28 ANNUAL REPORTS OF DEPARTMENT or AGRICULTURE, 1953 
S<-r«'\v-\\ orin Sterilization Studies Continued 
A field test has been conducted to determine whether the release of 
sterilized male screw-worm flies on an island at a rate of about LO times 
the natural population would reduce fertile egg production. Thi 
was conducted during the winter of L952 53 on Sanibel [sland and 
adjoining Captiva [sland, 2 to 3 miles off the coast of Fori Myers, Fla., 
where a natural screw-worm population was present. Sterile males 
were released at a rate of LOO per square mile per week for a period 
of about 17 week.-. During the first month of releases about BO percent 
of the egg masses deposited by wild flies on wounded goats were 
sterile. Subsequently only a few viable egg masses were collected and 
these probably came from flies migrating to the Island. It' the island 
had been completely isolated from any other fly source, elimination 
of the fly would probably have been accomplished. 
On Captiva Island where a higher natural population existed, only 
about 35 percent of the wild females deposited infertile eggs. Avail- 
able information indicates that the natural population on this island 
was much higher per unit area than the Statewide average in Florida. 
TOXICOLOGY OF INSECTICIDES 
Methoxychlor-Sprayed Hay Safely Fed to Dairy Cows 
It is highly unlikely that methoxychlor would be excreted in the 
milk of cows fed forage sprayed with recommended amounts of 
methoxychlor. Studies on the toxicology of some of the new insec- 
ticides when ingested by dairy cattle were made at Beltsville, Md., in 
cooperation with the Bureau of Dairy Industry. In one series of ex- 
periments al fa] fa hay containing methoxychlor residues ranging from 
16 to 109 p. p. m. was fed to dairy rows for periods of U) to 80 days. 
Samples of milk from the cows were analyzed at L0-day intervals. No 
methoxychlor could be detected in the milk. The amount of methoxy- 
chlor present in those experiments equals the maximum Likely to be 
encountered on forage treated for insect control. When methoxychlor 
dissolved at a concentration of 1«> percent in soybean oil was \\h\ at 
rate- of from 1 to L5 grams of metnoxychlor daily, no methoxychlor 
was detectable in the milk at dosages as high as 6 grams. When dos- 
ages of B to I-'- grams daily were i\^\. methoxychlor found in the 1 -per- 
cent fat corrected milk ranged from 0.18 to 1.1 s p. p. m. Approxi- 
mately 100 times as much met hoxychlor a- DDT must be administered 
orally for tin- insecticide to be detectable in the milk of dairy cows. 
Similar dairy -rati le feeding studies were undertaken with aldrin, 
dieldrin, and heptachlor. Increased organic chlorine content ^f the 
milk of the cows on the higher Levels of aldrin intake indicated the 
presence of this insecticide in the milk. The cow receiving a high in- 
take of l gram per day died. High organic chlorine content of the 
fatty tissues of this animal indicated the storage of appreciable quan- 
tities of this materia] in the animal's body. The experiments with 
dieldrin and heptachlor are still in progress. Results to date indicate 
that a low intake of dieldrin will cause excretion of this material in 
i he milk. Heptachlor is apparently metabolized into an epoxide com- 
pound and excreted in t he milk. 
