(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Treatments for the protection of stored southern-grown corn from rice weevil attack : exploratory tests"

Historic, archived document 

Do not assume content reflects current 
scientific l<nowledge, policies, or practices. 



C~1 ^^ i -»T f-W-t-^-m-—, 



y>/^ 



.'3 



L i B R 

•:i;RPEin SERIAL KLUu.^. 

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. : 

. 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 





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 








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 


-.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 

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 


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 




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 


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