THE CANADIAN ENTOMOLOGIST. 105 
agent in lessening their numbers is, in my opinion, the intense cold of 
winter, for, contrary to the rule with regard to insects passing the winter in . 
the pupal state, the chrysalis of P. rage, unless placed in a sheltered situa-_ 
tion, does not seem to resist the effects of frost. In early spring, I have. 
searched under the exposed coping-boards offences, where these pupæ 
were suspended in scores, and very rarely found one alive; nearly all 
were killed and blackened by the severe cold, and any living ones brought 
into the house invariably died in a few days. ‘The first brood of the year 
is, with regard to numbers, in wonderful contrast to the multitudes of 
larvee which must have come to maturity and pupated during the preceding 
autumn, and this difference can only be ascribed to the destroying effects 
of the winter’s cold upon the chrysalids. The species, in its new habitat, 
certainly has to pass through extremes of temperature which it has not 
been accustomed to in England—from which country it was most 
probably introduced ; and while the increased summer heat of Canada 
appears to have made it more prolific, by augmenting the number of 
broods, the greater cold of winter has balanced the account by killing off 
the surplus, which otherwise would have rendered the insect an intolerable 
pest. The “compensating” principle in the laws of Nature is thus in useful 
operation with regard to ?. rape, and as the power of cold decreases in 
effectiveness through the butterfly becoming acclimatized (which will 
probably happen in course of time), no doubt other agencies will arise in 
the shape of new parasitic enemies, to keep the species within due 
bounds. 
It would be interesting to know how far this insect has now extended 
its range, particularly towards the west of Canada. The prediction I made 
in 1864 has been fully verified, as it has now spread over the Province of 
Quebec and the New England States ; and last year destroyed $500,000 
worth of cabbages in the vicinity of New York alone, according to the 
estimate of a leading newspaper there. It does not seem, however, to 
have made equal progress in Ontario. Could not our Kingston friends 
give us some information on this point? It would be “ thankfully 
received and faithfully applied.” 
THE ENTOMOLOGICAL REPORT for 1871 has now been issued, and, 
we trust, is by this time in the hands of all our members. Should any 
fail to receive it, the Secretary will forward a copy on being notified. 
