Heat sterilization as means of controlling cereal insects
by James Hubert Pepper
A THESIS Submitted to the Graduate Committee in partial fulfillment of the requirements for the
Degree of Master of Science in Entomology
Montana State University
© Copyright by James Hubert Pepper (1932)
Abstract:
no abstract found in this volume HSAT STERILIZATION AS A MEANS OF CONTROLLING CSREAL INSECTS
"by
JAMES H. PEPPER
A THESIS
Subm itted to the Graduate Committee in p a r t i a l fu lfillm e n t
o f the requirem ents f o r the Degree of
M aster of Science in Entomology
a t Montana S ta te College
Approved:
In Charge of Major Work
Chairman Examining Committee
Chairman Graduate Committee
June, 1932 .
ilTATE CJlLE:
Vtl
Bozeman, Montana
TABLS OF CONTSUTS
Page
INTBOIUCTION..............................................................................................
I
ACKNOWLEDGMENT.........................................................................................
I
BSVISW OF PEEVIOUS WOBK..............................................................
2
EXPERIMENTAL METHOD AND APPARATUS....................................
U
DATA AND RESULTS.....................................................................................
8
DISCUSSION OF RESULTS..........................................................................
23
POSSIBLE ACTION OF HEAT ON INSECTS................................. ....
2j
THE POSSIBILITY OF SUCCESSFUL EEAT STERILISATION
IN MONTANA FLOUR MILLS.............................................................. 32
SUMMARY . . . . . . .
..........................................................................
BIBLIOGRAPHY..........................................................................................
43078
33
3%
HSAT STABILISATION AS A MEANS OF CONTROLLING CBBBAL INSECTS
By James H. Pepper*
INTRODUCTION
In recent years heat s te riliz a tio n , as a means of controlling
m ill and stored,-grain in sect p ests, has "been recommended hy many workers
and authors o f text hooks in the f ie ld of economic entomology. Most of
these recommendations are based on conclusions drawn when temperatures
were recorded at some distance from the flo o r and no means of a ir
circu latio n was provided.
A ir, when heated, rise s and tends to s tr a tif y , producing a
marked difference between flo o r and c e ilin g temperatures.
As the quantity
of heat applied i s increased the difference in these two temperatures
becomes g reater.
In m ill s te riliz a tio n , the production of a k illin g
temperature on a l l flo o rs above the basement w ill be influenced to a
marked degree by the rate a t which heat w ill penetrate the concrete flo o rs.
The rate of heat penetration into various m ill products i s also of v ita l
Importance since, when present, they provide a place o f escape fo r in sects
from the high surrounding temperatures.
This paper embodies the re su lts of experiments with controlled
flo o r and c e ilin g temperatures under varying conditions of heat and a i r
circ u la tio n .
In addition the re su lts are given on the ra te of heat
penetration into concrete, idieat, flo u r and bran.
*ACKNOWLEDGMENT
The w riter g ra te fu lly acknowledges h is Indebtedness to Doctor
-2 -
A. L. Strand fo r the proposal of, and helpful suggestions during th e
development of the problem, and to Professor 0. Allen Mall for helpful
criticism s and assistance.
EEVIEW OP PREVIOUS IOEK
Dean (l)* was one of the e a rlie s t workers to publish the
temperatures obtained when using heat s te riliz a tio n fo r controlling mill
insect p e sts.
He records the temperatures noted a t various selected
places throuf&out the m ill fo r a period of 24 hours.
The following Is a
b rie f summary of the more Important temperatures which he records.
The
average temperature in the m ill a t the time the heat was applied was
about 90®F.
The h i p e s t temperature recorded on the f i r s t flo o r was 10$
This was taken in the center o f the room and 6 feet above the flo o r.
The
lowest temperature on th is flo o r was 96tP. which was recorded a t a depth
of 3 inches in -flo u r in an elevator boot on the flo o r, in the center of
the room.
On the second flo o r the h i p e s t temperature, 133.5eF., was
registered by a thermometer hanging in the open in the center of the room
and 6 fe e t from the flo o r.
The lowest temperature reg istered by a
thermometer on th is flo o r was IlT-BeF., which was recorded a t a depth o f
3 inches in a sack of flo u r which was 3 fe e t above the flo o r.
On the
th ird flo o r the thermometer in the center of the room and 6 fe e t above
the flo o r reg istered IU leF., while the lowest temperature, 129«?., was
registered in a flo u r conveyor spout 4 feet above the flo o r.
*- Eeference i s made by number ( ita l ic ) to L iteratu re Cited.
On the
-3 -
fourth flo o r the thermometer 6 feet above the flo o r reg istered 128.6*?.
The lowest temperature which was reg istered on th is flo o r, 1 1 8 , was
recorded hy a thermometer in flo u r in a conveyor 6 fe e t above the flo o r.
Dean sta te s th at on a careful examination of the three upper flo o rs, a l l
p a rts of the m ill, even the deepest accumulations in the most inaccessible
p a rts, fa ile d to show liv e in se c ts, save one corner on the upper flo o r.
I t w ill be noted th a t no actual temperatures were recorded on
the flo o r surface.
The clo sest point to the flo o r a t which temperatures
were recorded was in an elevator boot restin g on the flo o r.
