\.\\r.\L REPORTS OF DEPARTMENT OF AGRICULTURE, 1. 
As ii has Dot been proved thai pyrethrins are the only toxic constituei 
ta were made of various purified fractions of a pyrethriun con- 
centrate i" find "in whether any of them were moi tan their pyrethrln 
content would Indicate. Certain fractions were bo highly toxic that further 
Lnvestig ition of them la warranted. 
A ii- •. metal Insectid g turntable <>r improved desig 
and used for i « • — i i 1 1 ^r Liquid household Insecticides bousefliea Certain 
samples provided by the National Association ot insecticide and Disinfectant 
M.-n.i. perated in these investigations, were tested <»n the turn- 
table and these same samples were a s by the Peet-Grady method in 1<> 
■ ; ie as social Ion. These result - wei e a - 
As n result of this work the association decided for the firs »pt a 
standard or control insecticide for comparative tests. The use ol this 
will facilitate the detection of low-quality insecticides and will tend to 
the general level of quality. A standard specification based on insecticidal 
( flBciency can now be formulated. 
TOXICITY OF INSECTICIDAL COMBINATIONS OF TOBACCO AM) TOBACCO PRODI I Is 
ON INSECTS 
A physiological study of the effect of nicotine In solution on the heart action 
in the adult stages of the American cockroach and the larval the 
southern armyworm was carried out during the year. The investigations showed 
that 0.4 percent of nicotine in a saline solution, when applied to the isolated 
heart of a cockroach, produces a temporary stimulation of the rate <>f contrac- 
tion, followed by little or no depression. When the heart, after being held in 
the nicotine-saline solution for .■'»<• to 60 minutes, was transferred to the saline 
solution there was a temporary depression followed by an increase which raised 
the rate of action to a new level. With the heart of the southern arinyworm. 
however, the effect of 0.4 percent of nicotine was relatively slight in most • 
it seems possible that this difference in the effect of nicotine on the heart action 
in the two differenl species of insects may be due to the fact that there are 
ganglionic cells within the heart tissue Of the cockroach while the heart of the 
larva of the southern armyworm apparently contains none 
in tests on the fumigation of weevil-infested dried peas and beans under 
reduced pressure, using volatilized nicotine, it was found possible to kill these 
insects within the seed with an exposure of <', hours. Voiatili/e-! nicotine, how- 
ever, 'iocs: not penetrate very well Into a mass of seed, and the results of this 
Investigation indicate that it Is neither so effective nor so cheap for thia pra 
a< arc some other fumigants. 
Quantitative injection of nicotine and nicotine sulphate into blowflies and 
certain lepidopterous larvae showed thai all Bpecies tested are inherently sus- 
ceptible to this poison. The ineffectiveness of nicotine as ordinarily applied 
probably indicates Its failure to reach the vital parts of the insects. 
ew, soluble, crystalline, nicotine compound called nicotine humate was aa 
effective as oicotine sulphate against aphids. The acid-alkali ratio of sodium 
oleate solutions, used as a spreader with nicotine, had no marked Influence on 
the toxicity of the mixt ure. 
A laboratory method has been developed for determinii u und< r i ontrolled con- 
ditions the concentration of nicotine vapor and the time required to kill pea 
aphids and other Insects. The effective concentration for the pea aphid was 
much lower than expected. Adsorption of nicotine on leaves was detected. 
Preliminary experiments have been made on ti.. of varioua salts on 
the toxicity <»f nicotine to mosquito larvae. 
A precise laboratory method was developed for determining the relative 
effectiveness of various substances against the eggs of the housefly. Nicotine 
compounds were not effective against the eggs of this species, hut oils from the 
dry distillation of tobacco stems and other waste plant material were promis- 
ing. Suspensions of the powdered rout- of certain rotenone bearing plants and 
extracts <>\' these plants were outstanding in their effectiveness against these 
Similar tests were also made against the eggs of the Angoumois grain 
moth, with better results from nicotine compounds. 
ii i n> DETERMINE EFFECT OF NEW INSECTICIDAJ MATERIALS ON INSECTS 
i' ■ were made during the year for the Division of Insecticide investiga- 
ted for the Bureau of riant industry t<> determine the insecticidal value 
of rarioUS plants that are new or that are not generally employed in 1his 
