation can be bought already mixed, or the farmer

can easily mix it himself (14)

This treatment creates only a slight fire hazard when prepared as

directed. It is relatively harmless to man. No open flames, such as

oil lanterns or lamps, and no smoking should be permitted in the

packhouse while the treatment is being applied. The mist should

be directed so as to fill the airspace. Thorough treatment is

important.

CONTROL IN STORAGE WAREHOUSES

INSECT TKAPS.—To provide an index of infestation and a guide for

timing control measures, suction/light insect traps (described below)

should be installed in all storage warehouses and operated continuously from early in spring until late in fall.

Such a trap consists of a barrel, a flange of sheet metal, and a cone

of 20-mesh bronze, brass, or stainless-steel screen wire. To the small

end of the cone is soldered the rim of a fruit jar lid, and into this lid

is screwed a glass jar of suitable size. A 40- to 50-watt light is suspended from the front of the flange. A fan operated by a small

electric motor in the barrel of the trap provides suction. The motor

is usually of %o horsepower or less, so that the fan and light combined consume less than 1 kilowatt of electricity in 24 hours.

Since the cigarette beetle is attracted to light, a suction/light insect trap aids in reducing populations of this insect. The tobacco

moth is only slightly attracted to light, but any insect flying near

the mouth of the trap is caught by the suction. Consequently, although a trap may not significantly reduce the population of tobacco

IS
moths, it does catch a sufficient number to indicate the beginning,

peaks, and end of seasonal variations in numbers of the insect.

A trap, preferably mounted on a cord and pulley so that it can be

readily lowered for examination, should be suspended from the ceiling

of the warehouse above the top of the hogsheads or bales of tobacco.

In small storage units, one trap per unit should be used. For use

merely as a measuring device to record the relative insect population,

one trap per one-story warehouse is satisfactory in storages up to

500,000 cubic feet.

All traps should be operated 24 hours a day. Operation for only

part of the day will not give an adequate sample.

Traps should be cleaned thoroughly and the motors oiled every 3

months. The wire gauze cone should be brushed off at least once a

month, otherwise the meshes will become clogged with dust and the

suction will be reduced.

STORAGE PROCéDURE.—Flue-cured tobacco is highly attractive to the

cigarette beetle, but burley and Maryland tobaccos are rarely, if ever,

damaged. For this reason the burley tobaccos, which would not need

to be fumigated, should be segregated. It is not economical to miy

hogsheads of flue-cured and burley tobaccos throughout a number

of warehouses so that all will require treatment.

The cigarette beetle is particularly attracted to "stems" of fluecured tobacco (midribs that have been stripped from the lamina of

the leaf). It seems to prefer to lay its eggs in the crease or fold of

these stems. The stems are so coarse and rigid that they cannot be

tightly compacted ; hence, the beetles can readily crawl through and

BN-B276

Figure 7.—Interior of a storage waretiouse containing hogsheads of flue-cured tobacco.

Note screened door and suction/light insect trap.

u
penetrate the entire mass. Stems are nearly always heavily infested

by the cigarette beetle, and a few hogsheads can serve as a dangerous

focus of beetle infestation. Stems should never be stored in a warehouse with other susceptible tobacco.

For many years all cigarette manufacturers have customarily stored

3 crop-years of tobacco in each warehouse. For economic reasons it

is impractical to segregate the stocks by crop years. About i/¿ of the

contents of each warehouse is used and replaced each year. As a result of this practice, warehouses are never emptied of tobacco, and

"clean" tobacco is always stored in infested buildings where it is immediately exposed to infestation.

SCREENING.—During the summer, adults of both the cigarette beetle

and the tobacco moth are constantly flying about. Therefore, all

warehouses should be screened, particularly open warehouses where

mists are used (fig. 7). In an unscreened warehouse, insects may

readily fly out of the building ahead of the spray, only to return

within a few minutes after the spraying is done. Furthermore, even

should all beetles and moths in a storage be killed, the building will

probably become reJnfested in a few hours. Observations have been

made in screened warehouses where one building was very heavily infested and an adjoining building remained very lightly infested all

summer. Such differences would rarely, if ever, appear in unscreened

storages.

Over a period of years it has been shown that mists give

significantly better control of the tobacco moth in screened than in

unscreened warehouses. Galvanized-wire screen may be used, but

usually will rust out in 3 to 5 years, A more durable wire, such as

copper, bronze, aluminum, or plastic, will probably prove more economical in the long run. The size of mesh used is important. To

exclude the cigarette beetle, the openings in the wire should not exceed

0.0396 inch. A 20-mesh wire (20 strands to the inch) is preferable,

but an 18-mesh wire is satisfactory if the wire strands are at least

0.02 inch in diameter (19).

Open-Type Warehouses

An open-type warehouse is merely a shed with open or partly open

sides. It consists of a roof and a wooden framework with the sides

partly covered by sheet metal, usually with louvers (fig. 8). The floor
may be of cinders, crushed rock, concrete, or wood. Storages of this

type vary in size, but most of them exceed 100 by 150 feet by 16 to 18

feet high. The capacity of a single section may range from 800 to

more than 3,000 hogsheads. Few of the more modem warehouses have

a capacity of less than 1,500 hogsheads.

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

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

stored in open-type or semiclosed warehouses. This tobacco is attacked by both the cigarette beetle and the tobacco moth, and in such

buildings insect control is a difficult problem. Fumigation is impossible or impractical and aerosols or vapor-phase insecticides are almost useless in open sheds.

An insecticide for use in tobacco warehouses must meet several requirements. Besides being an effective insecticide, the material should

be volatile, leave no objectionable odor, leave no harmful or objectionable residues, impose no serious fire or explosion hazards, and be easy

and safe to apply. Water sprays are not advisable because they may

increase the moisture content of the tobacco and cause the development of molds and rots.

Pyrethrum in oil fits these specifications. Pyrethrum is a good

contact insecticide and one of the least hazardous to man. The mist

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

permanent odor or objectionable residue when correctly applied. Care

should be exercised in its use. Repeated wetting of hogsheads or

bales of tobacco with the liquid insecticide may taint the tobacco.

Concentrated accumulation of pyrethrum mists on large sprinklersystem pipes full of water can cause moisture to drip on hogsheads

directly below and has been known to taint tobacco {1J^). The oil

recommended for use as a diluent for pyrethrum for treatment of tobacco warehouses is of a light volatile type. The specifications for

such an oil are given on page 15. Pyrethrum-oil mists kill insects

that they hit directly. They do not penetrate the hogsheads or bales

of tobacco and cannot reach the insects in the tobacco.

