TACHINID PARASITES OF THE GIPSY MOTH. 209 



P. Jiyalinus was thus peculiarly an enemy of fall weWorm parasites, 

 and thus a friend of the fall webworm. Neither, when it was present 

 (which it was not, as a rule) , was it ever known to emerge from infested 

 puparia of the " summer issuing species" until long after the flies 

 had ceased to emerge. From the puparia of species which hiber- 

 nated as pupae it never emerged until the spring and then appeared 

 before the flies themselves. It was thus possible to provide against 

 its escape with little trouble, and it is now considered as distinctly 

 less menacing than the species which follows. 



Melittobia acasta Walk. 



Another most extraordinary parasite of tachinids in Europe is 

 Melittobia acasta, according to a determination furnished some years 

 ago by Dr. Ashmead. It is thought probable that a careful com- 

 parison between the parasite of the tachinids and M. acasta will 

 reveal specific differences, but at the time of writing such comparison 

 has not been made. Of all of the secondaries which have been 

 imported with the parasite material this has proved the most 

 annoying. 



Its most annoying characteristic is its minuteness, which enables 

 it to pass through 50-mesh wire screen at will, and this, coupled with 

 an extreme hardiness and an insidious inquisitiveness which seems 

 to know no bounds, has resulted upon two occasions in an infestation 

 of the laboratory which is comparable to a similar infestation, which 

 will receive further mention, by the mite Pediculoides. 



No one knows where it came from upon either occasion or how it 

 first succeeded in gaining a foothold in the laboratory. Its first 

 appearance was in 1906, when Mr. Titus encountered it in several 

 lots of puparia of different species of tachinids from several European 

 localities. Mr. Titus evidently thought, judging from his notes, 

 that it had been imported in each instance with the material from 

 those localities. He studied its habits that first year, and found 

 that it would oviposit freely in confinement and that such oviposition 

 was successful. He did not give it full credit for its insidiousness, and 

 as a result it succeeded in eluding his vigilance and gaining access 

 to a number of the lots of hibernating puparia of Blepharipa, upon 

 which it reproduced with great freedom. 



In the spring of 1907 this circumstance became evident through 

 its emergence in some numbers from several of the lots of hibernating 

 puparia early in June, after most of the flies had issued. An examina- 

 tion of the remaining puparia was thereupon undertaken and a vast 

 number of larvae, pupae, and unissued adults destroyed. 



At that time it was supposed that each of the lots of puparia were 

 infested at the time of their receipt, but when an even larger amount 



05677°— Bull. 91—11 14 



