Control of the vetch bruchid in western Oregon, with special reference to DDT


Material Information

Control of the vetch bruchid in western Oregon, with special reference to DDT
Physical Description:
10 p. : ; 27 cm.
Rockwood, L. P
Reeher, Max M ( Max Moore ), b. 1892
United States -- Bureau of Entomology and Plant Quarantine
United States Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington, D.C
Publication Date:


Subjects / Keywords:
Vetch bruchid -- Control -- Oregon   ( lcsh )
DDT (Insecticide) -- Testing   ( lcsh )
federal government publication   ( marcgt )
non-fiction   ( marcgt )


Statement of Responsibility:
by L.P. Rockwood and Max M. Reeher.
General Note:
Caption title.
General Note:
General Note:
"April 1945."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030289959
oclc - 779851244
System ID:

Full Text
*. i *11 i IU.W r-'~ "
April 1945 E-650

United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine


By L. P. Rockwood and Max M. Reeher
Division of Cereal and Forage Insect Investigations

The vetch .bruchid (Bruchus brachialis Fahraeus) has greatly reduced
the quality and quantity of hairy vetcl seed in the area of western Ore-
gon that in recent years has produced more than three-fourths of the
American crop of this seed.. Production in that area is declining rapidly,
and will continue to do so unless methods for the control of the bruchid
are found that are economically feasible. This decline has usually been
noticeable within 5 years after the insects first appearance in a seed
district. The production of hairy vetch seed has already become unprof-
itable in about half of the Willamette Valley, and the vetch bruchid is
known to occur in all parts of the Valley.

Control of the vetch bruchid in this area is especially difficult
because hairy vetch has escaped from cultivation and has become a common
weed. Although there is but one generation of the insect a year, the
overwintered weevils are long lived and are widely prevalent outside of
seed fields. Hence infiltration into fields left for seed occurs over a
long period, from the time the first seed pods appear, usually about
June 1, until harvest in late July when some pods are still green*

Control experiments conducted from 1940 through 1943 indicated that
90 percent or more of the bruchids actively moving about in a field at
the time of treatment could be killed by an application of 25 pounds per
acre of a dust containing 0.75 percent of rotenone. A temperature of
6707. or above is necessary to insure good results. In 1943 a poisoned-
bait spray composed of sodium fluosilicate 2.5 percent and sugar 10 per-
cent by weight in water, applied at the rate of 10 gallons per acre,
gave similar results under like conditions. However, these treatments
reduced the weevil populations in seed fields for only a very brief
period, and the results were almost nullified by the infiltration of
weevils from outside the treated areas. It became evident that several
applications would be necessary to obtain satisfactory control with these
materials* Repeated treatments are not economically feasible,since the
average crop of clean hairy vetch seed in the Willamette Valley is only
about 250 pounds per acre. Furthermore, they would increase the mechani-
cal damage to the crop.

23 1945

Field. experiment in 1944, especially those on the Red. Hill
Soils Experimental Area at Oregon City, confirmed the conclusions ob-
tained in previous yeari concerning rotenone dust and bait sprays.
These experiments demonstrated that excellent control of the vetch
bruchid, even in areas where this insect is extremely abundant, can
be obtained with two applications of 3 to 5 percent DDT dusts at 25
or more pounds per acre. They also indicated that one thorough and
properly timed treatment of these dusts should give adequate control
and a profitable increnoe in we'wvil-free seed.*

Materials Used

In July 1943 10 pounds of a mixture containing 50 percent of DT?
was received from the Division of Insecticide Investigations. This
mixture had been prepared by grinding equal weights of DDT and
pyrophyllite (Pyrax A:3) in a hammer mill, and. contained many small
lumps or concretions of DDT. Small amounts of this stock were mixed.
with Frianite (a volcanic ash) in a mortar to make a series of dusts
containing 0.5 to 7.5 norcent of DDT, for trial in laboratory experi-
ments during the following winter and early spring. A 5 percent =T-
pyrophyllite dust was also prepared from this stock for use in repli-
cated field-plot experiments at Oregon City during the summer of 1914.
A 1 percent rotenone duet and a poisoned-bait spray, prepared by dissolv-
ing 4 pounds of sugar Li 5 gallons of water and adding 1 pound of
calcium arsenate, were &l;o included in the Oregon City experiments.

