• TABLE OF CONTENTS
HIDE
 Front Cover
 Front Matter
 Introduction
 Heat resistance of insects
 Heat resistance of corn
 Heating stored corn
 Summary and conclusions






Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 239
Title: Heat treatment for controlling the insect pests of stored corn
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026561/00001
 Material Information
Title: Heat treatment for controlling the insect pests of stored corn
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 24 p. : ill., charts ; 23 cm.
Language: English
Creator: Grossman, Edgar F
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1931
 Subjects
Subject: Corn -- Storage -- Diseases and injuries -- Florida   ( lcsh )
Food storage pests -- Control -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Edgar F. Grossman.
General Note: Cover title.
Funding: This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Florida Sea Grant technical series, the Florida Geological Survey series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.
 Record Information
Bibliographic ID: UF00026561
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924092
oclc - 18204443
notis - AEN4696

Table of Contents
    Front Cover
        Page 1
    Front Matter
        Page 2
    Introduction
        Page 3
    Heat resistance of insects
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Heat resistance of corn
        Page 14
    Heating stored corn
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
    Summary and conclusions
        Page 23
        Page 24
Full Text


Bulletin 239


September, 1931


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director






HEAT TREATMENT FOR

CONTROLLING THE INSECT PESTS

OF STORED CORN

By EDGAR F. GROSSMAN






CONTENTS
PAGE
INTRODUCTION .................... ................. ......... ..... ............ 3
HEAT RESISTANCE OF INSECTS ........................................- 4
HEAT RESISTANCE OF CORN ................- ................ .............. ......- 14
HEATING STORED CORN .--- ....... .......................... ............... 14
SUMMARY AND CONCLUSIONS ................................... ................. 23






TECHNICAL BULLETIN



Bulletins will be sent free upon application to
the Agricultural Experiment Station
GAINESVILLE, FLORIDA


LIBRARY
PLORIDA EXp YEttinErNT STATION










BOARD OF CONTROL

P. K. Yonge, Chairman, Pensacola
A. H. Blanding, Bartow
W. B. Davis, Perry
Raymer F. Maguire, Orlando
Frank J. Wideman, West Palm Beach
J. T. Diamond, Secretary, Tallahassee


EXECUTIVE STAFF

John J. Tigert, M.A., LL.D., President of the
University
Wilmon Newell, D.Sc., Director
H. Harold Hume, M.S., Asst. Dir., Research
Sam T. Fleming, A.B., Asst.Dir., Administration
J. Francis Cooper, M.S.A., Editor
R. M. Fulghum, B.S.A., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Secretary
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant


MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S., Agronomist
W. A. Leukel, Ph.D., Associate
G. E. Ritchey, M.S.A., Assistant*
Fred H. Hull, M.S., Assistant
J. D. Warner, M.S., Assistant
John P. Camp, M.S., Assistant
ANIMAL HUSBANDRY
A. L. Shealy, D.V.M., Veterinarian in Charge
E. F. Thomas, D.V.M., Assistant Veterinarian
R. B. Becker, Ph.D., Associate in Dairy In-
vestigations
W. M. Neal, Ph.D., Asst. in Animal Nutrition
P. T. Dix Arnold, B.S., Assistant in Dairy In-
vestigations
CHEMISTRY
R. W. Ruprecht, Ph.D., Chemist
R. M. Barnette, Ph.D., Associate
C. E. Bell, M.S.. Assistant
J. M. Coleman, B.S., Assistant
H. W. Winsor. B.S.A., Assistant
H. W. Jones, M.S., Assistant
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural Economist
Bruce McKinley, A.B., B.S.A., Associate
M. A. Brooker, Ph.D., Assistant
Zach Savage, M.S.A., Assistant
ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Head
L. W. Gaddum, Ph.D., Biochemist
C. F. Ahmann, Ph.D., Physiologist
ENTOMOLOGY
J. R. Watson, A.M., Entomologist
A. N. Tissot, Ph.D., Assistant
H. E. Bratley, M.S.A., Assistant
E. F. Grossman, M.A., Asso., Cotton Insects
P. W. Calhoun, Assistant
HORTICULTURE
A. F. Camp, Ph.D., Horticulturist
Harold Mowry, B.S.A., Associate
M. R. Ensign, M.S., Associate
G. H. Blackmon, M.S.A., Pecan Culturist
C. B. Van Cleef, M.S.A., Greenhouse Foreman


*In cooperation with U.S.D.A.


PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist
George F. Weber, Ph.D., Associate
R. K. Voorhees, M.S., Assistant
Erdman West, M.S., Mycologist


BRANCH STATIONS

TOBACCO STATION. QUINCY
L. 0. Gratz, Ph.D., Associate Plant Pathologist
in Charge
R. R. Kincaid, M.S., Asst. Plant Pathologist
W. A. Carver, Ph.D., Asso. Cotton Specialist
R. M. Crown, B.S.A., Field Asst., Cotton
Jesse Reeves, Farm Superintendent

CITRUS STATION, LAKE ALFRED
John H. Jefferies, Superintendent
Geo. D. Ruehle, Ph.D., Asst. Plant Pathologist
W. A. Kuntz, A.M., Asst. Plant Pathologist
B. R. Fudge, Ph.D., Assistant Chemist
W. L. Thompson, B.S., Assistant Entomologist

EVERGLADES STATION, BELLE GLADE
R. V. Allison, Ph.D., Soils Specialist in Charge
R. W. Kidder, B.S., Farm Foreman
R. N. Lobdell, M.S., Associate Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
H. H. Wedgeworth, M.S., Asso. Plant Path.
B. A. Bourne, B.S., Asso. Plant Physiologist
J. R. Neller, Ph.D., Associate Biochemist
A. Daane, Ph.D., Associate Agronomist
M. R. Bedsole, M.S.A., Assistant Chemist
Fred Yount, Office Assistant

SUB-TROPICAL STATION, HOMESTEAD
H. S. Wolfe,Ph.D.,Asso. Horticulturist in Chg.
L. R. Toy, B.S.A., Asst. Horticulturist
Stacy O. Hawkins, M.A., Field Assistant in
Plant Pathology


FIELD STATIONS

Leesburg
M. N. Walker, Ph.D., Asso. Plant Pathologist
W. B. Shippy, Ph.D., Asst. Plant Pathologist
K. W. Loucks, M.S., Asst. Plant Pathologist
C. C. Goff, M.S., Assistant Entomologist
J. W. Wilson, Ph.D., Assistant Entomologist
Plant City
A. N. Brooks, Ph.D., Asso. Plant Pathologist
R. E. Nolen, M.S.A., Field Asst. in Plant Path.
Cocoa
A. S. Rhoads, Ph.D., Asso. Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Asso. Plant Pathologist
West Palm Beach
D. A. Sanders, D.V.M., Associate Veterinarian
Monticello
Fred W. Walker, Assistant Entomologist
Bradenton
David G. Kelbert, Field Assistant in Plant
Pathology








