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L- nr.T2 7lS58
'.' S. uEFARTMENT OF AGRICULTURE
Marketing Research Report No.272
Treatments for
the Protection of
Stored Southern-Grown Corn
from Rice Weevil Attack
— Exploratory Tests ~
Marketing Research Division
Agricultural Marketing Service
U.S. DEPARTMENT OF AGRICULTURE
WARNING
No tolerances have been established for the use of lindane,
methoxychlor, or ryania as insecticidal applications to the entire
bulk of stored grain for the prevention of insect infestation. The tests
reported herein were exploratory studies to develop information that
could be used in considering the establishment of tolerances. Until
such tolerances are announced, lindane, methoxychlor, or ryania
protective treatments should not be used. A tolerance of 2 p. p.m.
for methoxychlor in grain permits the spraying of bin walls and some
surface applications, but is not high enough to cover protective treat-
ments in the sense considered here.
CONTENTS
Page
Summary 1
Introduction 2
Techniques 2
Tests with lindane 4
Tests with malathion 6
Tests with methoxychlor 8
Tests with synergized pyrethrum 12
Tests with ryania 16
Findings 19
Washington, D. C. September 1958
For sale by the Superintendent of Documents, U. S. Government Printing Office
Washington 25, D. C. - Price 15 cents
TREATMENTS FOR THE PROTECTION OF STORED SOUTHERN-GROWN
CORN FROM RICE WEEVIL ATTACK— EXPLORATORY TESTS
By D. W. La Hue, Herbert Womack, and B. W. Clements, Jr.
Stored-Product Insects Laboratory-
Georgia Coastal Plain Experiment Station
Tifton, Ga.-"-
SUMMARY
Exploratory studies were made at Tifton, Ga. , between 1951 and 1958, on the use
of lindane, malathion, methoxychlor, synergized pyrethrum, and ryania as insecticides
to protect stored corn against rice weevil infestation. Results were to be used as a basis
for evaluation studies on a commercial scale. Samples of treated ear corn in the husks,
husked ear corn, and shelled corn were exposed for varying lengths of storage in 1 -gal-
lon jars and 5-cubic-foot drum-type bins. Protection was measured by the increase of
infested ears and the increase in weevil-damaged kernels, compared to increases in
untreated checks, during the selected storage periods.
Lindane protective dusts and sprays applied at dosages of 2 to 5 parts per million
(p. p.m.) of lindane were highly effective in protecting husked ear corn and shelled corn
for periods up to 18 months.
Malathion protective dusts and sprays were effective at dosage rates of 10 p. p.m.
and above on shelled corn. Wettable powder sprays were more effective than emulsion
sprays.
Methoxychlor protective dusts applied at dosages of 100 to 200 p. p. mi. of methoxy-
chlor to husked ear corn and shelled corn were effective in preventing damage or infes-
tation, but emulsion-type sprays at the same dosages were ineffective.
Synergized pyrethrum protective dusts and sprays were not too effective at dosage
rates of 0.9 to I. 42 p. p.m., but I inadvertent application at 36 p. p. m. of pyrethrins
quickly suppressed the self-contained weevil population and finally wiped it out.
Ryania protective dusts, composed of ground ryania stems containing approximately
0.25 percent ryanodine, with and without the synergists N-propyl isome and sulfoxide,
gave excellent protection against infestation and damage when applied to either husked
ear corn or shelled corn at 50 to 100 pounds per 1,000 bushels.
Three materials, methoxychlor, malathion, and synergized pyrethrum, were
selected for future large-scale evaluation studies. Ryania and lindane were dropped
from further consideration because it appeared improbable that residue tolerances could
be established in the foreseeable future in view of unresolved residue and analytical
problems.
^ This laboratcffy is a field station of the Stored-Product Insects Section, Biological Sciences Branch, Marketing Research
Division, Agricultural Marketing Service, U. S. Department of Agriculture. Aklee Cagle, W. O. Farmer, and Huey Hall, of
the laboratory staff, assisted in many phases of these studies.
-I
INTRODUCTI ON
The rice weevil, Sitophilus oryza (L.), is a serious pest of stored corn in the
Southern States, from Virginia to Texas. Not many storage structures in this area are
tight enough to permit fumigation, so an urgent need exists for some other nneans of
preventing rice weevil infestation. The most promising control method other than fumi-
gation appeared to be a protective treatment that could be applied to corn after harvest,
the dual objective being to destroy the rice weevil infestation that had already been
started in the field as the corn matured and to protect the corn from reinfestation from
other sources during storage. Such studies were begun at Tifton, Ga. , in 1951 and con-
tinued until 1958. The Tifton location was considered representative of the Southern
area as far as rice weevil infestation in stored corn was concerned.
Other insects are often found in stored corn in the South, including "bran bugs, "
such as the flour beetles, saw-toothed grain beetle, flat grain beetle, and foreign grain
beetle, and moths such as the Indian-meal moth and Angoumiois grain moth. It was con-
sidered that a satisfactory protective treatment against the rice weevil would control the
bran bugs. Infestation by the Indian-meal moth is confined to the surface layer of binned
shelled corn, and it was considered that supplementary applications of the formulation
used as a protective treatment would be necessary on the top surface. Infestation of
unhusked corn, which is the form of most Southern cribbed corn, by the Angoumois
grain moth is not frequent.
This report presents the results of exploratory tests made with five insecticides- -
lindane, malathion, methoxychlor, synergized pyrethrumi, and ryania. At the start of
the studies, these materials were considered as offering possibilities at application
rates that would not create objectionable residues, but as these studies and others else-
where were continued, the attitudes on acceptability of certain insecticides were altered
somewhat. The experimental data on these insecticides are presented with the others,
nevertheless, as a matter of record.
This study is part of a national program to improve the marketing of farm products
including their protection during storage.
TECHNIQUES
Jar Test
Some of the tests with protective dusts were conducted in wide -mouthed gallon jars
with samples of shelled corn weighing approximately 5 pounds. The samples were
treated by placing the shelled corn and the appropriate amount of dust in a jar, capping
it, and rolling and shaking it to distribute the dust. The uncapped jars were then exposei
to weevil infestation in an unheated building. In some instances, as indicated in the text,
weevils were confined on the samples by leaving the caps on the jars.
Drum-type Bin Test
Drum-type bins were made by rolling 2- x 8-foot sheets of masonite into cylinders
and fastening the overlapping edges with roundheaded stove bolts. Each cylinder was
placed upright on a 2-foot square of masonite and the shelled or ear corn was placed in
it (fig. 1). Each drum contained about 5 cubic feet and could hold 4 bushels of shelled
corn or 2 bushels of ear corn. These bins were placed at random on the second floor
of an unheated and rather open barn on the grounds of the Georgia Coastal Plain Experi-
ment Station, where they were exposed to a vigorous infestation of rice weevils in in-
fested corn stored in the same building. Although the bins were tight, their open tops
provided adequate opportunity for invasion of weevils from nearby sources.
