Zz 
1 Pes., 1900.] QUEENSLAND AGRICULTURAL JOURNAL. 139 
considerable acreage of potatoes had been gnawn down. As a rule it ix not 
until the caterpillars are nearly full grown that attention is directed to their 
presence, which happens then by reason of the extent of their depredations 
(‘the crop looking thir,” as is often said) or the occurrence of such a moving 
host as has been alluded to. 
The caterpillar takes from four to five weeks to mature, but this period is 
subject to variation in length, a circumstance connected with the amount of 
suitable food that is available for its consumption, as well-as the occurrence or 
absence of congenial climatic conditions. Thus, during the winter, the insect 
will persist as a caterpillar for quite three months, during a portion of which 
time it remains in a semi-dormant condition. 
When mature, it changes, as previously remarked, to a lighter colour, and 
its stripes grow paler. It then, under normal conditions, enters the ground toa 
depth of about 2 inches. Here, still outwardly a caterpillar, it becomes even 
ele: in colour than before, and its body meanwhile becomes considerably 
shortened. In this position it may remain for two days (this period is also 
subject to variations in length), during which time, by special movements in 
different directions, it forms an oblong smooth chamber measuring about 1 inch 
in length, and meanwhile changes into a chrysalis such as has been described. 
In exceptional cases, however, it crawls beneath a stone, piece of fallen timber, 
sod of earth, or “land” in ploughed ground, and then transforms without 
constructing any chamber, though sometimes it covers itself with earth. 
The insect having thus passed into a chrysalis remains in that condition 
usually for about two weeks; but again the time passed in this phase may vary 
from ten days to three or four weeks. At the expiration of this period the 
perfect insect or moth arises, a warm evening after rain being usually chosen 
for its appearance. 
Although the caterpillars occurring even in the same field exhibit great 
yariation in size and consequently in age, there are good grounds for concluding 
that, generally speaking, there are at least three broods, if not four, every year, 
although it is only during two periods of the year—September-October and 
March-April—that they occur of such exxtent as to prove noticeably destructive; 
their comparative smallness in the intervening periods being due to the operation 
of natural checks upon their growth and increase, as well as to the condition of 
growing crops. ‘These three or four separate broods, however, overlap to a 
considerable degree. he caterpillars that were observed during 1899 in the 
Ma Ma Creek district from the second week in August onwards, and which had 
already transformed—in part—to moths by the third week of September, were 
no doubt derived from moths that had deposited their eggs, where these 
caterpillars were met with,in May. It was inferred that a similar state of 
things had obtained on the Darling Downs, since, in many instances, whereas 
wheat sown in April or May was subsequently attacked by caterpillars, that 
which had been planted in the same locality in June and July had escaped their 
visitation ; a remark that also applied to both oats and barley. Where it had 
been otherwise, there was generally evidence forthcoming to point to a migration 
of caterpillars from the earlier to the later sown crop. ‘The explanation of this 
is to be found in the fact that the crops, in order to evince the presence of 
caterpillars in September, require an access of the moths in May. If this 
is impracticable, they may escape their presence. 
NATURAL ENEMIES. 
Tt has already been stated in the introductory paragraph that under normal ~ 
conditions the caterpillars of Leucania unipuncta, Haw., do not occur in such 
numbers as to inflict noticeable damage to pasturage, cereal, or hay crops. It 
is also true that when, under special circumstances, these pests have exceeded 
these limits in respect to numbers, forces come into operation to restore the 
balance of Nature by checking the enormous numerical development of these 
caterpillars that would follow the free exercise of their powers of increase. 
