i6 
F. STOWARD, D.SC. : 
unfrequently proceed with considerable rapidity, and are marked 
by the gradual tunnelling into and consumption of the starchy 
tissue of the tuber by the larva ; the more advanced stages ol 
larval infestation lead to the almost complete destruction of the 
tuber, which finally rots as a result either of fungal or bacterial 
invasion, or dessicates and mummifies (Fig. 2). I he net result 
of larval attack and the activities of commonly associated fungi 
and bacteria which are pathogenic to the potato tuber is, on the 
one hand, to render it valueless as a commercial product, on the 
other to furnish a medium for the propagation of the pest. 1 he 
larva thrives at the expense of the tuber, increases markedly in 
body dimensions, and then pupates. Ihe pupa remains for 
some time in a dormant condition, the life cycle being completed 
by its metamorphosis into the moth. Incidentally it may be 
stated that in the case of plant invasion the eggs are chiefly 
deposited on the leaflets, through the epidermis of which the 
young larva penetrates and thence into the mesophyll, which is 
gradually consumed, the infested leaf as a result of the dessication 
of the remaining epidermal layers presenting the characteristic 
parchment-like appearance which is diagnostic of larval invasion 
of the vegetative portion of the plant. 
Various methods have been advocated from time to time 
to control the pest in stored tubers. These methods may be 
conveniently set out as under : — 
(1) The dipping of tubers in toxic solutions, as a means 
either of destroying the infesting agents in tubers 
already attacked, or of preventing infestation ; 
(2) The dressing of tubers with solid chemical substances 
as a means of preventing infestation ; 
(3) The spraying of tubers with various antiseptic or 
odoriferous mixtures either in solution or suspension 
as a means of protecting tubers against infestation ; 
(4) The fumigation of tubers as a means of destroying 
the infesting agents. 
The potato moth normally goes through a certain life cycle, 
which embraces the following phases or life forms : the egg, 
larva and pupa. At the outset it was recognised that, excluding 
the moth itself, these different life forms are very diversely 
insensitive to the action of toxic chemical compounds. Thus, 
in the course of this experimental enquiry it has been shown 
that of these different units when exposed, in separate series of 
experiments, either to the influence of formalin in solution or 
to the poisonous fumigant carbon bisulphide, the egg is the most 
and the moth the least insensitive, the degree of insensitivity 
of these diverse life-forms of the insect towards these reagents 
being in the order the egg, pupa, larva, moth. In addition, 
