G8 [March, 



ALEURODES PROLETELLA, LINN., AND A. BRASSICjE, WALK.: 

 A COMPAKISON. 



BY J. W. DOUGLAS, F.E.S. 



Adverting to my notes on these reputed species (vol. v, 2nd ser., 

 p. 40) I have now to saj that owing to the kindness of Mr. W. H. 

 Bonnewell, I am in possession of living imago, larvae and pupa? of 

 both. A. proletella, taken on the 7th inst. at Coddenham, Suffolk, on 

 the leaves of celandine {Ohelidonium majiis), and A. hrassicce on the 

 14th inst., found on the leaves of savoys {Brassica oleracea, var.), and 

 also on others of the cabbage tribe, in his garden at Ipswich. This 

 enables me to state positively that A. p^'oleteUa is indigenous, and it 

 also gives opportunity for the following observations. The species, 

 especially in the mature form, are very much alike, and Signoi'et says 

 (Ess. sur les Aleurodes) that without study of the larvae it would have 

 been impossible for him to decide if they were distinct ; but after 

 investigating the larvae he agrees with Eeaumur, Walker, Koch and 

 Frauenfeld, that they are really different. On the other hand, West- 

 wood says that proletella (chelidonii, Latr.) is found on cabbages, 

 evidently deeming hrassicce to be the same, and Walker himself adds 

 to his description of hrassicce the query that it may be only a variety 

 of proletella, and others (without examination) have practically said 

 that it is so. 



The points of difference in the perfect insects that are most appreciable are, as 

 Signoret states, that in proletella the head is broader than in brassias, and in front 

 has the form of a crescent, while in hrassicce it is narrower, triangular, more pro- 

 duced on to the thorax, and nearly as long as wide. All the wings of proletella are 

 white, with two blackish spots, one of them at the end of the median nervure, the 

 other transverse in the middle of the wing, just where the nervure is deflected, is 

 more or less fascia-form. In hrassiccB the wings are also white, but the dark spots, 

 although in the same position, are differently disposed, the median divided into two 

 parts, one on the median nervure, the other furcating from it towards the anterior 

 margin, the terminal spot also furcate, one branch going upwards and the other 

 downwards. 



As to the larvae, Signoret finds in them the greatest differential 

 characters, especially when they are very recently disclosed from the 

 eggs (naissant). Thus he says — 



In proletella they are oval, with a border of rather long hairs all round, 34 — 36 

 in all, of which four of the more important are at the exti-emity of the abdomen : — 

 in brassiccB the newly-disclosed larvse are more elongated ; on the segments of the 

 body no hairs, and only two long ones towards the extremity. 



I have not been able to verify these observations for want of 

 larvae young enough, all that reached me having passed beyond that 