Treatment should be started when the weekly trap catch reaches 10

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

insect activity is slowed by low fall temperatures. The object of the

space treatment is to kill the adult insects before they have laid many

eggs. Applications should be made weekly or more often, preferably

on the same days each week, and care should be taken to see that all

parts of the warehouse are reached.

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

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

and for use against this insect the formulation should contain 1 percent of pyrethrins. The dosage rate should be about 3 fluid ounces

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

airspace of a warehouse is the volume of the building less the volume

of space occupied by tobacco.) Formulations of pyrethrins with a

Synergist added are available for use as space treatments if desired.

Follow the manufacturers' recommendations if these are used.

Flight activity of the cigarette beetle is largely restricted to late

afternoon and early night. During the working day (7 a.m. to 5

p.m.), less than 10 percent of flight activity occurs. Flight activity

of the tobacco moth is more uniform throughout the 24 hours, but

this insect also is slightly more active during the afternoon and early

18
BN-4595

Figure 9.—Applying pyrethrum-oil mist in a tobacco wareliouse containing flue-cured

tobocco.

evening. Because more insects are active in the airspace of a warehouse from 4 p.m. to midnight, it is important that mist applications

be made at that time. Evening applications consistently have given

better results (Iß and I4.).

A mist blower has been especially designed for operation inside

open-type tobacco warehouses. This blower will deliver about 2,400

cubic feet of air per minute at an initial velocity of about 5,700 feet

per minute. Such a machine will blow a mist 100 feet or more, and

reasonably good coverage can be obtained in open warehouses, even

with a breeze of 6 to 7 miles an hour (fig. 9).

Fire-insurance underwriters have approved the use of pyrethrumoil space treatments in tobacco warehouses when prepared and used

as directed. Although the flash point of the oil generally used in

these sprays is approximately 17.5° F., such oil is moderately flammable and might be explosive under certain conditions. Wlien the

equipment is to be taken into a building, only electric macliines should

be used. Sparkproof motors and switches and heavy-duty rubberjacketed extension cord containing a grounding wire should be used

on the blowers.

All precautions recommended by tlie interested fire insurance companies should be carefully followed (l-i).

Semiclosed Warehouses

Since World War II some of the larger cigarette manufacturers

have eliminated the louvers and closed the sides of their open-type

19
BN-iei98

Figure 10.—Semiclosed type of tobacco warehouse. Note corrugated metal siding and

absence of windows and ventilators.

warehouses. These semiclosed warehouses are rather loosely constructed of corrugated iron, usually with concrete floors. They may

be of one- or two-story construction, with or without ventilators and

windows, and with doors on opposite sides of tlie ground floor. However, as a rule, the doors on one side are never used. Such buildings

have numerous cracks at the joints of tlie corrugated metal siding,

but they have no cross ventilation. They cannot be sealed for fumigation, but they can be efficiently treated with aerosols, mists, or

vapor-pliase insecticides. A typical example of sucli a warehouse is

shown in figure 10.

AEROSOLS AND MISTS

Pyrethrum-oil aerosols can be used to advantage in semiclosed

warehouses. The same formulations, concentrations, and dosages are

recommended as for mists in open-type warehouses. The advantage

of an aerosol over a mist is that the finer particles permit better distribution of the insecticide. However, the finer droplets of an aerosol

may remain suspended in the air for 1 or 2 hours, and it is essential

that all doors and ventilators be kept closed during this period. Distribution or coverage is essential, because the insects in the airspace

must be hit with the insecticide.

When a thermal aerosol is used, adequate distribution of the particles often is not obtained. Because of the fire hazard, fire insurance

miderwriters have banned taking an aerosol generator into tobacco

warehouses. Tlie machine is usually stationed at a door and the aerosol is blown through the door and into the central aisle (fig. 11). An

aerosol so introduced may not be well distributed because of the large

size of the building, tlie racking of the hogsheads, and the low headspace above the liogslieads. If the hogsheads are racked four tiers

high with dunnage between tlie tiers, they form an almost perpendicular wall more than 16 feet high on each side of the aisle. If there

20
BN-iaift9

Figure 11.—Introducing a tiiermaj aerosol into a semiclosed tobacco warehouse.

is onljf 2 or 3 feet of headspace between the top of the hogsheads and

the ceiling, the aerosol may not penetrate to the back areas of the

building in sufficient quantity to be effective. If the headspace is

partly blocked by large beams or by sprinkler pipes, distribution of

the aerosol is fiirther restricted. Numerous tests have demonstrated

that under such adverse conditions, adequate quantities of aerosol do

not reach the rear areas of the storage.

In using aerosols, a concentration of 0.2 percent of pyrethrins for

the tobacco moth or 1 percent of pyrethrins for the cigarette beetle is

needed, the same as m using the mist. A dosage-rate of 3 fluid

ounces of insecticide per 1,000 cubic feet of airspace is essential to

give adequate distribution in large warehouses. However, in small

warehouses of 15,000 square feet or less of floor space (such as are

sometimes used for Turkish or cigar tobaccos), with a clear head-space

of 5 or 6 feet or more, and with numerous open aisles between the

bales, a lower dosage is satisfactory. In such buildings good results

have been obtained with 2 to 21/2 ounces per 1,000 cubic feet of airspace.

The recommendations for the use of mists in open-type warehouses

are also applicable in semiclosed warehouses.

VAPOR-PHASE INSECTICIDES

DDVP (2,2-dichlorovinyl dimethyl phosphate) can be used advantageously in semiclosed warhouses. This is a vapor-phase insecticide, which kills by means of a vapor that is released from the

21
deposit when used as an aerosol ; kill is increased by contact of DDVP

particles with the insect. At the recommended dosages, DDVP wiU

not aifect the flavor or aroma of tobacco. This phosphate insecticide

is somewhat dangerous to handle and apply but has certain advantages

over contact materials that are effective only for the short time the

particles are in the air.

DDVP may be applied as an aerosol at a dosage rate of 1 to 2 grams

actual DDVP per 1,000 cubic feet once or twice a week. One gram per

1,000 cubic feet once a week will give good control of the tobacco moth.

