﻿306 THE ENTOMOLOGIST. 



The same phenomenon occurred here with the former species in 

 1884, but the previous season was a very floriferous one, and 

 several species of Noctuse appeared in unusual numbers (Entom. 

 xxii. 37). In reviewing the various causes Mr. Adkins remarks : 

 — " If, therefore, we are to account for the cases of occasional 

 abundance by purely local influences, we must find some irregu- 

 larity in the working of Nature." In referring to the great 

 abundance of the same species in the past season in New Zealand, 

 Mr. G. V. Hudson says (Entom. xxiii. 133) : — " I am inclined to 

 believe that the abundance, or the reverse, of a given species is 

 largely determined by certain conditions of existence, with which 

 we are at present most imperfectly acquainted, and that, in the 

 case of a periodical insect like V. cardui, these conditions only 

 recur occasionally." If the occasional abundance of this species 

 in Britain be explained by migration from the Continent, it could 

 only follow certain causes which favoured the great increase of 

 the species the previous year, and no doubt identical with the 

 causes which produce its recurrence in New Zealand at intervals 

 of several years. The migration theory, as explained by Mr. 

 G. V. Hudson, can have no bearing on the question in New 

 Zealand : indeed, I have long been convinced that the great num- 

 bers of certain species which occasionally appear in New Zealand, 

 especially among the more specialized groups, invariably follow 

 seasons of luxuriant growth of the native flora. I would, how- 

 ever, mention that the economy of many species of New Zealand 

 Lepidoptera are quite unknown at present ; but when such has 

 been fully worked out by entomologists, it will, no doubt, be dis- 

 covered to be the principal cause. The same facts, of course, 

 will apply to continental areas ; but the faunas and floras of such 

 are not so rapidly modified as in insular areas, while-at clearly 

 shows that the larva of certain species of Lepidoptera arVwhblly 

 dependent on certain pabulum for their subsistence, the fuller 

 development of which, in mild or otherwise favourable seasons/ 

 again increases, and fully explains their appearance in vast num- 

 bers in the succeeding season. The last two mild winters, and 

 hot summers in succession, with the favourable influence on the 

 native flora, unquestionably shows that such are likewise extremely 

 favourable to the development of much of our Lepidopterous 

 fauna : it has shown the same results with several introduced 

 species belonging to other orders, which have also increased at an 

 unprecedented rate during the last summer. Every year the 

 indigenous flora and fauna of New Zealand are becoming more 

 and more modified, and it is difficult — and in many cases impos- 

 sible — to record faithfully the effects of such on certain species 

 of native Lepidoptera, especially on fast-expiring forms ; yet it is 

 cheering to the naturalist to witness an occasional season fruitful 

 to the native flora, and a consequent regeneration of many species 

 of our ancient Lepidopterous fauna. I regret that I have no 



