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Summary

Results of experiments conducted to determine
the effect of natural or simulated climatic conditions
on the residual toxicities of several chlorinated hydro-
carbon and organophosphorus insecticides to several
species of cotton pests are summarized in this pub-
lication.

In tests on the boll weevil with the chlorinated
hydrocarbon insecticides, the residual properties of
endrin and Sevin appeared to be quite similar under
a variety of weathering conditions. Based on residual
properties alone, toxaphene and dieldrin ranked with
endrin and Sevin, but the initial toxicities of dieldrin
and endrin to the boll weevil were appreciably greater
than those of toxaphene. The mortality rate among
weevils confined on spray residues of these insecti-
cides was reduced by 20 to 30 percent after exposure
of the residues to simulated wind or rain. This re-
duction could result in failure to control the boll
weevil under field conditions.

The residual properties of aldrin and BHC were
inferior to those of endrin, Sevin, dieldrin and toxa-
phene under a variety of climatic conditions. The
results obtained with heptachlor were erratic.

The results obtained in tests on the boll weevil
were similar to the data from tests with the cotton

leafworm, the salt-marsh caterpillar and the garden
webworm.

Among the organophosphorus insecticides used
in tests on the boll weevil, Guthion appeared to be
more resistant to weathering than malathion, methyl
parathion or Phosdrin. Malathion appeared to have
residual properties intermediate between those-t" of
Guthion and methyl parathion, while the period of
residual effectiveness of Phosdrin was very short
under all conditions.

Simulated rain was the only weathering agent
which appreciably reduced the residual toxicity of
Guthion. In general, weathering did not reduce the
residual toxicities of the organophosphorus insecti-
cides as much in tests with cotton aphids and spider
mites as in tests with the boll weevil.

When treated plants were held under varying
temperature and humidity conditions for 48 hours
prior to the release of insects on the plants, the
residual toxicities of all the insecticides tested were
reduced appreciably.

Losses in residual effectiveness among insecti-
cidal dusts exposed to wind and rain usually were
greater than among sprays of the same materials.

Con ten ts
Summary ________________________________________________________________________ __ 2 Chlorinated Hydrocarbon Insecticides ............ .. 8
E . t 1 M th d 3 Qrganophosphvrlls Insecticides ......................... u 9
xperimen a e o s ............................................... --
Insecticides ............................................................ ._ 3 Effect of Slmulated Wmd """"""""""""""""""""" " g
Clilnatic Conditions e 3 Chlorinated Hydrocarbon Insecticides ............ .. l0
Test Insects _ _ _ _ A _ _ _ ‘ _ e _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ 4 Organophosphorus Insecticides ........................ .. l0
Bioassay Techniques ___________________________________________ __ 4 Effect of Simulated Dew on Insecticides ................ .. ll
Effeet of Temperature and Humidity ____________________ __ 4 Effect of Sunlight on Insecticides ............................. .- ll
Chlorinated Hydrocarbon Inseotioides ____________ __ 5 Effect of Climatic Factors on Sevin ........................ .- ll
Orsanophosphorus Insecticides ------------------------- -- 7 Literature Cited ........................................................... _. 11
Effect 0f Simulated Rain ........................................... .- 8 Acknowledgments ......................................................... _. ll

   
  
  
 
 
   
 
  
    
 
 
 
  
 
  
  
 
  
 
 
  
 
 
  
 
   
 
 
  
  
   
  
 
 
  
 
  
 
  

V PERSISTENCE OF INSECTICIDE RESIDUES was recog-
(ed as a factor in insect control shortly after
I (vent of the chlorinated hydrocarbon and organo-
 orus insecticides. Research on the effect of
(tic factors on the residual toxicities of insecti-
‘~10 cotton insects was begun at the Texas Agri-
 Experiment Station by Gaines and Dean
Data on the effect of sunshine and simulated
n insecticide residues were presented by Gaines
can (1950). Further research on the effect of
ted rain, sunlight, high natural temperatures
wind on insecticide residues was conducted by
‘s and Mistric (1951, 1952) , Mistric and Gaines
1- , 1954), Mistric (1954), Owen (1954) , Mistric

rowers are offered a choice of many different
cides for use in the control of the major cotton
pests. Many of the chlorinated hydrocarbon
rganophosphorus insecticides are recommended
e control of several diverse groups of insects.
p dition t0 selecting an insecticide known to be
f. t0 a particular pest species, it would be advan-
'- s for the grower to know what residual proper-
lo anticipate from a given insecticide under
 s weather conditions in the field.