-2-
BN-6654
Figure 1. --View of drum-type small bins arranged in random pattern in unhealed barn.
The protective treatments were applied by two methods, both of which were con-
sidered to distribute the insecticide adequately. With one method, the sample of ear or
shelled corn was placed in a tight drum, and the proper amount of protective dust added.
The drum was sealed and then rolled to distribute the dust. With the second method,
either protective dusts or sprays were applied to the samples as they were transferred
into the drum -type bins by a belt conveyor.
Chemical Analysis of Residues
The residue analyses for samples treated with lindane, malathion, methoxychlor,
and synergized pyrethrum were made by the Chemical Unit, Stored-Product Insects
Section, Savannah, Ga.
Measurement of Protection
The degree of protection against insect infestation and damage provided by the
various materials under test was determined by several methods. In tests with shelled
corn, the original lot from which all the samples in a series were prepared was well
mixed and the average percentage of weevil-damaged kernels determined. Not all
weevil-damaged kernels were necessarily infested at the pre -treatment determination,
but any appreciable percentage of damaged kernels was considered evidence of a vig-
orous infestation. In the final readings, the weevil-damaged kernels represented the
total amount of weevil attack, and the damage could have been caused by several con-
secutive generations of weevils. The percentages of weevil-damaged kernels at the
beginning and end of storage periods were sometimes supplemented by counts of the
number of dead and live weevils present per unit measure at selected sampling periods.
-3
In tests with ear corn, the percentage of weevil-damaged kernels was supplemented
by counts of infested ears. At the start of storage tests, the number of infested ears
was determined by evidences of weevils at the time the ears were husked- -either dam-
age or live weevils. At the end of the storage tests, the determination of infested ears
was based solely on visible weevil damage. Companion counts of weevil-damaged ker-
nels from ear corn were made by shelling a number of random -selected ears, and by
sampling the shelled corn to learn the percentage of weevil-damaged kernels.
TESTS WITH LINDANE
Two series of tests (A and B) were made with lindane, the first in 1952 and the
second in 1954-55.
Series A
Two lots of Dixie 18 hybrid corn of the 1951 crop were used. For the first lot,
husked ear corn with a moisture content of 16 to 18 percent and with 28 percent of the
ears infested and 20.4 percent of the kernels weevil-damaged was used. This was
treated with 0. 5 -percent lindane dust in an inorganic carrier at application rates
of 2 and 4 p. p.m. of lindane, and was stored for 8 months, from December 1951
until August 1952. Four replicate drum -type bins containing 2 bushels each were
set up for each treatment level. After 8 months' storage, the corn was removed
from the bins and the percentages of infested ears and of weevil-damaged ker-
nels were recorded;
The second lot was shelled, and contained 23.7 percent of weevil-damaged kernels.
The moisture content was not determined but was below that of the first lot. The lot
was divided, and half was fumigated to destroy the self-contained weevil population.
Two replicate samples of 3 bushels of each portion were dusted with 0.5 percent lindane
in an inorganic carrier, at an application rate of 4 p. p.m. , and each replicate was
stored in a drum-type bin for 8 months, from March until November 1952. The corn
was then rennoved from the bins and the percentage of weevil-damaged kernels deter-
mined.
The results of this series of tests are presented in table 1. In the shelled corn
where the self-contained infestation was killed by fumigation, very little infestation
from outside sources occurred in the 8 months, as evidenced by an increase of only
2.1 points in the percentage of weevil-damaged kernels. The unfumigated shelled corn
and the ear corn showed greater increases in damaged kernels, but the degree of pro-
tection as compared with the checks was still very favorable.
Series B
Three lots of Dixie 18 hybrid- shelled corn were given identical treatments in this
series except that they were stored for different lengths of time, concurrent with tests
in Series M (p. 18), A single -source lot of corn was used, but, as each lot was treated
on a different date, the percentages of weevil-damaged kernels varied a few points.
Nine treatments were applied to replicates of 3 samples in each lot. Dusts were
applied at rates of 2 and 3 p. p.m. of lindane, and 3 volumes of dust were applied at
each rate by using concentrations of 0.5, 1, and 2 percent lindane in the dusts. The
diluent in these dusts was an organic material, corncob flour, because other work had
shown that an inorganic diluent as used in series A would cause a gritty feeling in the
corn with resultant downgrading. Sprays were applied at rates of 3 and 5 p. p.m. of
lindane, and at the 5 p. p.m. level the spray was applied at 2 concentrations so as to
make 1 application half the volume of the other.
-4-
Table 1. --Average increase in infested ears and in weevil-damaged kernels during 8 months'
storage following application of lindane dusts to husked ear com and shelled com
Type of com and
application rate
Pretreatment
preparation
Fteplica-
tions
Increase in
percentage of
weevil-infested
ears
Increaise in
percentage of
weevi 1-damaged
kernels
Ear com:
2 p.p.m
3 p.p.m
Check
Fumigated
Unfumigated
Fumigated
Unfumigated
Mumber
U
2
2
2
2
Points,
14.9
62.9
Points
12.6
4.7
40.5
Shelled com:
4- p.p.m
Check
2.1
12.1
40.9
64.2
The first lot, which was stored for 9 months, from January 1955 until October 1955,
had 10.52 percent weevil-damaged kernels at the start, and a moisture content of less
than 13 percent; the second lot, 4. 3 percent weevil-damaged kernels and 14.01 percent
moisture content; the third lot, 4.6 percent damaged kernels and 13.71 percent mois-
ture. The second lot was stored for 15 months, from October 1954 until January 1956,
and the third lot for 18 months, from November 1954 until May 1956.
The lindane residues on the treated samples in the first lot after 3 months in stor-
age were chemically analyzed to indicate the relationship between the application rate
and the residue.
The results of the performance tests are presented in table 2. Both dust and spray
formulations at rates of 2 and 3 p.p.nn. of lindane protected the shelled corn from rice
weevil infestation for periods as long as 18 months.
The residues of lindane found by chemical analysis are tabulated below. In no case
did the residue exceed the application rate, and the overall average of residues was 43
percent of the applied rates.
Application rate and
concentration of lindane
Residue (p.p.m.)
Application rate and
concentration of lindane
Residue (p.p.m.)
Dusts
Sprays
2 p.p.m.
3 p. p. m.
0. 5 percent
1.30
0. 26 percent
.65
1.00
.65
1 percent
1.90
1.30
5 p. p. m.
2 percent
.65
0. 87 percent
1.90
.75
1.30
3 p. p. m.
0. 44 percent
2.00
75
0. 5 percent
1.30
1.90
1 percent
1.60
1.30
2 percent
1.30
.75
-5-
Table 2.— Average increase in weevil-damaged kernels and in the number of live weevils per gallon during 9, 15, and
18 months' storage following application of lindane dusts and sprays at various rates; 3 replications
Type and application
rate of formulation,
and concentration
of lindane
Dusts, 2 p. p.m. :
0.5 percent
1 percent
2 percent
Dusts, 3 p. p.m. :
0 . 5 percent
1 percent
2 percent
Spray, 3 p. p.m.:
0.26 percent (8 gal./l,000
tiu.) r...
