August 1945 E-667
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
TESTS OF DIT ON CERTAIN SUCKING INSECTS ASSOCIATED WITH EUM
By T. J. Parr and W. L. Baker,
Division of Forest Insect Investigations
Phloem necrosis, a virus disease, affects the American elm in
epidemic proportions in parts of the Ohio, Mississippi, and Missouri River drainage systems. It is probable that one or more species of sucking insect serves as the vector of this disease. Complete protection of susceptible trees from feeding by this group of insects migt therefore prevent new inoculations and the subsequent spread of the disease. To accomplish this the new insecticide DIT (l-trichloro-2,2-bis(p-chlorophenyl)ethane) appears to offer promising possibilities, primarily owing to its residual effects.
Tests of the effect of DDT on sucking insects associated with elm were begun in August 1944 at Columbus, Ohio, and continued to the end of the growing season in October. Unfortunately, because of the extremely dry season in central Ohio, populations of these insects had dropped to a very low point by mid-August, and neither a great many species nor large populations of any one species cov1,d be located thereafter.
In all tests the technical grade of DDT was used.
Tests with Suspensions
The first tests were on a small scale, with a suspension of
DIT plus Pyrax (pyrophyllite) in water. Sprays of this mixture containl"3 a 0.1 to 1 percent of DIT were applied to elm foliage with a ht~d atomizer. As soon as the spray was dry, cloth sleeves with cellophane windows were placed over the sprayed branches and several species of leafhoppers introduced into the sleeves. After 18 hours, during which time a heavy shower occurred, one adult leafhopper (Phlepsius sp.) was found dead in the sleeve over the foliage sprayed with the 1-percent suspension. After 4f8 hours all the remaining insects were still alive. As a result of this experience no further tests with this material were made.
There was no foliage injury in this experiment from any, of the sprays.
Tests with Emulsions
Emulsions of DDT containing xylene and usually Triton X-100
(polyethylene glycol phenylisooctyl ether) as the emulsifying agent, were tested as sprays both in the laboratory and in the field. DDT was dissolved in xylene at the rate of 1 gram of DDT to 2 ml. of xylene) and sufficient emulsifier and water were added to give 1 part of emulsifier in 1000 parts of the finished spray, the amounts varying with the concentration of DDT desired.
Laboratory tests. -- For laboratory tests several collapsible
cages were constructed. These cages had removable panels of cloth In the sides, tops, and bottoms, placed in such a manner that the entire inner surface was covered and could be sprayed. Elm seedlings in buckets, with the tops of the buckets covered with cloth, were placed in these cages. In most of the experiments the entire inside of the cage, the bucket, the tree, and the cloth covering the top of the bucket were sprayed with a hand atomizer. Check cages were set up in the same way, and were either unsprayed or sprayed with the solvent, emulsifier, and water without DDT. Certain species of sucking insects, including 12 cicadellids, a fulgorid, a cercopid, and a membracid, were then exposed in the cages.
In the first experiment emulsions containing from 0.125 to 1 percent of DI were tested, with Triton X-l00 as the emulsifier except in tests with Philaenus spp. and Jassus olitorius, Say where bentonite was used. The insects were allowed to remain in the cages continuously. The number of insects per cage ranged from 22 to 110.
All concentrations killed all the insects except Philaenus spp.
in 16 to 24 hours, and 76 percent of these cercopids were dead in that time. The 1-percent DDT killed nearly all of Scaphytopius frontalis (Van D.), Draeculacephala mollipes (Say), and Chlorotettix spp. T 9 insects) and all of the five other species of ccadellids (11 insects) in 6 hours. There was no mortality in the check cages after 24 hours) except in those containing Graphocephala coccinea (Forst.) and Agplia constricta (Van D.). All the Jhilaenus spp. (25 insects) were dead in 40 to 42 hours, although they were exposed only to the
0.25-percent DDT, but 28 percent of the insects in the check cages were also dead.
In one test 24 Lepyronia quadranuularis (Say) adults were exposed in a cage in which only the tree had been sprayed with 2-percent DDT. The insects were killed as they attempted to feed. The 3 insects that remained alive after 19 hours had occupied the same position on the side of the cage from the time they were confined. Sometime during the second night they probably attempted to feed, as all were found dead under the tree on the second morning. In the check cage only 15 insects out of 59 were dead after 42 hours.
When it was found that DT in low concentration Is lethal to
many species of sucki~ insect codine-to srayed surfaces continuously, tests were undertaken to determine in a preliminary manner the effect of these concentration when the inaets were permitted to contact sprayed surfaces for only short periods. It was considered possible that higher concentrations might be more efficacious in preventing feeding after short periods of exposure.
In these tests cellophane or cloth was sprayed with DIDT emulsion in the desired concentration, and the sprayed material was taped over a window in the insectary. Test insects were then liberated and allowed to congregate on the window. After various lengths of time they were collected in an aspirator and transferred to unsprayed cages, each of which contained an unsprayed elm seedling. Check insects were confined to other cages after being removed from similar unsprayed surfaces.
The following species were used in these short-exposure tests:
Cicadellidae: Scaphtopius frontalis (Van D.), S. acutus (Say),
Kolla bifida Say Draeculacephala mollipes rSay ,7Chloroett x app., Graphocephala coccinea (Forst.), Stirellus bicolor (Van D.), Phlepsius app., Pagaronia tripunctata
(Fitch), Gyponana spp., Aulaoizes irrorata (F.), Agallia constricta Van D., Xerophloea sp., Latalus 1 (Fitch),
Deltocephalus app., Idiodonus kennicotti (hler), Driotura
Umaoides (Van D.), Neokol)a h thic (Sign.)