On June 17, 1944, a Lxply of factory-mixed 10 percent DDT-
pyrophyllite dust was revived. A portion of this mixture was diluted
with pyrophyllite or :-;.anite to maika a 3 1/3 percent DDT dust.l/ and
was used on June 20 n D." f;,- ton, Oreg.
Laboratory Experiments
Laboratory expsraments were carried out at Forest Grove, Oreg.,
in March, April, and 1La;r with vetch bruchids that had emerged in the
fall of 1943, and had bu3en kent in cages in an unheated closet over winter.
Only weevils that showJl aonmal activity when brought into a warm room
were used. In some experiments a st-aight calcium arsenate dust and dusts
containing different pA cer-tages of DDT were tested as stomach poisons by
applying them at a known rate to paraffin cells (small block of paraffin
hollowed out in center) in a dusting chamber. The cells were then filled
with dilute honey wat.?: and each one was caged with 20 weevils in a clean
shell vial. In other etxoeriments DDT and rotenone dusts were tested as
contact poisons by appli;'inv thsam at a known rate to small, dry glass
dishes and then confining 20 weevils in each dish for 3 days. The pois-
oned-bait mixtures were eitaier placed in paraffin cells or sprayed onto
glass slid-es, which "' 3 i 1.ce&i in large glass cages each containing 100
weevils. Each treatment was replicated at least 5 times. To determine
the residue! effect, the same paraffin cells or glass dishes used in ear-
lier experiments werE. again used for fresh lots of bruchids 23 to 24 days
after the dust was apT1Hed., -nd after some of it had been removed by
weevils killed in prior *eri'enimts. Results of these experiments are
given in Table 1.

I/ Prepared by the courtesy of H. J. GL.-A.y.


Table 1.-Mortality of vetch bruchid adults confined in dry glass dishes
dusted with DDT or rotenone. Forest Grove, Oreg., 191X

....Mortality of adults..
Dust Dosage After exposure 23 days
treatment per acre for 3 days after treatment

Percent Pounds Percent Percent

0.5 Rotenone 30 100-/ 29
0.75 Rotenone 10 1001/ 20

0.5 30 95 (5 days) 17
1.0 30 100 37
2.0 30 100 81
3.0 10 100 23
3.0 20 100 83

Check (Prianite) 30 2 5

Differences required for significance
Odds of 99:1 18
Odds of 19:1 1

I/Some alive, but paralyzed, a long tire after treatment.

About 30 pounds per acre of a 2 percent DDT dust or about 20 pounds
per acre of a 3 percent DDT dust was necessary to obtain a high residual
effect against the adult bruchids.

In the experiments in which dusted paraffin cells were filled with
honey water,the residue from a 5 percent DDT dust applied at :he rate of
30 pounds per acre killed 100 percent of two successive lots of weevils,
end 74 percent of a tV.rd lot introduced 23 days after the cells were
dusted. It was just as effective a stomach poison as the residue from
30 pounds per acre of straight calcium arsenate, which had killed only 73
percent of one previous lot of weevils. The residue from a 3 percent
DDT dust originally applied at the rate of 30 pounds per acre killed
only 54 percent of the third lot of weevils which -vas significantly less
than that caused by the residue of the 5 percent DDT dust. The residual
effect of DDT varied with both the percentage strength and the dosage
applied, and for field dusting it was found advisable to use at least 25
pounds per acre of a lust containing not les than 3 percent of DDT.
Derris dust containing 0.75 percent of rotenone 1n applied at 10 pounds
per acre killed only '40.6 percent of the second lot of weevils, and its
residual effect was therefore much less than that of the 5 percent DDT
dust or the calcium arsenate.