Spray, 5 p. p.m. :
0.87 percent {A- gal./l,000
bu.)
0.44 percent (8 gal./l,000
bu.)
Check
9 months ' storage
Live weevils
per gallon
of com
f/umber
13.2
6.3
5.3
4
2.7
2.7
4
2.7
313
Increase in
percentage
of weevil-
damaged
kernels
Points
15 months ' storage
Live weevils
per gallon
of com
//umber
3
4
2
0
1
102
Increase in
percentage
of weevil-
damaged
kernels
18 months ' storage
Points
11.4
13.7
6.0
8.4
5.7
4.7
8.0
5.7
3.4
65.0
Live weevils
per gallon
of com
t/uTjiber
1
1
0
0
0
135
Increase in
percentage
of weevil-
damaged
kernels
Points
12.0
7.0
9.4
3.4
8.7
16.7
3.7
8.7
4.0
63.0
Discussion
These tests demonstrated that lindane protective treatments, either dusts or
sprays, gave excellent protection to stored ear or shelled corn, at application rates
ranging from 2 to 5 p. p.m. of lindane, for periods up to 18 months.
TESTS WI TH MALATHION
Two series of tests (C and D) were made with malathion, 1 in 1954-55, and the
other in 1955-56.
Series C
This series paralleled series B, G, and M in that 3 lots of Dixie 18 hybrid shelled
corn were given identical treatments but stored for 9, 15, and 18 months, respectively.
Dusts composed of 0.25 percent malathion in wheat flour were applied at rates of 1, 2,
and 5 p. p.m. of malathion; emulsion-type sprays were applied at 20 p. p.m. of mala-
thion. The dust and spray applications were made in the same manner as described for
series B.
The first lot had 10. 52 percent of weevil-damaged kernels, and a moisture con-
tent of less than 13 percent. It was stored from January until October 1955. The second
lot had 4.3 percent of weevil-damaged kernels and 14.01 percent moisture. It was stored
from October 1954 until January 1956. The third lot had 4.6 percent of weevil-damaged
kernels and 13.71 percent moisture. It was stored from November 1954 until May 1956.
The malathion residues on the treated samples in the first lot were chemically
analyzed after the first 3 months in storage, to indicate the relationship between the
application rate and the residue.
The results of the performance tests are given in table 3. It was demionstrated that
an effective rate for dust application would need to be 3 p. p.m. of malathion or above.
The emulsion spray application at 20 p. p.m. of malathion was highly effective in pro-
tecting the shelled corn.
-6-
Table 3. --Average increase in weevil-damaged kernels and in nximber of live weevils per gallon during 9, 15, and 18
months ' storage following application of malathion dusts and sprays at various rates
Type and application
rate of fonmilation
Replica-
tions
9 months ' storage
Live weevils
per gallon
of com
Increase in
percentage
of weevil-
damaged
kernels
15 months ' storage
Live weevils
per gallon
of com
Increase in
percentage
of weevil-
damaged
kernels
18 months ' storage
Live weevils
per gallon
of com
Increase in
percentage
of weevil-
damaged
kernels
Dust:
1 p. p.m.,
2 p. p.m. .
3 p. p.m. .
Spray:
20 p. p.m.
Check
Number
3
3
3
Number
198
21
12
3
313
Points
Number
200
230
135
1
102
Points
61.7
32.7
19.0
.7
65.3
Number
285
15-4
17
1
135
Points
50.0
20.7
K.4
5.4
63.0
The residues found on the samples of shelled corn after 3 months of storage were
all less than 1 p. p.m. , which at that time was the limit of sensitivity of the analytical
method.
Series D
This series of tests was conducted in gallon jars, following the completion of part
of series C, to define better the type of formulation and the range of effective applica-
tion rates, as a prelude to large bin tests to be made later. Samples from 1 lot of Dixie
18 hybrid shelled corn, containing 5.1 percent of weevil-damaged kernels and an un-
determined moisture content, were treated with dusts composed of 0.5 percent malathion
in wheat flour, and with emulsion-type sprays, at rates of 5, 7.5, and 10 p. p.m. of
malathion. A second lot of Dixie 18 corn from the same source was carefully handpicked
to eliminate all ears showing evidence of weevil infestation or damage, then shelled
and treated at the same rates as the first lot. To insure uniform distribution of the in-
secticide, 3 -bushel lots were treated. In each instance 4 replicated samples were
treated with each application rate, then emptied into drum -type bins. One week later,
1 -gallon samples were taken by probing fromi each replicate for the jar tests, and the
remainder was discarded. The samples from the first lot, which contained an average
of 5. 1 percent weevil-damaged kernels, were held in jars for further observation. Two
hundred adult weevils were confined on each sample from the second lot, which contained
no weevil-damaged kernels. The weevils were added to each jar, which was then capped.
This technique was used to demonstrate the amount of protection against damage from
invading insects, as compared with that against a self-contained infestation, since pre-
vious experience had indicated that protection was better against invading weevils. Rec-
ords were made of the mortality of adult weevils in the samples after a selected expo-
sure period, and also of the subsequent emergence from eggs laid during the exposure
period.
The third lot was U. S. 13 hybrid corn, which is not as hard as Dixie 18 and there-
fore more susceptible to infestation. The percentage of weevil-damaged kernels was
6.45 at the start of the tests, and the moisture content was 14. 1 percent. In this group,
the relative effectiveness of dusts and wettable powder sprays was compared, and rep-
licate samples of 3 bushels each were treated with dusts at rates of 7. 5, 10, and 15
p. p.m. of malathion, and with sprays at 5, 7.5, 10, and 15 p. p.m. One-gallon samples
were taken from each replicate for the jar tests. These tests were conducted between
December 1955 and June 1956.
The results are presented in table 4. Two points are demonstrated by these data.
First, the dust formulations produced greater mortality of adults and reduced the sub-
sequent populations to a greater degree than did the emulsion spray. In turn, the wet-
table powder sprays slightly outperformed the dusts. Second, the invading weevils, as
•7-
represented by the adults confined on the treated samples, were killed to a greater de-
gree than were the self-contained infestations, and the subsequent developnnent and
emergence was less than in the self-contained infestations.
Table 4. --Percentage of dead v/eevils in those removed at end of first storage period, number of weevils emerging sub-
sequently, and increase in percentage of weevil-damaged kernels following treatment of shelled com with various
fonmilations and rates of malathion dusts and sprays; 4 replications
Type of infestation, type
of fomulation, and
application rate
First storage period
(20 to 40 days)
Second storage period
ending 100 days
after treatment
Third storage period
ending 160-180 days
after treatment
Percentage of
dead weevils
in those re-
moved
Increase in
percentage
of weevil-
damaged
kernels
Weevils emerging since
first period
Weevils emerg-
ing since
second
period
Further in-
crease in
percentage
of weevil-
damaged
kernels
Self-contained infestation:
Dusts
5 p.p.m
7.5 p.p.m.
