1900.] 69 



ON THE LARV^, HABITS, AND STRUCTURE OP LITHOCOLLETIS 

 CONCOMITELLA, Bankes, AND ITS NEAREST ALLIES. 



BT JOHN H. WOOB, M.B. 



{Continued from page 34). 



FOOD-PLANTS. 



Roughly speaking we may say that spinicolella and cerasicolella 

 confine themselves to the various species of Prunus ; concomitella and 

 its allies to Cratcegus and Pyrm spp. The only exception apparently 

 is sorbi, which in addition to its ordinary food-plant, Pyrus aucuparia 

 or mountain ash, is also found not uncommonly on Prunus padus, 

 the bird cherry. Mr. Bankes has already abundantly shown that 

 the old idea, that each species is limited to a single and special 

 food-plant, is altogether erroneous. In fact, concomitella and hlan- 

 cardella are the only two in which this limitation still continues to 

 hold good. What, then, becomes of that further idea, that these 

 insects present a good example of a phytogenetic group, in which the 

 diflFerent forms have arisen from one another or from a common an- 

 cestor by the use in each case of a different food-plant ? Beyond 

 modifying such trivial characters as size and colour, food has probably 

 little direct influence in striking off new forms, and it must be remem- 

 bered also that in these cases the choice of the food is an instinct of 

 the imago, and therefore one of its specific characters, in other 

 words, the exercise of the choice shows that the insect is already 

 differentiated. 



Before leaving this part of the subject a word must be said from 

 the collector's point of view. His desire is to know bow he may 

 collect and breed the several species without admixture. Spinicolella 

 and cerasicolella present no difficulties ; from cherry and peach leaves 

 he will breed nothing but the latter, and from different kinds of plum 

 nothing but the former. Primus padus, so far as is at present known, 

 will as certainly produce sorhi ; Cratcegus oxijacantha, oxyacanthce ; 

 and Pyrus torminalis and P. aria, mespilella ; whilst rather low in the 

 scale of certainty comes the pear and its speciality, ^yWyore/Za, — oxy- 

 acanthcB undoubtedly feeds at times upon pear, and its mine might 

 perhaps be identified by its position on the edge of the leaf, did 

 not pyrivorella also occupy occasionally the edge instead of its usual 

 place, the middle. There remain mountain ash and apple, and here 

 the diflSculties come in. A mine in mountain ash may be one of 

 three species, sorhi, mespilella or oxyacanthae, placing them in the order 

 of probability. The largest mine of the three is that of sorbi ; it 



