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Agricultural Experiment Station,

URBANA, NOVEMBER, 1903.

BULLETIN No. 89.

NOTES ON THE INSECTICIDE USE OF
THE GASOLINE BLAST LAMP

BY S. A. FORBES, STATE ENTOMOLOGIST.

The use of the ordinary plumber's torch, or some modification of it,
for the destruction of injurious insects on their food plants seems to
have occurred independently to several persons during the last few
years, and to have been tried with some care as a practical measure by
several disinterested men competent to make exact observations and to
report results without bias or prejudice.

Mr. S. A. McHenry, recently superintendent of one of the horticul-
tural substations of the Texas Agricultural Experiment Station, is re-
ported to have used it for several years against the harlequin cabbage-
bug, and Professor J. M. Stedman, of the Missouri Experiment Station,
has also used it against the same insect. Professor E. H. Pettit, of the
Michigan Agricultural College, tried it on the San Jose scale as far back
as 1897, publishing in the Bulletin of the Michigan Experiment Station
the earliest report of an exact experiment with it which I have seen ; and
Professor Carig, o'f the Horticultural Department of Cornell University,
has also tried it on this scale. Professor E. Dwight Sanderson, of the
Texas Agricultural College and Experiment Station, has used a form of
it on the cotton boll-weevil. Professor Thomas B. Symons, of the Mary-

145

146 BULLETIN NO. 89. [November,

land Agricultural College and Experiment Station, used it experiment-
ally on the San Jose scale, and on beetles infesting the aster. Professor
J. L. Phillips, State Entomologist of Virginia, has also tested it on the
San Jose scale with unusual thoroughness ; Professor F. M. Wehster, En-
tomologist of the Ohio Agricultural Experiment Station, had it tried
four years ago by an assistant, Mr. C. W. Mally (now Government Ento-
mologist in Cape Colony, South Africa), on a variety of insects, includ-
ing the chinch-bug; and two of my own assistants, Mr. E. S. G. Titus
and Mr. G. I. Eeeves, have used it on scale insects, caterpillars, and
moths, have tested it for the destruction of fungus parasites of the
green leaf, and have determined its effects on various kinds of vegetation
when applied in a way to kill the insect enemies of the plant. Most of
these experiments are unpublished, but their results have been gener-
ously placed at my disposal for use in this brief discussion.

Although no one of those here mentioned has made a trial of the
gasoline torch for all the insecticide and fungicide purposes which it
might possibly serve, the total results have a considerable value as show-
ing definitely some things which can and some things which can not be
done with it, and as indicating the directions in which further trials
may be made if, indeed, it appears that further trial is necessary or
worth while. Some variation and conflict in the reports of some of
these experiments are evidently due to differences in the apparatus used,
this varying from a poorly constructed and feeble torch, made in Illinois
especially for insecticide work, to a large and powerful blast-lamp, used
in Texas for burning the thorns off prickly-pears.

The idea that exposed insects of small size may be quickly destroyed
by the sudden and brief application of a blast of very hot air, or even
of actual flame, without injury to the plant on which they may be feed-
ing at the time, strikes one favorably at first thought; and there seems,
in advance, to be no obvious reason why this method may not have a
considerable practical value. The living animal is often more sensitive
to sudden heat exposures than the living plant, and the margin between
exposures fatal to each may, in some cases, be so wide as to make this
method fairly safe in ordinary practice. The smaller the insect, of course
the more quickly it may be killed by the hot blast; and the better the
living tissue of the plant is protected by a lifeless cuticle or a layer
of bark, the longer it may be exposed to this blast without being heated
to the point of injury. Bark-lice on trees and shrubs are thus favor-
able objects for experiment; but where thick-bodied insects, like cater-
pillars and large beetles or bugs, themselves covered with a dense crust
of lifeless cuticle, are feeding on the young green leaf, the margin of
safety is greatly narrowed and may wholly disappear. The practical
utility of this method of destroying insects in any case, evidently de-
pends on the existence and extent of this margin of safety.

1903] INSECTICIDE USE OF THE GASOLINE BLAST LAMP. 147

The gasoline blast may, in fact, be used to kill any insect on any
plant. The time and method of use necessary to kill the insect will
vary widely for different kinds of insects and for the different states
and stages of each kind; and the time and method of use sufficient to
injure various kinds of plants will likewise differ widely according to the
kinds and condition of the plants themselves. The actual effect of the
blast on either insect or plant will also vary enormously according to
small details of the method by which it is applied. They will vary, first,
with variations in the pressure, which determines the extent and heat
of the flame; second, with the distance from the object at which the torch
is held; third, with the rate of movement at which the flame is passed
over the surface treated; fourth, with the temperature at the time and
the amount and direction of the wind; fifth, with the direction of the
blast, whether perpendicular or oblique to the surface; and sixth (not
to specify further), with the steadiness with which the flame is applied
to a given surface, whether held at one point for a definite time or
swayed back and forth over a considerable surface for a variable num-
ber of times.