The significance
of th is w ill be brougit out in a la t e r discussion on the subject of surface
temperatures.
Ooodwin ( 2) determined the rela tiv e su sc e p tib ility o f d ifferen t
developmental stages of in se cts to heat and found th at even though a
difference as great as 8 to IO0P. was required to e ffe c t the destru ctio n:
of d iffe re n t species, most of the common insect pests succumb readily to
a temperature of 120 to 130 0P. with p ra c tic a lly no in ju ry to the substances
on which the in sects feed. In determining the influence of a i r circ u latio n
he found th a t circu latio n of a i r in the te stin g oven by means of a small
electrically -o p erated fan caused the death of the Confused flo u r b eetle,
Trlbollum confusum. the minute grain b e e tle , Laemonhlaeus minutus. and
the larvae of the Mediterranean Plour and Indian Meal moths, a t a
temperature o f two to three degrees below th at required in the oven in
an undisturbed atmosphere.
This w riter s ta te s th at the required h lg i
temperatures in a flo u r m ill may be secured by any safe method which w ill
give dry heat a t 122 to I t o eP. and he outlined several methods fo r
calculatin g radiation surface required to bring about these temperatures.
-It-
Orosanan ( ] ) , In deteralning temperatures attain ed a t d ifferen t
depths In com , used the thermocouple method fo r taking temperatures.
He found with a surface temperature o f approximately 2450F. a le th a l
temperature was obtained to a depth of about one foot a f te r heating fo r
a period of 48 hours.
In shucked com with a surface temperature of
approximately 235®?. a le th a l temperature was obtained to a depth of 2^ f t .
In th is case the heat was applied fo r 18 hours.
Many papers and tex t books on entomology outlined methods fo r
heat s te riliz a tio n , but since they do not s ta te any temperatures except
those, desired to be obtained, no mention need be made o f them here.
EXPBEIMENTAL METHOD MD APPARATUS
The thermocouple method as described by Bobinson (4) fo r
determining temperatures was used.
In studying heat penetration in a
concrete block i t was desired to obtain temperatures at the surface of
the co n crete,, every quarter inch fo r the f i r s t inch, every h a lf inch
fo r the next two inches and every inch fo r the remaining six inches.
Figure I shows the diagram of the apparatus used.
In order to
study heat s tr a tif ic a tio n near the surface and heat penetration in m ill
products, a se rie s of thermocouples (not shown in diagram) were extended
to a distance o f 8 inches above the flo o r surface.
The distances between
these couples were as follows; sta rtin g from the flo o r surface, every
quarter inch fo r the f i r s t 2 inches, every h a lf inch fo r the next 2 inches,
and every inch fo r the remaining 4 inches.
The p a rt of the apparatus
buried in the cement consisted of a piece of I by’l in . tohrd t& whibh a l l the
-5 -
CEMCNT SURFACE
JUNCTION
I---p
GALVANOMETER
LEGEND
----------- COPPER WIRE
........... CONSTANTAN WIRE
F ig .I .
Diagram showing the system o f w irin g used in the
apparatus fo r tak in g the tem peratures in the concrete
block.
couples were attached.
This eliminated any chance of then not holding
th e ir correct position when the cement was being poured around then.
inch
tbp
Holes 1 /8 / in diameter were bored through, the board at/req u ired distances.
Glass tubes which were 6 inches long and had one end sealed were in serted
in these holes u n til the ends were flush with the back o f the board, leaving
5 inches of tube projecting.
A 28-gauge Constantsa wire was led down to the
9 inch hole where a junction was made with a 28-gauge copper wire.
The
constantan wire was tapped by short leads to the remaining holes and a
junction made at each one with a copper wire.
The insulated copper wires
were tw isted together and were wrapped with in su latin g tape, a f te r which
they were le d throu^i the sid e o f the cabinet to the recording instrument.
Each junction was then pushed through the hole and up to the end o f the
glass tube.
The single constantan wire was led to the cold junction,
which was in a Dewar fla sk containing cracked ice and water.
The copper
wire from th is junction was connected to a Pyrovolter and galvanometer to
the common terminal on the switch board.
The copper wires were then in turn
connected to the terminals on the switch board.
The board containing the
thermocouples was fastened in the center of a wooden frame which was U ffeet
square and 10 inches deep.
The frame was then f ille d with a I to 3 mixture
of concrete to the point where the top couple, shown in Figure I , was
ju s t restin g on the surface of the cement.
The cement block was covered
by a cabinet U feet square and U fe e t high.
This was b u ilt o f a Ixaaber
frame and covered with cello tex .
To prevent too great a lo ss of heat a
double lay er with an a i r space between was put on the c e llin g .
A small
double glass window in the fro n t served as a place through which
observations on in se c ts could be taken.
In order to determine c e llin g
temperatures a thermometer was Inserted in a horizontal p o sitio n
through a small hole in the w all I inch from the c e ilin g .
The heating element con sisted o f two Independent u n its o f
l 4 B & S gauge nlchrome resistan ce w ire.
One u n it was capable o f
d eliverin g 3036 B.T.U. per hour and the other one 2337 B.T.U. per hour.
The high est temperatures which w ill be discussed were obtained by using
both o f the u n its which delivered 5373 B.T.U. per hour.
When a ir circu la tio n was required an e le c t r ic a lly driven fan
was placed d ir e c tly behind the heating u n its .