Experimental Methods

FCTICIDES

_ ch insecticide included in these studies was
hed by the manufacturer. All spray materials
?“were prepared from emulsifiable concentrates,
.811 dusts were formulated with commercial
 ts. Fresh stocks of insecticides were obtained
I - at the beginning of each new season.

arch was conducted on the following chlori-
ighydrocarbon insecticides: toxaphene, dieldrin,
 aldrin, benzene hexachloride and heptachlor;
the following organophosphorus insecticides:
ion, methyl parathion, malathion, Guthion and
in. Also, several preliminary tests were con-
 Ywith Sevin, a carbamate insecticide.

a,

‘ATIC continuous

tory so that individual climatic factors could
 er controlled or simulated. Natural or out-

i ively, formerly assistant professor and head, Department
‘mology.

of the experiments were conducted in the’

RESIDUAL TIIXICITIES 0F INSECTICIDES T0 CIITTIIN INSECTS

B. G. Hightower and J- C. Gaines*

door climatic conditions were utilized for weathering
the residues in some of the tests when it was possible
to avoid any complicating conditions.

In order to evaluate the weathering effect of a
particular combination of climatic factors affecting
insecticidal residues for a specified period of time,
potted cotton plants were sprayed or dusted and
separated into the following groups for detailed
observation:

1. Initial toxicity - Insects were released on the
sprayed or dusted plants within 45 minutes after
treatment. Maximum mortalities usually were ob-
tained on these plants and all losses in toxicity from
weathering were estimated on this basis.

2. Twenty-four hour exposure-Insecticides on

cotton plants were exposed to certain weather con?

ditions for 24 hours prior to the release of the test
insects on the treated plants.

3. Wind or rain-Insecticides on cotton plants
were exposed to wind or simulated rain for all or
part of 24 hours prior to the confinement of the
insects on the treated plants.

Temperature during the exposure periods ranged
from 54° to 115° F. and the relative humidity varied
from 28 to 98 percent. An uninsulated room was used
in some of the tests to subject treated plants to high
temperatures in the absence of bright sunlight. The
sun raised temperatures in the room from 110° to
115° F. for about 4 hours during a 24-hour period.
For comparison, similar groups of treated plants were
held in the laboratory at 85° i 5° F. during the
24 hours prior to the release of the insects on all the
treated plants.

After the insects had been released on the various
groups of treated plants, they were all held under
identical conditions for the remainder of the test.

Natural wind currents were simulated in the
laboratory by means of a 16-inch oscillating electric
fan, Figure 1. The insecticide-treated plants exposed
to simulated wind were placed in a single row about
3 feet in front of the fan within the range of oscilla-
tion. A later modification of this technique involved
placing the fan vertically in a rigid mount about
a circular plywood table. Treated plants situated
around the rim of the table were exposed for 24 hours
to the uniform air currents produced by the fan.
Wind velocities in both techniques varied from 3.5
to 5 miles per hour (m.p.h.) .

Figure 1. Modified Dustan table for applying simulated
wind to treated cotton plants.

Rain was simulated by means of a circular garden
sprinkler mounted vertically in the top of a steel
frame 3 feet square and 5 feet high, Figure 2. A
l6-mesh screen wire tray was mounted 15 inches below
the sprinkler t0 break the stream of water into drops.
The sprayed or dusted plants were placed on the floor
directly under the sprinkler and water was allowed
to fall until 0.5 inch had collected in a gauge on the
floor between the plants. This simulated a hard un-
interrupted shower for 3 minutes.

TEST INSECTS

Field-collected boll weevils, Anthonomus grandis
Boh., were used in some of the tests. However, more

Figure 2. Apparatus for applying simulated rain to treated
cotton plants.

4

uniform results generally were obtained when the
insects were reared from infested squares collected in
the field and held under controlled temperatures in
the laboratory until the adults emerged.

Laboratory-reared third and fourth instar larvae
were used in the tests involving the salt-marsh cater-
pillar Estigmene acrea (Dr.) and the cotton leafworm,
Alabama argillacea (Hbn.).__E?<periments with the
garden webworm Loxostege sinliilalis (Guen.) were
conducted only on fourth-instar larvae.

Cultures of the cotton aphid Aphis gossypii
Glov. and the tumid spider mite Tetranychus tumidus
Banks maintained in the laboratory on seedling cotton
served as sources of supply for tests with these cotton
pests.

BIOASSAY TECHNIQUES
In the tests with spray residues, cotton plants

were passed by means of a turntable device through.

a spray delivered by two hollow-cone nozzles operat-
ing under a pressure of 60 pounds per square inch
(p.s.i.) , Figure 3. The volume of liquid applied in
one revolution of the turntable at a speed of 4.5
m.p.h. is equivalent to a field dosage of 5 gallons of
spray per acre. The desired dosage in terms of pounds
of toxicant per acre was obtained by varying the
amount of concentrate in a constant volume of spray.
Sprays in some of the tests were applied from the
top of a tower through a solid cone nozzle at a
pressure of 40 p.s.i. and at a dosage equivalent to
7.5 gallons of spray per acre, Figure 4. Insecticidal
dusts were applied by compressed air from the top
of a 44-inch dusting chamber. All dosages are ex-
pressed in terms of pounds of toxicant per acre and
an effort was made to approximate commonly recom-
mended field dosages.

