February, '10] fiske: superparasitism 95 



enough so to indicate that it has a certain basis upon fact. It is prob- 

 able that the actual curve would vary under identical conditions, but 

 with different species of parasites in accordance with the development 

 of the maternal prescience of each, but it is probable that in every 

 instance it would lie somewhere between the lines AB^and AC, which 

 represent the limit of variations under conditions as given. 



Actuallj', in the field or in the laboratory, it would frequently fall 

 outside of AC ; that is to say, superparasitism would be distinctly 

 more prevalent in proportion to the percentage of total parasitism. 

 It is usually the case that a part of the hosts are more exposed and 

 therefore more liable to parasite attack than the rest, and these will 

 be attacked to the benefit of the others. Repeated instances of this 

 sort have arisen in the course of the work. 



Economic Importance. If, as seems probable, the utilization of 

 the natural enemies of injurious insects becomes a well established 

 method of insect control (if indeed it has not already become so), 

 every phase of insect parasitism takes on economic importance propor- 

 tionately. Superparasitism is undoubtedly the equal of hyperpara- 

 sitism in its effect upon the natural control of parasitic insects, and 

 should be given equal attention. Only upon very rare occasions, as 

 shown in the table of its manifestations, does it permit both of the 

 parasites involved to reach full maturity. In the minority of occa- 

 sions only one of them does so, and in the majority both are seriously 

 affected, if not destroyed outright. 



As stated above, its actual prevalence is apt to be greater than indi- 

 cated in the diagram, and has been greater in certain work which has- 

 been carried on at the Melrose Highlands laboratory. In the course of 

 this work three genera of parasites have been brought under success- 

 ful laboratory control, and their propagation undertaken as an eco- 

 nomic enterprise. In every instance superparasitism has resulted to 

 an extent comparable to that indicated by the table, counting anly 

 those Jiosts whicJi are equally exposed to attack by the parasite, and 

 leaving out of consideration those which were partially protected. In 

 the instance of two of the parasites, superparasitism resulted in the 

 production of dwarfed and worthless individuals, which proved to be 

 of little, and in one instance of no, value for continued reproduction. 

 In the instance of the third parasite, superparasitism resulted in the 

 death of all but one of the individuals attacking an individual host, 

 and the survivor emerged apparently . none the worse for its prioristic 

 combats. In this case the outcome was nothing worse than a reduction 

 in the rate of multiplication ; in the others there was a serious addi- 

 tional loss due to the degeneration of the survivors, which was not 