This gave an e ffe c t
comparable to that produced by un it h eaters.
Before any se r ie s o f temperatures were taken the temperature
o f the various couples was f i r s t recorded.
The heat was then turned
on and the temperature noted at hourly in te r v a ls fo r a 10 or 15 hour
period.
As a check on the surface temperatures a movable thermocouple
which could be operated from outside the cabinet was used.
This con sisted
o f a rubber stopper with a thermocouple secu rely fastened to one end o f i t .
The other end was connected by a hinge to one end o f a wooden rod, the
other end o f which passed through a small h ole in the c e ilin g .
In order
to prevent lo s s o f heat the space around the rod, where i t passed through
the c e ilin g , was packed with ground up asb estos.
By u sin g th is movable
couple, which could be operated from outsid e o f the cabinet, temperatures
could be taken at any poin t on the flo o r , at any time, without introducing
a source o f error by opening the cabinet and so u p settin g the experimental
conditions.
-g -
DAIA AND HiSULIS
The experiments were planned with the object of determining;
f i r s t , the rate of heat penetration into concrete; second, the ra te of
heat penetration in wheat, bran, and flo u r; and th ird , flo o r surface and
ce ilin g temperatures when no means o f a i r circu latio n was provided and
again when a fan was used to keep the a i r in constant motion.
Table I shows the hourly temperatures obtained in concrete when
5373 B.T.U. of heat per hour were supplied. In th is experiment a fan was
used to keep the a i r in circ u latio n .
Figure 2 shows graphically that while the surface temperature
increased from &5.Q°!F. to 150. 5^% in ten hours, a r is e of 85.5*7»» the
temperature 9 Inches below the surface only increased from 65.5 to IOUeFt
a rise of 38.5^F»
The average drop in temperature in the f i r s t quarter
inch is about 7*7., th is amount decreasing a t each successive couple.
This experiment was allowed to run fo r an additional 5 hours TwflHwg a
to ta l of 15 hours to see i f any sig n ifican t changes would take place.
It
was found th at the changes were very snail and to be sig n ifican t the heat
would have to be applied fo r perhaps 24 hours o r more.
Table I I shows the rate of increase in temperature at the surface
and 4 and 9 inches below the surface when applying 3036 B.T.U. of heat per
hour. Also a comparison o f s t i l l a i r against th at kept in c irc u latio n by
means of a fan.
Figure 3 shows a comparison of surface temperatures, also a t
4 and 9 inches below the concrete surface, with and without a i r circ u latio n .
The same amount of heat (3036 B.T.U. per hour) was used in both cases.
When a fan was used the surface was 7 to 10°F. h ig ie r than when no means
of a i r circu latio n was provided, but at lower depths th is difference was
not as sig n ifican t.
TABLE I .
Hours
Surface Temp.
T. a t 1 /4 in .
T. a t 1/2 in .
T. a t 3 /4 in .
T. at I in .
T. at 1& in .
T. a t 2 in.
T. a t 2& in .
T. a t 3 in .
T. a t 4 in.
T. a t 5 in .
T. a t 6 in .
T. a t 7 in .
T. a t 8 in .
T. a t 9 in .
O
65.0
65.O
65.O
65.0
64.5
64.5
64.5
64.0
64.0
64.0
64.0
64.5
64.5
65.0
65.5
TABLE I I ,
Honrly Temperatures Attained to a Depth o f 9 inches in Concrete
with 5373 B.T.TJ. per hour and a ir c ir cu la tio n .
1
103.0
100.0
95.0
93.0
90.5
88.5
86.5
84.5
82.5
82.0
8I .5
81.0
80.0
80.0
79.5
2
3
116.5 126.5
102.0 113.0
97.0 110.5
95.5 108.5
93.5 106.5
93.9 104.5
89.5 100.0
97.0
87.9
85.0
95.0
84.5
92.5
84.0
90.5
83.75 88.0
86.0
83.5
83.25 84.5
83.0
84.0
5
l4 i.5
132.0
128.0
124.0
122.0
120.0
116.0
114.0
112.0
106.0
102.0
97.0
95.0
92.0
90.0
145.0
139.0
133.0
131.0
129.0
126.5
122.5
120.0
116.5
111.0
105.0
102.0
99.5
98.0
96.5
7
147.5
l4o.o
138.0
136.0
134.0
129.0
124.0
121.0
119.0
115.5
109.5
105.0
101.0
100.0
99.0
8
9
148.5 149.5
143.5 145.5
139.0 142.0
136.5 140.0
135.0 138.0
132.0 136,0
127.5 132.5
124.5 129.0
121.5 125,5
117.0 121.5
111.0 115.0
107.5 109.5
105.5 106.5
104.0 . 105.0
102.0 103.0
10
150.5
146.0
143.0
142.0
140.0
137.0
135.0
131.0
128.0
126.0
122.0
119.0
113.0
107-5
104.0
Hourly Temperatures A ttained in Concrete when 3036 B.T.U. per hour were
applied, with an undisturbed atmosphere and with a i r c irc u latio n
Hours
0
Without fan
O
S urface Temp. 68.0
T. a t 4 in .
70.3
I . a t 9 in .
71.3
I
2
77.8
75.1
74.0
With fan
Surface Temp.
