764 
Journal of Agricultural Research 
Vol. XXI, No. 10 
from the place of capture to the point of release, and in the third and 
fourth tests the south traps were about in line. 
Climatic influences are unquestionably important in relation to the 
spread of these species of Diptera. Probably temperature, humidity, 
sunshine, wind (direction and velocity), precipitation, barometric pres¬ 
sure, and electrical phenomena each exert an influence. It is difficult in 
experiments of this kind to weigh reliably these various factors because 
the results are extended over a considerable period with a corresponding 
change in meteorological conditions, and hence an equalizing of the 
effects of the stimuli. Those factors which would stimulate activity, 
such as high temperatures and sunshine, are no doubt potent. Another 
stimulus is probably to be found in those combinations of climatic 
conditions experienced with the change of seasons. This seasonal 
stimulus may account for the marked activity in dispersion and food¬ 
seeking found in P. regina in the fourth experiment. 
COMPARATIVE TENDENCIES OF THE SPECIES TO DISPERSE 
The relative tendencies of the several species toward dispersion are 
suggested 1 by a comparison of the percentages of marked specimens 
recovered with those liberated and those in the total catch in the recovery 
traps. These figures indicate that this tendency is more marked in 
Chrysomya macellaria than in Musca domestica. The percentage of 
marked C. macellaria as compared with the total marked flies re¬ 
covered in all of the distant migration tests nearly equaled or sur¬ 
passed the percentage of that species among the flies liberated, while 
in M. domestica the percentage of marked specimens recovered was 
approximately one-half of the percentage liberated. Under favorable 
climatic conditions for the species, Phormia regina showed a very strong 
migratory tendency, the percentage of marked specimens recovered in 
the third test being 14 times the percentage of that species in the release. 
Ophyra leucostoma and O. aenescens also exhibit a decided tendency 
toward dissemination, the percentage of marked specimens of these 
species recovered being in all cases greater than in the liberation. The 
number of specimens of other species liberated was too few to be used 
in this comparison, but several appear to travel quite freely. 
SUMMARY AND CONCLUSIONS 
The dispersion of several species of flies important in the economy 
of man, both as carriers of disease and as parasites of man and animals, 
is discussed in this paper. 
The experiments carried out show that under rural and urban condi¬ 
tions flies have marked powers of diffusion. 
The maximum distance of spread from the point of release as recorded 
in these tests was as follows for the several species: Musca domestica , 