HEAT TREATMENT FOR
CONTROLLING THE INSECT PESTS
OF STORED CORN

By EDGAR F. GROSSMAN

INTRODUCTION

The annual losses in stored corn caused by grain insects can
be conservatively estimated at from 20 percent to 40 percent in
Florida. This loss is not being reduced, even though the success-
ful use of carbon bisulphide as a fumigant has been repeatedly
demonstrated. The fact that the majority of the corn cribs
in Florida are not built sufficiently air-tight for successful fum-
igation, and the stressing of the necessary precautions attached
to a correctly applied fumigation method of insect control, have
apparently hindered the general adoption of carbon bisulphide
as a means of insect control. The insect pests of stored corn
have also been combated by the use of various poisons and sprays
as insecticides, but again the farmer apparently prefers to lose a
large percentage of his corn rather than apply poisons which he
feels will injure the stock subsequently when feeding on the corn.
There remains, however, still another possible method of con-
trolling the insect pests of stored corn, namely, heat treatment.
A detailed discussion of the heat resistance of both the insect
pests and corn, and a preliminary report on heating stored corn
are herewith presented in three sections: first, a section deal-
ing with the heat resistance of insects, in which the lethal tem-
peratures and their variations are noted; second, a section deal-
ing with the heat resistance of corn, in which the effects of heat
on the germination of the seed and the vigor of the plants grow-
ing from heat-treated seed are noted; and third, a section dealing
with heating and accurately measuring the temperatures at-

ACKNOWLEDGMENTS: The author is indebted to R. E. McColskey
and S. F. Hardee of Hague, Florida, for granting the use of their tobacco
barn for experimentation at Hague; G. B. Merrill of the Florida State
Plant Board for the identification of the insects used; and the following
members of the Florida Agricultural Experiment Station: A. L. Shealy
and W. E. Stokes for supplying the corn which was heat-treated in the
tobacco barn; A. H. Eddins for supplying corn seed and apparatus for
germination tests; A. F. Camp for the use of the apparatus for tempera-
ture measurements and advice concerning its operation; and J. R. Watson
for suggesting heat treatment of stored corn for insect pest control.







Florida Agricultural Experiment Station


trained in various positions in a mass of 300 bushels of (a), slip-
shucked and (b), shucked corn, placed in a tobacco barn.

HEAT RESISTANCE OF INSECTS

To determine the lethal temperatures and the duration of ex-
posure to temperatures required to kill the insect pests of stored
corn, three types of beetles were selected for a detailed study,
namely, the rust-red flour beetle, Tribolium ferrugineum
(Fab.); the rice weevil, Sitophilus (Calendra) oryzae (L.) ; and
the square-necked grain beetle, Silvanus gemellatus Duv.
The insects were placed in test-tubes, each tube containing 10
specimens, which in turn were placed in a water bath maintained
at the desired constant temperature for varying lengths of time.
After each exposure the insects were removed from the test-
tubes, placed in small open containers and kept at room tem-
perature for a period of 24 hours. They were then separated into
two classes, those active and those dead. Though a large per-
centage of the insects termed active were so injured by the heat
that they soon died, they were nevertheless grouped with the
active or surviving insects.
The rust-red flour beetle (Tribolium ferrugineum (Fab.)),
was found to show more resistance to heat than the other insects
which were studied. A 15-minute exposure to 500C. (1220F.)
100













5 10 if 4S 60 /20 /80
MINUTES EXPOSED
Fig. 1.-Chart showing the comparative effect of different constant tem-
peratures on the survival of the rust-red flour beetle, Tribolium ferru-
gineum (Fab.), exposed for the periods of time indicated.







Bulletin 239, Heat to Control Insects of Stored Corn


10 20 30 40 fO 60 70 80 30
HOURS EXPOSED
Fig. 2.-Chart showing the comparative effect of different constant tem-
peratures on the survival of the rust-red flour beetle, Tribolium fer-
rugineum (Fab.), exposed for the periods of time indicated.

killed all the adults, while an exposure to 42C. (107.60F.) re-
quired over 114 hours to kill. Intermediate temperatures show
a corresponding gradation of the length of time necessary to
render the exposures lethal. The results of treatments varying
from 42C. to 52C. are represented in Table I. The same data
are also presented in Figs. 1 and 2 in graph form so that the
comparative effectiveness of the various temperatures and ex-
posures can be seen more easily.
The lethal effect of temperature on the rust-red flour beetle,
when exposed for 10-minute periods, is most pronounced between
the narrow range of 49C. to 50C. though a few adults die at
470C. and 480C. and a few live at exposures between 500C. and
51C. A comparative graph of this phenomenon is presented in
Fig. 3, the data having been obtained from Table I.
It is a significant fact that the larvae and pupae are able to
withstand a given temperature for a longer period of time than
the adult, or, on the other hand, higher temperatures when ex-
posed for the same length of time. Though a number of the lar-
vae and pupae were not killed by either higher temperatures or
longer exposures, they were, nevertheless, unable to develop
into normal adults. The fact remains, however, that exposures
which inactivate the adults fail to affect the larval and pupal
forms similarly.








Florida Agricultural Experiment Station


TABLE I.-LETHAL EFFECT OF DIFFERENT DEGREES OF HEAT ON THE ADULTS
OF Tribolium ferrugineim (Fab.) AS SHOWN BY THEIR SURVIVAL WHEN
EXPOSED TO CONSTANT TEMPERATURES FOR DIFFERENT LENGTHS OF TIME.


Time Temperature Number
ex- degrees adults
posed Centigrade used

5 min. ........ 52 30
10 min ....... 52 30
15 min. ........ 52 30
Check .............. 30

5 min. ........ 51 90
10 min. ........ 51 90
15 min ........ 51 30
Check .............. 30

5 min. ........ 50 90
10 min. ....... 50 90
15 min ........ 50 30
30 min. ........ 50 60
Check .............. 30

5 min ........ 49 90
10 min ....... 49 90
15 min ........ 49 90
30 min. ........ 49 120
Check ............ 30

5 min. ........ 48 90
10 min ........ 48 90
15 min. ........ 48 90
30 min. ........ 48 150
45 min ........ 48 120
60 min........ 48 120
90 min. ....... 48 60
Check .............. 30

5 min. ........ 47 60
10 min......... 47 60
15 min. ........ 47 60
30 min........ 47 60
45 min. ........ 47 60
60 min .. ..... 47 60
90 min. ........ 47 110
2 hrs. ....... 47 120
3 hrs. ........ 47 120
4 hrs. ........ 47 120
Check .............. 30

10 min. ........ 46 120
15 min........ 46 120
30 min ........ 46 180
60 min ........ 46 180
90 min. ........ 46 180
2 hrs ........ 46 200
3 hrs. ........ 46 210
4 hrs. ....... 46 210
5 hrs. ........ 46 210
6 hrs. ........ 46 180
7 hrs. ........ 46 120
Check ........ .... 30