10 p.p.m
Check
Percent
28.7
48.8
76.8
11.7
18.9
36.5
59.4
9.9
80.3
86.9
93.9
18.4
74.5
61.3
84.3
15.2
54.4
68.8
84.6
6.1
57.9
74.7
84.3
93.6
7.8
Points
3.4
2.3
.3
6.1
3.0
.6
0
-.3
5.8
Nvmber
162.8
34.3
15.8
281.0
102.5
48.0
22.5
311.3
18.3
8.3
3.8
55.3
30.5
10.3
5.0
44.8
153.3
86.5
27.0
346.0
111.5
50.8
28.3
10.0
371.8
.Vuwber
266.0
81.5
80.0
525.3
312.3
143.3
100.5
372.0
41.5
19.8
7.5
236.5
47.0
23,5
9.3
219.8
87.3
39.5
18.8
449.3
65.0
36.3
20.8
10.0
590.5
Points
Qmilsion sprays
5 p.p.m
7.5 p.p.m
10 p.p.m
Check. ...•
200 weevils added:
Dusts
5 p.p.m
7.5 p.p.m
10 p.p.m
Check
Emulsion sprays
5 p.p.m
7.5 p.p.m
10 p.p.m
Check
Self-contained infestation:
7.5 p.p.m
15 p.p.m
0.3
.6
.4
74.6
5 p.p.m
7.5 p.p.m
10 p.p.m
15 p.p.m
Check
2.8
1.0
.4
0
71.0
Discussion
The results of these series indicate that an effective application rate of malathion
would be between 10 and 15 p.p.m. , and that dusts or wettable powder sprays would be
preferable to emulsion-type sprays.
TESTS WITH METHOXYCHLOR
Three series of tests were made with methoxychlor--Series E in 1952, Series F in
1953, and Series G in 1954-55.
-8-
Series E
Two lots of Dixie 18 hybrid corn of the 1951 crop were used in tests parallel to
series A. In the first lot, husked ear corn with a moisture content of 16 to 18 percent
and with 28 percent of the ears infested and 20.4 percent of the kernels weevil-dam-
aged was treated with 10 percent methoxychlor in an inorganic diluent at application
rates of 100 and 200 p.p.m. of methoxychlor, and stored from December 1951 until
August 1952. Four replicate 2-bushel samples of each treatment were placed in drum-
type bins and stored for the 8 months, after which the corn was removed and the per-
centages of infested ears and of weevil-damaged kernels were recorded.
The second lot was shelled, and had 23.7 percent of weevil-damaged kernels. The
moisture content was not determined. Half was fumigated to destroy the self-contained
weevil infestation. Two replicate samples of 3 bushels of each portion were dusted with
10 percent methoxychlor in an inorganic diluent, at an application rate of 200 p.p.m. of
methoxychlor, and each replicate was stored in a drum -type bin for 8 months from
March until November 1952. The corn was then removed from the bins and the per-
centage of weevil-damaged kernels determined.
The results are presented in table 5. In the shelled corn, where the self-contained
infestation was killed by fumigation, very little infestation from outside sources occured
in the 8 months, as evidenced by only a 2. 1 increase in the percentage of weevil-dam-
aged kernels. The unfumigated shelled corn and the ear corn showed greater increases
in damaged kernels, but the degree of protection as compared with the checks was still
very favorable.
Table 5. --Average increase in infested ears and in weevi 1-damaged kernels during 8 months'
storage following application of methoxychlor dusts to husked ear com and shelled com
Type of com and
application rate
Pretreatment
preparation
Replica-
tions
Increase in
percentage of
weevil-infested
ears
Increase in
percentage of
weevil-damaged
kernels
Ear Com:
100 p.p.m
200 p.p.m
Check
Fumigated
Unfumigated
Fumigated
Unfumigated
Mumber
4
4
4
2
2
2
2
Points
25.8
18.3
62.9
Points
23.2
12.4
40.5
Shelled com
200 p.p.m
Check
2.1
15.3
•■40.9
64.2
Series F
Dixie 18 hybrid corn of the 1952 crop was used in this series. At the time of treat-
ment, in July 1953, 59 percent of the ears were infested, with an average of 6.6 live
adult weevils per ear.
The lot of corn was divided, and half was fumigated to destroy the self-contained
infestation. Methoxychlor dusts were applied to replicate samples of unhusked ear corn,
husked ear corn, and shelled corn, at various dosage rates and with various volumes of
dust. Dosages of 20, 40, 60, 80, and 100 p.p.m. of methoxychlor were applied, using a
10 -percent dust, and dosages of 20 and 60 p.p.m. were applied, using both a 25-percent
dust and a 50 -percent dust. The diluent in these dusts was an inorganic carrier. Each
sample was then stored in one of the drum-type bins for 6 months, from July 1953 until
-9-
January 1954. The corn was then removed from the bins and two 1 -gallon samples were
taken from each bin of shelled corn for determination of the adult weevil population. The
husked ear corn from each bin was shelled, thoroughly mixed, and two 1 -gallon samples
of the shelled corn were examined for adult weevils. Fifty ears were selected at ran-
dom from each bin of unhusked ear corn and the number of ears infested with live wee-
vils and the average number per ear were determined.
The results are given in table 6. It was evident that the weevils invading the bins
from outside sources were well controlled by the dust applications, as there were
fewer live weevils in bins containing corn fumigated at the start than in bins containing
unfumigated corn. The weevils emerging from larvae or eggs contained within the ker-
nels at the time the dusts were applied apparently survived in greater numbers than the
invading ones. The application rates of 60 and 100 p. p.m. of methoxychlor were much
more effective than was a rate of 20 p. p.m. against the emerging population, but even
the 100 p. p.m. rate was not enough to give a high degree of protection. There was
some indication that the 10 -percent dust gave better protection than did the 25- or 50-
percent dusts at the same dosage of methoxychlor, but this is not pronounced. This was
undoubtedly due to better coverage because of the greater volume. The dusts did not
give much protection to the unhusked ear corn. From 34 to 86 percent of the ears in
fumigated lots became reinfested within 6 months in spite of the presence of the dusts.
The level of infestation per ear was almost as great in the fumigated as in the unfumi-
gated samples.
Series G
Three lots of Dixie 18 hybrid shelled corn were given identical treatments in this
series, except for a difference in the length of storage, a procedure similar to that in
series B and M. Ten-percent methoxychlor dusts were applied at rates of 100 and 200
p. p.m. of methoxychlor, and sprays were applied at the same rates. One lot was stored
9 months in drum-type bins, a second 15 months, and a third 18 months.
