54 



RESULTS FROM GIPSY MOTH PARASITE LABORATORY. 



single instance out of hundreds has more than one adult Perilampus 

 issued from any cocoon or puparium under observation. 



In a recent discussion of this phase of parasitism by Mr. W. F. 

 Fiske ^ an attemi)t was made to classify its varied manifestations in 

 accordance with the manner in which the parasites interested are 

 ultimately affected. Superparasitism by Perilampus appears to fall 

 in "I, b." of the scheme, i. e., one parasite lives and the other or 

 others die, and the survivor brings about the destruction of the 

 others by causing the premature death of the host. Several planidia 

 may begin to feed at about the same time, but one invariabl}" molts 

 for the last time a little in advance of the others, and even though 

 the difference is but a few hours it quickly devours the host, or else 

 reduces it to such a condition as to render it unfit food for the next 

 in succession. In no case has one larva been known to make a direct 

 attack upon another. 



In the article referred to above an attempt was made to indicate 

 diagrammatically the probable amount of superparasitism accom- 

 panying a given amount of parasitism provided its prevalence was 

 governed b}^ chance alone. Whenever opportunity has permitted, the 

 validity of the calculations which served as the basis for this diagram 

 has been tested, and in nearly every instance, to date, the results 

 have tended to confirm the contention at the time that ''in the field 

 * * * superparasitism would be distinctly more prevalent in 

 proportion to the percentage of total parasitism" than these calcula- 

 tions demanded. This has proved to be true of Perilampus, as will 

 be seen by Table II, which gives the results of a series of counts to 

 determine the point. 



Table II. — Prevalence of superparasitism of Perilampus 07i Varichasta, 1909. 



Puparia examined number. . 



Perilampus planidia found do — 



Supernumerary planidia do — 



Puparia parasitized do — 



Parasitism percent. . 



Loss in efficiency through superparasitism: 



Actual do 



Theoretical ' do 



Losses sustained by Perilampus through superparasitism: 



Actual do 



Theoretical i do — 



Lot 3. 



57 

 47 

 19 

 28 

 49 



33 



26.6 



40.2 

 32.4 



' In accordance with calculations upon which the diagram published in the Journal of Economic Ento- 

 mology (loc. cit.) was based. 



It will be noted that in each instance the numerical loss sustained 

 by Perilampus, and the decrease in its efficiency as a parasite, is 

 greater than is theoretically called for. 



I Journal of Economic Entomology, vol. 3, pp. 88-97, 1910. 