It is desirable to apply 2 grams per 1,000 cubic feet twice a week for

the cigarette beetle {17 and 18). At a dosage rate of 2 grams per 1.000

cubic feet, the vapor will liave a continuous killing action for 3 to 4

days. However, any appreciable ventilation will dissipate the vapor

so that a lethal concentration cannot be maintained. The killing

action of DDVP vapor is relatively slow, and the vapor concentration

decreases each day following treatment. Nevertheless, although

beetles may survive many hours' exposure, few eggs are laid while the

beetles are continuously exposed to the vapor.

Liquid DDVP is highly dangerous. Every precaution should be

taken to avoid getting it on the skin or clothing. It can be absorbed readily through the skin, and if accidentally spilled on

the body it should be quickly washed off with liberal use of soap

and water. If the liquid is spilled on shoes or clothing, they

should be removed immediately and not worn again for several

weeks or until washed or dry cleaned. It is highly dangerous to

breathe DDVP aerosol (Jf and 77). However, there is no danger to

laborers working continuously 8 hours a day in warehouses treated

at the dosages recommended provided they do not enter the building either (a) for 4 hours after application of DDVP or (b) before the building has been ventilated. It is preferable to apply

DDVP m the evening after working Iiours. The next morning, work

may be carried on as usual in the treated storages.

DDVP also may be applied by sprinkling it upon a Vfooden surface. It should not be applied on concrete as there is a chemical

reaction that reduces the effectiveness of the insecticide. However,

it can be applied on boards laid on a concrete floor. This method of

application has certain advantages over an aerosol. It is cheaper,

smce expensive equipment is not required and solvent for further

dilution is not needed, and it is effective over a longer period. The

emulsifiable concentrate (4 pounds per gallon) may be used. Because

of the danger involved in handling DDVP, this insecticide should be

applied by qualiñed pest control operators, who should wear gas

masks during the application. It should never be trusted to unsupervised, unskilled laborers.

Both contact insecticides and vapor-phase insecticides have definite

limitations. Such materials can reach and kill only those insects in

the airspace. Since they do not penetrate hogsheads, cases, or bales,

they cannot reach those insects buried in the tobacco; consequently,

they are no substitute for fumigation, which does penetrate. However, they can be used where fumigation is impractical. Both pyrethrum and DDVP are highly effective against the tobacco moth, but

much less effective against the cigarette beetle. The cigarette beetle

can and does breed within the mass of the tobacco, and in a, well22
established infestation many beetles never emerge from the tobacco

to where they can be reached by pyrethrum or DDVP.

Closed-Type Warehouses

The closed-type warehouse differs from the open-type and the semiclosed type in that it can be sealed for fumigation. In closed warehouses winter temperatures do not drop so low, and the cigarette

beetle is often a more important pest than the tobacco moth. Warehouses of this type may be one story or several stories, but all have

doors, windows, and/or ventilators (figs. 12 and 13). The buildings

vary greatly in size—from 25,000 to more tlian 1 million cubic feet.

Many closed warehouses consist of long rows of sections separated by

brick fire walls. Some of them contain more than 100 million pounds

Figure 12.—An old, closed-type tobacco warehouse.

windows.

BN-1618B

Note brick construction and numerous

Figure 13.—A large group of closed-type tobacco warehouses.

23
Figure 14.— -A melal-clad, closed-type tobacco warehouse, especially designed to make

fumigation easier. Note ventilators on side; others are on roof.

of tobacco. The cost of labor in moving sucli large quantities of

tobacco to fumigation chambers makes chamber fumigation impractical. The only feasible method of insect control, therefore, is to fumigate each warehouse.

One type of closed warehouse, the idea for which was developed by

the Stored-Tobacco Insects Laboratory, of the Market Quality Research Division, has been widely adopted. The walls are of flat

"V-crimped" sheet metal over a wooden frame. The joints of the

metal are locked and sealed with a calking compound. Ventilators

and doors close against gaskets, so that the storage can be quickly and

easily sealed for fumigation. Such a building is shown in figure 14.

A similar, but more substantial, warehouse can be constructed of

cinder block, cement block, or brick.

MISTS, AEROSOLS, AND VAPOR-PHASE INSECTICIDES

Pyrethrum-oil mists or aerosols and DDATP are more effective in

closed-type warehouses than in open-type or semiclosed storages. The

systematic use of DDVP or of pyrethrum can almost completely eliminate an infestation of the tobacco moth. Weekly applications of

DDVP have proven more efficient and much cheaper than fumigation

in controlling this insect. DDVP or pyrethrum treatments may also

aid in holding down a cigarette beetle infestation, and may decrease

the number of fumigations necessary. In light beetle infestations,

such treatments may give satisfactpry control, but in heavy infestations they will not. Against a heavy, well-established beetle infestation, there is no substitute for fumigation.

The recommendations for use of DDVP or of pyrethrum treatments

in semiclosed warehouses also apply to closed-type warehouses.

WAREHOUSE FUMIGATION

For efl'ective control of insects by warehouse fumigation, the building must be adequately sealed. All openings in the walls, floors, and

ceiling, such as windows, doors, ventilators, eaves, skylights, and elevator shafts, must be closed and the building made gastight.

One method of sealing warehouses, which has been used for many

years, uses a heavy gastight paper (such as sisal kraft), paste, asphalt,

elastic roofing cement, calking compound, and paper maskmg tape.

Large openings are closed with heavy paper sealed with paperhangers' paste or masking tape (fig. 15). The eaves are sealed with tarred

24
BN-16201

figure 15—Door of o tobacco warehouse partly sealed for fumigation. Sisal kroft paper

has been tacked and pasted over screen door.

paper and asphalt. Polyethylene sheeting of 4-niil thickness may be

substituted for heavy paper. Cracks are filled with a mixture of four

parts asbestos fiber to one part of calcium chloride and enough water

to make a stiff dough. For small cracks calking compound or elastic

roofing cement is excellent (fig. 16).

Since the late 1940's or early 1950's, many warehouses have been

sealed by spraying a vinylite plastic over cracks and around doors,

windows, and ventilators. The plastic is applied with a paint spray

gun powered by compressed air. When properly done this sealing is

semipermanent. It requires less labor than other common methods of

sealing, but a greater capital investment is needed for an air compressor, airhose, spray guns, and a motortruck (fig. 17). Companies

that have many warehouses can afford such equipment, but the cost is

too high for small companies. Sealing with plastic has one great advantage—it can be done very rapidly. Sometimes the need for fumigation develops quickly, and speed in preparing the building is important. Sealing a warehouse with vinylite plastic is shown in figure 18.