The first lot was stored for 9 months, from January 1955 until October 1955, and
had 10. 52 percent of weevil-damaged kernels at the start and a moisture content of
less than 13 percent. The second lot had 4. 1 percent weevil-damaged kernels, and
14.01 percent moisture, and was stored for 15 months, from October 1954 until Janu-
ary 1956. The third lot had 4.6 percent weevil-damaged kernels, and 13.71 percent
moisture, and was stored for 18 months, from November 1954 until May 1956,
The methoxychlor residues on the treated samples in the first lot were chemically ,
analyzed after the first 3 months in storage, to indicate the relationship between the
application rate and the residue.
The results of the performance tests are presented in table 7. Both dust applica-
tions gave excellent protection from infestation for the 18-month period, but the spray
applications gave little or no protection.
The residues of methoxychlor found by chemical analysis are tabulated below. In
no case did the residue exceed the application rate, and the overall average of residues
was 69 percent of the applied rates.
Application rates Residues (p. p.m.) Application rates Residues (p. p.m.)
Dusts
100 p. p. m.
200 p. p. m.
Sprays
85
100 p. p.m.
70
80
60
170
200 p. p.m.
100
105
125
■10.
Table 6. --Average number of weevils found per gallon of shelled com from shelled com and husked ear com samples,
and percentage of ears infested and weevils per ear in unhusked ear com samples following treatment with various
methoxychlor dusts and storage for 6 months
Type of com, concentration
of methoxychlor, and
dosage rate
Pretreatment
preparation
Replica-
tions
Adult v/eevils per gallon
of shelled com
Alive
Dead
Unliusked ear corn
Ears
infested
Weevils per
ear
Shelled com
10-percent methoxychlor dust
20 p.p.m
60 p.p.m
100 p.p.m
25 -percent methoxychlor dust
20 p.p.m
60 p.p.m
50-percent methoxychlor dust
20 p.p.m
60 p.p.m
Check
Husked ear com
10-percent methoxychlor dust
20 p.p.m
60 p.p.m
100 p.p.m
25 -percent methoxychlor dust
20 p.p.m
60 p.p.m
50-percent methoxychlor dust
20 p.p.m
60 p.p.m
Check
Unhusked ear com
10-percent methoxychlor dust
20 p.p.m
60 p.p.m
100 p.p.m
25 -percent methoxychlor dust
20 p.p.m
60 p.p.m
50-percent methoxychlor dust
20 p.p.m
60 p.p.m
Check
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfiimlgated
Fumigated
Unfumigated
number
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
2
A'umber
9
469
1
106
1
107
13
429
6
105
45
389
1
121
35
493
36
124
3
54
0
9
194
127
30
82
33
213
12
302
102
233
Number
149
467
122
415
38
520
139
1,094
100
1,153
189
832
151
547
75
120
400
233
120
239
132
249
332
2'i-5
191
2C1
228
223
145
234
158
133
Percent
54
35
57
39
34
43
58
nz
66
76
56
86.
16
48
91
90
Mumbet
5.4
7.3
4.2
3.3
3.7
4.3
3.1
4.9
3.8
4.8
4.1
8.8
2.2
4.3
10.1
10.0
-11-
Table 7. Average increase in weevil-damaged kernels and in number of live weevils per gallon during 9, 15, and 18
months' storage following application of methoxychlor dusts and sprays at various rates; 3 replications
Type and application
rate of formulation
Dust:
100 p. p.m.
200 p. p.m.
Spray:
100 p. p.m.
200 p. p.m.
Check
9 months ' storage
Live weevils
per gallon
of com
//umber
19
12
52'i
808
939
Increase in
percentage
of weevil-
damaged
kernels
Points
15 months ' storage
Live weevils
per gallon
of com
number
1
273
558
102
Increase in
percentage
of weevil-
kernels
Points
6.9
6.6
A3.9
73.9
65.2
18 months ' storage
Live weevils
per gallon
of com
Sumber
0
212
350
135
Increase in
percentage
of weevil-
damaged
kernels
Points
8.0
2.7
31.^
72.7
63.0
■'■ Two replications only; the third was destroyed by weevils before the test was terminated.
Discussion
These tests indicate that the effective application rate of dusts would be 100 to 200
p. p.m. of methoxychlor for shelled or husked ear corn. The failure of the spray formu-
lation was unexpected, and sprays should not be discounted until further studies con-
firnn or explain these results.
TESTS WITH SYNERGIZED PYRETHRUM
Three series of tests were conducted with synergized pyrethrum, in 1951-52,
1952-53, and 1954-55. These are designated as series H, I, and J.
Series H
Three lots of Dixie 18 hybrid corn of the 1951 crop were prepared as unhusked ear
corn, husked ear corn, and shelled corn. Replicate samples of each lot were treated
with protective pyrethrum dusts and placed in storage for 8 months to observe whether the
spread of infestation from infested to uninfested unhusked and husked ears could be
prevented, and whether the increase in weevil-damaged kernels in shelled corn could
be suppressed.
Two-bushel samples of unhusked ear corn were treatedinNovember 1951 and stored
until July 1952. At the time of treatment, 15.6 percent of the ears were infested, as
measured by the presence of live weevils within the husk or by weevil-damaged kernels,
and 2. 85 percent of the kernels showed weevil damage. The moisture content was be-
tween 16 and 18 percent. The corn was divided, and half was fumigated to destroy the
self-contained infestation. Samples of each portion were treated with a commercially
available protective dust used elsewhere in the country, composed of 0.05 percent py-
rethrins and 0,8 percent piperonyl butoxide in an inorganic carrier, at the rate of 100
pounds per 1,000 bushels (1.6 ounces per bushel), which gave a dosage of 0.9 p. p.m. of
pyrethrins.
Two-bushel samples of husked ear corn were treated with the same dust in Decem-
ber 1951 and stored until August 1952. In this instance, none of the lot was fumigated.
At the time of treatment, 28 percent of the ears were infested, and 20. 4 percent of
the kernels were weevil-damaged. The moisture content was between 16 and 18 per-
cent.
•12-
Three -bushel samples of shelled corn were treated in March 1952 and stored until
November. At the time of treatment, 23.7 percent of the kernels showed weevil damage.
The moisture content was not determined but was assumed to be less than in the ear
corn lots. The lot was divided, and half was fumigated to destroy the self-contained in-
festation. Two dust formulations were then applied to replicate samples of each portion
of the lot. One formulation was the commercially available protective dust used in the
ear corn tests. The other was an experimental formulation composed of 0.08 percent
pyrethrins and 1.2 percent sulfoxide in an inorganic carrier. Both were applied at the
rate of 100 pounds per 1,000 bushels.
All samples were placed in the drum -type bins, where they remained undisturbed
until they were removed at the end of their respective 8-month periods. The percentage
of infested ears in the ear corn lots and the percentage of weevil-damaged kernels in
all lots were then determined.
The results are presented in table 8. The treatment prevented reinvasion of the
fumigated unhusked ear corn by weevils from outside sources, and movement from in-
fested to noninfested ears in the unfumigated unhusked ear corn, since there was prac-
tically no increase in the number of infested ears. There was apparently some invasion
from outside sources into the fumigated check sample of unhusked ears, and some move-
ment from infested to noninfested ears. The protective dust partially suppressed weevil
development in the husked ear corn, as the increase in infested ears and in weevil-damaged
kernels was about one -third that in the check. There was little difference in the degree
of protection to the shelled corn from the two protective dust formulations, and the in-
crease in infested ears and weevil-damaged kernels was about two -thirds that in the check.