To determine the effect of all these different classes of variations
with sufficient exactness for practical guidance, and then to combine
all the various results of this inquiry with each other in a way to form
a system of practice which can be accurately described and safely recom-
mended for general use, is a task which no intelligent investigator would
enter upon lightly, or without such preliminary tests as would enable
him to judge whether any important result was likely to come from
more exact and extensive experiments. The observations here reported
are all in the nature of such preliminary tests, made by different persons,
each for his own satisfaction, on different objects, and in different parts
of the country. They are practical tests rather than complete scientific
experiments, and their value is hence suggestive rather than final. Those
which have to do with the San Jose scale, the harlequin cabbage-bug,
and the cotton boll-weevil are perhaps of the greatest interest, and will be
given first.

THE SAN JOSE SCALE. — In the fall of 1897, Professor Pettit, of
Michigan, had five parallel burners fitted to an ordinary plumber's blast
lamp in such a way that a flame about ten inches wide could be directed
against the surface of a tree, and several trials of this apparatus were
made during the following winter on peach- and pear-trees badly infested
with the San Jose scale. "The heat produced by this lamp," he says,
"is very intense, and great care must be observed not to allow the
flame to remain at any one point long enough to injure the tree. The
best results were obtained when the flame was steadily moved so that
it covered a space of a yard in length in from five to ten seconds. The
results seemed to show that the blast will kill the scale-insects with

148 BULLETIN NO. 89. [November,

little or no injury to the tree. The trees were scorched in places where
the flame had moved too slowly, and the care necessary to avoid the
scorching appears to be the most serious drawback to the use of the
blast lamp. In careless hands much injury may be done in a very short
time, while the skillful handling necessary for success would be rather
expensive under ordinary circumstances. Good judgment must be exer-
cised always, and the rapidity and effectiveness of the work will be much
modified by the temperature of the air, the direction and force of the
wind, the age of the trees and the thickness of the incrusting scales."
Eeferring to these statements in a recent letter, Professor Pettit writes
that he intended that the lamp should be used only in connection with a
spray for burning off or loosening the outer layers of a crust of scales
so that a fluid insecticide might penetrate to those beneath. "I now
realize," he says, "that the same effects may be obtained much more
cheaply in other ways/'

By Professor Craig, of Cornell University, a torch much advertised
for the destruction of insects was used, May 19, 1903, against the San
Jose scale on the apple, medlar, buffalo-berry, and dogwood. Different
branches were flamed in various ways to ascertain the time necessary
to kill the scale and to determine the minimum exposure to the flame
of the torch which would kill the cambium layer of the tree or shrub.
In respect to time of exposure three methods of treatment were used:
passing the flame so rapidly over the surface that it merely touched each
point for an instant; moving it at the rate of one foot per second; and
holding it stationary on the infested spot long enough to count one.
The scales were reported to have been killed in every case save one, in
which a twig of dogwood had been very rapidly flamed. "The general
results," writes Professor Slingerland, "were summarized as follows:
First, the torch is impracticable for large trees of apple, plum, pear,
peach, or cherry, because of the amount of time required to flame the
whole tree. It would take a man several hours thus to go over one
large tree; second, there is great danger of injuring buds or the cambium
layer on thin-barked trees; third, the torch might be used on small
nursery stock or ornamental shrubs by an experienced operator who
knew exactly what time to expose the plant to the flame."

Professor Phillips, of Virginia, made use, against the San Jose scale,
in 1903, of a torch sent by the manufacturing company for trial to Pro-
fessor Alwood, of that state. "March 28 of this year," he says, "I used
this gasoline torch on two apple-trees four years of age. These trees
were moderately infested with the San Jose scale, and were treated by
running the torch over the surface several times. One tree was exposed
to the torch about twice as long as the other. This treatment did not
appear to injure the trees, neither did it kill a perceptible number of
insects.