In the boll weevil tests, four potted cotton plants
were used for each treatment under each condition
on a given date. Each treatment was repeated three
to eight times on different dates. Ten to l5 boll
weevils were released on each plant so that each
treatment was tested with at least 120 insects. Essen-
tially the same procedure was followed in tests with
the cotton leafworm, the salt-marsh caterpillar and
the garden webworm. Larger numbers of cotton
aphids and spider mites were used in the tests on
these pests. In most instances, each treatment was
repeated eight times for each climatic condition under
study. Mortality percentages in all tests were based
on the number of insects killed within 3 to 5 days
after the release of the insects on the treated plants.

Effect of Temperature and
Humidity
Insecticide residues on cotton plants were exposed

to prevailing temperature and humidity conditions
for 24 hours before the insects were placed on them.

 

 During the tests temperatures ranged from 54° to
 115° F. and relative humidities varied from 28 t0
 98 percent. Losses in toxicity attributed t0 these
climatic factors are shown in the column marked
"24-hour exposure” in each graph.

Temperature and humidity changes did not
greatly alter the residual toxicities of toxaphene,
dieldrin, endrin “and Guthion. Losses in toxicity were
much greater among the more volatile insecticides
such as BHC, parathion, methyl parathion and
 Phosdrin. Within the effective limits, the ranges of
B, temperature and humidity were not important in
é< determining the period of residual toxicity of either

group.

CHLORINATED HYDROCARBON
INSECTICIDES

TOXAPHENE. Toxaphene sprays were applied
to plants at a dosage of 1.5 pounds of toxicant per
acre, and the plants were exposed to temperatures
 ranging from 68° to 106° F. and relative humidities

' ranging from 34 to 98 percent. A reduction of 10
i, percent in mortality occurred among weevils confined
 on these plants compared with weevils confined on
freshly sprayed plants, Figure 5. The reduction in
mortality increased to 56 percent when the weevils
were released on treated plants which had been
weathered for 48 hours.

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In tests with the cotton leafworm confined on
toxaphene residues which had been exposed to an
‘effective temperature range of 76° to 106° F. and a
‘humidity range of 36 to 62 percent, the reduction
in mortality averaged 15 percent, Figure 6. Under
temperatures ranging from 67° to 77° F., a spray of
0.5 pound of toxaphene per acre was more toxic to
the sleafworm than 0.06 pound of toxaphene per acre
applied as a dust.

Salt-marsh caterpillars were confined on the resi-
idues of toxaphene sprays applied at dosages of 0.3
frftol pound of toxicant per acre. Mortality among
{the insects confined on freshly sprayed plants aver-
aged 25 percent greater than that recorded when
"aexposure of the insects on treated plants was delayed
Tfor 24 hours, Figure 7. In a similar series of tests
with the garden webworm only a 7 percent reduction
i1 mortality was recorded.

DIELDRIN. Spray dosages ranging from 0.15
£0 0.33 pound of dieldrin per acre were used to
evaluate the residual toxicity of this insecticide to
file boll weevil. A 20 percent reduction in mortality
curred when treated plants were weathered 24 hours
before the weevils were confined on them. The
‘liresidual toxicity of dieldrin was greatly reduced after
a 48-hour weathering period.

Loss of residual toxicity of dieldrin was more
triking in tests with the cotton leafworm. A 74
. percent reduction in the residual toxicity of dieldrin

Figure 3. A machine for spraying cotton plants in the
laboratory. The plants are revolved through the spray at a
speed of 4.5 miles per hour, simulating tractor spraying in the
field.

to this pest occurred after the insecticide had been
on the plants for 24 hours. However, it should be
noted that only 0.05 pound of dieldrin per acre was
used in these tests.

In tests with the salt-marsh caterpillar, dieldrin
was applied on plants at the rate of 1 pound per
acre. Mortalities were reduced by 22 percent on
treated plants which had been exposed to prevailing
temperatures for 24 hours.

Residues from a spray application of 0.5 pound
of dieldrin per acre killed 47 percent fewer garden

Figure 4. Tower used to apply predetermined dosages of
spray emulsions or dusts of insecticides to individual cotton
plants.

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Figure 5. Effect of various climatic factors on the toxicities

weevil, Anthonomus grandis Boh.

webworms after the treated plants had been held for
24 hours prior to the release of the worms. Tempera-
tures during this period ranged from 74° to 110°
F. and relative humidities varied between 22 and
98 percent.

BENZENE HEXACHLORIDE. In tests with
the boll weevil, emulsion sprays of BHC were applied
to cotton plants at a dosage equivalent to 0.33 pound
of BHC per acre. On treated plants weathered for
24 hours, weevil mortality averaged 50 percent less
than on freshly sprayed plants.

After plants were treated with BHC and exposed
to prevailing temperature for 48 hours, less than 20
percent of the weevils confined on them were killed.