Table 8. —Average increase in infested ears and in weevil-damaged kernels during 8 months'
storage following application of synergized pyrethrum dusts to unhusked ear com, husked
ear com, and shelled corn
Increase in
Increase in
Type of com and
Pretreatment
Replica-
percentage of
percentage of
application rate
preparation
tions
weevi 1- infested
weevi 1-damaged
ears
kernels
Unhusked ear corn:
Pyrethrum-piperonyl
;■-
butoxide dust
Number
Points
Points
0.9 p. p.m. pyrethrins
Fumigated
U
-5
1.7
Unfumigated
4
.3
4.3
Check
Fumigated
4
10.3
6.1
Unfumigated
4
26.5
14.4
Husked ear com:
Pyrethrum-piperonyl
butoxide dust
0.9 p. p.m. pyrethrins
4
20.0
14.9
Check
L
6? 9
40 5
Shelled com:
•T
\JfJ • ^
*-r\J • -/
Pyrethrum-piperonyl
■ ••
butoxide dust
' .■
0.9 p. p.m. pyrethrins
Fumigated
2
^ --
21.9
Unfumigated
2
— ■'
39.6
Pyrethrum- sulfoxide
dust
1.-42 p. p.m.
.
pyrethrins
Fumigated
Unfumigated
?
?7 7
r^ mj ^^ \^^A^ ^m * AlfcJ 9v9v9#V«9#
2
.M
£, f m 1
40.7
Check
Fumigated
2
--.
40.9
Unfumigated
2
—
64.2
13-
" Series I
Two lots of shelled corn with a self-contained infestation were treated with py-
rethrum dusts and stored in gallon jars for observation of the degree of protection
against weevil damage exerted by several proposed formulations.
Three formulations were applied to the first lot early in December 1952, one of
them a commercially available protective dust used elsewhere in the country, and the
other two experimental formulations with a portion of the pyrethrins replaced with
allethrin. The composition of the formiulations was as follows (all were applied at the
rate of 100 pounds per 1,000 bushels of corn):
0.05 percent pyrethrins, 0.8 percent piperonyl butoxide, in an inorganic
carrier;
0. 04 percent pyrethrins, 0. 03 percent allethrin, 0. 8 percent piperonyl
butoxide, in an inorganic carrier;
0.03 percent pyrethrins, 0.06 percent allethrin, 0.8 percent piperonyl
butoxide, in an inorganic carrier.
The second lot of corn, with 26.9 percent weevil-damaged kernels, was treated in
Novemiber 1952. Two formulations were used; one was the commiercially available pro-
tective dust containing 0.05 percent pyrethrins and 0. 8 percent piperonyl butoxide in an
inorganic carrier, and the second was a wettable powder that was applied as a dust,
which contained 2 percent pyrethrins and 20 percent sulfoxide. Both were applied at a
rate of 100 pounds per 1,000 bushels. The high concentration of pyrethrins in the
wettable powder was not realized until the tests were under way.
Eight replicate samples of each treatment were prepared, then four of them were
screened to remove excess dust that did not adhere to the shelled corn. The samiples
were examined periodically and all adult weevils removed each time until the samples
were destroyed or had been in storage for 12 months. The percentage of weevil-dam-
aged kernels was determined for the samples remaining at the 12 -month period.
The results are given in table 9. The commercial protective dust applied at 0.9
p. p.m. , and the experimental formulations with allethrin replacing a portion of the py-
rethrins were not at a high enough concentration to suppress the development of the wee-
vils under these conditions, and the corn samples were totally consumed at the end of
7-1/2 months of storage. On the other hand, the inadvertent high rate of application of
the pyrethrin-sulfoxide formulation rapidly suppressed the weevil population and finally
wiped it out.
Series J
This series paralleled series B, C, G, and M. Three lots of Dixie 18 hybrid
shelled corn were given identical treatments; one was stored 9 months, one 15 months,
and one 18 months. Four formulations were used. One was the comimercially available
protective dust used in series H and I, containing 0. 05 percent pyrethrins and 0. 8 per-
cent piperonyl butoxide in an inorganic carrier, applied at the rate of 150 pounds per
1 , 000 bushels, giving a dosage of 1.34 p. p.m. of pyrethrins. Three protective spray
formulations were applied at a dosage of 1. 14 p. p.m. of pyrethrins. One was composed
of 0. 2 percent pyrethrins and 2 percent piperonyl butoxide applied at the rate of 4 gal-
lons per 1,000 bushels; one was half the above concentration, applied at the rate of 8
gallons per I, 000 bushels; and the third was composed of 0. 2 percent pyrethrins alone
applied at the rate of 4 gallons.
The first lot was treated in January and stored until October 1955, and at the time
of treatment it had 10.52 percent weevil-damaged kernels. The second lot was treated
in October 1954 and stored until January 1956, and at the time of treatment it had 4. 6
percent weevil-damaged kernels. The third lot was treated in November 1954 and was
-14-
stored until May 1956, and at the time of treatment it had 4.6 percent weevil-damaged
kernels. Three replicate samples of each treatment were stored in the drum -type bins.
At the end of the respective storage periods, the corn was removed from the bins and
the percentage of weevil-damaged kernels determined.
The residues of piperonyl butoxide on the treated samples in the first lot were
determined after the first 3 months of storage, to indicate the relationship between the
application rate and the residue.
Table 9. --Average number of adult weevils found in 5-paund samples of shelled com treated with various synergized
pyrethrum formulations, and increase in percentage of weevil-damaged kernels during the total 12-month storage
period
Post-
treatment
handling
Replica-
tions
Average number of weevils removed after exposure of —
Increase in
percentage
of weevil-
damaged
kernels
Formulation and dosage
rate per 1,000 bushels
4 months
5-1/2 months
10 months
12 months
Alive
Dead
Alive
Dead
Alive
Dead
Alive
Dead
Pyrethrum dust
0.9 p. p.m. pyrethrins
Pyrethrum- allethrin dusts
0.71-0.53 p. p.m. py-
rethrins , allethrin
0.53-1.06 p. p.m. py-
rethrins , allethrin
Check
Pyrethrum-piperonyl butoxide
dust
0.9 p. p.m. pyrethrins
Pyrethrum-sulfide dust
36 p. p.m. pyrethrins
Check
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
/fimber
A
4
4
4
4
4
4
4
4
4
4
8
Number
253
237
205
181
203
175
555
611
248
234
11
19
582
Number
337
395
275
261
300
380
16
15
337
269
219
213
16
Number
219
184
200
189
199
188
116
135
219
184
4
3
124
Number
45
69
39
37
36
38
17
79
45
69
170
176
48
Number
(^)
(^)
1
1
Number
149
214
Numbe r
1
1
Number
9
9
Points
-0.3
-.9
■"■ Sanqsles completely consumed by the end of 7-1/2 months' storage.