T. a t 4 in .
T. a t 9 in .
96.0
77.2
76.0
63.6
64.6
66.0
4
134.0
128.0
125.0
121.0
120.0
119.0
111.0
IO9.5
106.0
102.0
97.0
93.0
92.0
9&.0
87.5
95.3
84.0
76.0
3
96.8
85.8
78.0
102.5
86.2
78.2
107.6
86.8
80.5
4
6
7
8
98.6
87.0
80.0
5
102.5
89.5
83.0
105.3
• 92.2
85.0
109.5
92.8
86.8
113.0
87.9
82.0
113.8
90.5
84.0
114.8
93.5
86.2
116.8
94.8
87.5
111.2
97.0
87.5
9
112.2
100.8
93.5
10
113.2
103.5
96.8
119.8
98.0
90.3
123.0
102.0
95.3
125.6
107.0
98.0
—10—
a hours
' a hours
,3 hours
•z hours
INCHES BELOW SURFACE
F ig .2.
Hourly tem peratures o b tain ed to depth o f
from I to 9 Inches In co n crete with the
a p p lic a tio n of 5373 B.T.U. p e r hour and
w ith a i r c ir c u la tio n .
-1 1 -
o — o wiMt fan
■>---- - wiMtour fan
I Surfbct femb wifi fan ( M ltm )
H Surface femp wifhour fan ( io ita r u )
HlTem(t of t inehej Mifh fon (io ita iu )
TlTemfi of 4 inches wilhouf fan (Mltej.it)
z Temh of s inches Mifh fan (last tiu )
S ITemh o f »inches Milheuf fan (lo st a.tu)
t
F ig .3 .
Hourly tem peratures obtained in concrete
idien 3036 B.T.U. p e r hour were a p p lied
and under co n d itio n s of an un d istu rb ed
atmosphere and with a i r c ir c u la tio n .
-1 2 -
Comparlng Pigore U with Pigore 3 i t w ill he seen th at a t higher
temperatures the fan has a more pronounced e ffe c t in raisin g the flo o r
surface temperature.
The degree o f penetration to lower depths i s
d ire c tly proportional to the difference in surface temperatures.
I t w ill
he noted th a t th is was also the case when lower temperatures were used,
th is being shown in figure 3«
In figure 5 the surface •temperature was taken in contact with
the m aterial hut with the top o f the couple exposed.
I t w ill he seen
th at th is temperature i s the same as that o f the a i r which is d irec tly in
contact with the wheat.
I t i s prohahle in th is case th a t temperatures
a t the lower depths, th at i s S and 8 inches, were influenced to some
extent hy the temperature o f the flo o r so th at some of the 9* ris e in
temperature could he a ttrib u te d to th is f a c t.
In figure 7 i t i s quite possible th a t, as in the case of wheat,
the temperatures a t the lower depths were Influenced to some extent hy
th a t of the flo o r.
Table TII shows flo o r surface and c e llin g temperatures obtained
when 3036 B.T.TT. p er hour of heat were applied.
A comparison is shown
when no means of a i r circ u latio n was supplied*when a fan was used.
Also
the temperatures obtained when 5373 B.T.TT. p er hour of heat were applied.
In the l a t t e r case a fan was used fo r a i r circ u latio n .
In th is experiment ( figure 8) flo o r and c e ilin g temperatures
were taken fo r a short in te rv a l when no fan was used hut the ce llin g
temperature became so high a f te r the f i r s t hour th at i t was decided to
discontinue the experiment.
TABLE I I I . Hourly Temperatures Attained In Concrete when 5373 B.T.U. per hour of heat
were applied with an Undisturbed Atmosphere and with Alr Circulation.
2
3
4
5
6
7
8
9
10
96.0
78.5
75.2
102.0
8O.5
77.8
105.8
84.0
80.0
199.5
87-5
82.0
116.0
89.5
84.0
118.0
92.1
119.0
94.0
125.0
85,0
86.0
122.0
97.5
64.4 103.0 116.5
85.O
64.4 82.5
60.2 79-5
83.5
126.5
90.5
85.3
134.2
97.2
87.5
141.5
101.8
90.0
145.0
105.0
96.5
147.5
148.5
112.0
102.0
O
Hours
Without fan
Surface Temp.
T. a t U in .
T. a t 9 In.
62.6
66.0
60.2
With fan
Surface Temp.
T. a t 4 in .
T. a t 9 In.
Hours
Surf. Temp.
T. &t 2 In .
T. a t 4 in .
T. a t 6 in .
T. a t 8 In .
89.8
74.5
73-5
109.5
9 8 .8
98.2
87.5
88.5
149.5
114.8
150.6
117.0
105.5
103.5
Temperatures' Obtained In Wheat a t the Depths Uot6d fo r a Period of 15 Hours.
0
I
68.0 i4 i.o
64.0 71.0
62.0 66.0
64.0
6l.O
6l.O
62.0
2
159.5
76.0
68.0
67.0
63.5
4
3
5
173.0 179.0 183.0
81.0 85.0 90.0
71.0 74.O 76.5
69.O 72.1
74.2
65.O 66.5
68.0
8
6
10
7
9
187.0 191.0 194.0 196.0 198.0
95.0 99.0 104.0 107.0 111.0
84.5 87.O 90.0
79.0 81.5
76.0 78.5 81.2
82.5 85.0
69.O 70.0 71.5 73.0 74.0
15
200.0
122.0
101.0
91.0
79-0
-13-
TABLE IT.
