- 80 - 
for 2, 5, 10, or 15 minutes to a surface to which 144 mg. of the active In- 
gredient had "been applied per square foot. Of the flies exposed for 2 
minutes 97.6 percent of the laboratory line and 94.9 percent of the Ellen- 
ville line were killed. All flies of each line were killed when exposed for 
the longer periods to this residue. Of 210 flies of the laboratory line 
exposed to this residue an average of 99»5 percent were killed, and of 208 
flies of the Ellenville line similarly exposed 99*0 percent were killed. 
Five tests were made in which flies were exposed for 15, 30, or 45 minutes 
or for 1 or 2 hours to a surface to which 14.4 mg. of the active ingredient 
had been applied per square foot. Of a total of 172 flies of the labora- 
tory line exposed to these surfaces an average of 66.9 percent were killed 
and an average of 71 «1 percent of 152 flies of the Ellenville line were 
killed hy similar exposures. — Barber and Schmitt (27) . 
In Italy Bettini and Barachini QO. .21) reported that flies resist- 
ant to high doses of DDT (5*3 g./sq. m.) all died when they came in con- 
tact with chlordane and BHC. 
The susceptibility or resistance of the various strains of flies studiei 
was determined from data obtained "by topical applications of the toxicant to 
the thorax of female house flies. Acetone solutions of the insecticides 
were used in all tests. The dosage-mortality data were used to calculate 
the LD-50 values in terms of micrograms of toxicant per gram weight of fly. 
The data indicate that the acquisition of tolerance for one insecticide con- 
tributes to tolerance for the others. The LD-50 of chlordane to the SAIDM 
strain of flies was 8.2 (DDT ■ 16.8); whereas tc the flies that had become 
resistant to DDT (LD-50 = 18,728), the LD-50 of chlordane was 15. 6 micro- 
grams per gram weight of fly. — -Bruce (5*5 ) . 
Two strains of flies (one laboratory reared, the other collected in 
the field) were exposed to residues of seven insecticides. The materials 
tested, in order of decreasing effectiveness to the non-resistant flies, 
were dieldrin, gamma isomer of benzene hexachloride, aldrin, DDT, chlordane, 
methoxychlor , and emulsifiable pyrenone. The field collected flies were 7 
times more resistant than the laboratory reared flies to DDT. There was 
no detectable difference in the reaction of the two strains to dieldrin, 
gamma-BHC, aldrin, chlordane, and emulsifiable pyrenone. — Pimentel and 
Dewey (366) . 
In Denmark DDT-resistant and control flies reacted uniformly toward 
chlordane. — Keiding and Van Deurs (242). 
In Italy flies resistant to DDT were somewhat more resistant to chlor- 
dane than were non-DDT-resi3tant flies. — Alessandro and Smiraglia (12) . 
Experiments with chlordane and other insecticides against DDT-resist- 
ant flies are critically discussed by Patrissi e^t a^. ( 359 ) . 
Siphon a lrr jtans (L.), the horn fly 
In laboratory knockdown tests against the hornfly small screen-wire 
cages were dipped in preparations containing 0.5 percent of different 
