STATE PLANT BOARD
Septeber 1945 E-.671
United States Department of Agriculture
Agricultural Research Administration Bureau of Entomology and Plant Quarantine
THE EFFECTS 0F DDT DUST AND SPRAY PREPARATIONS ON LARVA! 07 THE !UROP!A CORN BORER
By D. D. questel, Division of Cereal and Forage Insect Investigations
During the winter of 1914445 laboratory experiments-were conducted
with a number of DDT dusts to determine the effects of different particle
sizes, diluents, and concentrations of DDT on hibernating and actively feeding larvae of the European corn borer (M ut nubilalis (Hbn.)).
The results of these studies and their relation to fiel experiments conducted during the season of 1944 are presented herein.
Experiment With Hibernating Larvae
In this experiment various DDT dusts were compared with lead
arsenate and rotenone dusts. Approximately 0.5 gram of each preparation
to be tested was placed in each of ten 2-inch glass vials. A single
hibernating larva, which had been collected during October and held in
storage for 2 months at 390 7., was placed in 'each vial. The vials were
shaken so as to cover the larvae thoroughly with dust. They were then
stoppered with a plug of cellulose fiber and placed in an incubator where the temperature remained constant at 960. No attempt was made to control the humidity. All tests were duplicated. The number of dead larvae was
recorded every 24~ hours.
Various characteristics of these dusts, as determined by the Division
of Insecticide Investigations, are given in table 1. The bulk measurements were made with the Scott volumeter.
From the data in table 2 it is apparent that particle size is of some
importance, since all micronized dusts were more efficient than the micropulverized dusts containing the same diluent. However, it is evident that
other factors related to the carrier itself were operating, since the
micronized talc mixture, although having a sms-ller mean diameter than the
micropulverized clay or diatomaceous earth mixture, was less toxic than either of them. Of the three diluents used in the 50-percent DDT dusts,
the clay and diatomaceous eartft we much more efficient than the talc.
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The relatively high efficiency of the 10.8 percent DD-pyrophllite dust in comparison vihthe other mixtures is in agreement with the results obtained with thil material in spray form in previous tests against feeding larvae,./ and is in strong contrast with the extremely low mortality caused by the undiluted DDT powder. The lack of effectiveness of the 5 percent DDT in an unknown carrier is in general agreement with previous results obtained in the field. where it was less effective than either the 10.8 percent D-pyrophyllite or the undiluted DDT, a1 applied as spray suspensions in approximately the same concentration of DMT.
The ground derris root killed all the larvae within 2 hours, but these larvae, in contrast to those killed by some of the MDT preparations, remained soft and normal in sie. Lead arsenate caused no mortality until the fourth day, when only 5 percent were dead, and it did not cause any additional mortality on the fifth day.
Pyropbyflite alone caused no mortality and thus demonstrated that this diluent in itself was not responsible for the greater effectiveness of the 10.9 percent DDlyrophyllite dust than that caused by the undiluted DDT. What physical or chemical characteristics of the mixture were re nsible for its much higher toxicity are not known. The comparative efficiency of the different mixtures tested apparently was associate ~w~ith both particle size and identity of the diluents they contained,
hxperiments With Teeding Larvae
The results of two feeding experiments, one in the laboratory and one in the field, to determine the toxicity of different DDT dusts used in spray suspensions to newly hatched corn borer larvae are given in tables 3 and 4. The comparative efficiency of the materials tested against feeding larvae was similar to that shown by the tests with hibernating larvae. These results suggest that for field use against the European corn borer a micronized DDT-absorbent clay mixture would be the most satisfactory of any of the preparations tested.
I/ Yatchelder, C. H., and questel, D. D. 1945, lxeriments with DDT foi te control of the Ruropean corn borer infesting sweet corn at Toledo, Ohio, in 1944. U.S. Bur. Int. and Plant u ar. 3-659, 11 pp.
Table 3.-Iffect on newly hatched larvae of exposure for a 38- o "tod
to cauliflower leaves sprayed with various DD prrey ons.
