BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 25 
maciilatus, and A. dorsalis mosquitoes in irrigated regions of the 
Central Valley in California is becoming increasingly difficult. 
Tests with EPN showed that rates of application as low as 0.035 
pound of the insecticide per acre completely controlled the mosquito 
larvae. In large-scale control operations a dosage of 0.075 pound 
per acre gave excellent results. EPN is regarded as one of the more 
hazardous insecticides. However, the rates required for mosquito 
larva control are only about one-fourth to one-third the rates of 
DDT and toxaphene. Operators applying EPN in the cooperative 
work in California experienced no toxic reactions to this insecticide. 
It is believed that careful handling of the insecticide by experienced 
mosquito control workers will permit its safe use. The material has 
not yet been recommended for such use. 
Malathion and tetrapropyl dithiopyrophosphate, two other phos- 
phate insecticides that are much less hazardous to man and animals, 
gave good control of mosquito larvae at dosage rates of 0.4 to 0.5 
pound per acre. 
Heptachlor gave excellent control of larvae and adults of Aedes 
mosquitoes in Oregon. The dosage rates required ranged from 0.1 
to 0.15 pound per acre. Chlordane proved somewhat less effective 
than heptachlor. 
Successive generations of colonies of Culex quinquefasciatus mosqui- 
toes have been exposed to EPN and DDT in the larval stage in an 
effort to determine the capacity of this species to develop resistance 
to these two insecticides. The rapidity and degree to which mosqui- 
toes develop resistance to insecticides are criteria that must now be 
considered in determining the value of new insecticides for mosquito 
control. There have been no conclusive results from these studies 
to date. 
There has been a need for economical and practical mosquito-control 
methods in small communities not having funds or technical leader- 
ship for consistent control programs. As a demonstration of control 
work possible in such a community, a residual DDT spray was applied 
to a village in eastern Oregon. Two applications of spray to the en- 
tire community during the mosquito season provided good protection 
to the inhabitants. Residual spraying without larviciding may also 
retard the development of resistant mosquitoes. 
Insecticides Highly Effective in Destroying Imported Fire Ant 
Colonies 
Investigations at Mobile, Ala., to develop more satisfactory methods 
for controlling the imported fire ant showed that for individual mound 
treatment, a concentration of 0.25 percent of chlordane, dieldrin, al- 
drin, or heptachlor may be used with equal effectiveness in controlling 
this destructive, introduced pest now widespread in the Southern 
States. The research was done in cooperation with several State 
agencies in Alabama. Water emulsions or suspensions containing 
the 0.25-percent concentration should be applied at the rate of about 
3 gallons per mound. Two insecticides, EPN and parathion, at con- 
centrations as low as 0.03 percent, were also highl}^ effective. These 
materials are also highly toxic to man and animals. It is not yet 
certain whether they can be used without undue hazard. 