In a series of tests with the cotton leafworm,
BHC was sprayed on plants at the rate of 0.25 pound
per acre. After a 24-hour weathering period the
mortality rate was 22 percent less than kills of leaf-
worms confined on freshly sprayed plants.

Benzene hexachloride was sprayed on seedling
cotton plants at the rate of l pound per acre and
cotton aphids were placed on one group of plants
shortly after the spray had dried. In a second group
the plants were exposed to prevailing temperature
for 24 hours prior to the release of the aphids. Kills
among the aphids were reduced 25 percent after the
24-hour delay period.

ALDRIN. On aldrin-treated plants, which had
been exposed to prevailing temperatures for 24 hours,
the mortality rate among confined weevils was 45
percent less than among those confined on freshly
treated plants. The dosage was equivalent to 0.33
pound of aldrin per acre. The mortality rate among
weevils confined on aldrin-treated plants which had
been exposed to prevailing temperatures for 48 hours
was reduced by 84 percent below the kills obtained
on freshly sprayed plants.

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of six chlorinated hydrocarbon insecticides and Sevin to the boll

ln tests with the cotton leafworm, aldrin was

sprayed on the plants at the rate of 0.25 pound per
acre. After the treated plants had been exposed to
prevailing temperatures for 24 hours, the mortality
rate among leafworms released on them was reduced
by 30 percent compared with mortalities obtained
from releases on freshly sprayed aldrin.

Plants were sprayed with aldrin at the rate of ;
2 pounds of toxicant per acre in tests with the salt- 
marsh caterpillar. Kills among the insects confined _-
on the residues were reduced by 7O per cent after the in

treated plants had been exposed to prevailing tem-
peratures for 24 hours. Similar results were obtained
in tests with the garden webworm.

ENDRIN. Spray residues of endrin on cotton
plants were equally toxic to the boll weevil both

before and after a 24-hour exposure to prevailing y

temperatures. The spray was applied at a rate equiva-
lent to 0.12 pound of endrin per acre. Forty-eight
hours after the plants had been sprayed kills of weevils
on the residues were reduced by l8 percent below
mortalities obtained on freshly treated plants.

Endrin applied to plants at the rate of 0.01 pound
per acre was highly toxic to the cotton leafworm. A
reduction of 17 percent in mortality occurred when
the leafworms were confined on treated plants which

had been exposed to prevailing temperatures for 24 if

hours. Similar results were obtained in tests with
the salt-marsh caterpillar and the garden webworm.
However, the spray dosageswere increased up to 0.30
pound of endrin in the latter tests. In general endrin
dusts were as effective as sprays.

HEPTACHLOR. Sprays of heptachlor applied
to plants at the rate of 0.33 pound of toxicant per
acre were used in tests with the boll weevil. Mortali-
ties among weevils confined on freshly treated plants
varied from 41 to 85 percent. After the sprayed plants

  

had been exposed to prevailing temperatures for 24
hours, weevil kills 0n the residues were reduced by
25 percent.

ORGANOPHOSPHORUS INSECTICIDES

PARATHION. In tests with the cotton leaf-
worm, parathion was sprayed on plants at the rate
of 0.005 pound per acre. High mortality rates were
noted when leafworms were exposed to residues on
treated plants which had been kept in the laboratory
for 24 hours; however, leafworms were not killed by
feeding on treated plants which had been left out-
doors for 24 hours. I

Sprays of parathion were toxic to the tumid spider
mite, Figure 8. Parathion was applied to plants at
a rate of 0.1 pound per acre. A reduction in mortality
of 20 percent occurred when mites were placed on
treated plants which had been weathered for 24 hours.
Kills of mites on freshly sprayed plants were used
for comparison.

A spray dosage of parathion equivalent to 0.1
pound per acre was used in tests with the cotton
aphid. The mortality rate among cotton aphids con-
fined on freshly sprayed plants was 38 percent higher
than among aphids confined on treated plants which
had been exposed to temperatures ranging from 65°
to 98° F. for 24 hours, Figure 9.

METHYL PARATHION. In tests with the boll
weevil, methyl parathion was sprayed on plants at
dosages equivalent to 0.125 to 0.33 pound of toxicant
per acre. Almost 100 percent of the weevils confined
on freshly sprayed plants were killed, Figure l0. The
mortality rate was reduced by about l9 percent when
weevils were confined on treated plants which had
been held in the laboratory at 85° F. for 24 hours.
No further reduction in weevil mortality occurred
on treated plants which had been held in the labora-
tory for 24 hours at temperatures up to 110° F. How-
ever, the. average mortality was reduced by 65 percent
when weevils were placed on treated plants which had
been held outdoors for 24 hours. Bright sunlight may
have contributed to these losses in residual toxicity.

Tests with the cotton leafworm showed that the
residual toxicity of methyl parathion to this insect
was reduced when treated plants were held in the
laboratory for 24 hours before leafworms were placed
on them.

“When both insecticides were applied at the same
dosage, methyl parathion was less toxic to the tumid
spider mite than parathion under all test conditions.
Essentially the same ,__results were obtained in tests
with the cotton aphids.”