Percent
sur-
vival

0.0
0.0
0.0
100.0

0.0
0.0
0.0
100.0

62.2
11.1
0.0
0.0
100.0

100.0
86.7
12.3
0.0
100.0

100.0
96.2
98.9
57.3
35.8
0.0
0.0
100.0

100.0
100.0
100.0
100.0
100.0
100.0
53.6
43.3
1.7
0.0
100.0

100.0
100.0
98.9
95.0
83.9
71.5
32.9
13.8
1.4
0.0
0.0
100.0


Time Temperature Number Percent
ex- degrees adults sur-
posed Centigrade used vival


30 min. ........ 45
60 min. ....... 45
2 hrs. ........ 45
3 hrs. ....... 45
4 hrs. ....... 45
5 hrs. ........ 45
6 hrs. ........ 45
7 hrs. ........ 45
8 hrs. ...... 45
9 hrs. ........ 45
10 hrs. ........ 45
11 hrs. ........ 45
12 hrs. ........ 45
13 hrs. ........ 45
Check .............

4 hrs ........ 44
5 hrs. ........ 44
6 hrs. ........ 44
7 hrs. ........ 44
8 hrs. ........ 44
9 hrs. ........ 44
10 hrs ....... 44
11 hrs. ........ 44
12 hrs ........ 44
13 hrs. ........ 44
14 hrs. ........ 44
15 hrs. ........ 44
16 hrs. ........ 44
17 hrs. ........ 44
18 hrs ........ 44
19 hrs. ........ 44
20 hrs. ........ 44
21 hrs. ........ 44
22 hrs. ........ 44
23 hrs. ........ 44
24 hrs. ........ 44
25 hrs ........ 44
26 hrs. ....... 44
27 hrs. ........ 44
29 hrs. ........ 44
31 hrs. ........ 44
35 hrs. ........ 44
39 hrs. ....... 44
43 hrs. ........ 44
46 hrs. ........ 44
48 hrs ........ 44
50 hrs. ........ 44
52 hrs. ........ 44
Check ..........


11 hrs.
12 hrs.
13 hrs.
14 hrs.


....... 43
........ 43
........ 43
........ 43


100.0
100.0
100.0
80.6
41.0
36.8
31.6
34.4
20.0
7.5
0.8
0.0
0.0
0.0
100.0

100.0
100.0
100.0
100.0
74.3
74.0
56.5
65.9
50.6
52.2
46.7
19.2
27.5
9.2
19.2
10.0
9.1
6.4
18.3
8.3
18.1
22.5
0.8
15.8
10.0
9.2
10.0
1.7
0.8
1.7
0.8
0.0
0.0
100.0

98.3
93.3
98.3
91.7


.







Bulletin 239, Heat to Control Insects of Stored Corn 7

TABLE I.-LETHAL EFFECT OF DIFFERENT DEGREES OF HEAT ON THE ADULTS
OF Tribolium ferrugineum (Fab.) AS SHOWN BY THEIR SURVIVAL WHEN
EXPOSED TO CONSTANT TEMPERATURES FOR DIFFERENT LENGTHS OF TIME.
-(Continued).


Time Temperature Number
ex- degrees adults
posed Centigrade used


15 hrs.
17 hrs.
19 hrs.
21 hrs.
23 hrs.
25 hrs.
28 hrs.
30 hrs.
32 hrs.
36 hrs.
37- hrs.
40 hrs.
42 hrs.
44 hrs.
46 hrs.
48 hrs.
50 hrs.
52 hrs.
54 hrs.
56 hrs.
58 hrs.
60 hrs.
62 hrs.
Check


Percent Time Temperature Number Percent
sur- ex- degrees adults sur-
vival posed Centigrade used vival
95.0 23 hrs ........ 42 60 98.3
90.0 25 hrs. ........ 42 60 95.0
62.5 27 hrs. ........ 42 60 93.3
51.7 31 hrs. ........ 42 60 91.7
52.0 37 hrs. ........ 42 50 96.0
54.0 43 hrs. ........ 42 180 64.5
70.0 49 hrs. ........ 42 180 31.1
60.0 54 hrs ........ 42 170 34.1
40.0 60 hrs. ........ 42 180 32.2
52.0 66 hrs. ........ 42 180 22.8
48.3 72 hrs. ........ 42 170 27.6
39.2 78 hrs. ........ 42 180 16.1
40.8 84 hrs ....... 42 170 7.6
47.5 88 hrs. ........ 42 120 1.7
33.3 90 hrs. ........ 42 180 1.1
26.7 94 hrs. ........ 42 120 0.8
21.7 98 hrs. ........ 42 110 2.7
15.8 102 hrs. ........ 42 120 1.7
1.7 106 hrs ........ 42 120 2.5
6.7 110 hrs. ........ 42 120 3.3
1.7 114 hrs. ........ 42 110 0.9
0.8 Check .............. 30 100.0
0.0
100.0


When eggs were exposed to 490C. (120.20F.) for 30 minutes
they failed to hatch. The same exposure killed all adults, but
19.2 percent of the larvae and 46.2 percent of the pupae sur-
vived. A 45-minute exposure at this temperature, however,
killed all of the larvae, but a three-hour period was necessary to
kill all of the pupae, though the pupae treated for one hour or
over failed to develop into vigorous adults. The comparative
data secured from this test are presented in Table II.

TABLE II.-LETHAL EFFECT OF EXPOSURE TO A TEMPERATURE OF 490C.
(120.2F.) FOR VARYING PERIODS ON THE EGG, LARVA, PUPA AND ADULT
STAGES OF Tribolium ferrugineum (Fab.)
Length No. Percent No. Percent No. Percent No. Percent
exposure eggs sur- larvae sur- pupae sur- adults sur-
(minutes) used vival used vival used vival used vival

0 (Check) 30 83.4 50 100.0 40 100.0 50 100.0
5 5 80.0 130 93.8 25 100.0 150 93.3
10 10 10.0 130 60.0 55 60.0 150 38.7
15 30 16.7 130 40.0 65 50.8 150 10.0
30 30 0.0 130 19.2 65 46.2 180 0.0
45 25 0.0 110 0.0 75 28.0 90 0.0
60 20 0.0 70 0.0 75 28.0 60 0.0
90 10 0.0 60 28.3
120 40 35.0
150 30 6.7
180 ____ 30 0.0_


"~""'






Florida Agricultural Experiment Station


60


40--
20-- - - - -

"=O^

23 -- -- -- -- -- -- -V -- -- -


47 48 49
DEGREES CENTIGRADE


51 52


Fig. 3.-Chart showing the lethal effect of heat on Tribolium ferrugineum
(Fab.) when exposed for a period of 10 minutes at various tem-
peratures.