I
o — o niHifon
o---- o Miltiovt fan
Surface fem|i. with fon (j J i J m u)
u Surface f e r n t without fan ( jjis a tu )
m T e m h o ta in c h e s with f a n f s s u e r u )
s Temp, at * inches without fon(s sis b t u )
x Tem p ot I in ch es with fan ( s s i s i i u )
B T e m p at I in ch es without fan ( s s is m u ]
I
HOURS
F ig .4.
Hourly tem peratures obtained in concrete
when 5373 B.T.U. p e r hour were ap p lied
and under co n d itio n s o f an un d istu rb ed
atmosphere and with a i r c ir c u la tio n .
-1 5 -
EMPE
Rafe of heof |>enefrofion
in M h e a f
HOURS
F ig .5.
Temperatures obtained a t d iffe re n t depths in wheat
fo r a p e rio d o f 1 5 hours.
Hours
Surf.
T. a t
T. a t
T. a t
T. a t
Temp.
I in .
2 in .
3 In.
U in .
Tfflnperatures Obtained, in Bran a t the Depths Noted fo r a Period of 15 Hours.
O
68.0
68.0
68.0
68.0
68.0
TABLE TI.
Hours
Surf.
T. a t
T. a t
T. a t
Temp.
2 in .
4 in .
6 in .
I
b
J
2
3
151.0 169.0 179.5 186.0 190.0 195.0 196.0
102.0 121.0 131.0 138.0 144.0 149.0 153.0
84.0 102.0 113.0 118.0 123.0 126.0 129.0
80.0 92.0 100.0 106.0 111.0 113.0 115.0
8 3 .0
8 8 .0
89.O 91.0 93.0 95.0
77.0
8
9
197.5
156.0
131.0
117.0
96.0
199.0
I 59.O
133.0
118.0
97.0
10
15
201.0 203.0
161.0 168.0
134.0 138.0
120.0
121.0
98.0
104.0
Temperatures Obtained in H our a t the Depths Noted fo r a Period of 15 Hours.
0
I
68.0 123.0
64.0
68.0
62.5 66.5
60.0 64.0
2
4
6
8
3
10
5
7
9
15
142.0 156.0 163.0 173.0 179.5 183.0 187.0 190.0 192.0 196.0
75.0 81.0 87.0 91.0 97.0 102.0 107.0 109.0 112.0 120.0
71.0
75.0 79.0 82.5 86.0 90.0 93.0 96.0 98.0 101.0
66.0
68.0 70.0
71.0
72.0 74.0 75.0 76.0 76.5 80.0
- 91-
TABLl V.
-1 7 -
S urfoce
zinches
■03 inches
R ofe of h e o h p e n e fro fio n in b ra n
HOURS
F ig. 6 .
Temperatures obtained a t d iffe re n t depths In bran fo r
a p e rio d o f 15 hours.
-IS -
-o s u r/o c e
Rofe of h e o f p en e fra h o n in flow
-» 4 inches
HOURS
Fig. 7.
Temperatures obtained, a t d iff e r e n t depths in f lo u r fo r
a p erio d o f 1 5 h o u rs.
-1 9 -
In Table VIII temperatures are given a t the flo o r surface,
quarter of an inch above the flo o r surface and h a lf an inch above the
floor surface, when 5373 B.T.U. p er hour of heat were supplied, and a
fan used to keep the a i r in circu latio n .
Figure 9 shows the a i r s tr a tific a tio n in the f i r s t h a lf inch
above the flo o r surface.
from 9 to IGeB1.
The a i r temperatures in th is distance vary
After ten hours the temperatures remain f a ir ly constant.
The fluctuations occurring a f te r th is time could be a ttrib u te d to
radiation brou#it about by the changes in the outside a i r temperature.
TABLlS VII.
flo o r and Celling Temperatures.
