52 Transactions. 



Art. VII. — Notes on Flightless Females in certain Species of Moths, with 

 an Attempted Explanation,. 



By G. V. Hudson, F.E.S. 



[^Read before the Wellington Philosophical Society, 31st July, 1912.^ 



The existence of semi-apterous females in certain species of moths has 

 long been known to entomologists, and has been fully described in many 

 entomological works, but, as far as I have been able to ascertain, no attempt 

 has yet been made to explain why the semi-apterous condition has been 

 assumed by the female sex, or in what respects such a condition in that sex 

 can benefit the species. 



Owing to the limited number of foreign works on entomology, and the 

 restricted nature of the exotic collections at present available for study 

 in the Dominion, I have been obliged to confine my attention to species 

 inhabiting New Zealand and the British Islands. The circumstances in 

 connection with the occurrence of flightless females in both these regions 

 prove, however, to be strikingly similar, and this fact merits careful con- 

 sideration when seeking to obtain an explanation of this interesting 

 phenomenon. It is perhaps needless to point out that the loss of the power 

 of flight in one sex, whilst fully retained in the other, is a very remarkable 

 and interesting circumstance, and the present requirements of natural 

 history demand not only that a detailed account of the surrounding facts 

 be given, but that a provisional theory at least be set up to account for it. 

 I should perhaps here point out that these semi-apterous females are quite 

 on a different footing to those insects where the power of flight has been lost 

 in both sexes. The general question of apterous insects has very often been 

 dealt with, and many adequate explanations have been given to account 

 for the loss of flight under the most varied conditions. The present paper, 

 however, is solely concerned with those insects in which the wings of the 

 female are so abbreviated as to render that sex incapable of flight, the male 

 retaining his flying-powers quite unimpaired. 



Before proceeding further it will be desirable to consider the following 

 list of Lepidoptera in which the females are semi-apterous. In addition 

 to general remarks, this list gives, as far as is known, the food plant of the 

 larva of each species, as well as its distribution, and the time of the year 

 when the perfect insect appears. 



In ihe Psychidae, which are represented in New Zealand by two species 

 — i.e., Oeceticus omnivorous and Orophora unicolor — the females are not 

 only apterous, but have rudimentary legs, and are incapable of walking, 

 being, in fact, mere egg-bags. I have not included these insects in the 

 present paper, as the species here dealt with have the females normally 

 developed except in respect of the wings. 