In tests with poisoned-bait mixtures the same technique was used
as outlined previously. Sodium fluosilicate was found to be less
effective than calcium arsenate in a sugar solution, and entirely inef-
fective after the bait had dried on the slides. As shown in table 2, a
bait spray containing as little as 0.5 percent of 3DT was as effective
as a spray containing 2.5 percent of calcium arsenate, whereas a bait
spray containing only 0.05 percent of rotenone was almost as effective
as the calcium arsenate spray. Stock molasses from sugarcane used as a
sweetening agent appeared to repel the weevils. Solutions of brown
sugar and white sugar were equally effective, but residue from the brown
sugar solution seemed to have better physical characteristics. There
was no difference in attractiveness between 10- and 5-percent sugar
solutions. In fact none of the baits could be observed to attract the
weevils. Slides sprayed with bait mixtures were caged with weevils both
before and after the slides had been air-dried. The mortalities shown
in table 2 indicate that ,although water in the bait mixtures appeared to
be the main attractent,there was considerable feeding on the dried resi-
These experiments indicated that calcium arsenate would be the best
poison of those tested and now available for field use in bait sprays,
end that a dosage of about 10 gallons per acre would be sufficient* For
a single application at this rate the materials should cost not more
than half as much as the dusts, and where spraying equipment is avail-
able it might be an effective substitute for rotenone dust. For worth-
while control, however, more than one application would probably be
Table 2.-Mortality of vetch bruchid adults caged with sweetened bait
sprays containing different poisons. Forest Grove, Oreg*.,

Poison Strength Lqd Mortality
Liquid bait Dried bait
Percent Percent Percent
DDT 0.5 99 73
Derris (rotenone) 0,05 85 -
0.13 69
Calcium arsenate 2.5 90 57
Sodium fluosilicate 2.5 96

Check (sugar water)


The Red Hill Soils Experimental Area at Oregon City was selected
for 1 set of field experiments. This area was divided into 3 courses
running north and south, each course containing 23 one-twentieth acre
plots. Fifteen of these plots were hairy vetch, interspersed with
grain plots or summer fallow. The courses were divided into 3 blocks
running east and west. This allowed for 3 replications of each treat-
ment, 1 in each block and 1 in each course. There were also 3 unplotted
strips of hairy vetch on the area planted as follows: 1.2 acres east,
0.6 acre west, and 1 acre north of the plots. In order to avoid imme-
diate infiltration of weevils into the test plots after dusting, these
strips were also treated. No untreated check plots were left except
the hairy vetch that could be found outside the area within a radius
of 2 miles. A check was found for a count of eggs on the pods in early
July, but by the time of seed harvest all hairy vetch within 3 miles
of Oregon City had been harvested for hay. Therefore, volunteer hairy
vetch at Forest Grove was used for a check on seed-infestation counts.
This vetch had shown almost the same egg count on the pods as the
check at Oregon City. The Oregon City neighborhood is known to be one
of the sections of western Oregon most heavily infested by vetch
bruchids, and S0 percent infestation can be expected in any hairy
vetch seed grown in that vicinity.

In these experiments, except as noted below, all dusts were put on
at the rate of 22 to 25 pounds per acre, and the bait spray at 10 gal-
lons per acre. About 5 acres were treated with hand equipment at
Oregon City, of which 31 acres were treated twice. It was considerably
harder to treat the unplotted strips with hand dusters than it was to
treat the small, narrow plots. Consequently they were less thoroughly
dusted. The plots in block 1, course 1, dusted twice with 5 percent
DDT, received a heavier application on June 8 (35 pounds of the dust
mixture per acre) than the plots in the other blocks because they were
dusted before the experimental technique was standardized. Five percent
DDT dust was applied to the two unplotted strips east and west of the
plots on June 7 under cool, cloudy conditions, which conditions we Iknew
from experience were unfavorable for dusting with rotenone or for bait
spraying because of weevil inactivity. On June 8 the plots to receive
dust were dusted with 5 percent DDT in the morning at a maximum field
temperature of about 670 F.; as the sky became overcast and it became
too cool for weevil activity, the rotenone dust and bait spray were not
applied that day. On June 9, a warm, sunny day with a maximum tempera-
ture of 889, the remaining plots were treated with rotenone dust and
bait spray, and the unplotted north strip was treated with the bait
spray. All these treatments were put on at about the time the first
hairy vetch pods were setting.
Observations made on June 21 showed there had been a large ifliux
of weevils into the plots treated with rotenone dust and bait spray;
therefore all the plots were redusted or resprayed on June 23 under
very favorable conditions (maximum temperature 83 F.). The unplotted
north strip was also resprayed with the bait mixture because of heavy
weevil infiltration since the first treatment. The unplotted east and
west strips, dusted with 5 percent DDT on June 7, still showed few
weevils and were not retreated.