The basis of the vinylite plastic used for sealing tobacco warehouses

is a plasticized vinyl chloride-acetate copolymer resin. It is prepared

for spraying by adding solvents such as methyl ethyl ketone and acetone. After the solvents have evaporated from the sprayed material

(a matter of only a few minutes) a tough flexible film is left, which

is quite durable. Pigments may be added to the liquid material as it

is prepared for spraying, or the plastic may be purchased with a pigment included in the formulation. One of the best pigments found

is finely powdered aluminum. Such a pigmented film is more resistant to sunlight and to weathering, and coatings applied to the ex25
r#lí

^

m'^

.:

BN-16198

Figure 16.^-íave$ of a tobacco warehouse sealed on the inside with elastic roofing cement.

. :;,^il|^HI|

id^^^âfWÊtv

^^miwm

-^ S

fc^ '

Bflss

BN-16282-X

Figure 17.—Equipment used in seoiing tobacco warehouses witli sprayed-on vinylite plastic.

terior of tobacco warehouses over an adhesive base have been known

to last for more than 10 years. The only maintenance necessary has

been occasional touching up of spots that have been accidentally torn

or broken by equipment or laborers.

This plastic also can be applied without an adhesive to give a strippable film for temporary sealing of doors, windows, or ventilators that

must be reopened after fumigation.

Application of vinylite plastic should not be made to greasy surfaces or to asphalt and should not be attempted on exteriors in rainy

weather. The film will not adhere well to a wet surface (*).

26
BN-16202

Figure 18.—Scaling around window of a lobacco warehouse with sprayed-on vinylite ploslic.

In one method of fumigation, tlie warehouse sliould be piped with

s/g-inch copper or plastic tubing. Small brass spray nozzles should be

so located as to provide the proper distribution of gas—one nozzle for

each 15,000 to 25,000 cubic feet. The piping system should be so arranged that the gas pressure is about the same at all nozzles, i^arge

warehouses that have several floors require branch lines with separate

risers. From 10 to 18 nozzles may be used to a riser. Detailed plans

27
for piping warehouses can usually be obtained from any fumigation

company after a survey of the building.

Hydrogen cyanide fumigation also can be performed with portable

rubber hose lines. These lines, with nozzles about every 25 feet, are

laid on the floor of the central aisle. Usually two or more lines that

extend the length of the aisle are used.

In 1959-60, a new method was developed, which introduces fumigants into a tobacco warehouse by a blower fumigant applicator. The

liquid fumigant is introduced through an opening in a sealed door by

a high-velocity blast of air. A flexible duct connecting the warehouse

to the intake of the blower permits recirculation of air. This method

results in a more rapid volatilization of the fumigant, higher gas conFigure 19.-

BN-B324-X

-Blower fumigant applicator introducing hydrogen cyanide into a warehouse.

centrations, and a more uniform distribution of the gas during the

first hours of the fumigation than the older methods. Uniform distribution of high gas concentrations during the initial period produces greater penetration of the fumigant and gives better results.

Such an applicator is shown in figure 19.

For many years hydrogen cyanide has been the fumigant most generally used in tobacco warehouses. Liquid hydrogen cyanide in steel

pressure cylinders is used. An air compressor pumps air into the cylinder through an intake valve until a pressure of about 100 pounds per

square inch is reached. The pressure forces the fumigant through the

piping system or hose lines and out of the spray nozzles. When only

a part of a cylinder of gas is needed, the cylinder may be weighed on

portable platform scales until the required amount is used.

The operator should read the safeguards at the end of this

28
handbook and be certain that all persons and animals are out of

the building before beginning introduction of gas. When the

required dosage has been introduced into the building, the valve

on the cylinder should be closed and the piping system blown

clear of gas by air pressure. The inlet pipe into the warehouse

should then be capped.

The dosage of hydrogen cyanide needed varies somewhat with the

tightness of the warehouse. For years a dosage of 16 ounces per 1,000

cubic feet, with an exposure of 72 hours, has been considered more or

less standard. However, in warehouses with floors of cinders or

crushed roclf, or where more than the usual leakage is anticipated, the

dosage should be increased to 20 ounces. To obtain deeper penetration

of the hogsheads, much heavier dosages of fumigant sometimes may

be used advantageously in very tight buildings. A dosage of 48

ounces, with an exposure of 120 hours, gives much better penetration.

Under nearly ideal conditions, one such heavy fumigation may be as

effective as three standard fumigations. A former practice of controlling the heavy emergence of beetles by applying a series of low-dosage

(8 to 12 ounces per 1,000 cubic feet) fumigations is no longer considered effective or economical.

Methyl bromide also may be used in warehouses of flue-cured tobacco. This fumigant is equally as effective as hydrogen cyanide. The

standard dosage is usually 24 ounces per 1,000 cubic feet, with a 72-

hour exposure. This dosage should be increased to 2 pounds per 1,000

cubic feet, if additional leakage or Sorption factore are known or suspected. Methyl bromide penetrates better than hydrogen cyanide, but

occasionally has been reported as tainting tobacco.

In all warehouse fumigation, the temperature of the tobacco should

be 70° F. or higher. In the United States, therefore, fumigation

usually is limited to the summer and early autumn.

Under favorable conditions, warehouse fumigation at the standard

dosage kills all stages of the moth and beetle (eggs, larvae, pupae, and

adults) to a depth of 1 to 3 inches in the tobacco and kills a few insects

to a depth of 5 inches. In heavy-dosage fumigation with hydrogen

cyanide, complete kills may be expected to 5 inches and heavy kills to

7 inches. Unfortunately, however, some insects deep in the tobacco

usually survive.

The value of a fumigation may be destroyed by strong winds ; they

suck the gas out of a building very quickly.

Infested tobacco moving into a newly fumigated warehouse may

quickly reinfest it and nullify the benefits of the fumigation.

The following dosages of fumigants are suggested for warehouse

fumigation at 70° F. or above :

Fumigant and type of tobacco Lb^i^oo

Hydrogen cyanide : "*• ^*-

riue-cured 1 to 3

Turkish 1 to 1%

Cigar filler or binder 1 to 1%

Methyl bromide:

Flue-cured 1 to 1%

Turkish 1 to 1%

Cigar filler or binder 1 to 1%

Acrylonitrile-carbon tetrachioride :

Flue-cured 3% to 4

Turkish 3'/4 to 4

Cigar filler or binder ^hii to 4

29
Tarpaulin Fumigation

Small lots of tobacco may be fumigated under tarpaulins. For

this purpose, polyethylene sheeting of 4-mil thickness is satisfactory

and readily available. Widths of the sheeting can be sealed together

with masking tape. The edges can be sealed to a clean, tight, wooden

or concrete floor with masking tape or by a "snake"—a long bag or

tube filled with water or dry sand. Dosages of fumigants and the

length of exposure should be the same as those used in warehouse

fumigation.

