MEDITERRANEAN FRUIT FLY IN HAWAII. 97 



by Bridwell, and both sexes were obtained within the laboratory 

 without this precaution, possibly owing to the fact that the labora- 

 tories were remarkably well lighted. 



Cannibalism. — Although thousands of adults representing all three 

 of these opiine parasites have been reared during the past two years, 

 not more than a single individual has been reared from one fruit-fly 

 puparium. Larva? of the Mediterranean fruit fly within coffee cher- 

 ries which had been exposed to the attack of Diachasma fullawayi 

 during January, 1916, were found to have been attacked in several 

 places, and examination made of the body contents of the parasitized 

 fruit-fly larvae proved that as many as 8 eggs had been deposited in 

 certain instances. It seems very probable, therefore, that in the 

 field, under normal conditions, adult parasites do not discriminate 

 against larva? already parasitized when seeking a host and that due 

 to an excessive number of parasitic larva? within a single host a cer- 

 tain amount of cannibalism occurs. Cannibalism among opiine 

 parasites was first observed by the senior writer while examining the 

 body contents of larva? parasitized by Diachasma fullawayi as pre- 

 viously mentioned. A newly hatched larva was observed vigorously 

 and effectively to attack a second larva of the first instar with its 

 large mandibles. Later examination of large numbers of fruit-fly 

 larva? by the junior writer have proved conclusively (1) that the last 

 opiine parasite to hatch within a host first kills all other parasitic 

 larva? within the same host; (2) that the newly hatched larva is 

 more capable of vigorous attack than one which has become engorged; 

 and (3) that it may attack not only larva? of another species but 

 those of its own as well. As* many as eight dead and one living first- 

 instar larva? have been found in a single host. 



STRUGGLE FOR SUPREMACY AMONG PARASITES. 



The parasites of Ceratitis capitata have been introduced too recently 

 into Hawaii to warrant conclusive statements regarding the outcome 

 of the struggle for supremacy which is clearly taking place. Opius 

 humilis has an advantage among the opiines of being more hardy and of 

 being able to pass through the immature stages more rapidly, and it 

 is somewhat less affected by cool weather, whereas Diachasma tryoni 

 and D. fullawayi have the advantage of possessing much longer 

 ovipositors and are consequently better equipped to reach their host 

 larva? through the tissues of infested fruits. The more rapid develop- 

 ment of the egg and larva stages of Opius humilis is, however, not in 

 its favor when it is forced to compete within the same host with either 

 Diachasma tryoni or D, fullawayi, owing to the cannibalistic habits 

 of the newly hatched opiine larva, which impel it to seek out and 

 destroy larva? that have hatched earlier and already commenced 

 feeding within the same host. 

 81340°— 18— Bull. 536—7 