The bruchid populations on all parts of the area were checked
by sweeping the hairy vetch at various times before and after dusting.
These sweepings gave an indication of weevil movement onto the plots
and also the effects of the treatments. However, the activity of the
weevils is so dependent on temperature that counts of weevils swept
are not dependable enough for statistical analysis. Examination of
the ground under the vetch showed that all treatments, especially the
DDT, had. given good kills. All weevils on the plots treated with
dust containing 1 percent of rotenone had been knocked down 3 hours
after treatment, but 3 out of 10 weevils found on the ground in these
plots 12 days after treatment were alive and able to crawl; however,
2 of these were partly paralyzed. The sweepings, and later the in-
festation counts, showed that there was a heavy influx of weevils from
outside the area, especially from the south and west, between June 10
and 22.

In July counts of eggs on 300 to 400 hairy vetch pods from each
treatment, examined in 100-pod lots, were made. The sample pods were
collected from plants at intervals of 20 feet on each plot and on a
line through the unplotted strips. All the pods were taken from each
plant examined. Just before harvest seed samples were collected in
the pods, the samples from each plot or unplotted strip consisting of
all the pods on plants 10 feet apart. A similar sample was taken
from the untreated hairy vetch at Forest Grove, which had shown the
same egg count on the pods as the check at Oregon City. Each lot of
seed pods was hand-shelled, and the resulting samples of 3 to 8 ounces
of clean seed were reduced in a grain sampler to from 0.7 to 1 ounce
(800 to 1200 seeds). All the seeds in each of these small samples were
examined in 100-seed lots under a binocular microscope for larval
entrance holes and the percentages of infestation determined. Seeds
containing such holes or bearing suspicious abrasions were counted as
infested, even though a considerable number of bruchid larvae die soon
after entrance and before the seed is appreciably damaged. The mean
coefficient of variation among the 100-seed lots from individual plots
was rather high, 20 percent, but when the infestations in 8 to 12 lots
of 100 seeds from one treatment were paired with those from another
treatment it was possible to show that a difference of at least 10
percent between the mea-n infestations in the respective treatments was
necessary for significance. The results of these counts are given in
table 3-













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The two methods of estimating effectiveness of control gave
consistent results, but the percentage of control calculated on the
basis of seed infestation was uniformly lower than on the basis of
eggs on pods. This was probably due to late oviposition after the
egg counts early in July. The counts showed that infiltration of
weevils after treatment had been considerable from the south and.
west, enough in block 3, course 1, treated with the bait spray twice,
to cause a highly significantly greater infestation than en the
other balt-spray plots. They also showed that the control secured by
two treatments with 5 percent DD had. been highly significantly better
on block 1, course 1, where the first dust on June 8 was applied at
the rate of 35 pounds per acre, than on the other plots where the dust
was applied at 22 to 25 pounds per acre. Two applications of 5 percent
DDT dust were highly significantly better than 2 applications of 1
percent rotenone dust, or of bait spray containing 2.5 percent of
calcium arsenate, 10 percent of sugar, and water, the last two treat-
ments being equally effective. One early application of 5 percent DDT
dust on the unplotted east and west strips at the time the pods were
beginning to set, even though poorly applied, was equivalent to two
applications of rotenone dust or bait spray*

After receipt of the 10 percent dust on June 17, a 10-acre field.
near Dayton, Oreg., was found available for experimental purposes. The
field had been seeded to common vetch but had developed a thick stand
of volunteer hairy vetch. On June 20 the 3 1/3 percent DDT-pyrophyllite-
Frianite dust was applied to 5 5 acres of this field with a power duster
at the rate of 22 to 25 pounds per acre. The maximum temperature was
approximately 73. At least 25 percent of the pods were already formed
and many bruchid eggs were present, Indicating that the dust was applied
too late for best results, June 10 probably would have been the correct
date for this application. An untreated check of approximately 4 acres
on the north side of this field was delimited by cutting a 16-foot strip
of hay. As it was feared that weevils might move into the dusted part
from the check, north of the hay strip, a 214-foot buffer strip along the
south side of the check was also dusted. Egg counts on the pods were
made as at Oregon City. Seed samples were secured at harvest by taldng
samples from two places in each sack as it was dropped by the combine.
The large uncleaned samples, of which about 20 percent was hairy vetch
seed, were reduced to workable proportions in a grain sampler, and these
small samples were hand-cleaned and examined for bruchid infestation as
in the earlier experiments*