The results of the performance tests are given in table 10. The protective dust
performed better than did the sprays, but its effectiveness was inconsistent in that the
9- and 18-month tests indicated good protection but the 15-month one was only partially
effective. The 4-gallon rate of application for the protective spray appeared more ef-
fective than the 8-gallon rate. Pyrethrum alone gave protection of the same order as
the synergized pyrethrum at the same dosage of pyrethrins, but none of the sprays gave
more than partial protection at this dosage.
The residues of piperonyl butoxide were found to be more than half of the applied
rate, as follows:
Application rate (p. p.m.)
Residue (p. p.m.)
Dust
13.4
Spray
11.4 (4-gallon rate)
11.4 (8-gallon rate)
8
7
4
6
7
5
15-
Table 10.— Average increase in weevil-damaged kernels and in number of live weevils per gallon during 9, 15, and 18
months ' storage following the application of pyrethrum dusts and sprays at various rates
Replica-
tions
9 months ' storage
15 months ' storage
18 months ' storage
Type and application rate
of formulation
Live weevils
per gallon
of com
Increase in
percentage
of weevil-
damaged
kernels
Live v/eevils
per gallon
of com
Increase in
percentage
of weevil-
damaged
kernels
Live v/eevils
per gallon
of com
Increase in
percentage
of weevil-
damaged
kernels
Dust:
1.3A p. p.m. pyrethrins . . . .
Synergized pyrethrum spray:
1.14 p. p.m. pyrethrins,
4-gallon rate
1.14 p.p.m. pyrethrins,
8-gallon rate
Pyrethrum-only spray:
1.14 p.p.m. pyrethrins,
Nvmber
3
3
3
3
4
Number
55
98
209
209
313
Points
Nwnber
244
240
493
187
102
Points
24.1
41.4
48.7
58.4
64.7
number
2
388
538
315
135
Poinds
9.0
34.0
45.0
39.4
Check
63.0
Discussion
Tests elsewhere have demonstrated that pyrethrum protective treatments in the
range of 1 to 3 p.p.m. of pyrethrins are effective because of their repellency rather
than toxicity, and that repellency is not reflected in small samples but mostly under
bulk storage conditions. Therefore, these tests should be considered largely in rela-
tion to effectiveness from toxicity of the treatments. On this basis, they indicate that
dosage rates from 0.9 to 1.42 p.p.m. of pyrethrins are not toxic enough to give pro-
tection by this action alone against the rice weevil, but that at some point between 1.4Z
and 36 p.p.m. , complete toxicity and effective protection can be expected.
TESTS WITH RYANIA
Three series of tests were made with ryania. Series K was limited to jar tests
with shelled corn and was begun in November 195Z and continued for 12 months. Series
L was begun in December 1952 as soon as the probable results from the first series
began to be evident. It was divided into 2 parts, 1 consisting of drum-type bin tests
with shelled corn and the other of drum -type bin tests with ear corn. Series M was
started in October 1954 and continued for 18 months. It consisted of bin tests with
shelled corn.
Three formulations of ryania were used in the first 2 series. One was a dust cona-
posed entirely of ground stems of ryania without any other diluent, which contained
ryanodine as the active ingredient, at a strength of about 0. 25 percent. The other 2
consisted of ryania dust with 3 percent synergist added, N-propyl isome in 1 formula-
tion, and sulfoxide in the other. The third series included treatments with only the
ryania dust.
Series K
A lot of shelled corn with a moisture content of 1 3 to 14 percent was prepared, with
26.9 percent of the kernels showing weevil damage. It was composed of mixed hybrid
corn varieties harvested in the fall of 1952. Eight treatments were made in November
1952 with ryania formulations at the following rates: Ryania dust, 50, 75, and 100 pounds
per 1,000 bushels; ryania-N-propyl isome dust, 75 and 100 pounds per 1,000 bushels;
ryania-sulfoxide dust, 50, 75, and 100 pounds per 1,000 bushels.
-16-
Eight replicate 5 -pound samples were prepared for each treatment, and each was
placed in a 1 -gallon wide -mouthed glass jar. Four of each 8 replicates were then
screened to remove excess dust that did not adhere to the shelled corn. The samples
were examined and all adult weevils removed and counted periodically until the corn
had been exposed for 12 months.
The results are shown in table 11. It can be noted that the removal of the excess
dust not adhering to the kernels resulted in a slightly greater increase in the percentage
of weevil-damaged kernels. The synergized ryania formulations brought the original
infestation under control at an earlier date, and held the increase in damaged kernels
to a lower percentage than did the ryania dust. The ryania-N-propyl isome formulation
appeared slightly superior to the ryania-sulfoxide formulation.
Table 11. — Average number of adult weevils found in 5-pound san^iles of shelled com treated with various dosage rates
of ryania fonmlations and increase in percentage of weevil-damaged kernels during total 12-month storage period
Formulation and dosage
rate per 1,000 bushels
Post-
treatment
handling
Replica-
tions
Average number of weevils removed after exposures of —
<+ months
Alive Dead
5-1/2 months
Alive Dead
10 months
Alive Dead
12 months
Alive Dead
Increase in
percentage
of weevil-
damaged
kernels
Ryania
50 pounds
75 pounds
100 pounds
Ryania-N-propyl isome
75 pounds
100 pounds
Hyania-sulf oxide
50 pounds
75 pounds
100 pounds
Check
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Screened
Unscreened
Ntmber
A.
A-
i
4
Number
167
61
77
34
77
41
46
19
26
56
35
19
34
45
29
582
Number
47
368
140
381
340
294
184
123
59
29
274
391
231
379
174
125
16
Number
54
40
50
34
47
19
6
9
14
3
10
11
11
11
20
124
Number
200
239
248
249
198
275
171
105
133
71
284
279
270
234
174
199
48
Number
183
76
164
41
41
4
1
1
3
2
3
2
Number
208
54
91
69
128
218
134
69
126
226
94
94
104
140
260
303
Number
99
39
44
19
25
Number
13
9
12
9
31
43
7
3
13
9
7
16
14
16
39
39
Points
52
43
58
33
40
37
21
5
25
29
24
22
16
22
19
73
■"" The check samples were completely consumed by the end of 7-1/2 months' storage.
Series L
In this series, samples from a lot of shelled corn and from a lot of husked ear
corn were dusted with each of the ryania formulations used in the preceding series, at
a rate of 100 pounds per 1,000 bushels (or 1.6 ounces per bushel). The shelled corn
and ear corn lots were each divided in 2, and 1 part was fumigated to destroy the self-
contained weevil infestation so that any infestation would be from an outside source.