MALATHION. The residual properties of
malathion were similar to those of methyl parathion
in tests with the boll weevil. In these tests, malathion
was sprayed on plants at dosages equivalent to 0.5
pound of toxicant per acre. Mortalities among weevils

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Figure 6. Effects of various climatic factors on the toxicities
of toxaphene, endrin and aldrin to the cotton leafworm, Ala-
bama argillacea (Hubner).

confined on freshly sprayed plants were 19 percent
greater than mortalities among these insects confined
on treated plants which had been exposed to prevail-
ing temperatures for 24 hours. Temperatures above
100° F. in the absence of bright sunlight did not
further reduce the residual toxicity of malathion. The
residual effectiveness of this insecticide was greatly
reduced when treated plants were exposed to high
temperatures and bright sunlight before weevils were
confined on them.

In. tests with the cotton leafworm, spray residues
of malathion from an application equivalent to 0.25
pound per acre were no longer toxic to this insect
after the treated plants had been exposed to prevail-
ing temperatures for 24 hours.

The extent of mortality among cotton aphids
on spray residues of malathion was reduced 50 per-
cent after treated plants had been exposed to prevail-
ing temperatures for 24 hours.

GUTHION. Dosages of Guthion equivalent to
0.04 pound per acre were used in tests with the boll

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Figure 7. Effects of various climatic factors on the toxicities
of four chlorinated hydrocarbon insecticides to the salt-marsh
caterpillar, Estigmene acrea (Drury).

     
 

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GU-TIIION

Figure 8. Effects of various climatic factors on the toxicities
of parathion, Guthion, and Phosdrin to the tumid spider mite,
Tetranychus tumidus Banks.

weevil. Excellent kills of weevils were obtained on

freshly treated plants and also on treated plants which
had been exposed to prevailing temperatures for 24
hours. In these tests, temperatures above 100° F. did
not affect the residual toxicity of Guthion. Dusts of
Guthion were equally effective under these conditions.

Dosages of Guthion equivalent to 0.5 pound of
toxicant per acre were highly toxic to the tumid spider
mite. The extent of mortality among the mites was
reduced only 18 percent when they were confined on
treated plants which had been exposed to prevailing
temperatures for 24 hours. However, smaller dosages
of Guthion were ineffective under these conditions.

Effect of Simulated Rain

In general, simulated rain appreciably reduced
the residual toxicities of the chlorinated hydrocarbon
insecticides to all the test insects. It is doubtful that
the residues on treated plants remaining after a half-
inch rain would be sufficient to insure protection
from insect damage. Residues of endrin appeared to
be least affected by rain, while the residual toxicities
of aldrin and BHC were almost completely destroyed.

 

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Figure 9. Effects of various climatic factors on the toxicities
of parathion, malathion, and BHC to the cotton aphid, Aphis
gossypii Glover.

8

Among the organophosphorus compounds,
Guthion and malathion were considerably less effec-
tive after a rain. However, most of the other insecti-
cides in this group had short periods of residual
effectiveness even in the absence of rain.

CHLORINATED HYDROCARBON
INSECTICIDES

TOXAPHENE. Several experiments were con-
ducted to determine the effect of rain on the residual
toxicity of toxaphene to the boll weevil. All the
materials were applied as emulsion sprays. One-half
inch of simulated rain was applied as soon as the
sprays had dried on the plants and the weevils were
released on plants within 30 to 45 minutes. No
reductions in mortality could be attributed to the rain
treatments in four of the tests while reductions above
5O percent occurred in the remaining three tests. It
is noteworthy that reductions in mortality occurred
in those tests where the kill of weevils on the freshly
sprayed plants was relatively high. When all the
treatments were weathered for 24 hours and reduc-
tions in residual toxicity caused by other factors were
discounted, simulated rain did not further reduce the
residual toxicity of toxaphene.

In tests with the cotton leafworm, simulated rain

was detrimental to toxic residues of toxaphene. Mor- I

talities among worms were about‘ 30 percent less on
spray residues of this insecticide which had been
exposed to simulated rain than those obtained on

treatments held under the usual laboratory conditions. I I
The residual effectiveness of toxaphene dust were.

virtually destroyed by simulated rain in these tests.

In tests on the salt-marsh caterpillar, spray dos-
ages of toxaphene equivalent to 0.35 pound of toxi-
cant per acre killed 55 percent of the caterpillars on
the residues weathered by simulated rain. The
residual effectiveness of toxaphene dusts for these
insects was destroyed by simulated rain.

DIELDRIN. Mortalities among boll weevils con-
fined on plants treated with dieldrin were reduced
by approximately 50 percent after the plants had
been exposed to simulated rain. However, some of
the mortality rates averaged less than 30 percent even
on the freshly sprayed plants.

