THE POTATO MOTH. 
17 
destruction of the larva, particularly by the former means, is 
further complicated according as it is in the substance or on the 
surface of the tuber. 
Experiments, in which larva-infested tubers were dipped 
in solutions of formalin of varying strengths (.1-1 pt. to 15 gals, 
water) resulted in showing that a steeping of at least .48 hours’ 
duration is necessary to ensure complete annihilation of the 
adult larvae when in the tuber. Similarly established control 
experiments in which water served as the steeping medium 
demonstrated the fact that it is as effective as steeping in 
anv of the abovementioned formalin solutions. The com- 
paratively slow rate of diffusion of formalin solution into the 
starchy tissue of the steeped tuber, the power of relatively rapid 
movement possessed by the larva, and its possible power of ad- 
aptation to an increased tension of CO,, lead to the conclusion 
that in these experiments extinction of its vitality is due to 
asphyxiation rather than to direct formalin poisoning. The 
point is of economic importance since destruction of the larva 
may, in these particular circumstances, be as effectively' ac- 
complished by steeping infested tubers in water alone as in a 
solution of formalin. The chief function of formalin is to sup- 
press bacterial development, which invariably occurs after 
prolonged steeping of infested tubers in water, the substances 
which pass by diffusion from the tuber into the water rendering 
it a comparatively rich nutritive medium for certain bacterial 
types. 
Even when isolated adult larvae are placed in formalin 
solutions (l-i pt. to 15 gals, water), or in a solution of mercuric 
chloride of the strength mentioned below, thus eliminating the 
complicating factor of diffusion and ensuring complete contact 
of the larvae and solution, an immersion of 6 hours in the former 
and of 2 hours in the latter fails to ensure their destruction. 
An immersion of 6 hours’ duration in a solution of ii per cent, of 
copper sulphate, of 2 1 percent, sodium carbonate, or a mixture 
of equal volumes of these two solutions does not lead to 
annihilation of the larvae. 
The egg of the moth is particularly resistant to the action of 
such poisons as formalin or mercuric chloride, or sulphuric acid 
of either 5 or 10 per cent, strengths. Thus with egg infested 
tubers steeped either in formalin solution (2 pts. to 15 gals, water) 
for 48 hours, or mercuric chloride solution (1 oz. to 8 gals, water) 
for 12 hours, or in a 10 per cent, solution of sulphuric acid for 
2 hours, the eggs were not destroyed by any of these treatments, 
the experimental tubers in each instance becoming as badly 
infested as the corresponding controls of egg-infested tubers 
which had not been subjected to treatment. 
The pupa is equally difficult to annihilate by these means. 
Steeping experiments in which these objects, divested of their 
