66 



LV. F. Tattersfield, C. T. Gimingham and H. M. Morris. 

 " Studies cm Contact Insecticides/' Part 3. A 

 Quantitative Examination of the Insecticidal Action of 

 the Chlor-, Nitro-, and Hydroxyl Derivatives of 

 Benzene and Naphthalene. Annals of Applied Biology, 

 1925. Vol. XII., pp. 218-262. 



The toxicities of a number of chlor-, nitro- and hydroxyl 

 derivatives of aromatic hydrocarbons to Aphis rumicis, L. (adults) 

 and to Selenia tetralunaria, Hufn. (eggs) have been determined. 



The order of toxicity to aphides of the hydrocarbons and their 

 chlor- and nitro-derivatives is benzene < toluene < xylene < mono- 

 chlor-benzene < p-dichlorbenzene < o-dichlorbenzene < tri-chlor- 

 benzene < nitro-benzene < m-dinitrobenzene. The mono-chlor- 

 nitro-benzenes have about the same toxicity as nitro-benzene ; 

 l.-chlor-2.4-dinitrobenzeneis slightly less toxic than m-dinitrobenzene. 



Phenol and the three isomeric cresols are toxic to aphides only 

 at high concentrations. The mono-nitro-phenols and cresols are all 

 more toxic than the parent substances, the order of toxicity of the 

 phenols being o-nitro phenol < m-nitro phenol and p-nitro-phenol 

 < 2.4 dinitro phenol which is greater than tri-nitro phenol; the same 

 order applies to the cresols and their corresponding derivatives. 



d:-chlor naphthalene proved to be the most toxic of the 

 napthalene derivatives tested. 



With few exceptions, the relative toxicities of the various 

 compounds to the insect eggs are approximately in the s*ime 

 order as to the aphides. The nitro-derivatives of phenol and the 

 cresols were specially studied and it was shown that, as in the 

 case of aphides, the dinitro compounds are more toxic to eggs 

 than either the mono- or the tri-nitro compounds. 



The toxicity of 3.5 dinitro-o-cresol to adults of Aphis rumicis 

 and to the eggs of Selenia teralunaria is of the same order as 

 that of Nicotine. 



Some of the compounds tested, although injurious to foliage, 

 may prove of value as winter spray fluids for trees in a dormant 

 condition and experiments on a practical scale are in hand. 



No simple generalisation as to the correlation of toxicity 

 with any one chemical or physical property seems possible in the 

 present stage of our knowledge. It is probable that the nature of 

 the toxic activity depends on chemical constitution, while the 

 intensity of activity is determined by one or more physical 

 properties. 



See also paper LXXV. 



(b) FUNGUS PESTS AND THEIR CONTROL. 



LVI. Mary D. Glvnne. " Infection Experiments with 

 Wart Disease of Potatoes, Synchytrium Endobioticum 

 tSchUb.)." Annals of Applied Biology, 1925. 

 Vol. XII., pp. 34-60. 



A study of certain conditions controlling infection of potatoes 

 by the winter sporangium of Synchytrium endobioticum in the 

 soil and by the summer sporangium in the laboratory has been 

 made with a view to finding a reliable method of pot experiment 