1903] INSECTICIDE USE OF THE GASOLINE BLAST LAMP. 149

"I was not satisfied with this trial, however, and detailed a student
assistant, Mr. E. F. Cole, to test the torch, which he did August 7. The
tree treated was a four-year-old apple, badly crusted with the San Jose
scale. As it would he entirely impracticable to use this torch against
the San Jose scale during the summer, this treatment was confined al-
most entirely to the trunks and main branches of this tree, but in
treating the tree in this manner, of course a few of the leaves were also
reached by the flame. The treatment was so severe that the leaves on
the treated portions of the tree were killed at once, and when examined
en August 20, portions of the bast tissues of the bark were found injured
also. Quite a large number of scale insects were alive at that date.

"Judging from these two tests, I consider that the use of this torch
is quite tedious and impracticable, even on small trees. Besides, such a
small per cent, of the San Jose scales were destroyed by it, even where
the trees were seriously injured by its use, that I do not consider it a
practicable remedy."

Professor Symons, of Maryland, writes me that he personally con-
ducted some experiments with the same kind of a torch on different
varieties of peach and plum infested by the San Jose scale, but that the
results were not at all satisfactory. Although the insects were dead two
weeks later on the parts which had been hit by the flame, young scales
were crawling about over the surface in considerable numbers, showing
that it had been impossible to reach all parts of the tree, especially at
the ends of the branches. If used when the tree was in leaf he could
not avoid burning the foliage. As a result of his experiments, Professor
Symons concludes that it is impracticable to control the San Jose scale
with this torch.

To these observations by experts I may add a note of a trial of the
torch made by a practical gardener, on some infested trees belonging
to J. W. Stanton, of Kichview, in this state. By oversight, these trees
were sprayed with whale-oil soap before they had been critically exam-
ined as to the final effects of the blast on the San Jose scale; but Mr.
Stanton Avrites me that from what he could see of the effects of the
treatment at the time, he is of the opinion that it would not be successful
on tree fruits. One of my horticultural inspectors, Mr. K. W. Braucher,
happened, however, to examine one of these trees after the treatment
with the torch and before the application of the whale-oil soap, and
found that the bark was scorched in some places, and that in others
the scales were still alive.

From the foregoing experiments, it is clear that the gasoline torch
has at best only a very limited application in the treatment of trees
infested by the San Jose scale. It might be occasionally used to advan-
tage, as suggested by Professor Pettit, to burn off the outer part of an un-
usually thick crust of scales on the trunk and largest branches of a tree,

150 BULLETIN NO. 89. [November,

preliminary to a treatment with the lime-and-sulphur wash. As this
insecticide does not penetrate readily to any great depth, it is sometimes
necessary to repeat a spraying after a time if the tree is too thickly
incrusted. This second spraying might perhaps be omitted if the torch
were first used on the crust of scales. It would be the merest folly, how-
ever, to think of using it as a substitute for an insecticide spray in the
treatment of the San Jose scale, or for any general treatment of orchard
trees for any purpose whatever.

This torch was also tried on certain other orchard scales at Urbana
during the fall of 1902, but for reasons to be given presently these tests
are reported separately farther on.

THE HARLEQUIN CABBAGE-BUG. — The introduction of the use of the
gasoline torch against the harlequin cabbage-bug in the South seems
to be due to Mr. S. A. McHenry, recently superintendent of one of
the substations of the Texas Agricultural Experiment Station. Indeed,
Professor Sanderson, official Entomologist of that state, writes me that
so far as he knows, Mr. McHenry was the first man to make practical
use of the blast torch against insects of any kind. He is said to have
used it successfully for several years, as have others in his section of
the state, but of late he has made comparatively little use of it for that
purpose because of the amount of work required to go over a cabbage
plant with the torch.

Professor J. M. Stedman, of Missouri, writes more confidently of
its usefulness against the cabbage-bug, saying, under date of October
28, 1903, "I have not found the gasoline torch of any special value as an
insecticide apparatus except in extreme cases when one has a sufficient
number of the harlequin cabbage-bugs in his cabbages to cause serious
trouble. I have then used this torch to good advantage. One can very
readily pass over the cabbages fast enough not to injure them, find at the
same time to kill the harlequin bugs. It is not necessary to have the bugs
scorched sufficiently to drop at once, as I have found that they will ulti-
mately die if this intense heat has been very rapidly applied/'

This cabbage-bug is not widely destructive in this state, although
it is continuously present in some parts of southern Illinois, and during
one season extended its injuries as far north as Champaign, and was
once found in Chicago by Mr. A. Bolter. The reported effectiveness
of this torch against this insect suggests the trial of it against other
bugs, which cannot be killed with arsenical poisons since they do not
eat the solid substance of their food plant but merely suck its sap.

