240 



HABITS OK llIK INSECT. 



When fully estiiblished in a district, both those potatoes which arc in the ground 

 and those which have been removed from it and are stored are subject to the attacks 

 of the moth. At Toowoomba, as far as we learn, it is only those tubers which have 

 l)een du<^ up which, as yet, suffer. * Mr. G. Searle, in rejily to our questions, re- 

 marks : 



" I am perfectly sure that the insect is uot in tlie potato while this is in the ground. 

 We are almost daily using potatoes which were all dug at one time, inniiediately 

 picked up, and placed in a dry-goods cask in which straw was placed between each 

 layer of tubers. The cask is covered up by a corn bag, and, with the exception of a 

 few near the top of it, none are affected by the moth." In Tasmania it was "in- 

 variably found that the moth attacks the roots. The ujipermost potatoes, those 

 which are nearest the surface, are of course most easily reached, nor is it by any 

 means a difficult matter for the insect to penetrate to the depth of three or four inches 

 when the soil is open, uncompressed, or lumpy. Not a single case of an infected stalk 

 has yet been detected, but constant and numberless have been the instances in which, 

 when uncovering the potatoes at the deptli just indicated, moths have been dislodged 

 and flown uninjured away." 



Of course some of these, however, as must have occurred to the author of these ob- 

 servations, nught have hatched from pupje still in the ground; l)ut in anticipation 

 of this objection he adds: 



" The potatoes, whilst lying exposed in rows, were attacked by the insects * * * 

 and it was always noted that the moths, when unengaged in laying eggs, were al- 

 most .always to be found beneath the clods of earth with which the ground was en- 

 cumbered. "' 



Otto Tepper remarks : 



" My opinion is that the eggs are first deposited by the moths under the stalk near 

 the ground, when the infant grub burrows through the soil till reaching the tubers; 

 or the moth itself burrows, as many are found to do, and deposits the eggs direct 

 iipon the tubers. My reason for this is the fact that the longer the tubers are left in 

 the soil the more infected they will prove to be." 



Boisduval's observations, too, though somewhat different as to detail, support this 

 view as to the mode in which ihe "moths find access to the tuber, whilst the latter is 

 still beneath the surface of the ground. 



What is the nature of the operations which take i)lace beneath the surface of the 

 ground may be concluded from Avhat was noticed in our breeding apparatus. The 

 moths had no partiality for perfectly sound tubers, but would attack those Avhich 

 had previously afforded sustenance to a generation of their kind. In a sound potato 

 the eggs were laid several side by side in contiguity to an "eye" of the tuber; in a dis- 

 eased (me, on the earth-covered snrface of a cocoon, within the hole previously exca- 

 vated by a caterpillar which had emerged for the purpose of pupating, or amongst the 

 "frass" surrounding the entrance to this cavity. As many as twenty-six eggs, laid 

 by a single moth, were in one instance counted in the same location. The eggs hatch 

 in a week or ten days, and often more quickly. 



The young caterpillars immediately proceed to burrow into the tuber, at first con- 

 cealing themselves Ijeneath numerous particles of rejected food material fastened 

 together witli web, the number of which particles is being continually increased by 

 similar matter brought to the surface. The channel thus formed is also lined with 

 web, so that when the substance of the tuber is l)roken down these burrows appear 

 as hollow tubular bodies. The caterpillars arrive at their full size in from two to 

 three weeks t and then find their way to the surface of the potato and burrow out- 



*We, however, bred a specimen of the insect from a potato leaf sent by Mr. G. 

 Searle. This the caterpillar had folded up. 



t Tepper makes the minimum to be forty-five days. 



