216 Infestation of Fungus Cultures by Mites 



All these compounds were chosen because of their definite insecticidal 

 value. With the exception of Ammonia, Mono- and Dimethylanihne this 

 is not considerable but it was thought to be sufficiently high for the 

 substances to prove effective in air saturated with their vapour against 

 a not very resistant pest. Moreover, it was considered that the toxic 

 effect of the majority of them to fungi would be small. 



(a) Action upon Fungi. 



As it was essential that the latter condition should be complied with, 

 these substances were all given a prehminary test to discover their action 

 against a common fungus. A green Penicillium was used, the cultures 

 being tested in dupHcate, one of each couple being exposed with the 

 cotton-wool plug in situ, the other with it removed^. The culture tubes 

 were put into a large boiling tube containing a quantity of the chemical, 

 sufficient to saturate the air with its vapour. The boihng tube was then 

 corked and put aside for three days after which the culture was taken 

 out and subcultured. The results are stated in Table I. 



Table I. 



Effect of Vapour of various Organic Chemicals on Penicilhum sp. 

 Culture exposed for three days and then suhcultured. 



(6) Action upon Mites. 



A selection of the above compounds was then tested upon mites. 

 Some flour mites, A.farinae, were placed in tubes which were vaseHned 

 round the outer lip to prevent the escape of the mites, but left unplugged. 

 Exposure to the toxic substance was made in exactly the same way as 

 described but for varying lengths of time. The results are shown in 

 Table II. 



^ The results of the two series showed no significant differences. 



