Nov. 25, 1918 Biology of Fruit-Fly Parasites in Hawaii 



423 



\vith short, narrow esophagus, large midintestine occupying the greater 

 bulk of the body and closed caudally, and the short proctodaeum ter- 

 minating with an apparently open, oval anus situated on the ventral 

 surface of the third to the last body segment. The only food taken that 

 is readily visible is the fat of the host. With the development of this 

 instar the midintestine becomes gradually filled and swollen with globules 

 of fat. Newly hatched larvae 

 generally are found moving 

 about in the fat body and have 

 been dissected frequently from 

 fly larvae with the mandibles 

 closed into portions of the fat. 

 Though the large, pointed man- 

 dibles enable the larva to lacer- 

 ate tissues other than the fat 

 body, through some unknown 

 influence the delicate vital or- 

 gansof the host larva seem never 

 to be injured, even in cases of 

 superparasitism when six or 

 eight newly hatched larvae may 

 be cutting about with their 

 mandibles, either in the sepa- 

 ration of food or in the de- 

 struction of one another. The 

 first-instar larva moves about 

 by contorting the body, and its 

 movements are aided by grip- 

 ping fresh tissues coming into 

 contact with the mandibles 

 coincident with the body move- 

 ments. The brownish, chitin- 

 ized head can be seen moving 

 within the host larva when 

 under strong light and fair en- 

 largement. The larva is leg- 

 less, but bears a pair of soft, 

 short, saclike appendages on 

 the ventral side of the body just back of the head (fig. 3,4). They are in- 

 capable of movement and may be gill-like in their function. No tracheae 

 can be seen leading into them even when examined under high magnifi- 

 cation. Extending along the ventral surface of the body, from the back 

 of the head to the tip of the abdomen, is a gelatinous mass of large cells. 

 These are the serosal cells of the egg and adhere to the larva until it molts 

 for the first time (fig. 3). Just before molting the larva becomes greatly 

 engorged with food and has increased to about 1.2 mm. in length. 



Fig. 4. — Diachasma tryoni: Larva of first instar, lateral 

 aspect, showing right main tracheal trunk with branches, 

 and characteristic position and volume of egg serosal cells 

 clinging to ventral surface. Length i mm. 