An Insect-Conlrol Program in Tobacco Warehouses

Suction/light insect traps should be placed in operation before the

earliest spring emergence of insects. This date ranges from March 1

in eastern South Carolina to April 15 at Richmond, Va., and about

May 1 in eastern Pennsylvania.

As soon as light traps in a warehouse show a weekly catch of 10

tobacco moths or cigarette beetles, insecticidal treatments should be

started. In open-type warehouses, pyrethrum mists may be used. In

semiclosed and closed warehouses, DDVP or pyrethrum is recommended. For the moth, weekly applications of 1 gram of DDVP per

1,000 cubic feet should be applied either as an aerosol or a mist or by

sprinkling on wood; or 3 ounces of pyrethrum in oil (containing 0.2

percent pyrethrins) per 1,000 cubic feet of airspace should be applied

as a mist or an aerosol. These treatments will give excellent control

of the tobacco moth but are inadequate for the cigarette beetle. Therefore, as soon as the beetle appears, the dosage should be increased to

2 grams of DDVP per 1,000 cubic feet, applied twice a week as an

aerosol or once a week sprinkled on wood ; or to 3 ounces of pyrethrum

in oil (containing 1.0 percent pyrethrins) applied as a mist or an

aerosol. Such treatments will check the potential increase of a beetle

population but will not control a serious infestation.

When a weekly trap catch of beetles exceeds 2,000 per week in warehouses of flue-cured tobacco, need for fumigation is indicated. In

warehouses of cigar tobacco—especially cigar wrapper tobacco—

fumigation may be justified by a much lighter infestation.

The question of when and where to fumigate is sometimes difficult

to answer. The problem may be complicated by the type, age, and

value of the tobacco, the degree of infestation, and previous treatment.

As a rule it is advisable to fumigate a warehouse as soon as practical

after the peak of adult emergence of an insect brood or generation.

However, in very heavy infestations, it is sometimes impractical to

wait that long. Immediately after a peak of brood emergence, a

larger percentage of the insects are in the egg or early larval stage

and are nearer the surface of the tobacco. At this time they are more

exposed and more susceptible to the fumigant.

Complete kills of insects are rare in the fumigation of tobacco warehouses. For this reason it is important to keep a constant record of

the insect populations present by use of suction/light traps. A knowledge of the relative insect popidation is indispensable as a basis for

intelligent application of control measures.

30
CONTROL BY CHAMBER FUMIGATION

Atmospheric Chamber

Small chambers equipped for the fumigation of tobacco at atmospheric pressure are satisfactory in many tobacco plants. Most such

chambers are 2,000 to 5,000 cubic feet in size, but some are larger.

A chamber may be constructed of wood and tar paper, metal, concrete, or brick. It should be made tight by installing refrigeratortype doors that close against a gasket. The walls should be covered

with asphalt or heavy paint. An epoxy-type paint has been found

to be veiT satisfactory.

The chamber can be piped in the same way as warehouses. If

hydrogen cyanide or methyl bromide is to be used, the inlet of the

piping system should be in a small room attached to the chamber.

The room need be only about 3 feet square—just large enough to hold

a platform scale on which rests the cylinder of fumigant. From the

top of this room should extend a vent pipe connected to an electric

fan. The fan should be operated when gas is introduced into the

chamber, so that any leakage is drawn up and away from the operator. The fumigation charnber should have a vent pipe, operated by

readily accessible valves, extending well above the roof of the building. A powerful fan should be connected to this vent to exhaust

gases from the chamber quickly, and the fan should be kept running

when the fumigation chamber is entered after fumigation.

Acrylonitrile-carbon tetrachloride may be poured into shallow pans

in the chamber. The operator should wear a suitable gas mask

while pouring. A superior method is to place a large, shallow stainless-steel pan on a steam or hot-water coil near the ceiling of the

chamber and run a small pipe through the wall or ceiling of the

chamber so that it will discharge into the pan. The outer end of the

pipe is connected with a funnel, held in a vertical position. The

required dosage of fumigant is placed in a glass or stainless-steel

container which is then inverted over the funnel, and the liquid fumigant flows into the pan by gravity. However, the liquid acrylonitrile-carbon tetrachloride mixture is flammable, and care should

be taken to avoid exposure to spark or flame. At the d.osages

recommended the gas is not explosive, but like many other fumigants,

it is both flammable and explosive at high concentrations. Unnecessary electric or telephone lines therefore should be disconnected before

fumigation is begun.

Discoids impregnated with hydrogen cyanide may be used in atmospheric chambers, but they are more dangerous to handle than the

liquid hydrogen cyanide. The operator should wear a gas mask

with suitable canister, and he should leave the chamber as quickly

as possible after scattering the discoids. This is a dangerous operation and should not be undertaken by an inexperienced person.

If hydrogen cyanide is used, the dosage should be at least 16 ounces

per 1,000 cubic feet, and as much as 24 ounces may sometimes be used

to advantage. The exposure for hogsheads of tobacco should be 72

hours. If acrylonitrile-carbon tetrachloride is used, the amount

should be 32 to 48 ounces per 1,000 cubic feet, with an exposure of 72

hours for flue-cured tobacco in hogsheads. For bales of Turkish

tobacco and for bales or cases of cigar filler or binder tobacco, 32

ounces per 1,000 cubic feet, with an exposure of 48 hours, has proved

31
satisfactory. AU dosages given are to be used at a tobacco temperature

not lower than 70° F.

In the iumigation of tobacco in atmospheric chambers, bales and

cases should be stacked with slats between them and with airspaces on

all sides to facilitate penetration of the gas into the tobacco. In all

atmospheric chambers an explosionproof and sparkproof electric fan

should be operated for 1 to 4 hours at the start of each fumigation

to help distribute the fumigant and prevent p<»sible stratification of

the gas. Better penetration is usually obtained in atmosphericchamber fumigation than in warehouse fumigation. However, fumigation is not so effective in atmospheric chambers as in vacuum

chambers.

