320 



Tattkrsfii: I n (F.) ct Rohkrts (A. W. R.)- The Influence of Chemical 

 Constitution on the Toxicity of Organic Compounds to Wireworms. 



—JL Agric. Sci., Cambndge, x, pt. 2, April 1920, pp. 199-232. 

 18 diagrams. [Received 27'th April 1921.] 



The object of the present investigations was to study the toxic 

 values of a series of organic compounds with respect to wireworms, 

 Agriotes spp., and to correlate as far as possible the toxic values with 

 chemical constitution and physical properties. The observations of 

 various authors are reviewed ''R.A.E., B, v, 131, 174; A, vi, 

 200, 397]. 



The technique employed in the present experiments is described. 

 In all, more than 75 substances were tested, representing the more 

 important and readily obtainable series, though not covering the whole 

 range of simple organic groupings. The toxicity of certain organic 

 compounds apparently depends primarily on their chemical properties 

 and only secondarily on their rates of evaporation. Moore [R.A.E., 

 A, vi, 398] lays more stress on volatility than on chemical constitution, 

 but in many cases this is not applicable. In certain series, such as 

 the hydrocarbons, the toxic values increase with increasing molecular 

 weight, though this is not true of all substances. Solubility in water 

 also apparently plays an important part in the toxic effect of some 

 compounds. Physiological effects are not solely dependent iipon 

 any one physical property, although they determine how far matters 

 can go ; the chemical properties are the deciding factors. A liquid 

 is generally more certain in action than a solid. 



Whether the size of the insect materially alters its resistance has 

 not been definitely ascertained. During the tests the insects were 

 exposed to the vapour for 1,000 minutes in a darkened room at an 

 average temperature of 15° C. [59° F.]. When the concentration of 

 poison was gradually lowered, it was found that at a certain point 

 death did not occur and uncertain results were obtained. Toxicity 

 gradually increased in passing from the lower to the higher homo- 

 logues until a certain point was reached at which uncertain results 

 were obtained, death sometimes occurring and sometimes not, at 

 saturation concentrations. In such cases anaesthesia might result, 

 but the larvae were usually capable of recovery. This effect is the 

 result of the volatility of the compound being insufficient to produce 

 permanent injury, except to less resistant insects. The aromatic 

 hydrocarbons and halides are on the whole more toxic than the aliphatic 

 hydrocarbons and halides. Compounds such as allyl isothiocj^anate, 

 chloropicrin and benzyl chloride, with irritating vapours, have usually 

 a high toxic value which is not closely related to their vapour 

 pressures or rates of evaporation. Chemically inert compounds 

 boiling above 170° C. [338° F.] are generally uncertain in their poison- 

 ous effect on wireworms after an exposure of 1,000 minutes at 15° C. 

 [59° F.]. Nearly all organic compounds boiling above 215° C. [419° F.] 

 are uncertain in their action, while those boiling above 245° C. [473° F.] 

 are non-toxic. These limits depend on the resistance of the insect, 

 the length of exposure and the temperature at which the experiment 

 is carried out. 



Cir.vp.vis (J. C). L'Aphis du M61eze. [Larch Aphis.1— A^a/. Canad., 

 Quebec, xlvii, no. 9, March 1921, pp. 193-195. 



An Aphid, probably Aphis laricifex, Fitch, is recorded from American 

 larch (Larix americana). 



