Nov. 2^. 1918 Biology of Fruit-Fly Parasites in Hawaii 



441 



Fig. 22. — Opius kumilis: Larva of first instar, lateral aspect, showing 

 position and quantity of egg serosal cells clinging to ventral surface, 

 length 1.2 mm. 



LARVA 



The newly hatched larva (fig. 22, 23, 54) is almost exactly the same in 



size, structure, and habit as is the newly emerged lan^a of Diachasma 



tryoni, with the follow- 

 ing exceptions: (i) 



The two pointed teeth 



situated at the middle 



of the cephalic edge of 



the chitinized ventral 



plate of the head are 



closer together than in 



tryoni and are joined 



basally to form a 



smoothly rounded let- 

 ter " U "; (2) in tryoni 



the "U" formed by 



these two teeth is 



somewhat squarely 



made (compare fig. 3 and 24) ; (3) the head is some- 

 what smaller and squarer than is that of tryoni; 

 (4) the ventral mass of serosal cells, retained after the 

 hatching of the larva, is much smaller in volume, less 

 conspicuous, and is often broken away from the larva 

 before the latter molts to the second instar. The du- 

 ration of this instar and the circumstances influencing 

 the duration are almost identical with those of L>. tryoni. 

 The characters, habits, internal development, and 

 duration of the second and third larval instars are so 

 similar to those of Diachasma tryoni as to need no 

 special comment. With the inolt to the fourth instar, 

 however, some distinguishing characters are leadily 

 seen. The mandibles are smaller than are those of 

 D. tryoni, being 0.065 nim. long, more narrowly 

 pointed, and wholly lacking in chitinization at the base 

 (fig. 25). The dark chitinized ring at the base of the 

 mandibles of the mature larv^a of D. tryoni 

 immediately distinguishes it from larva of Opius hu- 

 milis in the same instar. The period of the mature 

 larv^a is short and does not extend much beyond five 

 days. The larva nev€r hibernates. As a large num- 



dorsai aspect, showing ber of larvae of species of Diachasma hibernate through- 

 head characters, com- , ..... 



piete tracheal system, o^t the year, the abscucc of this trait m O. humilis 

 and digestive canal, rcndcrs it a morc prolific parasite, in conjunction 

 engt I.I mm. W\\_\\, its Other characters, than is either of the two 



species of Diachasma. There are four larval instars. 



Fig. 23. — Opius humilis. 

 Larva of first instar 