2
Hours
0
I
3
Without fan
3036 B.T.T7.
Floor S u rf.T . 6g.O 77.8 95.3
96.8
Ceiling Temp. 6^.0 1S4.5 194.0 204.0
4
5
6
7
g
9
10
98.6
210.0
102.5
214.5
105.3
219.0
109.5
226.5
111.2
221. g
112.2
222.0
113.2
222^0
With fan
flo o r Surf. T. 63.6 96.0
Ceiling Temp. 63.6 119.0
102.5 107.6 113.0
122.0 129.0 131.0
113.8
133.0
114. S
134.5
116. g
135.0
119. g
136.2
123.0
138.2
125.6
146.0
With fan
5373 B.T.U.
f lo o r S urf. T. 64.4 103.0
C elling Temp. 64.4 149.0
116.5 126.5 134.2
156.0 165.0 174.0
lU i.5
176.0
145,0
177.0
147.5
178.0
146.5
178.5
149.5 150.6
179.0 180.0
TABLE T ill,
Air Temperatures a t Floor Surface and Quarter and H alf an Inch above the flo o r
Hours
0 "
I
flo o r S u rf.T. 63.6 96.0
T. a t 1/4 In . 63.6 IO5.6
T. a t 1/2 In. 63.6 113.0
2
102.5
115.5
120.5
3
107.6
117-5
124.0
IT
115.0
120.0
I 27.5
5
113.S
122.0
1)0.0
S :
7
nU .g n 6.g
124.0 126. 0
131.5 132.5
“
119.g
127.5
133.5
9
123.0
12S.2
134.0
10
125.6
129:6
134.5
-2 1 -
1 ------ - F b o ' MT fa c t Iemp viMieuf N n ( 3 n t « . i u )
I ' ----- - C eiling temp. w iM iwr fe n ( J e j t i t y
m ° - - = Fleer jerfoce Iem p wMi I e n (J e jtitu )
B o - - . Ceiliny Iem(). wiMi fen ( j o j t i t u )
S o — c Floor jurftice remfi wifi Ian(JJTJsru)
Ceiliny fem(i uilh foe y o u t t y
HOURS
F ig . 8 .
J
Floor su rface and c e ilin g tem peratures
obtained when 3036 B.T.U. p e r hour were
ap p lied , w ith and w ithout a i r c ir c u la tio n ,
and when 5373 B.T.U. p e r hour were a p p lied
w ith a i r c ir c u la tio n .
r
- I Floor surface Iem peralvre
D A ir rem p a n inches from floor
m A ir te m p o-j in c h e s from floor
HOURS
F ig . 9 .
Temperature s t r a t i f i c a t i o n a t flo o r su rface
q u a rte r and h a lf inch le v e ls , w ith a i r
c irc u la tio n during a p erio d o f 10 hours.
-2 3 -
DISCUSSIOE OF ESSULTS
While the temperatures obtained in these experiments were
Influenced by the degree of penetration of heat throu^i the m aterials
of which the cabinet was b u ilt, they were not influenced by radiation
through openings in the c e ilin g o r walls as would be the case in m ills.
Since the re su lts in each case are based on surface temperatures, radiation
would not play any p art in the ra te a t which heat would penetrate a ce rtain
m aterial with a given surface temperature.
By reference to figure 2 i t w ill be seen th at the temperatures
dropped rapidly in the f i r s t quarter Inch below the surface.
ThlB fact
has much significance in the controlling of in sects as they w ill move
down to the flo o r when the temperatures begin to ris e , and w ill escape
into any small cracks in the flo o r itiiere the high temperatures w ill not
affect them.
point.
The following observations w ill serve to demonstrate th is
During the construction of the cabinet the surface of the concrete
had been cracked in one corner to the depth o f about three-quarters of an
inch.
When confused flo u r b eetles, Tribollum confusum. were lib e ra ted in
the cabinet and a flo o r surface temperature of over 1200F. maintained f o r
10 hours, many of them escaped into the crack where they remained
unaffected by the h i# i temperature.
By means o f the movable thermocouple
described e a r lie r in th is paper, the temperatures were taken in several
places on the flo o r surface lm e d ia tely adjacent to the crack and were
found to average from IlS tT . a t the s ta r t of the experiment to 123®?. at
the end of 10 hours.
The rate a t which the heat penetrated the cement, as shown
graphically in Figure 4, indicates th at a f te r 10 hours, with a surface
temperature of 150 0F ., a k illin g temperature was reached to a depth of
6 inches.
Allowing the c e llin g temperature of a m ill to reach a maximum
of 180*F. and holding i t fo r 18 to 24 hours a temperature of 120?F.
should he reached on the surface of the next flo o r, with a flo o r thickness
of 8 to 10 inches.
The fa c t th at in m ills the floors are reinforced with
ste e l and iron beams, which are b e tte r conductors of heat than concrete,
should hasten the rate o f heat penetration and the obtaining of a k illin g
temperature on the next flo o r.
The rate of heat penetration as shown in Figure 3 would indicate
th at fo r lower ceilin g temperatures, the surface temperature obtained by
heat penetration through the flo o r from the room immediately below would
not be affectiv e in the destruction of in sects.
temperature o f 120 degrees
Since with a surface
the temperatures drop o ff rapidly in the f i r s t
inch or so, the k illin g o f insects which escape into cracks and crevices
i s dependent on heat which penetrates from the room below.
This would
suggest that the c e ilin g temperature should be allowed to reach a
temperature of ISOtB1. and held there in order to get the most e ffic ie n t
re su lts.
The ris e in temperature on the surface when the a i r was kept in
circu latio n i s also brought out in Figure 3.
I t shows th at a k illin g
temperature was reached in 8 hours when a fan was used while using the
same amount of heat,but not making any provisions fo r a i r circ u latio n
a temperature of only 103eF. was reached a f te r ten hours.
By reference to Figure 4 i t w ill be seen that as the "heat content"
Is increased the difference in flo o r temperatures brought about by a i r
-2 5 -
c lrc u la tion "becomes greater, th at is , the efficiency o f a fan increases
with the amount of heat supplied.
In p ractice , when a maximum ce llin g
temperature o f ISO??, i s obtained, i t should be possible to produce a
k illin g temperature to a depth of U inches in the flo o r.
In a previous
discussion i t was pointed out that with such a c e llin g temperature a
k illin g temperature should be produced on the flo o r surface by penetration
from the room below.
