53 



VARIETIES OF LEPIDOPTERA, AND THEIR CAUSES. 

 BT EOBEET C. B. JORDAN, M.D. 



In the Autumn of 1862, a curious variety of the larva of Smerinthus 

 Populi vpas brought to me, so light as almost to be called white rather 

 than green, although not a perfect albino. In June, 1863, the moth 

 appeared, and the same variation that occurred in the larva was repro- 

 duced in the perfect insect. This is worthy of note, as tending to 

 throw some doubt upon the validity of the test of a species afforded by 

 slight differences in the larva ; indeed, it must be confessed, that a 

 priori reasoning would lead us to expect, in local varieties, that there 

 would be a corresponding difference in the previous states. Our 

 experience, however, (though the subject has been little worked at) 

 as yet points to a contrary conclusion. The following classification of 

 varieties may at all events tend to place the different groups in some 

 order for study : 



VARIETIES OF LAEV^. 



1. Sexual. — As in the case of the common vapourer moth {Orgyia 



Antiqua), the sexual difference in larvae, according to my ex- 

 perience, is rarely as strongly marked as in perfect insects. 



2. Varieties of constant occurrence not apparently connected 



with sex. — The commonest example, perhaps, is given by 

 Sadena oleracea, in which, as is well known, two frequent 

 varieties — one brownish, the other green — occur. Heliothis 

 Marginata and DasycJdra pudihunda are other instances. 



3. Varieties in intensity of colour. — Intermediate shades occurring, 



as in Gheimatohia JBrumata, &c. 



4. Variations depending on the nature of food. — The simplest 



proof of this. occurs in Mamestra Brassicce, y^hioh may often 

 be met with feeding on the flowers of the dahlia, and 

 somewhat assuming the hue of its red petals. This is, how- 

 ever, a cause of variation worthy of study. It has seemed to 

 me that the red spiracular line was much more deeply marked 

 in larvae of Cidaria russata fouud feeding on dock, than in those 

 eating the Geum : but the character of a red or rose-coloured 

 Bpiracular line is often inconstant, as in the case of Q. russata, 

 and again in Ohrysoplianus Phlceas, in both of which it is 

 sometimes entirely absent, at other times well marked. 



5. Variations of the period of life in the larva state. — The most 



remarkable example of this is in Lnsiocampa CalluiKP, but 



