86 ANNUAL REPORTS OP DEPARTMENT OF AGRICULTURE, 1939 
FLY SPRAYS 
A.s a result of studies for developing more effective insect-killing 
and repellent sprays, a certain noninsecticidal vegetable oil has beer 
round which, when mixed with pyrethrum sprays, greatly increases 
the toxicity of the insecticidal prmciples. The addition of 5 percent 
of this oil to the spray effectively prevents recovery of houseflies, even 
from light doses of pyrethrum. For household sprays the quantity 
of pyrethrum necessary to produce a satisfactory kill of flies can be 
cut in half when 1" percent of the oil is added, but the action of such 
;i dilute spray is too slow to be satisfactory for use under more or le?^ 
open conditions such as dairy barns. It was found that the oil 
increases the repellent net ion of pyrethrum -pray- and enhances the 
efficacy <»}' water emulsions of pyrethrum extract. A patent covering 
the Free use of this material by the public has been applied for. 
MOSQUITOES 
Sn-ady progress has been made in studying the habits and biology 
of the 23 species of mosquitoes in the Pacific Northwest. These 
numerous pest species have been grouped in 7 or 8 general associa- 
tions so that practical information on mosquitoes and their control 
can be given the public. The classification of mosquito-breeding 
areas in this way as a result of surveys has been a distinct aid to 
mosquito-control agencies, since the mosquito problems vary greatrj 
in t he several physiogeographical areas of the Northwest . Two rather 
distinct and unique methods of control have been developed. (1) the 
destruction of the habitat of the floodwater specie- Aedes vexans 
(Meig.) and A. aldricM I), and K. by clearing out the brush where 
the eggs have been deposited, and (2) control of the snow-water 
species .1. aborigirm Dyar, .1. hexodontus Dyar, .1. fitchii V. and Y.. 
and .1. comm/unis D. and d. by maintenance of water levels. There 
are certain limits in the application of these methods, hut each is 
effective where it can be applied, and without undue injury to wild- 
life and fish. Definite information i> obtained each year on the 
longevity and viability of the eggs of the first two species. 
A comprehensive study of the effects of the Bonneville Dam on 
the mosquito population reveals that the impoundment of water by 
the dam has actually caused a decrease in the population of the 
important iloodwater species above the dam from Bonneville to The 
Dalle.-, a distance of 50 miles. 
[nvestigations of said-marsh areas in Delaware and New Jersey, 
when- extensive mosquito-control operations are under way. to deter- 
mine the (dlcct of ditching on marsh condition-, indicate (1) that 
changes in the flora and fauna of the mar-he- depend largely on the 
extent to which the water table IS lowered. (2) that drastic Lowering 
of the water table i^ not essential to effective mosquito control, and 
(3) that control measures should he adapted to meet individual con- 
ditions in each area. 
In view of the import ance of salt-marsh mosquitoes, a field labora- 
tory was established at New Smyrna., Fla., to initiate detailed studies 
on their biology, habits, and control. It is expected that emphasis 
will l»c placed on developing more satisfactory control measures than 