Fulgoridae: Acanalonia bivittata (Say), Bruchomorpha oculata
Membracidae: Campylenchia curvata (F.), Ceresa spp.;
Cercopidae: Lepyronia quadrangularis (Say).
The results of these tests are smmarized in table 1.
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From these labore'atory tests It appDears T"hat prolonged eosu~ire to concentrations c Z 4JT a. low at C.. 5iercent. Alil prove lethal to all species t ttd ith the Pc e_ b-r zxcaptioa. of certain ceropids. To obtain cwaparable mortality with~. a minimum exposure time of 10 minutes, a concentration of approximately 2 percent appears necessary. This concentration is also necessary to prevent insects from leaving sprayed trees and feeding on other vegetation. In all tests, including thoso at the lowest concentration at the shortest exposure, the mortality was higher at 18 to 21 hours than in the checks, and it Increased as the concentration and exposure period increased. It seems even more significant, however, that, unless the insects contacted enough DDTf to kill them quickly, they continLued to live as long as those that had not been exposed to the insecticide.
In these tests none of the insects that died within the first 18 to 24 hours ever attempted to feed.
Field experiments. -- In September a sufficient quantity of DDT was received for testing under field conditions. Therefore, although the season was well advanced and the sucking-insect population was extremely low, two field plots were sprayed with a power sprayer on September 19. Each plot was 50 feet square and each had a similar check plot adjacent to it. Both plots were sprayed with a 0.23-percent DUT emulsion made up according to the following formula: 33.1 ounces of DDTJ, 64 ounces of xylene, 12 ounces of Triton X-100, ad 99 gallons of water.
One plot and its adjacent check were laid out in a X :z~g ~a~d of natural elm reproduction with trees 15 to 30 feet in height. Approximately 35 gallons of spray (about 11 pounds of DDTr per acre) was required for complete coverage of the trees in this plot. Insect mortality was determined by covering 5 percent off the ground area with 3- by 3-foot cloth mats, from which dead insects were perio-ically removed, identified, and counted. Collection' were begun the day after the spraying and continued until all the foliage was off the trees in October.
The second plot, with its check, was in an area of bluegrass and other scattered herbaceous vegetation, and was Sprayed at the rate of 2 gallons per 100 square feet. Reduction of insect populations in the sprayed plot was determined by taking 25 sweeps with an insect net in both this and the check plot.
The results of the tests in the elm stand, which are shown in table 2, indicate that there was a considerable drop in the Insect population immediately after spraying. Subsequent mortality was probably confined to insects that migrated into the plot while the foliage remained on the trees. In the check plot the population remnained more or less constant except when flights of aphids occurred. After the first few days most of the dead insects collected in the
p. t were ins ob a matE4 c.loseat to u periphery, princibut exua too.a :: ~... A~~ X10- a utgh it is not
at tbe ?ue :m put1 o ic, father plot was at.any time,
taLity as 3.... .L cse' o i. Uae laboratory at
as sm tio, 11 ~nsee ii telG eat of tho sucking insects
~ srtored the toot jNot were klea cy the spray. In the sprayed
ai rate of kill ra d rom 2 to 50 times that in the check
s; approximate '-y the eas difference Ia mortality between sprayed ..xo nck insects w ,bservad in the laboratory.
i the plot of k-ans -nd herbaceous vegetation the spray was very
.,-Lee in holng down the insect population (table 3). The poputation in the check plot remained remarkably constant during the test
ble 2. -- Number of dead insects removed fran cloth mats placed on
the ground in an elm stand sprayed with a 0.25-percent DT emulsion. Plot sprayed September 19. Precipitation September 19 to
October 20, 1.52 inches.
Spray plot Check plot
Date : Total : Sucking insects : Total : Sucking insects
: insects : : Excluding : insects : : Excluding
: All: aphids : : All : aphids
20 144 51 50 4 1 1
21 71 19 19 4 4 4
22 77 26 12 5 4 4
25 74 27 15 9 6 4
26 67 31 9 10 10 5
29 32 10 4 4 2 2
2 44 14 6 4 2 1
6 24 9 1 4 1 0
9 48 19 4 2 0 0
16 19 6 1 6 5 1
21 13 6 1 2 2 0
5214 122 54 37 22
Table 3. Number of livlnz ; I-sects collected. in 25 sweeps with an
insect net from herbaiceous vegetation after spraying with a 0.25percent DDT emulsion. Plot sprayed September 19.
Spray plot Check plot :insrypo
Date : Total. Sucking : Total Sucking :over check plot
:insects insects : insects insects:
20 136 79 65 91
23 5 4 94 75 95
25 5 1 90 76 99
29 3 2 93 72 97
6 10 10 89 75 87
16 2 164 6o 98
21 0 0 47 45 100
31 1 1 74 64 98
Total 39 25 630 532
Effect on foliage. No foliage injury was observed from the DDT emulsions at any concentration used in these tests. Severe yellowing and foliage drop, however, occurred in all the check trees in cages from feeding by large numbers of insects. There were no indications of feeding on any of the sprayed trees in cages, and the foliage remained in excellent condition to the end of the experiments.
In laboratory tests it vas found that prolonged exposure to DDT emulsions in concentration as low as 0.125 percent effectively killed many species of cicadellids and certain membracidsa, fulgorids, and cercopids associated with the Amierican elm. However, a concentration as high as 2 percent was required to kill 100 percent of these insects ~when they were exposed to the material for only 10 minutes. Insect populations on elm trees, grass, and other herbaceous vegetation were effectively reduced for at least a month when field plots were sprayed with 0.25 percent DDT emulsions in late September. No injury to elm foliage occurred in any test involving the use of DDT! emulsions.
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