The combined effect o f these two facto rs should
insure a complete k illin g of a l l insects whether they be on the flo o r
surface o r in cracks o r such places o f concealment as would not be affected
by the downward penetration o f heat alone.
The m atter of penetration of gaseous fumigants into m ill products
has been studied quite extensively by several workers and rath er d efin ite
conclusions drawn as to the !im practicability o f such a method in the control
of insects in festin g these m aterials.
Eecommendatlons have been made fo r
the use of heat s te riliz a tio n in such situ atio n s as in m ills where
accumulations of grain, flo u r, etc. occur.
Dean ( l) showed that a k illin g
temperature could be produced to a depth of 6 Inches in flo u r, when i t
was exposed to temperatures ranging from 130 to I 1KJtT.
the flo u r was in conveyor spouts.
In some instances
I t can be readily seen th a t temperatures
obtained in such cases would not be comparable to those obtained when
the same amount of m aterial was spread to the same depth on the flo o r.
In order to elim inate e rro r due to heat conduction by the wires, when
studying heat penetration in wheat, flo u r and bran, the thermocouples
were lead up from the flo o r to the depths noted in Tables IV, V and VI.
In carrying out heat s te riliz a tio n in a m ill such surface
temperatures as are shown in the graphs (fig u res 5, 6 and 7) could not
-2 6 -
» . obtained wlthaut danger to the machinery In other p a r t, of the m ill.
Jrom a .tndy o f the graph. I t appear, quite evident th at heat .t e r l l l ,a t l o n
I . of no value In k illin g ln e e c t. In accumulation of material, .hen they
are more than one o r tmo lnche. deep. A fter determining the rate and
depth of heat penetration In bran I t was decided to attempt to k i l l the
I . csafueum with ehlch I t eas in fe .te d .
The amount of bran need covered
the flo o r to a depth of .lig h tly over U ln ch e,.
The heat was allowed to
continue fo r an extra 10 hour,, making a to ta l o f 25 hour., heating with
eurface temperature, ranging In the neighborhood o f 200 T .
A. fa r a .
could be ascertained a f te r cooling and lc p e c tln g the bran, not a eln g l.
specimen wa. k ille d a , they were a l l found to have Worired th e ir way down
to the flo o r surface Where k illin g temperature, were not obtained.
The
•erne c o n c is io n , a . are drawn In the =a.e „ bran can be applied to wheat
end flo u r a , the v ariatio n In heat penetration o f th e ,, m aterial. I , very
email.
Before discussing flo o r end c e llin g temperature, the m atter o f
heat ..r a tif ic a tio n w ill be considered.
Tlgure 9 Who., the flo o r surface
temperature, the temperature, quarter Inch and h a lf inch above the flo o r.
Which were recorded a t hourly In te rv a l,
over a period o f 10 hour, when ’
5373 B.T.tl. p er hour o f heat were applied and a fan used fo r a i r
circ u latio n .
I t w ill be seen that the temperature gradient In the f i r s t
h a lf inch was from 9 to I S * .
TM. f = t make. I t ^ t e obviou. that very
large e rro r, can be made when recording flo o r temperature, by mean, of
a thermometer, end that temperature, taken any place except in contsct
with the flo o r surface cannot be taken a . Indicative of the r e s u lt, th at
such recorded temperature, should produce,
men no mean, „ a i r c irc u latio n
-2 7 -
is provided the s tr a tific a tio n w ill obviously be g reater than the case
ju s t c ite d .
An inspection of fig u re 8 shows th at obtaining a le th a l
temperature on the flo o r surface without some means of a i r circu latio n
is not p ra c tic a l.
With undisturbed atmosphere the c e ilin g temperature
was 232^jp1 which, i s 50T . hig&er than the maximum temperature which could
be allowed with safety.
The flo o r which was only U fe e t below th is point
did not reach a k illin g temperature under such conditions.
she* the e ffe c t when the fan was turned on.
Curves 3 and 4
This resulted in a le th a l
temperature being obtained on the flo o r surface a f te r a period of 8 hours,
while the c e llin g temperature only reached IlfOeF. More heat was then
applied to raise the c e ilin g temperature to ISOtT.
Curves 5 and 6 show
the re su lts obtained.
POSSIBLE ACTION OF HEAT CU INSECTS
Up to th is point the p o ssib ility of k illin g in sects by heat
s te riliz a tio n has been discussed but no suggestions have been made of any
possible reactions th at may be involved.
I t i s a m atter o f common observation that in sects when exposed
to high temperatures become very active a t f i r s t and then gradually become
dormant and appear to be dead.
I f the in sects aw removed to a cool
place before a certain p o in t, yet to be determined, is reached they w ill
revive.
I t was thought th at possibly the activ atio n o f enzymes ty a ris e
in temperature produced the increased a c tiv ity and th at inactiv atio n of
the enzymes by continued heating eventually brou#it about the dormant
-2 5 -
sta te # i c h preceded death.
I t was fu rth e r thou^at th at the insects
would revive unless the point had been reached when complete in activ ation
of the enzymes had taken place.
In order to obtain some information on these points the follow­
ing experiment was carried out:
Twenty te s t tubes each containing 20
confused flo u r b eetles, T. cpnfusum. were placed in a th e m o etatic ally
controlled water bath, the temperature of which was held a t I lS 0F.