In tests on the salt-marsh caterpillar, the residual
effectiveness of dieldrin was adversely affected by
exposure of the sprayed plants to simulated ,. rain.
Mortalities among the caterpillars were reduced from
90 percent on freshly sprayed plants to 34 percent on
the treated plants subjected to simulated rain.

BENZENE HEXACHLORIDE. Simulated rain
completely destroyed the residual toxicity of BHC
dusts to the cotton leafworm when the dusts were
applied at dosages equivalent to 0.04 to 0.08 pound
of toxicant per acre.

The effect of rain on spray residues of BHC
could not be evaluated in tests on the boll weevil

  
 
 
  
 
  
 
  
 
  
 
  
  
 
 
  
  
 
  
  
 
  
  
   
 
 
   
  
  
 
 
 
  
 
 
 
  
 
 
  
 
 
  
 
 
  
 
 
  
 
 
  

the cotton aphid because a 24-hour exposure
I I in the absence of rain was almost as detrimental
he residual toxicity as exposure to rain.

 ALDRIN. Residues of aldrin on plants were no
er effective in killing boll weevils after being
ected to simulated rain. Simulated rain was
y, ied as soon as the spray had dried on the plants.
 this short exposure resulted in a 67 percent
ease in mortality compared with mortalities
ng weevils confined on freshly sprayed plants.

ENDRIN. Endrin spray applied to plants at a
ge equivalent to 0.196 pound per acre killed 80
em of the boll weevils released on treated plants
h had been exposed to simulated rain.

When the cotton leafworm was used as a test
t, simulated rain reduced the residual toxicity

Jndrin spray in one series of tests, but had no
t on the residual toxicity in the other.

Mortalities among salt-marsh caterpillars from
yresidues of endrin were reduced from 95 percent
percent by a 24-hour exposure period which
ded simulated rain.

*HEPTACHLOR. The residual toxicity of hepta-
sprays to the boll weevil was adversely affected
in. Mortalities among weevils confined on
ed plants were reduced by approximately 50
nt when the treated plants were exposed to
ated rain.

A spray application of heptachlor equivalent to
und‘ of toxicant per acre killed only 20 percent
salt-marsh caterpillars released on treated plants
hadbeen exposed to rain compared to a 77
nt mortality rate obtained on freshly sprayed

NOPHOSPHORUS INSECTICIDES

ARATHION. The residual toxicity of para-
 . to the tumid spider mite was not affected by
 ted rain when the spray was applied at a dosage
lent to 0.3 pound of toxicant per acre.

ills of the cotton aphid on spray residues of
ion were reduced by approximately 25 percent
wsthe kills obtained on residues held for 24 hours
“absence of rain. The initial dosages of para-
" in these experiments were equivalent to 0.25
of toxicant per acre.

ETHYL PARATHION. When boll weevils
used in tests with this compound, most of the
 in toxiciftyioccurred during the 24-hour weather-
iod. No additional losses due to simulated rain
ieéiapparent. Dosages of methyl parathion equiva-
4 0.2 pound per acre were ineffective to the boll
 24 hours after the insecticide was applied.
 results were obtained in tests with the cotton

E RAIN

INITIAL 555E335 24- HOUR
roxucnv  sxrosua:

 WINO

O

b
O

AVERAGE ‘Z CONTROL
N 0|
O O

'6

     

ION

Figure 10. Effects of various climatic factors on the tox-
icities of four organophosphorus insecticides to the boll weevil,
Anthonomus grandis Boh. '

MALATHION. Sprays of malathion were in-
effective for killing the boll weevil after the residues
were exposed to simulated rain. The reductions in
kills were less striking in tests on the cotton leafworm,
but the detrimental effect of rain was still clearly
evident. Exposures to simulated rain reduced kills
of cotton aphids from residues of malathion by more
than 5O percent.

GUTHION. Simulated rain was probably the
most important single factor contributing to the loss
of the residual toxicity of Guthion with all species
of the test insects. Toxic residues of this material
were relatively stable under all the other climatic
conditions encountered during these investigations.
In tests on the boll weevil, dosages of Guthion equiva-
lent to 0.125 pound per acre were ineffective after
the residues had been exposed to simulated rain. In
tests on the tumid spider mite, dosages of Guthion
equivalent to 0.5 pound per acre lost about 50 percent
of the residual effectiveness after weathering by rain.

PHOSDRIN. The effective residual period of
Phosdrin was too short to evaluate the effects of
simulated wind and rain on the residues. Tempera-
ture and humidity conditions incident to the holding
period were sufficient to destroy most of the residual
toxicity of this material.

Effect of Simulated Wind

Among the chlorinated hydrocarbon insecticides,
there was little difference between the effects of simu-
lated wind and rain on residual toxicities. However,
it is likely that under field conditions the effects of
rain would be more noticeable.

Simulated wind was less damaging than rain to
the residual toxicities of Guthion and malathion in
most of the tests. The results with parathion and
methyl parathion were about the same whether the
period of weathering included simulated wind or rain.

9

Generally, insecticide dusts were affected more
by simulated wind than sprays of the same materials.

