328 PROCEEDINGS OF SECTION D. 



to their relative insensitivity to the action of poisons in solution. 

 The pupa, for example, is able to withstand 48 hours' immersion in 

 solutions of formalin, either of ^ or 1 pint of this re-agent to 15 

 gallons of water. In these experiments it was found that the 

 majority of the objects survived, and from them healthy moths 

 emerged. 



Equally positive results attend the steeping of tubers infested 

 with the eggs of the moth. The material selected for experiment 

 comprised tubers on which were recently deposited eggs only; 

 separate lots of these were steeped in one or other of the following 

 solutions : — 



(1) Solutions of formalin (i, 1, or 2 pints to 15 gallons of 



water) for 48 hours. 



(2) A solution of mercuric chloride (1 oz. to 8 gallons of 



water) for twelve hours. 



(3) An aqueous 5 per cent, or 10 per cent, solution of sul- 



phuric acid for one to two hours. 

 These results are possibly explicable on the grounds that — 



(1) Little, if any, of these poisons are absorbed by the pupa 



and egg. 



(2) The respiratory activities of these life forms are of a low 



order of magnitude. 



When uninfested tubers are treated by steeping in an aqueous 

 solution of mercuric chloride, or a suspension of lead arsenate, 

 and these tubers are subsequently air-dried, and then exposed to 

 infection, it is found that they become as readily infested as 

 similar but untreated tubers. This applies with equal force 

 whether the infesting agents are juvenile or adult larvse. Treat- 

 ment of tubers according to either of these methods as a protection 

 against infection, therefore, cannot be regarded as likely to yield 

 satisfactory results. 



The spraying of uninfected tubers with various spray mixtures 

 (copper sulphate, soda mixture, phenyle emulsion, &c.), and the 

 dressing of tubers with air-slaked lime and mixtures of air-slaked 

 lime and sulphur or Paris green, in varying proportions, are 

 equally ineffective as a means of permanently preventing infection. 

 In none of these cases was there any very definite evidence that 

 the larva in its attack on the tuber consumed any of these poisons 

 with which the skin of the treated tuber was assumed to be either 

 covered or impregnated. Observation tended to show that the 

 larvse rejected the skin and did not ingest any material until it 

 had penetrated into the subjacent starchy tissue of the tuber. 



Carbon bi-sulphide fumigation has yielded the most satis- 

 factory results. Experimental trial over a considerable range of 

 conditions has shown that the larva, whether in the substance of 