A comparative test conducted to show the effectiveness of a
temperature maintained at 450C. (1130F.) in addition to the test
conducted at 49C. yielded similar results.


HOURS EXPOSED


Fig. 4.-Chart showing the comparative effect of different constant tem-
peratures on the survival of the rice weevil, Sitophilus (Calendra)
oryzae (L.), exposed for period of time indicated.







Bulletin 239, Heat to Control Insects of Stored Corn 9

Besides the different killing effects exerted by the same
amount of heat on the eggs, larvae, pupae, and adults of the
rust-red flour beetle, there is a marked difference in the suscept-
ibility of the adults themselves. The age of the individual ap-
parently determines the degree of its susceptibility to heat-treat-
ment, since a decidedly larger percent of the younger individ-
uals were found to resist 480C. (118.40F.) for a period of 45
minutes, than a mixed group of young and old individuals which
in turn showed a larger survival percentage than a mixed group
of young and old individuals which had been kept in captivity
for an additional period of two months. Data showing the per-
centage survival as well as the number of individuals tested are
presented in Table III.


HOURS EXPOSED
Fig. 5.-Chart showing the comparative effect of different constant tem-
peratures on the survival of the square-necked grain beetle, Silvanus
gemellatus Duv., exposed for the periods of time indicated.
The adult rice weevil, Sitophilus (Calendra) oryzae (L.), was
killed by a ten minute exposure to 500C., and longer exposures at
lower temperatures until at 420C., twenty-two hours were neces-
sary to effect a kill. The number of specimens used and the per-
cent survival for each exposure is presented in Table IV, while
Fig. 4 represents the same data in graph form.








Florida Agricultural Experiment Station


TABLE II.-LETHAL EFFECT OF HEAT ON THE ADULTS OF Tribolium fer-
rugineum (Fab.) AS SHOWN BY THEIR SURVIVAL WHEN EXPOSED TO
48C. (118.4F.) FOR 45 MINUTES.


Tribolium ferrugineum Number adults used
(Fab.)1


Percent survival


1-3 days old 510 58.2


Age undetermined:
Mixed culture 120 35.8

Age undetermined:
Mixed culture plus
two months 620 8.1
captivity

TABLE IV.-LETHAL EFFECTS OF DIFFERENT DEGREES OF HEAT ON THE
ADULTS OF Sitophilus (Calendra) oryzae (L.) AS SHOWN BY THEIR
SURVIVAL WHEN EXPOSED TO CONSTANT TEMPERATURES FOR DIFFERENT
LENGTHS OF TIME.
Time Temperature Number Percent Time Temperature Number Percent
ex- degrees adults sur- ex- degrees adults sur-
posed Centigrade used vival posed Centigrade used vival


5 min. ....... 51
10 min ........ 51
15 min. ....... 51
Check ............

5 min. ....... 50
10 min. ........ 50
15 min. ....... 50
Check ........ ....

5 min. ..... 49
10 min. ....... 49
15 min. ........ 49
30 min......... 49
Check ........ ....

5 min ....... 48
10 min. ....... 48
15 min. ....... 48
30 min. ........ 48
45 min. ........ 48
Check ..........

5 min. ....... 47
10 min. ........ 47
15 min. ........ 47
30 min. ....... 47
45 min. ....... 47
60 min. ....... 47
90 min. ........ 47
Check ........

5 min. ...... 46
10 min ........ 46


150
150
150
30

150
150
150
30

140
150
150
150
30

150
150
150
150
150
30

210
210
150
180
180
180
120
30

60
90


42.7
0.0
0.0
100.0

64.0
0.0
0.0
100.0

92.9
67.3
3.3
0.0
100.0

94.7
83.3
46.7
0.0
0.0
100.0

97.6
94.8
92.0
75.0
18.9
1.7
0.0
100.0

100.0
98.9


15 min. ........ 46
30 min. ....... 46
45 min. ....... 46
60 min. ....... 46
90 min. ....... 46
2 hrs. ........ 46
3 hrs. ........ 46
Check ..............

5 min. ....... 45
10 min. ....... 45
15 min. ........ 45
30 min. ........ 45
60 min. ....... 45
90 min. ....... 45
2 hrs. ........ 45
3 hrs. ........ 45
4 hrs. ........ 45
SCheck .............


30 min.
60 min.
90 min.
2 hrs.
3 hrs.
4 hrs.
5 hrs.
6 hrs.
7 hrs.
8 hrs.
Check


.......... 44
.......... 44
........ 44
........ 44
........ 44
....... 44
........ 44
........ 44
........ 44
........ 44


90
180
120
180
180
120
120
30

60
60
60
210
240
180
180
180
120
30

60
60
60
170
180
180
180
180
120
120
30


97.8
91.1
89.2
36.7
1.7
0.0
0.0
100.0

100.0
100.0
100.0
100.0
93.3
56.5
25.0
0.0
0.0
100.0

100.0
98.3
98.3
85.3
37.2
15.0
0.0
0.0
0.0
0.0
100.0


--









Bulletin 239, Heat to Control Insects of Stored Corn 11

TABLE IV.-LETHAL EFFECTS OF DIFFERENT DEGREES OF HEAT ON THE
ADULTS OF Sitophilus (Calendra) oryzae (L.) AS SHOWN BY. THEIR
SURVIVAL WHEN EXPOSED TO CONSTANT TEMPERATURES FOR DIFFERENT
LENGTHS OF TIME.-(Continued).


Time Temperature Number
ex- degrees adults
posed Centigrade used


2 hrs. ........ 43
3 hrs. ........ 43
4 hrs. ........ 43
5 hrs. ........ 43
6 hrs. ........ 43
7 hrs. ........ 43
8 hrs. ........ 43
9 hrs. ........ 43
10 hrs. ....... 43
11 hrs. ........ 43
12 hrs. ........ 43
13 hrs. ........ 43
14 hrs. ........ 43
15 hrs. ........ 43
16 hrs. ........ 43
Check ...........

90 min. ........ 42
2 hrs. ........ 42


Percent |
sur.
vival


99.0
97.8
80.6
52.8
32.8
36.7
12.8
17.1
9.6
4.6
4.6
1.7
0.8
0.8
0.0
100.0

100.0
98.3


Time Temperature Number
ex- degrees adults
posed Centigrade used


3 hrs.
4 hrs.
5 hrs.
6 hrs.
7 hrs.
8 hrs.
9 hrs.
10 hrs.
11 hrs.
12 hrs.
13 hrs.
14 hrs.
15 hrs.
16 hrs.
17 hrs.
18 hrs.
20 hrs.
22 hrs.
Check


....... 42
....... 42
....... 42
....... 42
....... 42
........ 42
........ 42
........ 42
........ 42
........ 42
....... 42
...... 42
........ 42
........ 42
........ 42
........ 42
........ 42
........ 42


Fig. 6.-Chart showing the lethal effect of heat on three kinds of grain
insects exposed to a temperature of 46'C. (114.8F.) for varying
lengths of time.