CHLORINATED HYDROCARBON
INSECTICIDES

TOXAPHENE. Simulated wind reduced the
residual toxicity of toxaphene sprays to the boll
weevil by approximately 40 percent after the effects
of temperature and humidity 0n the residues during
the exposure periods had been discounted.

The effect of wind on dust residues of toxaphene
was evident in tests on the salt-marsh caterpillar.
After dusted plants were exposed to simulated wind
for 24 hours, mortalities among caterpillars confined
on these plants were reduced 55 percent.

DIELDRIN. Spray residues of dieldrin were less
toxic to the boll weevil after exposure to simulated
wind. Kills of weevils on treated plants, which had

been subjected to air currents for 24 hours, were

reduced by 33 percent compared with those obtained
on treated plants exposed for the same period of time
in the absence of simulated wind.

In tests with dieldrin dusts on the salt-marsh
caterpillar, 80 to 90 percent of the test insects were
killed by dosages of dieldrin equivalent to 1.0 pound

"of toxicant per acre; however, only 30 to 40 percent

were killed when placed on treated plants which had
been subjected to simulated wind for 24 hours. Essen-
tially the same results were obtained with sprays of
dieldrin applied at dosages equivalent to 0.15 to 0.33
pound of toxicant per acre.

BENZENE HEXACHLORIDE. The residual
toxicity of BHC to the boll weevil was practically
destroyed by simulated wind.

In tests with the cotton leafworm BHC was
sprayed on plants at the rate of 0.25 pound per acre.
After the treated plants had been exposed to simu-
lated wind for 24 hours the kills among confined
leafworms were reduced by 30 percent.

There was little difference in the residual toxicity
of BHC to the cotton aphid when simulated wind
was added to the weathering factors affecting the
treated plants.

ALDRIN. Toxic residues of aldrin were dissi-
pated so rapidly by temperature and moisture con-
ditions during the exposure periods that it was
difficult to evaluate the role of wind in the reduction
of the residual toxicity to the boll weevil of this
compound. However, kills of the salt-marsh cater-
pillar and the garden webworm were reduced by
about 40 percent by the action of wind on spray and
dust residues of aldrin.

Simulated wind appreciably reduced the residual
toxicity of aldrin to the leafworm.

ENDRIN. Wind apparently had little effect on
the residual toxicity of endrin to the boll weevil.
Compared with 78 percent mortality obtained on

1O

freshly sprayed plants, spray residues of endrin sub-
jected to wind currents for 24 hours killed only 36
percent of the cotton leafworms released on them.
However, it should be noted that the dosage of endrin
used in this experiment was equivalent to only 0.01
pound of toxicant per acre.

Dosages of endrin equivalent to 0.25 pound of
toxicant per acre killed about 50 percent of the test
population of salt-marsh caterpillars on residues which
previously had been exposed toisirfiulated wind. How-
ever, when the dosage was reduced to 0.15 pound per
acre, the kills averaged about 60 percent less than
those obtained among the insects confined on the
residues weathered in the absence of simulated winji.

HEPTACHLOR. The residual toxicity of hepta-
chlor to the boll weevil was reduced appreciably by
simulated wind. Mortalities among weevils confined
on sprayed plants were reduced by 50 percent by
exposure of the treated plants to either simulated
wind or rain. Similar results were recorded in tests
with the salt-marsh caterpillar.

ORGANOPHOSPHORUS INSECTICIDES

PARATHION. Simulated wind did not reduce
the residual toxicity of parathion spray to the cotton
leafworm even when the dosages of insecticide were
reduced to 0.005 pound of toxicant per acre.

In tests on the tumid spider mite, simulated wind
acting on the parathion spray residues reduced the
kills about 19 percent below those obtained from
residues held in the absence of wind. Essentially the
same results were obtained in tests using the cotton
aphid.

METHYL PARATHION. When dosages equiva-
lent to 0.5 pound per acre of this insecticide were
applied to plants to kill boll weevils, simulated wind
did not reduce the residual toxicity below that on
treated plants held in the absence of wind. In this
instance most of the toxic residues were dissipated
by temperature and humidity conditions inherent in
the holding period. No additional losses of residual
toxicity could be attributed to wind in tests on the
tumid spider mite. However, mortalities obtained
on sprayed plants held for 24 hours in the absence
of wind were quite low.

The residual toxicity of methyl parathion to the
cotton leafworm was virtually destroyed when treated
plants were exposed to wind for 24 hours.

MALATHION. In tests with the boll weevil,
malathion was applied to plants at the rate of 0.5
pound per acre. At this dosage the residual toxicity
of malathion to weevils was not reduced appreciably
by simulated wind.

The residual toxicity of malathion to the cotton
leafworm was reduced by wind. However, the dosages
of malathion used in tests on this insect were equiva-
lent to only 0.025 pound of toxicant per acre.

A N0 reduction in residual toxicity of malathion
to the cotton aphid owing to simulated wind was
_ recorded.

