BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 77 
THE HORN FLY IN PUERTO RICO 
The horn fly was found to be well distributed along the coastal sections of 
Puerto Rico, occurring most abundantly in the region of the south coast where 
the annual rainfall is 50 inches or less; here it is a serious plague of cattle 
during the rainy season in April, May, and June. Along the northern and 
eastern coasts (annual rainfall 50 to 75 inches or more) this fly is not con- 
sidered an important problem except during seasons of unusual drought. At 
Mayaguez, where a long, very wet season occurs, the horn fly is very scarce. 
Over 75 species of insects were found breeding in cattle dung. The inter- 
relationship of these and their actual bearing on the horn fly problem was 
worked out as far as possible. The dung beetles Ataenius stercorator F., 
Aphodius lividus Oliv., and A. granarius L. var. guadaloupensis F. and S., oc- 
curred in, vast numbers at certain seasons and proved to be indirect enemies 
of the horn fly by tunneling through and scattering the dung. Ants play a 
very important role in dung by preying on the maggots of the horn fly and other 
flies, and of scarabaeid grubs. 
MOSQUITOES 
In addition to giving advice to other organizations on special programs for 
mosquito control, investigations have been carried on to determine the flight 
range of the more important species in the Pacific Northwest, the duration of 
viability of the eggs of flood-water and salt-marsh species, and control methods 
for snow-water, salt-marsh, and other pestiferous forms, including such meas- 
ures as the maintenance of water levels in lakes, the use of larvicides and 
repellents, and the clearing of brush. Surveys to determine the relative abund- 
ance of the different species in Florida were continued during the year. Manu- 
scripts have been prepared on the biology, habits, control, and taxonomy of 
species of the Southeast and of the more important ones of the Northwest so 
that such basic information will be available to persons in charge of or inter- 
ested in control work. 
An intensive survey was made in Puerto Rico to determine the number of 
species of mosquitoes present, their distribution, relative abundance and im- 
portance, breeding places, and ecological relationships. Thirty-five species were 
collected, among which were 12 species of Culex, 4 of Anopheles, 8 of Aedes, 
2 of Psorophora, 2 of Mansonia, 2 of Wyeomyia, 3 of Uranotaenia, 1 of Mega- 
rhinus, and 1 of Deinocerites. In general it was found that most of the mosquito 
trouble was caused by salt-marsh and irrigation-ditch breeders in the Coastal 
Plains and along watercourses, and by the domesticated species, Aedes 
aegypti L. and Culex quinquefasciatus Say, in towns and villages. Anopheles 
ulbimanus Wied. was the principal vector of malaria. The general principles 
to be followed in controlling the more important mosquitoes on the island have 
been outlined. 
SAND FLIES 
The discovery of a method for rearing Culicoides canithorax Hoff. has enabled 
the breeding places of this species to be located. It has been found that it 
breeds principally in open salt marshes, hence it will be more difficult to control 
than the tree-line breeders. A method has been devised for inducing oviposition 
of sand flies under laboratory conditions and this will facilitate studies on the 
biologies of the various species and expedite the development of control 
methods. 
Experimental diking and drying of marshes has shown this to be an effective 
method in preventing sand fly breeding in certain types of mangrove and 
pickleweed marshes subject to "trickle tides." 
EYE GNATS 
The studies on eye gnats have consisted principally of plot and field-cage 
recoveries to determine the history and species of Hippelates present in the 
vicinity of Winter Haven, Tex. While there has been a seasonal incidence of 
H. pusio Loew, corresponding somewhat to that in the Coachella Valley of 
California, it has been indicated that this species breeds more continuously 
during the year at Winter Haven. Four species not encountered in the 
Coachella Valley were collected. 
A check of the results obtained in the Coachella Valley by following the 
methods of eye gnat control advocated by the Bureau shows that trouble from 
this pest has been largely eliminated. 