At
hourly in te rv a ls extending over a period o f 10 hours, two te s t tubes "were
removed from the bath.
The beetles in one of the te s t tubes were placed
in a cool place and used to determine m o rtality while those in the other
were ground up fo r catalase determinations.
The determination was carried out as follows:
Five cc. o f an
aqueous ex tract of the ground up tissu e was placed in one arm of a Bunzel
tube.
Five cc. of a 1# solution of hydrogen peroxide, which had previously
been brought to a pH of 7 by the addition o f disodium phosphate, was placed
in the other arm of the tube.
The tube was then placed in an automatic
shaking device in a temperature cabinet which was held a t 25°C.
The tube
and contents were shaken fo r 10 minutes and the pressure of oxygen
lib e ra ted determined by reading the difference on a mercury manometer.
The pressures produced, in cm. of mercury, were taken as indicative of
the amount of catalase present.
Table IX shows the pressure produced in cm. o f mercury and the
m ortality a t the end of each successive hour.
There does not appear to be any relationship between the catalase
content and m ortality.
The curve (figure 10) shows th at a gradual in activation
of the enzymes is brought about but no abrupt change takes place in th is
-2 9 -
general trend even a f te r IOO^ m ortality was produced.
This lends more
evidence to the common explanation that death is brought about by
denaturatlon and coagulation of certain proteins "by heat.
IABLS IX.
0
Hours
cm.of Hg.
7.8
56 m ortality 0
Pressure o f Oxygen In cm. Hg. Obtained, a t Hourly In terv als fo r a Period
o f 10 Hours and percent M ortality fo r the same Period.
I
2
8.25
8.65
0
0
3
7.96
55.0
4
6.60
75.0
5
7.50
90.0
£
5.U5
100.0
7
5.65
100.0
8
5.60
100.0
9
3.27
100.0
10
2.55
100.b
- 30-
PERC EN TA G E
s ---- o catalase content'
o - — o mortality
HOURS
F ig . 1 0 .
P r e s s u r e o f o x y g e n i n cm . o f H g . o b t a i n e d a t h o u r l y
in t e r v a ls f o r a p e r io d o f 10 h o u r s , and p e r c e n ta g e
m o r t a l i t y o f T . c o n f u s u m d u r i n g t h e sam e p e r i o d .
-3 2 -
THB POSSIBILITY OP SUCCESSFUL HEAT STERILIZATION IN
MONTANA FLOUR MILLS
A study of the daily weather recorder in B illin g s, Great F a lls,
and Lewistown during the months of June, July, and August fo r the past
10 years, shows that during these months there are a number of
consecutive days in which the average daily temperatures are in the
neighborhood of 90TF.
have to he raised hy
This means th a t the temperature o f the m ill would
to 50*F.
In the experiment giving the most sa tisfac to ry re su lts which
are shown in Figure 8, curves 5 and 6, 5373 B.T.U. of heat p er hour were
used.
In order to produce these temperatures 84,000 B.T.U, per hour
per thousand cubic feet of a i r space, would have to he supplied.
By
interpolation i t was calculated that one of the large u n it heaters
operating under a steam pressure of 10 Ih s. would he capable of deliver­
ing three times th is amount of heat p er hour.
Under these conditions
i t can he seen that such a method could he readily applied with success
in the control of m ill in sects in th is S tate.
-3 3 -
SHMAHT
Laboratory equipment and apparatus fo r the conducting o f heat
s te riliz a tio n experiments on m ill insects and catalase determination is
described.
With a surface temperature of 150TF., a temperature o f 120cT.
was obtained to a depth of 6 inches in concrete a f te r 10 hours* heating.
When a means of a i r circu latio n was provided and the ce llin g
temperature allowed to ris e to I SO^P., a flo o r temperature o f l^O^P. was
obtained.
The a i r temperature gradient in the f i r s t h a lf inch above the
flo o r surface shows th a t, to be sig n ific an t, temperatures must be taken
in contact with the flo o r surface.
The experiments show that fo r sa tisfac to ry re su lts to be
obtained with heat s te riliz a tio n , a l l bags of flo u r and accumulations of
cereal, e tc . must be removed from the m ill before heat i s applied.
In Montana there are many days during June, July, and August
idien a i r temperatures are su ffic ie n tly high so that successful
s te riliz a tio n can be carried out.
There are large u n it heaters now on the market which are
capable of bringing about the desired h ig i temperatures.
The experimental re su lts show th at s te riliz a tio n , i f properly
carried out should be completed in a period of 24 hours.
There i s no apparent co rrelatio n between catalase a c tiv ity
and m ortality in Tribollum confusum.
-3%-
BIBLIOGBAPHT
( l)
Dean, G.A.
1913.
(2)
Mill and stored grain in sects. Kans. State
Agr. Col., Agr. Eatp. Sta. Bui. I Sg.
GoodwiH, W.H.
1922. Heat fo r control of cereal in se cts.
Exp. Sta. Bui. 35U.
Ohio Agr.
(3)
Grossman, E.F.
1931. Heat treatment fo r controlling the insect p ests
o f stored com . Univ. of F la ., Agr. Exp.
Sta. Bui. 239.
(U)
BoMnson, W.
1927.
The theraocouple method of determining temperatures.
Ann. Ent. Soc. Amer. 20:513-521. I Ilu s .