424 



Journal of Agricultural Research 



Vol. XX, No. 6 



Fir., i. — Opius flelcheri: Egg just deposited, 

 length 0.54 mm. 



which averages 0.66 mm., the cephalic end being drawn out into a dis- 

 tinct tubercle while the caudal end retains the blunt point. At this 

 time magnification renders the embryo plainly visible. 



Only by careful dissections of host larvae into which many eggs of 

 Opius fletcheri have been deposited during a short period is it possible 

 to ascertain accurately the duration of the egg stage. In the month of 

 July, 1918, 439 eggs were under observation, all of which hatched be- 

 tween 37 and 40 hours after oviposition. The eggs may hatch while 

 the host is still a larva, or after it has formed a puparium. Even though 

 a host larva contains several parasite eggs or newly hatched larvae, it is 



not killed but continues to feed in 

 an apparently normal manner and 

 eventually leaves the fruit and forms 

 its puparium. In fact, the parasite 

 seems to have no effect upon the 

 development of the fly until a com- 

 plete histolysis of the larval tissues within the puparium has taken place. 

 At this time all development of the parasitized fly ceases. No histo- 

 genesis occurs, and the young parasite larva develops rapidly by feeding 

 upon the liquid mass of the broken-down larval tissues of its host which 

 surround it. 



LARVA 



During this period of development there are four distinct instars, dur- 

 ing which many interesting changes occur. The first instar (fig. 3) is 

 easily distinguished by a large, chitinized head bearing the strong, pointed 

 mandibles, and by the chitinized ventral plate of the head which has a 

 distinct U-shaped cephalic line. In this stage a tracheal system is 

 present, but no open spiracles 

 can be seen, even with high 

 magnification. The two longi- 

 tudinal, lateral trunks throw 

 out branches into each body 

 segment, including the head, 

 and are connected at their 

 cephalic and caudal extremi- 

 ties by a transverse connecting branch. When first hatched, the 

 larva is surrounded by a mass of egg serosal cells, which cling to 

 it until it is almost ready to molt into the second instar. This mass, 

 however, has never been observed clinging to the first larval molt 

 (fig. 4), as it does in the case of the three Mediterranean fruit-fly para- 

 sites (Opius humilis Silvestri, Diachasma iryoni Cameron, and D. fulla- 

 wayi Silvestri). 1 The digestive tract, which is a simple tube the greater 

 portion of which consists of the large intestine, is closed at the caudal 

 end, although an apparently open anus is present. 



1 Pemberton, C. E., and WlX.LA.RD, II. F. A CONTRIBUTION TO THE lilOLOOY of fruit-fly parasites 

 in Hawaii. In Jour. Ayr. Research, v. \-. no. 8, p. 419-465, 41 fig., pi. 32. 1918. Literature cited; p. 465. 



Opius fletcheri: Mature egg. Length 0.66 nun. 