The following dosages of fumigants are suggested for atmospheric

chambers at 70° F. or above :

Dosage Lt./lfiOO

Fumigant and type of tol)aGco cu- ftHydrogen cyanide :

Flue-cured, Turkish, cigar filler or binder 1

Methyl bromide :

Flue-cured, Turkish, ci^ar filler or binder 1 to 1%

Acrylonitrile-carbon tetrachloride :

Flue-cured, Turkish, cigar filler or binder 3^ to 5

Vacuum Chamber

The fumigation of tobacco in a partial vacuum is the most effective

method known for destroying insect infestations. When properly

performed, it should kill all stages of the cigarette beetle and the tobacco moth at all depths in the tobacco. Vacuum chambers are expensive, but they are extensively used because of their eificiency and the

rapidity with which they can be operated.

BN-4C93

Figure 20.—Vacuum-fumigaHon chambers filled with hogsheads of tobacco.

32
EQUIPMENT AND PROCEDURE

Vacuum fumigation equipment usually consists of a pair of steel

chambers strong enough to withstand considerable pressure, a pump

of suitable size to evacuate the chambers, a volatilizer for the fumigant (tor use m cold weather), and recording gages. The chambers

vary widely in size; most of those in commercial use range from 400

to 5,000 cubic feet. In some of the larger units, each chamber has

a capacity of more than 30 hogsheads (fig. 20).

The tobacco to be fumigated is placed in the vacuum chamber, the

door IS closed, and the air is pumped out until a vacuum of 28 to 29

inches is registered on a standard mercury gage. The degree of

vacuum obtainable varies from day to day with the barometric

pressure, but any vacuum of more than 28 inches is usually satisfactory. The proper dosage of fumigant is determined by weighing.

The cylinder or drum of fumigant is placed on a platform scale

and connected to the intake line of the chamber. When a valve is

opened the gas is sucked into the chamber and drawn all through

the tobacco by vacuum. The chamber is held under sustained vacuum

until the end of the exposure period; then the gas is pumped out

of the chamber and vented above the roof of the building. Air is

then admitted to restore normal pressure in the chamber. This air

is exhausted by pumping, and air is again admitted. This procedure—called air washing—is usually performed twice for each lot

of tobacco. Electric fans in the vacuum chamber to facilitate distribution of the gas are desirable. The fan should be operated for about

1 hour at the start of each fumigation.

The manufacturers of vacuum-fumigation equipment can supply

estimates and specifications to meet the needs of individual factories

or warehouse operators.

FUMIGANTS AND DOSAGE

Several fumigants may be used in vacuum fumigation of tobacco

Hydrogen cyanide is popular, particularly for cigarette tobaccos.

It is seldom used for cigar tobaccos just before manufacture or on

cigars, because the odor may persist for several weeks.

Methyl bromide has been used to a considerable extent and is an excellent fumigant, but on a few rare occasions obnoxious odors have

developed in tobacco fumigated with it. Apparently the odor is due

to a chemical reaction of the methyl bromide with a tobacco that is

unusually high in protein nitrogen, unfortunately, it is impractical

to make a chemical analysis of each lot of tobacc« before fumigation,

so this reaction is unpredictable.

A 1: 9 mixture of ethylene oxide and carbon dioxide has long been

used for vacuum fumigation of cigars and cigar tobacco. It leaves

no objectionable odorj but it is expensive and is sometimes erratic

in effectiveness—especially at temperatures below 60° F.

A 34:66 mixture of acrylonitrile and carbon tetrachloride has become widely used as a tobacco fumigant. This gas is slightly less

dangerous than hydrogen cyanide or methyl bromide, is relatively

cheap, leaves no odor on tobacco, does not injure tobacco, and is highly

effective. However, it attacks rubber gaskets and corrodes iron and

steel. A 50-50 formulation of this fumigant was formerly marketed

and was reported to be flammable. The present 34:66 formulation

33
has caused no trouble with fire and is apparently as safe m this respect

as other fumigants. All fumigants are flammable and explosive

at very high concentrations. The dosages recommended for tobacco fumigation are well within the accepted tolerances for safety.

For several days after fumigation, an additional danger from all

fumigants may arise from handling tobacco. Small quantities of

sorbed gas are gradually released from the tobacco, which may become a hazard in confined areas.

Much tobacco is fumigated in vacuum during the fall, winter, and

spring, when the temperature of tobacco is below 70° F. At such

temperatures it is necessary to increase the dosage of fumigant, and

sometimes the results are erratic, perhaps because the insects are

less active and therefore more resistant.

Exposure of infested tobacco to vacuum alone for practical lengths

of time is relatively ineffective in controlling stored-tobacco pests.

Tests showed that continuous exposure to a high vacuum (above 28

inches) for 3 days killed all stages of the tobacco moth and all stages

of the cigarette beetle except the egg. An exposure of 10 days was required to destroy the eggs of the beetle. However, even a 3-day exposure is impractical under most conditions.

The following dosages of fumigants are recommended for the

vacuum fumigation of tobacco at a 4-hour exposure:

Fumigant and type of tobacco

70° r. or

above

35° to 69°

F.

Hydrogen cyanide:

Flue-cured

Turkish

Cigar filler or binder

Cigar wrapper

Ethylene oxide-carbon dioxide:

Cigar filler or binder

Cigar wrapper

Cigars

Acrylonitrile-carbon tetrachloride

Flue-cured

Turkish

Cigar filler or binder

LbJUOOOcu.ft.

4

4

4

5

60

65

45

4

4

4

U./LOOOai.tl.

5

5

5

CONTROL IN TOBACCO FACTORIES

Prevenling Infestation

An important source of factory infestation has always been the

night of cigarette beetles from storage warehouses nearby. The

various processes—stemming, blending, bulking, handling, and manufacturing—need as much light as possible. In the past, large windows permitted entrance of the beetles. Fluorescent lighting and air

conditioning have eliminated tliis problem in some modem buildings

with screened air intakes. Unfortunately, only a few factories are

so equipped.

Probably the greatest source of trouble in factories is infested tobacco that is brought into the building. Because tobacco is often held

34
for hours or even days before it is processed, great care should be taken

not to bring infested tobacco into the manufacturing plant. In cigarett« manufacture the hogsheads of tobacco almost always receive a

thermal-vacuum treatment to moisten and condition the tobacco so

that it can be handled without bréatmg. This process raises the temperature of the tobacco high enough to kill all stages of the cigarette

beetle and the tobacco moth. However, it is important that the hogsheads move directly into the processing chambers as they are brought

in from the warehouse ; otherwise there is always danger of infesting

the factory. Tobaccos that do not receive the thermal-vacuum treatment should be fumigated in vacuum or atmospheric chambers before

being brought into the factory. If it is necessary to bring untreated

tobacco into a manufacturing plant and hold it for even a short time,

it should be placed in a receiving room screened with 20-mesh wire.

