28 ANNUAL REPORTS OP DEPARTMENT 01 kGRICULTURR, 1951 
and a search for new materials to use as alternate treatments. Ben- 
eene hexachloride and lindane insecticides were used successfully in 
the summer of 1950 by Florida mosquito-abatement districts and by 
Hie Department of Defense in areas where I>I>'I 
salt-marsh mosquitoes were prevalent. In preliminary field evalua- 
tions, heptachlor has shown promise as an effective insecticide against 
bot li adult - and larvae. 
House Mie> Develop Resistance to Nen Insecticides 
The use of new insecticides to replace DDT has not solved the 
problem of controlling DDT-resistant strains of house flies. In the 
vicinity of Orlando, Fla., house flies resistant to I >I >T have developed 
within one season a high degree of resistance to Lindane, chlordane, 
dieldrin, and toxaphene. Flies around some dairies in that area 
cannot be controlled by the sole use of any insecticide new available, 
including pyret hrum. 
The possibilities of utilizing baits along with i i u: i * 1 sanitation prac- 
are being studied in efforts to control flies. Various agi icultural 
products, such as molasses, fermenting grains, and dried milk, are 
being evaluated as attractants for house flies. The addition of am- 
monium carbonate to baits appears to enhance the attractiveness "t" 
Mich baits. 
House Flies Survive Lifetime Exposure to DDT 
Physiological studies indicate that insecticides of residual type-, 
such as DDT, methoxychlor, lindane dieldrin. and aldrin. may even- 
tually become completely ineffective as a control for house flies unless 
some way is found to overcome the resistance to them that rapidly 
lops in the flies. Laboratory -train- of house flies have now 
been bred that spend their entire adult life and lay eggs while 
confined in cages thoroughly coated with deposits of I >I >T. 
Flighl Range of Flies Studied With Aid of Radioactive Isotopes 
Studies were carried out by the Corvallis, Oreg., station, in coop- 
eration with Oregon State College, t" gain more information on the 
migration habits of the house fly, the green-bottle fly, and the black 
blow fly. 
Flies reared in the laboratory were given water containing radio- 
active phosphoric acid so that they could he readily detected with 
er counters or other equipment. A total of 35,000 house Hie-. 
" green bottle Hie-, and 1,200 black blow Hie- marked with radio- 
active |>h<>-|»h<>ric acid were released in the Willamette Valley near 
Corvallis. Within •_' I horn-- flies of all three species were taken in 
leap- I mile- from the point of release. Later, h<>u-e Hie- were recov- 
erea 12 mile- from the release point, black blow Hi.- I milt-, and 
bottle flies s mile-. In addition, a high percentage of the marked 
wrere recovered in 24 -mall traps operated within L8 miles from 
i he point of release. 
The percentage of recovery of the different species at all points 
i follows: Housefly, 1.6 percent; green-bottle fly, 3.6 percent \ 