Percent
sur-
vival


100.0
96.7
93.9
88.3
92.5
84.2
91.7
68.3
50.8
15.0
5.0
13.3
11.1
6.7
4.2
0.8
0.8
0.0
100.0







Florida Agricultural Experiment Station


TABLE V.-LETHAL EFFECT OF DIFFERENT DEGREES OF HEAT ON THE
ADULTS OF Silvanus gemellatus Duv. AS SHOWN BY THEIR SURVIVAL
WHEN EXPOSED TO CONSTANT TEMPERATURES FOR DIFFERENT LENGTHS
OF TIME.


Time Temperature Number
ex- degrees adults
posed Centigrade used

5 min. ........ 51 30
10 min. ....... 51 30
Check .............. 30

5 min ........ 50 30
10 min. ....... 50 30
15 min. ........ 50 30
Check .............. 30

5 min ........ 49 30
10 min........ 49 30
15 min. ....... 49 30
Check .............. 80

5 min ....... 48 30
10 min ........ 48 30
15 min ........ 48 30
30 min ........ 48 30
Check .............. 30

5 min. ........ 47 60
10 min. ........ 47 60
15 min ........ 47 60
30 min. ........ 47 30
45 min ........ 47 60
60 min. ........ 47 60
Check .............. 30

5 min ........ 46 60
10 min. ........ 46 60
15 min......... 46 60
30 min. ........ 46 60
60 min. ........ 46 60
Check .............. 30

5 min. ........ 45 60
10 min........ 45 60


Percent
sur-
vival

0.0
0.0
100.0

0.0
0.0
0.0
100.0

0.0
0.0
0.0
100.0

0.0
0.0
0.0
0.0
100.0

75.0
0.0
0.0
0.0
0.0
0.0
100.0

100.0
95.0
65.0
0.0
0.0
100.0

100.0
100.0


15 min. ........ 45
30 min ........ 45
60 min. ........ 45
90 min. ........ 45
2 hrs. ........ 45
3 hrs ........ 45
Check ..............

30 min. ........ 44
60 min. ........ 44
90 min. ........ 44
2 hrs. ........ 44
3 hrs. ........ 44
4 hrs. ........ 44
5 hrs. ........ 44
6 hrs. ........ 44
Check ..............

60 min ......... 43
90 min. ........ 43
2 hrs. ........ 43
3 hrs ........ 43
4 hrs. ........ 43
5 hrs. ........ 43
6 hrs. ....... 43
Check ..............

2 hrs. ........ 42
3 hrs. ........ 42
4 hrs ........ 42
5 hrs. ........ 42
6 hrs. ........ 42
7 hrs ........ 42
8 hrs ........ 42
9 hrs. ........ 42
15 hrs. ........ 42
Check ...........


The insect showing the greatest susceptibility to


heat was the


square-necked grain beetle, Silvanus gemellatus Duv. A 10-
minute exposure at 47C. (116.60F.) killed all of the adults,
while at 420C. only nine hours were required for killing. The
experimental data are presented in Table V and Fig. 5.
A striking comparison of the effect of heat on the three groups
of insects subjected to constant temperatures for different
lengths of time was obtained when they were exposed to 460
C. (114.80F.) for various time intervals until they were killed.


Time Temperature Number Percent
ex- degrees adults sur-
posed Centigrade used vival


98.3
100.0
0.0
0.0
1.7
0.0
100.0

100.0
78.3
23.3
0.0
0.0
0.0
0.0
0.0
100.0

100.0
100.0
81.7
55.0
11.7
0.0
0.0
100.0

70.0
93.3
29.2
0.0
0.0
0.0
1.1
0.0
0.0
100.0






Bulletin 239, Heat to Control Insects of Stored Corn 13

The rust-red flour beetle showed the greatest resistance to heat,
six hours being required to kill all of the adults. The rice weevils
were dead at the end of two hours and the square-necked grain
weevils were killed by an exposure lasting only 30 minutes. The
data showing the' comparative resistance of the three groups
are presented in Table VI and Fig. 6.

TABLE VI.-COMPARISON OF THE LETHAL EFFECT OF HEAT ON THREE KINDS
OF GRAIN INSECTS EXPOSED TO 460C. (114.80F.) WHEN EXPOSED FOR
DIFFERENT LENGTHS OF TIME.

Percent survival
ex d Tribolim ferrugi- Sitophilus (Cal- Silvanus
neum (Fab.) enra)oryzae gemellatus Duv.

5 min. ................ .... 100.0 100.0
10 min. ................ 100.0 98.9 95.0
15 min. ...... 100.0 97.8 65.0
30 min. ................ 98.9 91.1 0.0
45 min. ............... .... 89.2
60 min. ................| 95.0 36.7
90 min. ............... 83.9 1.7
2 hrs. ............... 71.5 0.0
3 hrs --............ 32.9
4 hrs ............... 13.8
5 hrs. 1.4
6 hrs. ............ 0.0


The Angoumois grain moth, Sitotroga cerealella Oliv., is com-
monly found in stored corn in Florida. Heating tests showed
that an exposure for 30 minutes at 490C. (120.20F.) killed all
of the adults, though two percent of the adults withstood an ex-
posure of fifteen minutes. The larvae and pupae could withstand
a slight increase of heat but could not live through an hour's ex-
posure at 500C. (1220F.).
The slender-horned flour beetle, Gnathocerus maxillosus
(Fab.) showed heat reactions very similar to those of the rice
weevil, all of the adults dying on being exposed to 480C. (118.4
F.) for a period of one-half hour.
The conclusions reached from the foregoing experiments in-
dicated that a minimum temperature of 420C. (107.60F.) main-
tained for about 200 hours or a maximum temperature of 500C.
(122F.) maintained for one hour would kill all stages of the
stored corn insect pests enumerated in this bulletin which are
commonly found in Florida.






Florida Agricultural Experiment Station


HEAT RESISTANCE OF CORN

Having obtained information relative to the lethal amounts
of heat required to kill the insect pests of stored corn, the in-
jurious effect of heat on the corn itself was next determined.
Three varieties of field corn which are well known in Florida
were selected for the study of possible injurious effects of heat
on the germination and plant vigor of the corn. The varieties
used are known as Cuban Yellow Flint (Zea indurata Sturt.),
Whatley (Zea indentata Sturt.), and Tisdale (Zea indentata
Sturt.).
These three varieties of corn were subjected to heat treat-
ment varying from an exposure of 144 hours at 470C. (116.60F.)
to an exposure of 10 minutes at 830C. (181.40F.). The per-
cent of germination of the seed treated 144 hours at 47C. did
not appear to be reduced, and the plants, on growing, did not
appear to be less vigorous than the non-treated plants. Ten
minutes at 83C., however, checked germination, as did a similar
exposure at 800C. (1760F.). Ten minutes at 75C. (167F.)
showed but slight plant injury, while 30 minutes killed all of the
seed. One-half hour at 700C. (1580F.) showed slight injury
while one hour killed the seed. An exposure of three hours at
650C. (1490F.) was successfully resisted but when the exposure
was increased to five hours a definite stunting of the plants was
subsequently noted. Five hours at 600C. (1400F.), however,
did not seriously affect the germination of the seed or vigor of
the plants and five hours at 59C. (138.20F.), 580C. (136.40F.),
57C. (134.6F.), and 56C. (132.80F.), respectively, appeared
to affect the seed very little, if at all, as vigorous plants grew
from the treated seed planted in the field.