In factories that are not air conditioned, all doors, windows, and

ventilators should be screened with 20-mesh wire. Homeowners more

than a mile from any tobacco storage or factory have complained of

large invasions of cigarette beetles. Unscreened doors and windows

are an open invitation to thisinsect.

Fan-Guarded Doors

In all tobacco factories and leaf processing plants, tobacco is constantly moving from one area to another. In many areas doors must

be kept open. Electric fans may be employed to prevent beetles from

flying from the receiving area or room into the manufacturing areas.

A large electric fan ( at least 16 inches) should be mounted above the

door at such an angle as to blow downwards and into the receiving

room. The cigarette beetle cannot fly through the blast of air.

Insecf Traps

Although light traps are of little value as a control measure in

tobacco facilities, they are a valuable aid in determining where the

insects are and in what numbers. One suction/light trap should be

installed in every room or area where tobacco is handled or stored. In

very large rooms there should be one trap to each 10,000 square feet

of floor space. These traps should be equipped with black-light

fluorescent tubes of more than 30-watt capacity (fig. 21). Traps

should be installed just below the ceiling and mounted on cords and

pulleys for easy servicing and inspection. They should be operated

continuously. A daily or weekly record should be maintained of

the beetles caught in each area. Traps equipped with black light

will attract a much higher percentage of female than of male beetles

and will capture two or three times as many beetles as traps with a

50-watt incandescent light bulb.

If the trap catch increases suddenly in any area, search should be

immediately started for the source of infestation so that it can be

eliminated.

Fumigation of Manufactured Tobacco

Cigarettes leaving the factory for channels of trade are not fumigated. A package of cigarettes is so tightly sealed that effective fumigation is impractical. However, cigarettes may become infested at

the factory, and sometimes they become infested while in the hands

of wholesalers or retailers. Wlien these are returned to the manu35
Figure 31.—Black-ljghI/suction insect trop.

facturer some of the tobacco can be cleaned and reclaimed, but infested

cigarettes should be fumigated, preferably in vacuum, before they

enter the factory. The cartons of cigarettes should be opened, and if

possible, the wrapping on the packages should be broken before

fumigation.

Cigars need protection from the time they are made until they are

shipped out of the factory. This interval may be as long as 40 days

or even more. If it is not possible to keep the cigars in cool storage

or an insect-tight room, it is desirable to fumigate in vacuimi with

acrylonitrile-carbon tetracMoride or ethylene oxide-carbon dioxide before shipment. When fumigating cigars it is advantageous to fumigate before wrapping them in cellophane. Cellophaned, boxed cigars

can be fumigated, but not when the boxes also have been overwrapped with cellophane.

Pipe and chewing tobaccos are rarely fumigated after manufacture. Therefore they must be protected during storage if losses are

to be prevented. Adequately sealed packages are valuable in this

respect. All returned goods should be fumigated before being received

into the factory for cleaning and salvage.

High- and Low-Ternperalure Treatments

As has been stated, the redrying process for leaf tobacco should

kill all stages of the tobacco moth and the cigarette beetle. This is

not necessarily true for the redrying of flue-cured strips, the laminae

of the leaves after the midribs have been removed. Strips are redried

36
at lower temperatures and for shorter periods than is leaf tobacco;

consequently the treatment is not always entirely effective.

In manufacturing cigarette or pipe tobacco, the shredded, granulated, or chopped-up tobacco is heat conditioned. In all such processes observed, the temperatures have not been high enough or maintained long enough to give appreciable insect mortality.

Cold or cool storage is of great value in preventing or checking

an insect infestation. Flue-cured tobacco for export is sometimes

held in storage at 50° to 60° F. to prevent loss of color and excessive

fermentation. It also prevents insect infestation. As the threshold

of activity for the moth and the beetle is 60° to 65°, a lower temperature will check activity and arrest insect development. If held long

enough at such temperatures, the insects will eventually die.

Cold storage is sometimes used as a substitute for fumigation and

has certain advantages. It does not injure tobacco, and there is no

danger from poison gas. At -10° F. all stages of the cigarette beetle

in bales or cases of leaf tobacco are killed in 3 to 5 days—the length

of time required for the cold to penetrate the tobacco (16).

Cool storage is also widely used in the cigar industry to prevent

cigarette beetle infestation. "Valuable sweated tobaccos and finished

cigars are stored in rooms at 34° to 55° F. No infestation can occur

at these temperatures, since the beetle is inactivated. When unprotected by tobacco or packaging, all life stages of the beetle are killed

by continuous exposure to 47° to 48° for 90 days, to 40° for 33 days,

to 36° for 16 days, to 25° for 7 days, or to 15° for 3 days (1Í and 16).

Other Treatments

When DDVP or pyrethrum is used, fumigation for the tobacco

moth is not needed. For the cigarette beetle, up to four fumigations

a season may be required, depending upon the infestation and other

control measures employed. At Richmond, Va., the most desirable

times for fumigation (based upon the peak of brood emergence) usually have been June 25 to July 5, August 10 to 25, and September 15

to 30. Of course, there may be appreciable variance from this in

some years, depending upon an early or late spring and an early or

late fall. In all fumigation of tobacco, the gas should be applied

only by a person especially trained for the work. An especially

trained employee should be solely responsible for atmospheric chamber or vacuum fumigation. For applications of DDVP or for warehouse or factory fumigation, it is best to employ a licensed pest-control

operator.

COST OF INSECT CONTROL

The cost of insect control varies from year to year with the price

of labor and insecticides, the amount of tobacco fumigated at one

time, and other factors. Actual cost figures are available only for

cigarette tobaccos. The cost of DDVP aerosol to control the tobacco

moth only was about 12 cents per hogshead per year in 1959 and

10 cents m 1960. The cost of DDVP to control the moth and the

beetle ranged from 2 cents to 33 cents per hogshead in 1959 and from

12 cents to 25 cents in 1960. In 1959 the cost of warehouse fumigation ranged from 12 cents to 52 cents per hogshead and in 1960

from 12 cents to 41 cents. In one large company storing more than

37
500,000 hogsheads of flue-cured tobacco, the total cost for insect

control was 40 cents per hogshead in 1959 and 37 cents in 1960.

