GRASS THR1TS. 101 



In the early spring months a large proportion of the females 

 produced are of the winged form. The}' lly about and infest 

 new fields, so that in a very short time a large area may become 

 badly infested with the insects. As the season advances the 

 number of the winged forms becomes less, until in the latter part 

 of the season, September or October, there are very few of the 

 winged form, among all those produced. 



LARVA. 



The larva, fig. I, resembles the adult in shape and color but is 

 smaller. Compared with the adult, the head of the larva is 

 small, the antennae short, and there is not as much difference in 

 the size and shape of the thoracic somites. There are very few 

 spines on the body, a tuft on each of the last two abdominal 

 somites being the only conspicuous ones. 



PUPA. 



The pupa, fig. 2, (last larval stage) has a very distinctive 

 appearance. It is encased in an external covering, probably the 

 last moulting case, which disguises the form of the insect to a 

 great extent. The head is about the same shape as in the larva. 

 The antennae are bent back so that they lie upon the dorsal sur- 

 face of the head and prothorax, and their covering shows neither 

 joints or spines. The prothorax is shaped like that of the adult. 

 The mesothorax is long and bears on its dorsal surface a pair 

 of wing cases, which in the pupae of the winged forms extend 

 posteriorly nearly the length of the abdomen. In the pupae of 

 the wingless forms the wing cases are very short. 



MOUTH PARTS. 



Fig. 4. 



The mouth parts of the Thysanoptera differ very much from 

 those of the other orders of insects. They have, in part, the 

 characteristics of the biting insects, and in part, those of the 

 sucking forms. If we accept the old interpretation, and consider 

 the piercing setae mandibles, the typical mouth parts are all 

 represented and are not much fused. 



