LIBRARY STATE PLANT BOARD August 19^5 E-667 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine TESTS OF DOT ON CERTAIN SUCKING INSECTS ASSOCIATED WITH ELM j 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 pro- tection of susceptible trees from feeding by this group of insects might therefore prevent nev inoculations and the subsequent spread of the disease. To accomplish this the nev insecticide DDT (l-trichloro-2,2-bis(p_-chlorophenyl)ethane) appears to offer promis- ing possibilities, primarily owing to its residual effects. Tests of the effect of DDT on sucking insects associated with elm were begun in August l$kh 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 could 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 DDT plus Pyrax (pyrophyllite) In water. Sprays of this mixture con- taining a 0.1 to 1 percent of DDT were applied to elm foliage with a head 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 (Phlepslus sp.) was found dead in the sleeve over the foliage Bprayed with the 1 -percent suspension. After kS 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 . AUG 2 7 1945 - 2 - Tests vith Emulsions Emulsions of DDT containing xylene and usually Triton X-100 (polyethylene glycol phenyl! sooctyl 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 per- cent of DDT were tested, with Triton X-100 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 2k 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 molllpes (Say), and Chlorotettlx spp . ( Q9 insects) and all of the five other species of cicadellids (11 insects) in 6 hours. There was no mortality in the check cagos after 2k hours? except in those containing Graphocephala coccinea (Forst.) and Agallia constricta (Van D.). All the Philaenus spp. (25 insects) were dead in 4.0 to 4-2 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 2k Lepyronia quadrangular is (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 dur- ing 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 k2 hours. - 3 - When it was found that DDT in low concentration ie lethal to many species of sucking insects confined to sprayed surfaces contin- uously, tests were undertaken to determine in a preliminary manner the effect of these concentrations when the insects were permitted to contact sprayed surfaces for only short periods. It was considered possible that higher concentrations might be more efficacious in pre- venting feeding after short periods of exposure. In these tests cellophane or cloth was sprayed with DDT emulsion in the desired concentration, and the sprayed material was taped oyer a window in the lnsectary. 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 in- sects were confined to other cages after being removed from similar unsprayed surfaces. The following species were used in these short -exposure tests: Clcadellidae: Scephytopius frontalis (Van D.)f S. acutus (Say), Kolla bifida (Say), pVaeculacephala mollipes fsay), Chloro- tettlx spp., Graphocephala cocclnea (Forst . ) , Stirellus bl color (Van P.), Phlepslus spp. , Pagaronia trlpunctata (Fitch) , Gyponana spp., Aulaolzes irrorata (F.), Agallla constrict a Van D. , Xerophloea sp. t Latalus a ay 11 (Fitch) , Deltocephalus spp., Idlodonus kennicott 1 ( tJhler ) , Drlotura gammaroldes (Van D.), Neokolla gothlca ^Sign.); Fulgoridae: Acanalonia blvittata (Say), Bruchomorpha oculata Newm.; Membracldae: Campylenchla curvata (F.) T Ceresa spp.; Cercopidae: Lepyronla quadrangular Is (Say). The results of these tests are stnaaarized in table 1. i - k - ® JO I •»» 5 J3 o ft o 0) *» u o 5S I I 6H » a ■ i-l O •»■« n «) q a o a o POP « h m ^> 3 ► CD Li V U « g & « a a! o u 3 CO o ft ,3 03 ul OVD CM O CM K% CM H*v tu f*-. »— iTs r— 60 On cm sr-,vo eu cm f~vo (To w (u«M(viir\r— -c^cvj^ cm cr* cr>v£& o o 60 VC' K sX> O CM Pi ^3- eo cm J" V£> CT\ H (M M H O SK\rl H 60 CM-3- «-l ^j" h-r*A CM r-t -3- 60 J" CM B0 ft O o o a o u A 1 J3 o a o I ft ca i ! - (—1 CM ca ■tJ O O » c/1 CM 60 CM CM O 3 I O CM CM CM ■ - 5 - From these laboratory testa It appears that prolonged exposure to concentrations of DDT as low as 0.125 percent will prove lethal to all species tested with the possible exception of certain cerco- pids. To obtain comparable mortality with a minimum exposure time of 10 minutes, a concentration of approximately 2 percent appears nec- essary. This concentration is also necessary to prevent insects from leaving sprayed trees and feeding on other vegetation. In all tests, including those 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 DHT to kill them quickly, they contin- ued to live as long as those that had not been exposed to the insec- ticide. In these tests none of the insects that died within the first 18 to 2^ hours ever attempted to feed. Field experiments . In September a sufficient quantity of DDT was received for testing under field conditions. Therefore, al- though 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 0.25 -per- cent DDT emulsion made up according to the following formula: 33*1 ounces of DDT, 64 ounces of xylene, 12 ounces of Triton X-100, and 99 gallons of water. One plot and its adjacent check were laid out in a young stand of natural elm reproduction with trees 15 to 30 feet in height. Approximately 35 gallons of spray (about 11 pounds of DDT per acre) was required for complete coverage of the trees in this plot. Insect mortality was determined by covering 5 percent of the ground area with 3- by 3 -foot cloth mats, from which dead insects were periodi- cally 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 popula- tions 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 re- mained more or less constant except when flights of aphids occurred. After the first few days most of the dead insects collected in the - 6 - prayed plot were found on the mats closest to the periphery, princi- ally on the side bordered by an open field. Although it is not known what the total insect population in either plot was at any time, from mortality data on insects in check cages in the laboratory at about the same time, it seems likely that most of the sucking insects which entered the test plot were killed by the spray. In the sprayed plot the rate of kill ranged from 2 to 50 times that in the check plot; approximately the same difference in mortality between sprayed and check insects was observed in the laboratory. In the plot of grass and herbaceous vegetation the spray was very effective in holding down the insect population (table 3). The popu- lation in the check plot remained remarkably constant during the test period. Table 2. — Number of dead insects removed from cloth mats placed on the ground in an elm stand sprayed with a 0.25 -per cent DDT emul- sion. 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 i : Insects Excluding : All : aphlds : All : aphids Sept. 20 ikk 51 50 k 1 1 21 71 19 19 k k k 22 77 26 12 5 k k 25 7^ 27 15 9 6 k 26 67 31 9 10 10 5 29 32 10 k k 2 2 Oct. 2 kk Ik 6 k 2 1 6 2k 9 1 k 1 0 9 kQ 19 k 2 0 0 16 19 6 1 6 5 1 21 13 6 1 2 2 0 Total 613 218 122 37 22 - 7 - Table 3» — Number of living insects collected in 25 sweeps with an insect net from herbaceous vegetation after spraying with a 0.25- percent DDT emulsion. Plot sprayed September 19* • rercen^ reduction spray piot Check: plot m spray pio& Date : Total Sucking : Total Sucking : over cnec& piox insects insects : insects Insects : • Sept • 20 13 6 79 65 91 23 5 k 9^ 75 95 25 5 1 90 76 99 29 3 2 93 72 97 Oct. 6 10 10 89 75 87 16 2 1 64 60 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 re- mained in excellent condition to the end of the experiments. Summary In laboratory tests it was found that prolonged exposure to DDT emulsions in concentration as low as 0.125 percent effectively killed many species of cicadellids and certain membracids, fulgorids, and cercopids associated with the American 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, UNIVERSITY OF FLORIDA 3 1262 09238 7439