STUDIES ON CONTACT INSECTICIDES. 
Table 1. — Results of spraying Aphis rumicis with organic compounds — Continued. 
ESSENTIAL AND FIXED OILS. 
Compound. 
urpentine spirits (technical). 
Terebene (U. S. P.). 
Pine oil 
Oil cedar wood 
Cottonseed oil. 
Concentra- Minimum 
tions toxic con- 
tested, centrations. 
Tolerance 
of plant. 
Grams per 
Grams per 
100 cc. 
100 cc. 
f 5 
2.5 
1 
>5 
0.5 
0.1 
2 
1 
1 ±2 
O.511 
1 
1 
0.5 
0.1 
5 
2.5 
1.25 
1 
>1 
±1 
= 2.5 
Grams per 
100 cc. 
<0.5 
±0.5 
<I 
11 Bv volume. 
DISCUSSION OF TABLE 1. 
The literature contains many references to the use of commercial 
and pure pyridine as an insecticide. As early as 1911, McClintock, 
Hamilton, and Lowe C£) 3 pronounced it valueless as a contact insec- 
ticide, and in the same year Cazeneuve (2) reported it as effective 
against Cochylis and Eudemis larvae. More recently Theobald (14) 
has claimed great value for it as a substitute for nicotine in the control 
of apple aphids. Frayer (Insect Pests and Fungus Diseases, Cam- 
bridge, Eng., 1920, p. 445) has made a large number of tests with 
pyridine, but finds it a weak insecticide, injurious to foliage when 
used at the strength required to kill aphids or capsids. Results of 
the present study indicate that carefully purified pyridine, boiling at 
115° C, shows little toxicity for Aphis rumicis. Alpha picoline, the 
next homolog, proved to be more toxic, killing at about 15 per cent. 
Experiments not included in this table indicate that the higher boiling 
fractions of the commercial product up to 160° C. have somewhat 
higher toxicity, though they offer little promise as contact insecti- 
cides. Quaternary pyridinium compounds gave little toxicity. 
Piperidine (hexahydropyridine) is to be noted as having five times 
the effectiveness of pure pyridine. When used as a sulphate, the 
toxicity was several times greater than that of the free base. This 
important difference is discussed on page 10. Quinoline is much 
more toxic than pyridine, killing at 2 per cent. Tetrahydroquinoline 
is equally toxic. The insecticidal effect of piperazine is slightly 
greater than that of piperidine, the chemical structure of which is 
very similar. Pyrrole produced little effect at the concentrations 
used. Pyridine, alpha picoline, and their homologs as found in com- 
mercial pyridine, are relatively noninjurious to nasturtium; most of 
the other compounds in this series are decidedly injurious. 
Alkaloids, with the exception of nicotine, showed little toxicity. 
Nicotine, however, is toxic at a concentration of 0.007 per cent, the 
i Reference is made by number (italics) to Literature cited, p. 15. 