THE COTTON BOLL-WEEVIL. — The appearance in Texas of the snout-
beetle known as the Mexican boll-weevil has caused general and justi-
fiable alarm among the cotton-growers of the South, and the Texas
State Entomologist, Professor Sanderson, has devoted himself to an
assiduous study of the insect and has made many experiments for its

1903] INSECTICIDE USE OF THE GASOLINE BLAST LAMP. 151

destruction and control. This is, indeed, the most important, pressing,
and perplexing problem which the economic entomologist now has to
deal with in the Southern States. In the course of his work against this
insect Professor Sanderson has tried two forms of the gasoline torch;
one, a. hlast-lamp known as the pear-burner, used in southwestern Texas
for burning the thorns off the prickly-pear, and the other a torch sent
him from Illinois by a dealer who offers and advertises it for sale for the
destruction of insects. The latter was found so faulty in construction
that it could not be used, and it was consequently returned.

The pear-burner, which generates a much more powerful blast than
any of the smaller torches, was tried by Professor Sanderson for burning
up the squares of the boll-weevil as they lay upon the ground, but so far,
as he writes me October 28 of this year, he has not had sufficient suc-
cess with it to indicate that it has any value for this purpose.

The only other beetles on which it has been tested by any of my
correspondents are certain unspecified species found on aster by Pro-
fessor Symons, of Maryland. "In this case," he says, "it was effective
in killing the beetles, but one has to be so extremely careful not to hurt
the flowers that I would hardly recommend it for practical use."

EXPERIMENTS AT URBANA. — In response to my request, made August
o, 1902, to the inventor and patentee of a modified form of the gasoline
torch intended especially for insecticide work, one of his instruments
was sent me with directions for its use, and was at once put into the
hands of my most experienced field assistant, Mr. E. S. G. Titus (now
assistant to the United States Entomologist), who, with the aid of an-
other assistant, Mr. George I. Beeves (now an assistant in the Entomo-
Jogical Department of the University of Missouri), tried it at various times
during the following two months on such kinds of injurious insects as
could be found in any number at Urbana at that time of the year. It
was further tried on a fungus parasite of the lilac leaf, and on various
kinds of vegetation to determine the effect on the plants of an exposure
sufficient to kill the insects infesting them. Although sent me expressly
for experimental purposes, this instrument proved to be relatively so
weak in action that its use by us should probably be regarded as a test
of the value of this kind of a torch rather than that of the torch method
in general ; and it is on this account that I have kept our own statements
separate from those made to me by others, most of whom seem to have
worked with a more efficient apparatus.

The results of our various trials are here given as reported to me by
Mr. Titus at the close of his series of experiments, about October 20.

"The torch is simply an ordinary "plumber's torch" fitted with a two-
gallon gasoline tank and a three-foot piece of rubber tubing. A short
iron discharge pipe connects the rubber tubing with the torch.

"Filled the tank about half full of gasoline according to directions.

152 BULLETIN NO. 89. [November,

The valve in this pump was of leather and by no means circular in out-
line, and it was at first rather hard to secure even pumping pressure.
The connections were all very dry and needed soaking. After an hour
or so of work, cleaning the discharge pipe and burner, we were able to
light the latter and get a flame.

"Under the heaviest pressure obtainable — sufficient to force air
bubbles from the pump valve and at the cut-off in the base of the pump
— the flame was tried at varying distances. At fifteen inches from the
burner the heat was scarcely sufficient to singe the hair from the hand,
but a little closer, ten to twelve inches distant, it would singe. The
burner was used when running at full force. The effects were about as
follows, examinations being made at several days' interval.

"The trunk and smaller limbs of an apple-tree were thoroughly treat-
ed. This tree was badly infested with Forbes and scurfy scales, and also
had on it considerable woolly aphis. The last mentioned insects were
killed where they were completely burned off the limb; but where only
the woolly covering was burned off and the insect not actually caused to
drop, there was little apparent injury. The Forbes scale appears not to
have been injured, except the young not yet old enough to form a scale.
The scurfy scale was not injured. The smaller limbs were sufficiently
treated to cause the bark to blister in spots, without having any appar-
ent effect on mature scales of either kind.

"I have tried the burner under ordinary pressure at different times
against various other insects and foliage. A colony of fall web-worms
in a box-elder tree was treated, and a number of worms that fell were
placed in a cage in the insectary. These were given plenty of fresh
food, and did not appear to be inconvenienced by the lack of hairs on
their bodies. They grew, and some of them pupated. Most of the
remainder were parasitized, and the few that died were full grown at
death. The parasites emerged in due time and were preserved.

