92 A.X.MWL BEPOKTS 01 DEPARTMENT OF AGRICULTURE, 1939 
Shipments to the United States from the Puerto Rico station com- 
prised a rearing stock of I he Sao Paulo si rain of the Amazon fly (M 
gam&tylwm minensi Town-.), a promising parasite of the sugarcane 
borer, and the following beetle predators of the coconut scale: 190 
Gryptognatha nodia ps Mshll., 600 PentUia castanea Muls., and 225 
Pi rUUia -p. 
( OOPERATION WITH FOREIGN ORGANIZATIONS 
In addition to the cooperative work with the Canadian Department 
of Agriculture, already mentioned, colonies of parasites have been 
forwarded to foreign count ries by this <>r other Divisions <d' the Bureau 
a- listed in table 13. 
Table 13. — Shipments >>f parasites to foreign countries, fiscal war tS 
fJitms :m>:t':\ bng 
I 
[Citrus bl icl fly 
<cale 
1 Pink bollworm 
Rndolia cardinal}* Muls. 
1 do 
Xc'.v Zealand 
Cabbageworm 
( 'njl'tolaemus montrouzifri Muis. 
Santo Domingo 
Mealybugs—.- 
CONTROL INVESTIGATIONS 
TESTING INSECTICIDES 
The work on testing insecticides was continued a- in previous years 
except that many more tests were made with a larger number of insects. 
In testing organic compounds 10 materials were found which showed 
sufficient promise to warrant intensive study. All these when used as 
stomach insecticides caused high mortality to well-grown larvae of 
3 or more species of insect pests. Some of these compounds may he 
of value in the commercial control of various insects. 
In cooperation with the Division of Drug and Related Plants of 
the Bureau of Plant Industry approximately 600 preparations of rote- 
none-bearing plants and 72 preparations from plants producing pyre- 
thrum, grown in the United Stales, were tested by biological assay to 
determine their inseeticidal value. The results of this work are prom- 
ising and indicate that it is possible by selection to obtain strains of 
plants with considerably higher insecticidal value. 
The effect of the diet of certain insects on their suscept ibility to poi- 
sons was investigated, and it was found to have a marked influence on 
the toxicity of some of tin 1 common insecticides, such as arsenicals. 
For example, Larvae of the southern armyworm reared on pokeweed 
leaves were practically immune to dosages of lead arsenate which 
killed !»:» percent of the individuals reared on young collards. Studies 
of household sprays on houseflies showed thai flies temporarily para- 
lyzed by the sprays were more resistant than the normally active Hies. 
four reports were prepared, mimeographed, and distributed making 
available I he results of approximately 4,000 tests on 800 different mate- 
rials made on about 21 species of insects. Preliminary results were 
obtained in tests with the more promising <d* these materials to deter- 
mine i heir effect on 1 he host plant s. 
