428 



Journal^pj Agricultural Research 



Vol. XX, No. 6 



Fig. 8. — Opius ftelcheri: Larva, fourth instar, lateral aspect, showing 

 general outline and spiracles. Length 4 mm. 



on the last segment. The only colored ehitinized parts occur in the 

 head, where a pair of strong, pointed mandibles (figs. 10, n) — of which 

 the distal half only is ehitinized — and the tentorial structures are ehitin- 

 ized a yellowish brown color. Small maxillae bearing minute papillae are 



present, together with 

 a well-defined labrum 

 and suboval labium. 



The most important 

 changes that take 

 place, then, during the 

 larval development of 

 Opius fletcheri occur in 

 such a manner as to 

 adapt it to the chang- 

 ing environment with- 

 in its host. Larvae of 

 the first instar are very active and have long, sickle-like mandibles, which 

 enable them to search out and destroy other parasite larvae which occur 

 in the same host individual. Second and third instar larvae live in and 

 feed upon the liquid or semiliquid medium contained in the host pupa- 

 rium. The mandibles, therefore, being useless, are small and incon- 

 spicuous, and there is no tracheal system whatever. In the fourth instar 

 the liquid within the host puparium has been nearly all consumed, and 

 the mature larva is 

 found with fairly 

 strong mandibles and 

 a well-defined tracheal 

 system connected with 

 easily observed spi- 

 racles. 



Two species of opi- 

 ine parasites of the 

 Mediterranean fruit 

 fly hibernate as mature 

 larvae for varying 

 lengths of time during 

 the cooler seasons of 



the year. 1 NO hiber- Fig. 9. — Opius fletckeri: Spines on body of mature larva. Length 



nation of Opius fletch- °'° 13 mm 



eri has been observed during any stage of its development, although 

 thousands of parasitized puparia have been under observation. In Sep- 

 tember, 1 91 8, 592 parasitized melon-fly pupae were held in a refrigerator, 

 where the temperature was constantly about 65 ° F., until two weeks 

 after all adults had emerged. All unhatched puparia were then exam- 

 ined and no hibernating larvae were found. One hundred and sixty 



1 PembErton, C H., and V.'ii.lard, H. F. op. cit. 



Back, E. A., and Pemberton, C. E. the mediterranean fruit fi,y in Hawaii. U. S. Dept. 

 Agr. Bui. 536, 119 p., 24 fig., 21 pi. 1918. 



