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



449 



DESCRIPTION AND LIFE HISTORY 



EGG 



Fig. 30. — Tetrastichus giffardianus: Egg newly deposited. 

 Length 0.25 mm. 



The newly deposited &gg measures from 0.20 to 0.25 mm. in length, is 

 less than a third as broad as long, is pale white, smooth, glistening, 

 cylindrical, and broadly rounded at each end (fig. 30). The eggs are 

 placed in clusters just beneath the larval integument. They are faintly 

 visible from the surface as 

 dark bodies if strong light is 

 transmitted through thelar\^a 

 from below. The Q.gg does 

 not undergo much change 

 in size as the development of 

 the embryo progresses. The 

 duration of the e.gg stage is 

 from 2 to 2% days. Of 400 eggs deposited January 4, 191 7, at 11 a. m., 

 all hatched in about 60 hours. Fruit-fly larvae containing eggs of this 

 parasite develop to maturity and form a perfect puparium, in the same 

 manner as do the other parasites under discussion. No fly pupa is 

 formed after the histolysis of the larval tissues in the puparium, and 



the &gg may hatch either before or after the puparium 



is formed. 



LARVA 



There is nothing of unusual interest in the develop- 

 ment of the larva, and only little external difference in 

 the appearance of the instars, with the exception of the 

 gradual increase in size. When first hatched, the larva 

 is about 0.25 mm. long (fig. 31). The body is composed 

 of 13 segments and head, the latter inconspicuous and 

 not unlike the other body segments in general appear- 

 ance. The mandibles are minute, short, curved, broad 

 at the base, and well chitinized. With only sHght 

 modification they are constant in the succeeding instars. 

 Most of the food ingested by this parasitic larv^a con- 

 sists of fat bodies. The larva bears 9 pairs of small 

 open spiracles on body segments 2 to 10, inclusive. 

 The tracheal system is open and becomes air filled as 

 soon as the larva hatches. In the first instar the trunks 

 and branches are very faint and threadlike. The larva 

 can move only very slowly and sluggishly in all of its instars. 



The number of larval instars has not been determined, though three 

 forms have been distinguished. The mature larva may be distinguished 

 readily by the large, heavy tracheae and stigmata. As 8 or 10 larvae 

 nearly always develop in a single host individual, and the food is rap- 

 idlv consumed, the necessity for well-developed tracheae is thus apparent 



Fig. 31. — Tetrastichus 

 giffardianus: Newly 

 hatched larva. 

 Length 0.25 mm. 