GUTHION. Residues from an application of
Guthion dust exposed t0 simulated wind for 24 hours
killed about 60 percent of the boll weevils released

 0n them compared t0 an 8O percent kill obtained on
a residues held in the absence of wind. However, it
_ should be noted that the dosage of Guthion in this
5 experiment was equivadent to only 0.06 pound of
.4 technical material per acre. Essentially the same
a results were obtained in tests on spray applications
 of Guthion. A 25 percent reduction in kills of weevils
 was noted after treated plants were exposed to simu-
§lated wind for 24 hours. Spray residues of Guthion
 did not appear to be adversely affected by wind in
 tests on the tumid spider mite when the initial dosages
 were equivalent to 0.5 pound of toxicant per acre.

 Effect of Simulated Dew on
 Insecticides

Exposing plants treated with dusts or sprays of
toxaphene-DDT and BHC-DDT to dews reduced the
toxicities of these materials to the boll weevil. In
c neral, the toxaphene and toxaphene-DDT sprays
mained more toxic after these exposures than toxa-
gphene dust or BHC sprays or dusts.

 

 

  
  
   
 
  
 
 
  
  
  
  
  
  
  
  
   
  
 
  
  
  
  
 
 

The residual toxicity of aldrin to the boll weevil
as virtually destroyed by a 24-hour exposure to
bient temperatures accompanied by a dew.

In general, dew was no more detrimental to the
idual toxicities of the organophosphorus insecti-
es than the temperature and humidity conditions
inherent in the holding periods.

Effect of Sunlight on
Insecticides

No techniques were devised to investigate the
' tof sunlight on insecticide residues in the absence
A igh temperature and low relative humidities. Out-
r climatic conditions during the summer included
imum light intensities of from 7,000 to 13,000
tcandles. The residual toxicities of all the in-
icides tested except Guthion were more adversely
ted by outdoor exposures than by exposures to
parable high temperature and low humidity con-
'ons on the laboratory or greenhouse. It is doubt-
that these differences were caused solely by varia-
t. in light intensities.

f ects of Climatic Factors on
Sevin

A.Several preliminary tests were conducted on the
ts of temperature and humidity conditions and

simulated rain on the residual toxicity of Sevin to
the boll weevil. Wettable powders of Sevin sprayed
on plants at a dosage equivalent to 1 pound of toxi-
cant per acre remained equally toxic to the boll weevil
after a 24-hour exposure to midsummer light, tem-
perature and humidity conditions, or to 0.5 inch of
simulated rain. The mortality rates among weevils
on these treated plants were not significantly different
from the kills obtained on treated plants held in the
laboratory at 85° F.

Literature Cited

Gaines, J._ C., and H. A. Dean. 1949. Effect of
temperature and humidity on» the toxicity of certain
insecticides. Jour. Econ. Ent. 42: 429-433.

Gaines, J. C., and H. A. Dean. 1950. Effect of
climatic factors on the toxicity of certain insecticides.
Jour. Econ. Ent. 43: 602-605.

Gaines,  C., and W.  Mistric, Jr. 1951. Effect

of rainfall and other factors on the toxicity of certain
insecticides. Jour. Econ. Ent. 44: 580-585.

Gaines,  C., and W.  Mistric, Jr. 1952. Effect
of environmental factors on the toxicity of certain
insecticides. Jour. Econ. Ent. 45: 409-416.

Mistric, W. J., Jr., and  C. Gaines. 1953. Effect
of wind and other factors on the toxicity of certain
insecticides. Jour. Econ. Ent. 46: 341-349.

Mistric, W. J., Jr., and J. C. Gaines. 1954. Effect

of weather factors on the toxicity of certain insec-
ticides. Jour. Econ. Ent. 47: 646-651.

Mistric, W. J., Jr. 1954. The effect of climatic factors
on the toxicity of certain organic insecticides. Dis-
sertation. A 8c M College of Texas.

Owen, B. L. 1954. The effect of air currents on the
toxicity of spray and dust formulation of toxaphene,
aldrin and dieldrin. Thesis. A 8c M College of Texas.

Mistric, W. J., Jr., and D. F. Martin. 1956. Effect
of sunlight and other factors on the toxicity of certain
insecticides. Jour. Econ. Ent. 49: 757-760.

Hightower, B. G., and D. F. Martin. 1958. Effect
of certain climatic factors on the toxicities of several
organic phosphorus insecticides. Jour. Econ. Ent.
51: 669-671.

Hightower, B. G. 1959. Bioassays of weathered resi-
dues of several organic phosphorus insecticides. Jour.
Econ. Ent. 52. 840-842.

Acknowledgments

The authors express their appreciation to H. A.
Dean, W.  Mistric, Jr., D. F. Martin, B. L. Owen
and H. J. Reinhard for their contributions.

This work was conducted in cooperation with
the Entomology Research Bureau, U. S. Department
of Agriculture.

ll

  

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