MEDITERRANEAN FRUIT PLY IN HAWAII. 



53 



instars. While normally white in color, it may appear creamy yel- 

 low, pink, or with colorations of red or black, according to the nature 

 of its food, which shows through the semitransparent body walls. 



First larval instar (fig. 8). — Length about 1 mm. The first-instar larva is so small 

 that it is seldom observed. Aside from its size, it is most easily distinguished from 

 the succeeding instars by the absence of anterior spiracles. The tracheal system in 

 this instar opens to the exterior only at the posterior spiracles, and consists of two main 



Fig. 7. — Third-instar larva of the Mediterranean fruit fly: a, Lateral view of entire larva; b, dorsal view of 

 anterior portion; c, lateral view of same; d, ventral view. (Original.) 



trunks extending the full length of the body. The posterior stigmatic plates, the 

 outer edges of which are about 0.061 mm. apart, have two instead of three slits, as 

 illustrated in figure 9, a. The mandibles or mouth hooks are not conspicuous and are ' 

 of the shape indicated in figure 10, a. 



Secdnd larval instar. — In size the second larval instar is sufficiently large to be dis- 

 tinct from the first instar, but not from undersized third-instar larvae. It may, how- 

 ever, be easily distinguished from the third instar by the shape of the anterior spiracles 



Fig. 8.— First-instar larva of the Mediterranean fruit fly, showing one of the two main tracheal systems 

 opening at the posterior spiracles. (Original.) 



(fig. 11, a), the mandibles (fig. 10, 6), and posterior spiracles (fig. 9, 6). The distance 

 between the outer edges of the stigmal plates is about 0.13 mm. 



Third larval instar. — The third-instar larva, which is about 7 to 8 mm. long, may 

 be distinguished when well grown from the two preceding instars by its jumping 

 habit when removed from its host, by the well-defined mandibles or mouth hooks 

 (fig. 10, c), and by the prominence of the posterior spiracles. The anterior spiracles 

 possess from 9 to 10 lobes (fig. 11, 6) and are borne on the second segment as in the 

 preceding stage. The posterior stigmal plates each bear three slits arranged as illus- 

 trated and are armed with four batches of delicate inconspicuous hairs (fig. 12). 



