Mr. F. Walker's Descriptions 0/ Aphides. 253 



the leaf assumes a sooty appearance, and the presence of the A]3his 

 has been supposed to promote the growth of Xyloma Acerinum 

 on sycamore-leaves, but the appearance of this black shining 

 fungus seems to be occasioned by the soil and the local situa- 

 tion of the tree. This Aphis is devoured by the Coccinelke or 

 lady-birds, by the larvae of the Hemei'obii or lace-winged flies, 

 and of the Syrphidce or hawk-flies ; it is carried by the Crahronida 

 to their nests, and is there stored up as provision for the larvae. 

 Its internal destroyers are Aphidius constrictus, a species of Alio- 

 tria, Megaspilus Carpenteri, Asaphes ceneay Cyrtogaster vulgaris, 

 Coryna clavata, and Encyrtus Atheas. Coccinella 7 -punctata, the 

 common lady-bird, was unusually abundant on the sycamore-trees 

 in the autumn of 1847 ; the beetle was of frequent occurrence in 

 the spring, and the grubs of the succeeding generation were ex- 

 ceedingly numerous, and attracted public attention when they 

 assumed the final state. 



The dark colour of Aphides appears first on the tips of the 

 feelers and on the tip of each of their joints, on the tip of the 

 mouth, on the head, the chest, the breast, and on the back of the 

 abdomen, on the tips of the nectaries, on the feet, and on the tips 

 of the shanks and of the thighs, and thence spreads more or less 

 over the rest of the body and of the limbs. When the skin has 

 been just shed, the body is pale and the limbs are white. 



The preparations of these insects in Canada balsam present a 

 view of the internal organization, and of the parasitic larva which 

 lies in the abdomen in a curved position, and by appropriating to 

 itself the food received by the parent hinders the formation of 

 the young ones, of which the winged female is rather more pro- 

 lific than is the wingless female with regard to eggs. The Aphis 

 when very young, and some time before birth, appears to consist 

 of an almost homogeneous yolk, and resembles the e^^, but is 

 much smaller. 



The oviparous wingless female. This form attains its full 

 growth in the beginning of October, and is distinguished by the 

 long tail-like part of the abdomen behind the nectaries; it is 

 yellow, and has a vivid green stripe on each side of the back : 

 there are a few black spots along the middle of the abdomen, and 

 some short black streaks near its tip : the feelers are a little 

 shorter than the body. 



1st variety. Very dark green, traversed by black bands : the 

 tip of the abdomen is dull yellow, slightly streaked with black. 

 2nd var. Almost black. 3rd var. Pale yellow, with a fine rose- 

 colour towards the head, and along each side of the body and 

 about the tip of the abdomen. 4th var. Green. 5th var. Yel- 

 low. 6th var. Bufi^. 7th var. Pale orange. 8th var. Brown. 

 It lays its eggs during November on the buds and on the shoots 