"Arctian caterpillars (woolly bears) treated to the full force of the
burner for ten to fifteen seconds, or even longer, had the hair thor-
oughly singed from their bodies, and some were blistered. The majority
of these finished their growth and pupated. I could see no greater
mortality among them than ordinarily occurs with this species under
insectary conditions. Several cabbage-worms were treated until they
rolled from the leaves. Most of these were not permanently injured,
and those that died were burned so badly that the outer skin was broken.
To produce this effect upon a caterpillar it must be treated with a
direct blaze long enough to cause the leaves to curl and blacken on the
plants.

"Meadow moths (Crambus) flying about in the grass were singed with
the flame. Some of these would fly through the flame so close to the
burner that the hair on one's hand would be quickly singed off. but they

1903] INSECTICIDE USE OF THE GASOLINE BLAST LAMP. 153

were usually uninjured by this experience. To kill one of these moths
it had to be followed with the flame until some parts were burned suf-
ficiently to cause it to fall, when it could, of course, be easily disposed of.

"Lilac leaves badly infested with mildew were thoroughly treated,
the burner being held at varying distances and acting for varying periods
of time. The mildew does not seem to have been affected where the
leaves were not injured, and was rarely affected where the leaves
were burned sufficiently to cause them to curl and later to wither.
Leaves that were treated to the flame for three seconds dropped off.
Other leaves treated one second remained on the bush and were not
perceptibly injured. Between these two times (which really represent
flashing the burner over the surface, and holding it there for an instant)
the leaves showed varying injuries. At first the mildew appeared to have
been burned off, but specimens which had been thoroughly treated and
left in the insectary, were again covered with the mildew in five days.

"Elm, Osage orange, box-elder, apple, cherry, plum, grasses, nastur-
tiums, cabbage, pine, cedar, Amorpha, walnut, rose-bushes, peach, and
several other trees and ornamental shrubs have been treated at various
times. I find that when the flame is held close to the foliage for a few
seconds this is visibly injured. If held a short distance away the injury
is not so great, but usually shows after a few days by the blackening of
the leaf or by the browning and curling of the edges. Often leaves so
treated will drop off.

"To sum up : The use of sufficient heat to destroy effectually insect
larvae of the kinds we treated, will injure the foliage and often the twigs."

Final mention may be made of a trial of the torch by Mr. Mally, in
Ohio, in 1898, the details of which can not now be given because the
record is not accessible. This torch, obtained from Illinois, was put into
Mr. Mally's hands by Professor F. M. Webster, with instructions to give
it a thorough test. It was taken by Mr. Mally on one of his field trips,
used on a variety of insects, including the chinch-bug, and returned with
the general report that it was unsatisfactory for its purpose.

Professors Webster and Pettit agree in a statement of its usefulness
rind convenience for "thawing out frozen water pipes."

CONCLUSION. — Notwithstanding the generally unfavorable character
of the statements made to me concerning this torch by those best able
to judge of its value, it seems to me that it may have a limited field of
usefulness secondary to other measures for the destruction of certain
kinds of injurious insects. One such use has already been suggested
in the preceding paragraphs on the San Jose scale. It should certainly
be tried for such bugs (Hemiptera) as can be lured away from valuable
crops to so-called trap crops of worthless plants. It might profitably be
tried in comparison with other adjuncts of the trap and barrier method
•for the destruction of chinch-bugs as they come out of small grain for

154 BULLETIN NO. 89. [November. 1903

their midsummer invasion of fields of corn. Exact experiments should
be made on the after effects of brief exposure to its flame, as reported
by Professor Stedman for the harlequin cabbage-bug, and by Mr. Titus
for the fall web- worm and other caterpillars.

It should be remembered, however, that it is probably the most dan-
gerous to vegetation of any insecticide apparatus which has ever been
brought forward for common use, and it consequently should not be
generally recommended for use on living plants of any value until
it has been so thoroughly tested under various conditions that a safe
method may be described in terms which cannot be misunder-
stood or misapplied by any ordinarily intelligent and reasonably careful
workman.

Thanks are due to the various gentlemen who have kindly communi-
cated their observations for my use, and also to Professor M. V. Slinger-
land, of Cornell University, who obtained for me the information above
reported concerning a test of the torch made in New York by Pro-
fessor Craig.

UNIVERSITY OF ILLINOIS-URBANA