Average percent mortality of a meeposed to Concentration indicated amount of DT per 100 ;y1ike9 of wat#
ofpDcn piunt 02 0.12 0.06 0.03 0.015 07
percent pound pound pound poun poro oun
50 Absorbent clay 100.0 100.0 99.0 62.9 13.3
10.8 Pyrophyllite 100.0 98.3 16.2 1 0
100 None 93.2 83.0 36.8 6,o 0 0
5 Unknown 96.3 4*2 2.2 0 1*7
50 Fibrous tale 100.0 92.6 11.2 5*3 0 0
Table 4.-Zffectiveness of various DDT preparations against larvae infesting
early-market sweet corn. Field tests, Toledo, hio, 19
ConDen-M per Larvae Reduction o borers
Conen-100 gallons of Per 100 In ears from Per 100 In ears from trof DDTet 10 lof DM~ water plants 100 plants plant 100 plants
Percent Pound Number Number Percnt weect
10.8 Pyrophyllite 0.432 38 4 97.9 99.2
100 None .50 70 20 96. 96.0
5 %known .1o 114 36 93"6 92*7
Cheek 1834 496
Action of Toxic Agent on Hibernating Larvae
A striking effect of the DDT dusts that killed the larvae in a comparatively short time was drinking, destocation, and hardening of tb larvae. When death 6:, no, occur rapidly, however, as in the treatments Au.ilizing undil te D shrinking and hardening did not take pIlce even though convulsive movements and partial paralysis were evident. The rapid mortality caused by ground derris root showed no evidence of shrindking, des cation, and hardening. The contrast In appearance of larvae killed qu ckly by MDT and by derris is shown in figure I The characteristi- inking and hardening of the larvae subjected to the rapidly .Nl.L. DDT mixtures may provide a clue to the manner in which the ac gent in these mixtures causes death.
It seems of particular Lrtrest to note from the foregoing obserations that (1) the percent e of )DT in a dust appeared to have less effect on toxicity than the p 3ical and chemical character of the mixture of ftDT and diluent, rapidly killing DDT dust mixtures caused a definite shrinkine- hardening of the hibernating larvae, whereas ground derris powde it killed equally as rapidly did not,
(3) the toxicity of the war materials tested as contact poisons
against hibernating larvae ,.l paralleled that obtained in feeding tests against newly hatched are in.the laboratory and against young larvae infesting sweet corn a field, in those cases where both
types of tests wero condued (4) a group of mixtures containing
an active agent which kills byc t can perhaps be evaluated readily
by laboratory tests to deterne their effects on hibernating larvae.
eriments with seveze ut and spray preparations conducted
against both hibernating and ely feeding larvae of the Ruropean
corn borer (Pyransta nubilL 0) indicate that the percentage of
DDT (1-tri o o-2,2-bia sp 1)ethane) may have less bearing
on te effectiveness of tn d sprays than some other factors
perhaps relate to the ph: hemical character of the diluent.
Hibernating larvae thoroul e with a powder containing 10. percent of in pyrophyll t 50 percent of DDT micronized with
an absorbs? clay or diato th, were all killed within 3 days,
where none, or not more eroentof those coated with powders
containing 50 percent of .ptuverized with a fibrous talc, or
with crcely ground undil haical DD, were killed within 5 days. The to. ct. of the various as to hibernating larvae closely paralleled that obtained in -gtsts against newly-.hatched larvae in
the labostory and against infesting sweet corn in the field.
Rapidly killing DDT dusts definite and characteristic shrinking, desiccatio., and hardening arvae Larvae killed as rapidly by
ground derria powder ('4.5 --cntenone) remained soft and normal In size.
pigure l.-ibernating European corn borer larvae kIlled within 24 hours by exposure at 96 F. to two insecticidal dusts: Left, larvae killed with a dust containing 50 percent of DDT. Right, larvae killed with a ground derris root powder (4. percent rotenone).
UNIVERSITY OF FLORIDA 3 1262 09238 7348