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



455 



part of 1 91 7. The rearing of these 7 individuals of Tetrastichus from 

 the melon-fly puparium was entirely owing to the parasitism of the 

 host, while a larva, first by this natural parasite, Optus flctcheri Silvestri, 

 and later by T. giffardianus. Proof of this is shown by the following 

 results. 



Prior to September, 191 7, many attempts were made to rear the fruit- 

 fly parasites from melon-fly puparia. No difficulty was experienced in 

 inducing all of the species to oviposit in the larvse, but all parasitized 

 individuals developed into noimal flies. The opiines were easily led to 

 oviposit into melon-fly larvae by transferring these larvae from various 

 vegetables to the fruits of Mimusops elengi, a fruit usually heavily in- 

 fested with fiuit-fly larvae. There was no need for transferring the larvae 

 for T. giffardianus , however, as it readily entered any of the hosts of the 

 melon fly, such as cu- 

 cumber, pumpkin, etc., 

 and quickly located 

 and oviposited into "^ 



the maggots. The in- 

 teresting results of / 

 these artificial at- \ 

 tempts to rearfruit-fly \ 

 parasites from the 

 melon fly may be 

 briefly summarized as 

 follows : 



During ]\Iarch, 1917, 

 through the handling ^1^.34, 

 of melon-fly larvae as 

 described, a total of 154 eggs of Diachasma ^ryowi were deposited into 4a 

 melon-fly larvae, 17 eggs of D. fullawayi were deposited into 8 larvae, 

 33 eggs of Opius humilis were placed in 8 lai-vae, and 232 eggs of 

 Tetrastichus giffardiamis were deposited into 19 larvae. All of these 

 larvae pupated normally. Some were mature when stung while others 

 were only about two-thirds developed. From two to five days after each 

 was stung, it was dissected, being now in the pupa stage, and the parasite 

 eggs were counted and carefully examined. None of the opiine eggs 

 hatched and only a small proportion of those of Tetrastichus. In every 

 case, without exception, the opiine eggs developed only a little and then 

 became closely encysted in a mass of transparent cellular material (fig. 

 34). The egg is at first only thinly surrounded with this encysting sub- 

 stance, but after two or three days it becomes densely inclosed, forming 

 a homogeneous, ovoid body. The egg has then collapsed a little and has 

 become brownish in color. It can be faintly distinguished as it lies in this 

 body. The Tetrastichus eggs and some larvae that managed to hatch be- 

 came similarly encysted. In no case did a Tetrastichus larva live long 



Diachasma tryoni: Dead encysted egg removed from melon-fly 

 pupa. Length of capsule 0.55 mm. 



