THYSANOPTERA 



343 



The metamorphosis of these insects is in some respects peculiar; 

 but it conforms more closely to the paurometabolous type than to 

 any other, the newly hatched young resembling the adult in the 

 form of its body (Fig. 392, ^) and in having similar mouth-parts and 

 food habits. The first two or three instars have no external wings; 

 these instars are commonly referred to as larv(S. The use of the term 

 larva in this connection is not inappropriate if the wings are de- 

 veloping internally during these early stadia. That this may be the 

 case is indicated by the large size of the wing-pads when they first 



Fig. 392. — Immature forms of the citrus thrips: A, first larval instar ; B, second 

 larval instar; C, propupa; D, pupa. (After Horton.) 



appear externally. After the last larval molt the insect asstmies a 

 form known as the propupa (Fig. 392, C). This resembles the larva 

 in form; the antenna are slender, and the insect is moderately active. 

 Its most striking feature is the presence of large wing-pads, which 

 extend at first to about the end of the second abdominal segment and 

 increase in length somewhat during this stadium. With the next 

 molt the insect becomes what is known as the pupa. In this stage 

 the wing-pads are longer (Fig. 392, D), the antennae extend back 

 over the head and prothorax, and the insect is quiescent. With the 

 next molt the adult form is assumed. 



The different species of thrips vary greatly in habits, some being 

 injurious to vegetation, while others are carnivorous, feeding on 

 aphids and other small insects, the eggs of insects, and mites, es- 

 pecially the "red spider." Their most important economic role, how- 

 ever, is that of pests of cultivated plants. The thrips that infest 

 plants puncture the tissue of the plant by their piercing mouth-parts 

 and suck out the sap. 



The order Thysanoptera is divided into two suborders, which can 

 be separated as follows : 



A. Female with a saw-like ovipositor; terminal abdominal segment of female 



conical; that of the male bluntly rounded Terebrantia 



. AA. Female without a saw-like ovipositor ; terminal abdominal segment tubular 

 in both sexes, p. 345 Tubulifera 



