




The spray used was Shell ACX~331 containing 10.75% DDT in light 
fuel oil with an auxiliary solvent. The two lower dosages (0.2 and 0.) 
are within the range normally utilized in larval control while the two 
higher rates cover a dosage range occasionally used for pre-emergence 
treatment. In typical control operations the interval between sprayings 
varies from a period of several weeks to more than a month, depending upon 
breeding conditions, but in this study, the amount of time required for pre- 
and post-spray investigations made it impossible to schedule treatments at 
intervals of less than one month. 
wach of the units treated in the first spraying was approximately 
100 acres with the exception of the one treated with the 1.6 dosage which 
was 50 acres (see Fig. 1). Before the second spraying, the 100-acre units 
were reduced to 90 acres for operational reasons. In addition, the. boundaries 
of the two higher dosage areas were shifted to provide a combination of 
Spray treatments in relation to time and number of application. Thus parts 
of each of the plots were sprayed only once and other parts twice. Study 
areas selected were representative portions of the marsh, including large 
and small creeks, ditches and ponds. Their large size helped to reduce 
effects of local differences in habitat and of immigration by unaffected 
animals after spraying. 
Studies on population fluctuations of marsh organisms were also 
made in nearby unsprayed habitats. These check areas included untreated 
portions of the marsh that were comparable to the test areas and that were 
well beyond the range of drift or drainage from the spray plots. 
The plane used for insecticide application was an N3N~3 single- 
engined biplane, equipped with a spray rig having an effective swath width 
of 90 feet at an altitude of 25 feet. Two sets of nozzles were employed. 
The set used on the 0.8 and 1.6 areas discharged one gallon per acre when 
the plane was traveling at an average speed of 35 miles per hour. The 
other set was used when spraying the 0.2 and 0.], areas and released one 
quart of insecticide per acre. On the 0.2 and 0.8 areas the plane made 
runs at 90-foot intervals while where the application was greater, the 
intervals were reduced to 45 feet. Flight lines were marked by men with 
flags at each end of the plots. 
The two higher dosage areas were treated in the afternoon of 
August 17; the 0.4 area in the afternoon of August 18; and the 0.2 area 
during the morning of August 19. The difference between tide stage at the 
time of spraying on the 0.2 area compared to that on the otber plots intro- 
duced a variable, as did the fact that a light drizzle on August 18 helped 
to wash off spray from the high dosage areas. 
The second treatment was started in the early morning of 
September 15. The 1.6, 0.8, and O.l: areas and a quarter of the 0.2 area 
were sprayed before unfavorable weather intervened. Cperations were resumed 
at low tide in the evening, at which time an additional half plot was 
treated. Spraying was finally completed in mid-morning of the 16th. 