Sweeping in all parts of the field after dusting showed that the
3 1/3 percent DDT dust had eliminated practically all of the weevils
present in the treated part of the field at the time of dusting, but
that some infiltration from the west and south occurred later. The
results of the egg-and seed-infestation counts are shown in table 4'
The yield of cleaned hairy vetch seed averaged 60 pounds per acre more

-9 a

on the treated part of the field than on the untreated check. Probably
some of the infested seeds were taken out in cleaning, as seeds in
which weevils have matured are lighter than uninfested seeds. The con-
trol was not so high as it was with one early (June 7) dusting at
Oregon City. This is attributed to the fact that about 25 percent of
the pods in the Dayton field were well developed and well sprinkled
with bruchid eggs at the time of dusting (June 20), whereas only the
first pods had recently set at Oregon City on June 7.
Table 4,--Results of late dusting (June 20) with 3 1/3 percent
MT near Dayton, Oreg., 1944

Iggs per Infested Germination Average
Treatment 100 pods Control seeds Control quick and .,yield
on July 11 per 100 hard seeds!I per acre

Number Percent Nhmber Percent Percent Pounds
DDT dust, 3 1/3% 234 60 32.0 44 1,14 312
Check (untreated) 590 57.3 75.8 250
Buffer strip 45.2 21 76.51 295

2/ Seed test made by seed company, after cleaning in mill.

Careful examination of the ground under hairy vetch at Oregon City
disclosed that 5 percent DDT had killed insects of several species, includ-
ing a large phalaenid larva (Caenurgina sp.), three or four species of
flies (agromyzids and scatophagids), many beetles (nitidulids, carabids,
silphids, elaterids, coi.inellids, and Diabrotica llpunctata Mann.), flea
beetles, weevils (Sitona sp. and Brachyrhinus sp.), pea w evils, ants, and
spiders. Syrphid and coccinellid larvae, which were abundant, appeared to
be unaffected. Pea aphids (Macrosiphum gI (Kltb.)) were present in large
numbers on some of the plots, but only a few appeared to have been killed
by DDT. Some of these insects, especially coccinellid beetles, were also
found dead on the rotenone dust and bait-spray plots. No dead bees were
found and no decrease was noted in the number of honey bees that were swept
from hairy vetch dusted with DDT. There were no ill effects On the opera-
tors, who found DDT to be much less irritating than the rotenone dusts.

Two applications of 3 to 5 percent DDT dust, at the rate of 25
pounds of the mixed dust per acre, gave excellent control of heavy infesta-
tions of the vetch bruchid (Bruchus brachialis Fahraeus) on hairy vetch.
The results of the experiment near Dayton, Oreg., inreicate that one thorough
accurately timed application at the time the first pods set will probably
give adequate control in most cases. The residual effect of DDT is especi-
ally valuable for bruchid control because of the long period during which
the fields are invaded biy weevils from outside. Judging from the field
trials conducted in 1914. bruchid populations in seed fields probably could


10- 3 1262 09238 7124

be kept down by repeated and carefully timed& treatments with 1 percent
rotenone dust, or a bait spray containing 1 pound of, calcium arsenate and \
4 pounds of sugar in 5 gallons of water. At least two treatments with
these materials would be necessary to secure control equal to one appli-
cation of DD.T, Cool, cloudy weather is likely to occur in western Oregon
during the very brief period when the first treatment should be put on,
and several trials have shown that rotenone dust and poisoned-bait spray
are not effective under these conditions. Because of the residual effect
of DDT, this material can be applied under such conditions and still be

Several questions still remain to be settled before final recommen-
dations can be made on the use of DDT for the control of the vetch bruchid.
furtherr work is needed to determine the best concentration, inert diluents,
dosages per acre, number and timing of applications, effect on other injur-
ious and beneficial insects including bees instrumental in pollination,
and the livestock-poisoning hazard of DDT residues remaining on the plants,
especially in the event that treated fields are used for hay or pasture
instead of for seed harvest.