4 BULLETIN" 1088, U. S. DEPARTMENT OF AGRICULTURE. 



was done on alternate days. This process merely involved slipping 

 a narrow strip of blotting paper, which had been soaked in a mixture 

 of honey and water, into the cage, and removing the old strip which 

 had been placed there two days before. 



Only a small proportion of the flies confined in the glass cylinders 

 or shell vials lived from 25 to 28 days, and then only upon receiving 

 particularly good care ; those in the wooden cages which were given 

 comparatively little attention lived five weeks and more. Two males 

 and one female, which were confined in one of these wooden cages, 

 were apparently in as good condition at the end of a 40-day period, 

 when the experiment was discontinued, as when first placed in the 

 box; several larger lots did about as well. The data obtained cer- 

 tainly demonstrate the ability of Z. nidicola to live a long time ; and 

 since even at best the artificial methods of the laboratory probably 

 can not provide the equivalent of natural conditions, it seems* safe to 

 assume that in nature the average life of Z. nidicola is at least 25 to 

 30 days. 



EMBRYONIC DEVELOPMENT. 



Mating takes place within a few hours after emergence, sometimes 

 even before either fly has fed. Following impregnation the uterus 

 of the female fly gradually becomes much elongated and coiled, ulti- 

 mately attaining a length of 7.5 to 8 mm., which is about the length 

 of the entire insect. This enlargement results from the stretching 

 of the walls of the organ as the enormous numbers of fertilized eggs 

 pass into it and arrange themselves in more or less regular spiral 

 layers. Embryonic development requires from seven ta eight days. 

 At the end of this period the lower part of the uterus contains a con- 

 siderable number of maggots, each still enclosed within its egg- 

 chorion. From 12 to 16 days after impregnation two-thirds of the 

 600 or more eggs in the uterus have fully formed first-stage maggots 

 within them, if the fly has not been ovipositing as rapidly as they have 

 developed. 



OVIPOSITION. 



The female fly prefers as its victims brown-tail moth caterpillars 

 that are from several days to two weeks old, but even those just out 

 of the egg are often successfully parasitized. Most of the oviposi- 

 tion by this species takes place during the first three weeks of Au- 

 gust, in normal seasons. 



Oviposition was readily obtained in the laboratory by confining 

 a fertilized female fly in a shell vial with a few brown-tail moth 

 larvas that had been placed upon a small piece of cherry leaf. Hav- 

 ing found the caterpillars, the parasite manifested much interest, 

 passing slowly from one larva to another and inspecting each 

 minutely. Then, with her face but a few millimeters from one of 



