ento:mology and plant quarantine 
71 
SCREWWORM CONTROL 
The cooperative campaign for control of screvvworms was similar to that of 
last year, except that some of the educational phases were of a more advanced 
nature, demonstrations on fundamental livestock practices for prevention of 
screwworm attacks were carried on by cooperating stockmen, and most of the 
supervisors were assigned to larger territories. By employing 155 field men 
for varying periods the program was effectively extended to practically all 
infested areas of the Southern States. 
The work for the year again made use of the State and Federal agencies 
interested in livestock. The State screwworm control committee in each State 
cooperated and assisted in effective work witli county agriculturiil agents, 
veterinarians, teachers of vocational agriculture, and individual stockmen and 
farmers. The procedures were directed from tield headquarters at San Antonio, 
Tex., and supervisors were supplied with posters, circulars, handbills, timely 
articles for the press, radio talks, exhibits, and supplies. In each State the 
suijervisors received special instructions on the life cycle, methods of detecting 
and preventing cases, proper metiiods of treating cases with benzol and pine- 
tar oil, and the principal variations in the causes of screwworm abundance in 
different areas. At these conferences the good preventive measures endorsed 
by State agencies usually included (1) controlled breeding to reduce cases in 
navels and in mothers of young; (2) dehorning of young animals during cool 
weather and horn tipping of older animals to reduce infestations caused by horn 
hooks; (3) use of bloodless emasculators on cattle, sheep, and goats in order 
to avoid cases which usually follow the use of the knife; (4) control of the 
Gulf coast and spinose ear ticks; (5) elimination of the use of catch dogs; 
(6) avoiding rough handling of livestock so as to reduce snags and scratches; 
and (7) the use of dehydrated pine-tar oil on all open wounds to aid healing 
and to prevent flies from laying eggs on wounds. 
During the year 7M)S demonstrations of recommended practices of handling 
and managing livestock for prevention or treatment of injuries of animals were 
made by good stockmen. These demonstrations were conducted by owners of 
farms and ranches as examples for different communities, and limited quantities 
of treating materials were furnished them. Small quantities of materials for 
treating carry-over infestations of the winter were also furnished to stock 
owners who cooperated in combating screw worms when the incidence of cases 
was at a low point. Altogether, 5.398 gallons of benzol and 7,262 gallons of pine- 
tar oil were used for such purposes. 
CONTROL WORK IN THE SOUTHEASTERN STATES 
Activity of screwworms during the winter is restricted to areas in which 
the mean winter temperature is above 55° F. This natural control does not 
become effective early enough in the fall to aid in preventing destructive out- 
breaks when animals are marked, castrated, and fattened in the fields of the 
Southeastern States. The high control of the pest obtained during the fall of 
1936 was due to good cooperation by stock owners throughout the year. Such 
continuous work resulted in continiug the pest principally to the southern 
counties of Georgia and to the peninsular portion of Florida, where there was 
some activity during the winter months. The additional work carried on in 
these areas during the winter (1) reduced the stock of parent flies in the spring; 
(2) served in keeping screwworms in check so that a big population did not 
breed up in navels of young animals; (3) greatly reduced the infestations from 
surgical operations; and (4) retarded spread of the pest. 
The following are the average rates of infestation among 100,000 animals in 
Florida: In 1935, July 3,447, August 3.613, September 2,802, October 2,049, 
November 2,148, December 1,105; in 1936, January 374, Februarv 257, March 
236, April 687, May 863, June 797, July 581, August 489, September 6;j3, October 
8o3, November 454. December 93 ; and in 1937, January 240, February 284, 
March 214. April 345. May 694, June 940. and July 867. 
The retardation of spread by control work was strikingly illustrateil by the 
first occurrence of cases of screwworms at Hinesville. Ga., during the last 
2 years. In 1936 the first cases occurred on May 1. and in 1937 the first case 
did not occur until May 25. This difference in the early occurrence of cases is 
attributed only to control work wiiich delayed spread of the pest and enabled 
southern Georgia to escape a generation of screwworms. The delay of spread 
