PROCEEDINGS OF SECTION D. 327 



conditions also the crop tubers may be invaded in situ. The 

 ravages of the larva are particularly severe in the case of stored 

 tubers, the " eyes" of which it enters and destroys, thus render- 

 ing these in a comparatively short space of time quite worthless 

 for " seed " or consumption. 



Various methods of a suggestive character have been advanced 

 from time to time as a means, either of preventing infection of 

 sound tubers, or of effecting the destruction of the infesting agents 

 (larvae, pupae, eggs), in or on tubers already infested. Such 

 methods comprise : — 



(1) The steeping of tubers in aqueous solutions of formalin, 



mercuric chloride, &c. 



(2) The dusting of tubers with finely powdered air-slaked lime, 



or mixtures of lime and other substances. 



(3) The spraying of tubers with fungicidal or insecticidal pre- 



parations. 



(4) The fumigation ©f tubers with carbon -bisulphide. 



Experimental investigation carried out by the writer has shown 

 that when tubers infested with larvae are steeped in solutions of 

 formalin prepared by mixing |, 1, or 2 pints of this com- 

 pound with 15 gallons of water, it requires an immersion of 

 24 to 48 hours' duration to destroy all the infesting larvae. 

 Control experiments, in which similarly infested material 

 steeped in water alone, under otherwise sim.ilar conditions, 

 indicate that this latter method of treatment is as effective as 

 steeping in solutions of formalin. It would appear from the 

 results furnished by these series of experiments, that even in the 

 case of the formalin-steeps, the larva succumbs to drowning rather 

 than to any poisoning effect produced by formalin. 



Similarly conducted experiments with larvae isolated from in- 

 fested tubers and completely immersed in one or other of the 

 following steep-media — (1) formalin solutions of the above-men- 

 tioned strengths for four to six hours, (2) mercuric chloride solu- 

 tion (1 oz. to 8 gallons of water), for half to two hours, (3) an 

 aqueous IJ per cent, solution of copper sulphate for six hours — have 

 demonstrated that these organisms are not only capable of surviv- 

 ing these treatments, but of completing their life cycle as readily 

 and perfectly as larvae not subjected to experimental treatment. 



Comparatively insensitive to these poisons as the larva appears 

 to be under the conditions of experiment selected, the pupa and 

 egg are endowed with still greater powers of resistance. In fact, 

 the larva, pupa, and egg represent an ascending series in regard 