HEATING STORED CORN

Having ascertained the lethal amounts of heat necessary for
controlling the insect pests of stored corn, and having determin-
ed that the corn itself is not injured when heated well beyond
the temperature which is necessary to kill the insects, there still
remained the problem of heating the stored corn to the lethal
temperature necessary for insect control.
A typical bright-leaf tobacco barn (see Fig. 7) was selected
for preliminary tests in which approximately 300 bushels of
slip-shucked corn could be heat treated. Weather-boarding 16
feet in length and 8 inches in width was laid lengthwise, with






Florida Agricultural Experiment Station


HEAT RESISTANCE OF CORN

Having obtained information relative to the lethal amounts
of heat required to kill the insect pests of stored corn, the in-
jurious effect of heat on the corn itself was next determined.
Three varieties of field corn which are well known in Florida
were selected for the study of possible injurious effects of heat
on the germination and plant vigor of the corn. The varieties
used are known as Cuban Yellow Flint (Zea indurata Sturt.),
Whatley (Zea indentata Sturt.), and Tisdale (Zea indentata
Sturt.).
These three varieties of corn were subjected to heat treat-
ment varying from an exposure of 144 hours at 470C. (116.60F.)
to an exposure of 10 minutes at 830C. (181.40F.). The per-
cent of germination of the seed treated 144 hours at 47C. did
not appear to be reduced, and the plants, on growing, did not
appear to be less vigorous than the non-treated plants. Ten
minutes at 83C., however, checked germination, as did a similar
exposure at 800C. (1760F.). Ten minutes at 75C. (167F.)
showed but slight plant injury, while 30 minutes killed all of the
seed. One-half hour at 700C. (1580F.) showed slight injury
while one hour killed the seed. An exposure of three hours at
650C. (1490F.) was successfully resisted but when the exposure
was increased to five hours a definite stunting of the plants was
subsequently noted. Five hours at 600C. (1400F.), however,
did not seriously affect the germination of the seed or vigor of
the plants and five hours at 59C. (138.20F.), 580C. (136.40F.),
57C. (134.6F.), and 56C. (132.80F.), respectively, appeared
to affect the seed very little, if at all, as vigorous plants grew
from the treated seed planted in the field.

HEATING STORED CORN

Having ascertained the lethal amounts of heat necessary for
controlling the insect pests of stored corn, and having determin-
ed that the corn itself is not injured when heated well beyond
the temperature which is necessary to kill the insects, there still
remained the problem of heating the stored corn to the lethal
temperature necessary for insect control.
A typical bright-leaf tobacco barn (see Fig. 7) was selected
for preliminary tests in which approximately 300 bushels of
slip-shucked corn could be heat treated. Weather-boarding 16
feet in length and 8 inches in width was laid lengthwise, with






Bulletin 239, Heat to Control Insects of Stored Corn 15


Fig. 7.-A typical log barn used for curing bright leaf tobacco.
about an inch space between the boards, across the lowest tier
poles in the barn which, in turn, were braced with pine saplings,
as illustrated in Fig. 8. Two 16-foot lengths of one-fourth inch
mesh hardware cloth were placed lengthwise in lieu of several
floor boards, in order to provide better means for heat penetra-
tion.
In the first test the flooring did not cover the entire area,
three boards along one side of the barn being omitted to form
an air-shaft which allowed a continuous circulation of the air
under and above the flooring. The 300 bushels of slip-shucked





Florida Agricultural Experiment Station


corn were then placed on the flooring in a pyramidal heap
measuring about seven feet in height and about 12 feet in di-
ameter at the base.


I 1


I 00R6OO _ING y ?-- DWflDWIRE C..LOTH


*PINE

SUPPORT




Fig. 8.-Cross-section of .log barn showing arrangement of tier poles, the
elevated flooring resting on the lowest tier poles, the vents covered
with one-fourth inch mesh hardware cloth, and the six foot pine
saplings used for supporting the flooring.
Thermo-couples were placed beneath the sheaths next to the
infested grain of five representative ears of the slip-shucked
corn. These ears were then distributed at various depths in the


--N.-


~


~


~






Bulletin 239, Heat to Control Insects of Stored Corn 17

mass of corn as indicated in Table VII. Two other thermo-
couples, one of which was placed in a centrally located point in
the air below the flooring and the other in a similar position
above the flooring, were also used. The furnace was then fired
and temperature readings were made from time to time. Table
VII and Fig. 9 present the data which were obtained.


HOURS HEATED
Fig. 9.-Chart showing the temperatures attained in slip-shucked corn
in a tobacco barn during a 48-hour period of heating. Numbers in
the lines indicate the thermo-couples described in Table VII. Line
"A" indicates outside air temperature.

The experiment was begun on January 21, 1931, and continued
for 48 hours. During this time the weather turned cold follow-
ing light showers which wetted the corn before it could be car-
ried into the tobacco barn. As a consequence the cold, wet corn
was heated with great difficulty and but a small part of the 300
bushels reached a temperature sufficiently high to effect a
control of the insects which infested the corn. The corn shucks
undoubtedly insulate the corn grains to such an extent that the
heat obtained in the tobacco barn was insufficient to effect a con-













TABLE VII.-TEMPERATURES ATTAINED IN SLIP-SHUCKED CORN HEATED IN A TOBACCO BARN FOR 48 HOURS.

