BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 
25 
were reared and forwarded to the Iowa Agricultural Experiment 
Station for field release. 
The cooperative project for the biological control of the citrus 
hlackfly on the west coast of Mexico was completed during the year. 
Twelve consignments of parasite material from the Panama Canal 
Zone yielded 8,767 adults of Eretmoct ruA s< rius Silv., a species known 
to be very effective in other sections of tropical America, and these were 
released m 60 infested plantings in the States of Sinaloa. Xayarit, and 
Colima. The parasite is now well established, and its effectiveness 
in control should be evident in the near future. Other shipments of 
parasites to Mexico included 1 consignment of Lixophaga diatraeou 
(Towns.), a parasite of the sugarcane borer, and 3 of Aphelirms riMi 
Raid. 
CONTROL INVESTIGATIONS 
TOXICITY TESTS AID IN FURTHER, IMPROVEMENT OF AEROSOLS AND SPRAYS 
The great demand by the armed forces for insecticidal aerosols and 
the critical shortage of pyrethrum made it necessary to intensify the 
search for substitutes for part or all of pyrethrum used in the aerosol 
dispensers. One new material has proved to be very promising, and a 
large number of formulas containing it have been tested. A thorough 
investigation is being made, however, before a final formula is. 
recommended. 
A number of commercial aerosol dispensers have been tested. Most 
of these are 1-pound containers equipped with valves for releasing 
whatever quantity of aerosol is needed to kill the insects in the space 
being treated. They were effective in controlling flies and mosquitoes 
except when the aerosol solution was discharged at too rapid a rate. 
With the present aerosol formula a discharge rate of 0.5 to 1.0 gram 
per second is most satisfactory. 
In tests comparing the effectiveness of pyrethrum in an aerosol and 
in a deodorized kerosene spray, the aerosol was found to be superior. 
In delayed-action tests the aerosol was found to be much better, since 
it remains suspended in the air for a much longer time. Approx 
imately 885 tests were made on 65 aerosol formulas to test their effec 
tiveness in controlling the housefly and malaria and yellow-fever 
mosquitoes. 
Approximately 375 tests were made with a large number of spray 
formulas to control disease-carrying mosquitoes. Materials were 
tested in deodorized kerosene and in emulsion form. The oil-base 
sprays were more effective than the water-base sprays per unit of 
toxicant, although the toxicity of the water-base sprays varied 
markedly with the formula used. 
Pyrethrum still remains the outstanding insecticide for the destruc- 
tion of adult mosquitoes. Two materials that act as synergists slightly 
increased the effectiveness of pyrethrum against the yellow-fever 
mosquito, but to a much less extent than in tests on houseflies. 
Of 123 new materials tested as synergists for pyrethrum in fly sprays, 
13 increased its toxicity. 
Of 171 samples of new materials, some in various concentrations, 
tested against the housefly, 1 plant material and 4 synthetic organic 
compounds showed high toxicity. Two of the latter are related to 
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