The shelled corn was an early maturing hybrid variety that had been harvested in the
fall of 1952 and stored as ear corn until December 1952, when it was shelled and
cleaned. This lot had 21.7 percent of weevil-damaged kernels, and the moisture con-
tent was approximately 15 percent. The lot of ear corn of the hybrid variety North
Carolina 27 had also been harvested in the fall of 1952 and stored unhusked until Decem'
ber, when it was husked preparatory to treatment. At that time, 26 percent of the ears
were weevil-infested (kernels showed evidence of weevil damage, or one or more live
weevils were observed), and 15.8 percent of the kernels showed weevil damage. The
moisture content was 13.55 percent.
-17-
Each dusted sample of fumigated shelled corn and of unfumigated shelled corn was
divided into 3 replications of 3 bushels each, each replication going into one of the drum -
type bins. The fumigated and unfumigated portions of the ear corn were divided into 4
replications of 2 bushels each for each dust formulation, and likewise stored in the
drum -type bins. The bins were left undisturbed for 10 months, until October 1953,
when the corn was removed and examined. A sample was taken from each bin of shelled
corn and the percentage of weevil-damaged kernels determined. In the ear corn samples,
the percentages of infested ears and of weevil-damaged kernels were determined.
The results are presented in table 12. In the shelled corn in which the self-con-
tained infestation was killed by fumigation, very little infestation from outside sources
occurred, as evidenced by the small increase in weevil-damaged kernels. In the un-
fumigated samples, the increase in percentage of weevil-damaged kernels was less than
20 points, whereas practically all kernels showed weevil damage in the check. In the
ear corn, the protection from insect damage was excellent.
Table 12. --Average increase in infested ears and in weevil-damaged kernels during 10
months ' storage following application of protective ryania dusts at rate of 100 pounds
per 1,000 bushels to husked ear com and shelled com
Type of com and
formulation applied
Pre treatment
preparation
Replica-
tions
Increase in
percentage of
weevil-infested
ears
Increase in
percentage of
weevil-damaged
kernels
Shelled com:
Ryania dust ■. . .
Ryania-N-propyl isome,
Ryania-su If oxide
Check
Husked ear com:
Ryania dust
Ryania-N-propyl isome.
Ryania-sulf oxide
Check ,
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Fumigated
Unfumigated
Number
3
3
3
3
3
3
3
3
4
4-
4
4
4
4
4
4
Points
2.9
1.8
-.2
1.2
2.3
2.0
53.2
74.0
Points
10. 1
20.3
8.0
17.9
5.6
19.5
35.9
75.3
-4.4
9.8
1.5
4.8
4.1
6.6
36.4
43.3
Series M
The third series was made with shelled corn of the hybrid variety Dixie 18, which
was harvested in the early fall of 1954. It was shelled soon after harvest, dried, and
cleaned. At this time, 4. 6 percent of the kernels showed weevil damage, and the mois-
ture content was 13.71 percent. Three replicate samples of 4 bushels each were dusted
with ryania at the rate of 100 pounds per 1, 000 bushels and stored in January 1955 for
II months; 3 others were treated in October 1954 and stored for 15 months; and a final
3 were treated in November 1954 and stored for 18 months. When the shelled corn was
removed from the bins at the end of the respective storage periods, the number of live
v^eevils per gallon in shelled corn was determined for all lots, and the increases in the
percentages of weevil-damaged kernels were determined for the 15- and 18-month
storage periods.
-18-
The results are given in table 13. The degree of protection was excellent, the num
ber of live weevils found after 11 months' storage was negligible, and the increase in
percentage of weevil-damaged kernels in 1 5 and 18 months was very small.
Table 13. --Average increase in weevil-damaged kernels and in number of live weevils per
gallon during 11, 15, and 18 months' storage following application of ryania dust at
rate of 100 pounds per 1,000 bushels
Length of
storage period
Replica-
tion
Live weevils
per gallon of com
Increase in
percentage of
weevil-damaged
kernels
11 months
Number
3
3
3
3
3
3
Number
5
263
1
102
0
135
Points
Check
15 months
U.l,
Check
64.7
18 months
.7
Check
63.0
Discussion
It was demonstrated by these tests that ryania dusts applied to either shTelled or
husked ear corn gave very good protection against damage by the rice weevil during ex-
tended periods of storage. When the initial infestation at the time of treatment was low
(series M, and fumigated lots in series L), the protection was excellent.
FINDINGS
The purpose of these studies was to develop information on the feasibility of using
five selected insecticides--lindane, malathion, methoxychlor, synergized pyrethrum,
and ryania- -as protective treatments for stored corn. As a result of the exploratory
studies, three materials, malathion, methoxychlor, and synergized pyrethrum, were
selected for further study under commercial storage conditions, and evaluation studies
were begun.
It is generally considered that an important limiting factor in establishing a resi-
due tolerance on corn under the Miller Amendment to the Food, Drug, and Cosmetic
Act will be the residue level in that portion of corn utilized as dairy feed. A tolerance
for methoxychlor residues of 100 p. p.m. has been established for some forage crops;
therefore, it is assumed that a tolerance of somewhat the same order may be possible
on corn. The excellent results with application rates of 100 p. p.m. in these explora-
tory tests were encouraging enough that this insecticide was selected for practical
evaluation studies.
A tolerance for residues of malathion on corn of 8 p. p.m. was recently established.
The exploratory tests with malathion indicated that application rates of 10 to 15 p. p.m.
are quite effective in protecting stored corn; therefore, this insecticide also was se-
lected for evaluation studies.
Synergized pyrethrum also is acceptable from the standpoint of residue tolerances,
because tolerances have been announced for pyrethrins of 3 p. p.m. and for piperonyl
butoxide of 20 p. p.m. The application rates studied in these exploratory tests of 0.9
to 1.42 p. p.m. of pyrethrins were only partially effective in preventing a buildup of
-19-
infestation. However, because of the small size of the samples, any effect of repel-
lency was reduced to a minimum. In addition, the 1 application at the rate of 36 p. p.m.
of pyrethrins was so positive in its effectiveness that it can be assumed that an increase
in the application rate with the attendant increase in both toxicity and repellency may
give excellent protection. Therefore, synergized pyrethrum also was selected for
evaluation studies.
Ryania gave excellent protection against infestation, but it is doubtful that a resi-
due tolerance can be established on stored corn for this insecticide for some time.
Attempts to develop a specific chemical analysis method for the level of residues of
ryanodine that would be present following effective application rates have not been
successful. Also, additional data are needed on the toxicological effects of ingested
ryania to evaluate the hazard of residues in the event that the level of residues can be
determined. Therefore, this insecticide was not included in the evaluation studies.
The limiting factor in establishing a residue tolerance for lindane on corn is like-
wise the consideration of the effect of lindane in dairy feed. It has been established
that a low level of lindane residue in dairy feed will result in the appearance of lin-
dane in milk. No tolerances have been established for lindane residues in forage crops
or in milk; therefore, it is unlikely that tolerances will be approved on corn. For this
reason, this insecticide was not included in the evaluation studies.
20-
r>U. S. GOVERNMENT PRINTING OFFICE : 1958 O -479581
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