ILocation of thermo-couples


No. 2
Air, 9% feet
above flooring


C. OF.

S56.2 133.2


63.3 145.9

*16.0 *60.8

69.0 156.2

69.4 156.9

75.3 167.5

78.6 173.5

69.5 157.1

82.8 181.0

83.0 181.4

82.0 179.6

82.0 179.6

78.8 173.9


No. 3 No. 4
In corn, one In Corn, one
foot below sur- foot below sur-
face, one foot face, one foot
above flooring above flooring
away from oven over oven


C. F. O OC. F.


21.8 71.2

23.9 75.0

26.6 79.9

*25.8 *78.4

26.0 78.8

30.2 86.4

35.3 95.5

39.8 103.6

40.3 104.5

42.8 109.0

46.3 115.3

46.8 116.2

48.0 118.4

46.7 116.1


23.5 74.3

23.5 74.3

27.9 82.2

*23.5 *74.3

28.0 82.4

31.0 87:8

36.3 97.3

43.7 110.7

43.0 109.4

46.8 116.2

50.0 122.0

50.0 122.0

57.7 135.9

48.6 119.5


No. 5
In corn, 3
feet below sur-
face, 4 feet
above flooring


No. 6
In corn, 4
feet below
surface, 3 feet
above flooring


C. OF. C. OF.


13.5 56.3

15.0 59.0

18.9 66.0

*21.2 *70.2

23.1 73.6

26.8 80.2

29.4 84.9

32.5 90.5

32.9 91.2

33.2 91.8

34.0 93.2

33.4 92.1

33.4 92.1

32.0 89.6


19.8 67.6

21.2 70.2

25.0 77.0

*25.0 *77.0

25.5 77.9

28.0 82.4

31.2 88.0

35.2 95.4

35.8 96.4

38.2 100.8

40.6 105.1

40.4 104.7

43.5 110.3

41.2 106.2


No. 7
In corn,
center
of pile


OC. oF.


18.6 65.5

19.0 66.2

23.5 74.3

*24.4 *75.9

25.3 77.5

26.6 79.9

30.4 86.7

33.5 92.3

34.0 93.2

34.4 93.9

37.0 98.6

37.0 98.6

37.4 99.3

37.0 98.6


Time
elapsed
after firing
the furnace


*After the furnace had been fired for eight hours the 2x4 inch braces used to support the flooring buckled. The fire was put out and the barn
was cooled sufficiently to allow the substitution of pine saplings for the 2x4 inch braces.


No. 1
Air, 3
feet below
flooring


4 hours ........

5 hours

7 hours

*9 hours

10 hours ........

14 hours

17 hours

24 hours ........

25 hours ......

28 hours ........

34 hours .....

35 hours ..

40 hours

48 hours ........


-A-
Air tempera-
ture outside
of barn

C. oF.

7.0 44.6

8.0 46.4 *

10.0 50.0

7.2 45.0

7.0 44.6

3.0 37.4

3.0 37.4

3.0 37.4

3.0 37.4

10.0 50.0 r-

15.0 59.0

13.0 55.4 ,

1.0 33.8

-1.0 30.2


oC. oF.

90.6 195.1


79.9 175.8

*20.6 *69.1

69.0 156.2

76.0 168.8

58.3 136.9

80.4 176.7

69.5 157.1

83.5 182.3

100.0 212.0

96.2 205.2

118.0 244.4

107.3 225.1


-






Bulletin 239, Heat to Control Insects of Stored Corn 19

trol. When wet, the shucks apparently offered especial resist-
ance to heat penetration.
After the furnace had been fired for eight hours the experi-
ment was interrupted since the six-foot 2 x 4" braces originally
used to support the flooring buckled. In order to avoid the pos-
sibility of having the flooring collapse, the fire was put out and
the barn cooled until the 2 x 4 inch braces could be replaced by
six foot pine saplings measuring between four and six inches
in diameter, after which the furnace was again fired. The pine
saplings were subsequently found to be satisfactory since con-
tinued heating did not cause them to buckle.
The temperature in the center of the pile of corn reached
33.5C. (92.30F.) after a period of 24 hours and increased but
little during the additional 24 hours of heating, reaching a max-
imum temperature of 37.4C. (99.3F.). The temperature of
the corn near the flooring over the oven increased gradually until
a maximum of 57.70C. (135.90F.) was reached. The temperature
,of the air in the barn fluctuated in accordance with the inten-
sity of the fire in the furnace.
The conclusion reached at the end of this test indicated that
in a tobacco barn slip-shucked corn could not be successfully
heat-treated for insect pest control. Additional experimenta-
tion with shucked corn was planned immediately.
The second experiment was started as soon as all of the corn
had been shucked. The corn was then spread evenly over the
floor in a layer measuring about three feet in depth. The out-
side air temperature varied from 10C. to 20C. (500F. to 68
F.) and consequently a temperature of sufficient effectiveness
for insect control was reached after an 18-hour period of firing.
The fact that the corn had been shucked and spread out added
so to the effectiveness of the heat treatment that a satisfactory
kill of the insects usually infesting corn was assured during this
test. Continued heating up to 47.90C. (118.20F.) and an ad-
ditional hour at this temperature-the coolest location measured
-is sufficient to kill all stages of the insect pests infesting corn
in Florida.
Seed corn, however, should not be heat-treated together with
the other corn in the barn because the temperatures attained
throughout the barn are not uniform, some of the corn having
reached temperatures which killed the seed, thereby stopping
germination and rendering the corn unfit for planting.






Florida Agricultural Experiment Station


It is a significant fact that thermo-couple number 8, imbedded
in a mass of shelled corn kernels, failed to register over 37.70C.
(99.90F.). Heat-treatment, therefore, to be effective must be
applied to the corn on the cobs because heat penetration into
a mass of kernels is too slow to be effective when large masses
of kernels are heat-treated in a tobacco barn. The data secured
in this test are presented in Table VIII and Fig. 10.
The third experiment also was conducted with shucked corn,
but the entire floor area was boarded over and the corn was
spread evenly over the entire flooring. As a consequence there
was no air shaft connecting the air below and above the corn.
The heated air therefore passed through the corn before it
reached the air above, and consequently some of the corn reached


Fig. 10.-Chart showing the temperatures attained in a three-foot layer
of shucked corn heated in a tobacco barn for 18 hours. The num-
bers in the lines indicate the thermo-couples described in Table VIII.
Line "A" indicates the outside air temperature readings.






Bulletin 239, Heat to Control Insects of Stored Corn 21

higher temperatures than the upper stratum of air. At the
end of 13 hours all of the corn was heated above the tempera-
ture required to kill the insects. Had the higher temperatures
been maintained for a period of but 10 minutes a satisfactory
kill would have been obtained. The pocket of shelled corn ker-
nels which was again included in the test, however, did not at-
tain more than 38.60C. (101.50F.).
The barn was vigorously heated during the experiment,
though after the first reading the temperature of the air below
the flooring could not be measured, a condition due to the ac-
cidental severance of the thermo-couple wire installed for taking
those particular temperature readings. The data for this ex-
periment are presented in Table IX and Fig. 11.


HOURS HEATED
Fig. 11.-Chart showing the temperatures attained in a 2%-foot layer
of shucked corn heated in a tobacco barn for 13 hours. The numbers
in the lines indicate the thermo-couples described in Table IX.













TABLE VIII.-TEMPERATURES ATTAINED IN A THREE-FOOT LAYER OF SHUCKED CORN HEATED IN A TOBACCO BARN
FOR 18 HOURS.
SLocation of thermo-couples


No. 1
Air, 3
feet below
flooring


No. 2
Air, 9% feet
above flooring


No. 3
In corn, 3
feet below
surface on
flooring in
center of
barn


oC. OF. C. OF. C.

