144 TRANSACTIONS OF THE ILLINOIS 



species, if found, may be readily located in their proper place. So far 

 but few species belonging to this family have ever been particularly inju- 

 rious, either in this country or in Europe, but every now and then the 

 cultivation of a new plant, increased cultivation of one hitherto but little 

 used, or some similar cause, produces the sudden increase of a species 

 previously scarcely noticed. 



Genus Psylla. (Jumping Plant-lice.) 



In this genus the head is strongly inclined and flat above, and usually, 

 if not always, obtusely triangular in front ; the front cleft is not generally 

 as distinct and marked as in Livia. The eyes are usually globular and 

 prominent, not flattened as they commonly are in the previous genus ; 

 ocelli or little eyes distinct, three in number, placed in a triangle on the 

 upper side of the head, one on each side, near the inner border of the eye, 

 the other in front. The antennas are usually as long or longer than the 

 body, slender and threadlike ; the first two joints short and thicker than 

 the others, the third the longest, the last short with two short bristles at 

 the top. Beak very short, arising apparently from the breast, a little 

 behind the first pair of legs ; in repose it usually remains nearly perpen- 

 dicular, composed of three joints, the last very short. The wings thin 

 and transparent, the front pair a little thicker than the hind pair. The 

 hind legs adapted to leaping ; the tarsi or feet two jointed. 



The eggs of the species, so far as observed, are oval and somewhat 

 conical in form, pointed at one end and rounded at the other, and fur- 

 nished, usually, at least, with a kind of beak or appendage near the larger 

 end. They are very commonly deposited in a cottony substance, and are 

 usually yellowish or reddish. It is stated, in reference to some species, 

 that the female punctures the bark and places her eggs in the punctures, 

 but this does not appear to be the general rule; at least, the Psylla of 

 figure I deposits its eggs in the little crevices and under the little scales 

 around the leaf-bud, turning the beak underneath out of view, and possibly 

 slightly inserting it into the bark to secure the egg in its place. 



The larvae are usually somewhat long in proportion to their width, 

 and often covered with a cottony substance, formed by a secretion which 

 exudes from the pores of the body ; but our best known and most common 

 species form an exception to this somewhat general rule. The pupaj are 

 easily distinguished by the two scales on each side, which are rudimentary 

 wings ; also by their rounder and more plump form. 



Their normal method of passing the winter appeals to be in the ^gg 

 state, but this is by no means the universal rule, as the same species is 

 sometimes found both in the egg and larvae state during the winter, resem- 

 bling in this respect some true Aphid ians. There are usually several 

 broods during the summer, all produced from eggs deposited by the female 

 after fertilization by the male, agamic generation being apparently un- 

 known in this family. But all the females which deposit eggs do not 

 acquire wings. According to Macquart the eggs deposited in the summer 

 hatch in eight or ten days, soon after which (in the case of the Psylla of 

 the larch) the young larva; disperse upon the foliage. 