Vacuum fumigation may range from $1 to more than $4 per hogshead. At Newport News and Norfolk, Va., the charge for commercial

vacuum fumigation of tobacco in 1960 was $1.70 to $1.75 per hogshead. This included the cost of the fumigant, labor, use of motorized

equipment, and amortization of equipment.

SAFEGUARDS IN FUMIGATION

Carelessness is responsible for most of the accidents in industrial

fumigation. The following precautions should always be taken:

Employ only trained men, preferably licensed pest-control operators, in the fumigation of warehouses and factories. Operators must abstain from intoxicants while working.

Except where electric fans are to be used, disconnect all electric

lines and telephone lines into the building or chamber—preferably outside the building. Use only sparkproof and explosionproof

electric fans.

Keep all persons and domestic animals outside the building or

chamber when it is finally closed and sealed for fumigation. Post

placards in prominent places on the building or chamber, warning

that it is being fumigated with poison gas.

Keep guards and night watchmen on duty to see that no person

or domestic animal approaches a building under fumigation.

Wear or carry gas masks equipped with the proper canisters

at all times when handling gas.

Local authorities should be notified of the intention to fumigate

and any necessary permits obtained from them. These officials should

be notified again when the fumigation is completed and the building

has been properly ventilated.

Before fumigation, the interested fire insurance underwriters should

be notified, and their approval of the procedure should be obtained.

LITERATURE CITED

(1) AUIEBI, A.

1931. LES INSECTES DE LA TOMBE DE TOUTANKHAMON. SoG. ROy. Eût

d'Egypte, Bul. 1931 (3-4) : 188-189.

(2) ATKINSON, G. F.

1886. THE CIGARETTE BEETLE {LASIODEBMA SEEEICOENE FAB.). EUsha

Mitchell Sei. Soc. Jour. 1885-1886: 68-73.

(S) BACK, B. A., and REED, W. D.

1930. EPHESTIA ELUTEÜA HUBNER, A NEW PEST OF OUBED TOBACCO IN THE

UNITED STATES. Jour. Econ. Bnt. 23: lOOt-1006.

(4) HATES, WATLAND J., JB.

1957. TOXICOLOGICAL STUDIES OF DDVP APPLIED TO TOBACCO WAEEH0F8E8

AS A THERMAL AEROSOL. U.S. Dept. Health, Education, and

Weltare, Public Health Service. (Processed.)

(5) HOWE, R. W.

1957. A LABORATOAY STUDY OF THE CIGARETTE BEETLE LASIODERMA SEEEICORNE (F.) (COL., ANOBIIDAE) WITH A CRITICAL REVTEW OF THE

LITERATURE ON ITS BIOLOGT. Bul. Bnt. Res. Vol. 48, Part 1,

pp. 9-56, iUus.

(6) REED, W. D., and LIVINGSTONE, E. M.

1937. BIOLOGY OF THE TOBACCO MOTH AND ITS CONTROL IN CLOSED STORAGE.

U.S. Dept. Agr. Cir. 422, 38 pp. illus.

38
(7) REED, W. D., and VINZANT, J. P.

1M2. CONTROL OF INSECTS ATTACKING STORED TOBACCO AND TOBACCO PRODUCTS. U.S. Dept. Agr. Oir. 635, 40 pp., illus.

(8) HOOP, QDENTIN W.

1949. PLASTIC SEALING OF TOBACCO-STOEAGE WAREHOUSES U S DEPT

Agr. Miso. Pub. No. 684, 34 pp., illus.

(9) SiviK, FRANK P., TENHET, JOSEPH N., and DELAMAB, CARL D.

1957. AN ECOLOGICAL STUDY OF THE OIGABEÏTE BEETLE IN TOBACCO STORAGE

WAREHOUSES. Jour. Bcon. Bnt. 50(3) : 310-316, illus.

(10) STORED-PEODUCT INSECTS SECTION.

1955. OIL BASE FOE INSECTICIDE SPRAYS IN TOBACCO WAREHOUSES. U.S.

Dept. Agr., Mktg. Res. Div. 1 p. (Processed.)

(11) SWINGLE, M. C.

1938. LOW TEMPERATURE AS A POSSIBLE MEANS OF CONTROLLING THE CIGARETTE BEETLE IN STORED TOBACCO. U.S. Dept. Agr. Cir. 462, 8 pp.,

illus.

(12) TENHET, JOSEPH N.

1955. TIMING OF SPEAYS TO CONTEOL THE CIGAEETTE BEETLE. U.S. DEPT.

Agr. AMS^9, 6 pp., illus. ( Processed. )

(13) TENHET, JOSEPH N.

1957. TOBACCO FUMIHANTS AND FUMIGATION. Tobacco 144(12) : 22-26,

illus.

(14) TENHET, JOSEPH N.

1959. PYEETHRUM MISTS AND AEEOBOLS FOE CONTEOL OF INSECTS IN TOBACCO WAREHOUSES. U.S. Dept. Agr. Mktg. Res. Rpt. No. 334,

21 pp., illus.

(15) TENHET, JOSEPH N., and BARE, CLARENCE O.

1954. THE TOBACCO MOTH AS A PEST IN FARMERS' PACK HOUSES. U.S.

Dept. Agr. BS-CANo. 4. (Processed.)

(16) TENHET, JOSEPH N., BARD, CLARENCE O., and CHILDS, DANA P.

1957. COLD STORAGE AND COOL STORAGE OF TOBACCO TO CONTROL THE CIGARETTE BEETLE. Tobacco Sei. 1: 169-174, illus.

(17) TENHET, JOSEPH N., BAEE, CLARENCE O., and CHILDS, DANA P.

1958. FURTHER STUDIES ON THE CONTROL OF THE CIGARETTE BEETLE WITH

DDVP. Tobacco Sei. 147(6) : 106-110, illus.

(18) TENHET, J. N., BAEE, C. O., CHILDS, D. P., and DURHAM, W. F.

1957. STUDIES OF DDVP FOE CONTROL OF CIGARETTE BEETLES IN TOBACCO

WAREHOUSES. U.S. Dept. Agr. AMS-214, 16 pp., illus.

(Processed.)

(19) VINZANT, J. P., and REED, W. D.

1941. TYPE OF WIRE SCREEN REQUIRED FOR EXCLUDING CIGARETTE BEETLES

AND TOBACCO MOTHS FEOM WAEEHOUSES. Jour. Econ. Bnt. 34(5) :

724.

39

U.S.GOVERNMENT PRINTING OFFICE: 1962 O—644454