27.9 82.2 25.7 78.3 18.0
57.5 135.4 40.2 104.4 18.0
95.0. 203.0 73.0 163.4 53.7 1
92.0 197.6 83.6 182.5 55.8 1
112.7 234.9 89.0 192.2 73.7 1
103.0 217.4 83.0 181.4 75.0 1


No. 4 No. 5
In corn, 2% In corn, 1%
Feet below sur- feet below sur-
face, 1 foot face, 1% feet
above flooring above flooring
in center in center
of barn of barn


oC. F. C.


No. 6
In corn, No. 7
% foot be- In corn, % foot
low surface below surface
2% feet 21/ feet above
above floor- flooring over
ing in center furnace
of barn


No. 8
In heap of
shelled corn
1 foot deep
on floor
away from
furnace


F. IC. F. oC. OF.

69.1 20.0 68.0 21.0 69.8
68.0 23.0 73.4 23.5 74.3
107.8 51.3 124.3 54.4 129.9
111.6 53.9 129.0 57.1 134.8
131.0 67.1 152.8 70.0 158.0
132.1 67.0 152.6 69.3 156.7


TABLE IX.-TEMPERATURES ATTAINED IN A 21/-FooT LAYER OF SHUCKED CORN HEATED IN A TOBACCO BARN FOR 13 HOURS.

Location of thermo-couples
No. 6 No. 7 No. 8
No. 3 No. 4 No. 5 In corn, 11% In corn, 1 In shelled
Time No. 1 In corn, 21 In corn, 2% In corn, 2 feet below foot below corn, 1 foot
elapsed Air, 3 No. 2 feet below sur- feet below sur- feet below sur- surface, 1 foot surface, 1% thick, 1% feet Air tempera-
after firing feet below Air, 91 feet face on floor- face, on floor- face, 1 foot above flooring feet above below surface ture outside
the furnace flooring above flooring ing in center ing over hard- above flooring in center flooring away away from of barn
Sof barn ware cloth near barn door of barn from furnace furnace

C. F. C. F. C. F. C. F. | C. F. C. F. | C. F. C. F.

1 hour 94.8 202.7 35.0 95.0 37.1 98.8 36.0 96.8 38.0 100.4 35.5 95.9 32.1 89.8 33.8 92.8 22.0 71.6
8 hours. 56.6 133.9 73.7 164.7 109.0 228.2 54.5 130.1 54.2 129.6 43.2 109.8 34.1 93.4 8.0 46.4
13 hours .. .... .... 59.8 139.6 78.5 173.3 110.1 230.2 68.1 154.6 66.7 152.0 55.3 131.6 38.6 101.5 6.0 42.8


Time
elapsed
after firing
the furnace


14 hour
1 hour
7 hours
8 hours
17 hours
18 hours


-A--
Air tempera-
ture outside


I-


I






Bulletin 239, Heat to Control Insects of Stored Corn 231

The two preceding experiments indicate strongly that heat-
treatment of corn for the control of the insect pests of stored
grain can be successfully conducted.
There are advantages to be found in heat-treating stored corn
for insect control rather than treating it by the use of either
fumigation or poisoning methods. In the first place, if the corn
is to be heat-treated it can be picked early, a factor which elim-
inates field losses due to insect, bird, and storm damage. Early
picking is furthermore advisable because it is accomplished with
much greater ease, especially when velvet beans are planted in
the corn. Without heat-treatment, however, the early picking
and storing of corn tends to favor natural "heating" and sour-
ing of the more or less green corn, besides stimulating the breed-
ing of fungus diseases. Heat-treatment prevents these dis-
advantages by thoroughly drying the corn. The corn, however,
to be successfully heat-treated, must be shucked, but after the
shucking is accomplished it can be stored in a smaller space
than that which is necessary for unshucked or even slip-shucked
corn. Finally, the materials for heat-treating corn are always
available, and there is relatively little danger attached to firing
the furnace for heat-treatment. In case a new infestation oc-
curs later in the year, the corn can be treated again without dif-
ficulty. The tobacco barn or corn crib equipped for heating also
provides an excellent storage place for the corn.
The disadvantages of the heat-treatment method of insect
control involve the initial cost and depreciation of the furnace
and flues and the labor costs attached to shucking the corn.
But as a matter of fact, the use of any method of controlling
the insect pests of stored corn, such as fumigation or poisoning,
entails shucking of the corn.

SUMMARY AND CONCLUSIONS

The rust-red flour beetle (Tribolium ferrugineum Fab.), the
rice weevil (Sitopholus (Calendra) oryzae (L.)), the square
necked grain beetle (Silvanus gemellatus Duv.), the Angoumois
grain moth (Sitotroga cerealella Oliv.), and the slender-horned
flour beetle (Gnathocerus maxillosus Fab.), are killed when ex-
posed to 500C. (1220F.) for one hour. Exposure to a tempera-
ture of 420C. (107.60F.) for 200 hours is also lethal. The tem-
peratures between 500C. and 420C. will kill all of the insect
stages according to the experimentally determined lengths of
exposure.






Florida Agricultural Experiment Station


The pupae resist a given temperature for a longer period of
time than the larvae, which in turn, are able to resist longer
exposures than the egg and adult stages.
Young adults can resist more heat than older ones.
Three varieties of corn well known in Florida, Cuban Yellow
Flint (Zea indurata Sturt.), Whatley (Zea indentata Sturt.),
and Tisdale (Zea indentata Sturt.) were heat-treated to de-
termine the limits of heat exposures which did not affect germ-
ination or subsequent plant vigor.
An exposure to a temperature of 47C. (116.60F.) for 144
hours did not reduce the germination percent or the vigor of
the growing plants. Five hours at 560C. (132.80F.), 570C.
(134.60F.), 58C. (136.40F.), and 590C. (138.20F.) appeared to
affect the seed very little, if at all, as vigorous plants grew from
the treated seed which were planted in the field. An exposure
to a temperature of 700C. (1580F.) for one-half hour showed
but slight injury, while one hour's exposure killed the seed. Ten
minutes at 800C. (1760F.) killed the seed.
Slip-shucked corn piled in a pyramidal heap on flooring built
on the lowest tier poles of a tobacco barn cannot be effectively
heated for the control of insect pests of stored corn.
Shucked corn, however, when spread to a depth of 3 feet on
the flooring can be effectively heat-treated with an 18-hour ex-
posure and with a 13-hour exposure when spread to a depth of
21/2 feet, if the air in the tobacco barn is maintained at a min-
imum temperature of 830C. (181.40F.). When the outside air
temperature falls below 100C. (50F.), longer exposures are
necessary.
Seed corn should not be heated together with the corn to be
used for feeding purposes, since the higher temperatures which
are reached in the barn will injure germination and plant vigor.




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