400 BIOLOGICAL CONTROL 



Lepidopterous larvae he arrives at the conclusion that about 

 one-third ^ of the cocoons and puparia of the primary parasites 

 are destroyed in this way. Since the Lepidopterous hosts are 

 notable defoliators, etc., and their primary parasites are important 

 factors in their control, the activities of the hyperparasites function 

 to a great disadvantage. His observations support the conclusion 

 that one of the chief causes of the reduction in numbers of the 

 parasites imported into New England to aid in controlling the 

 gypsy moth, the brown-tail moth and other Lepidoptera has been 

 the activities of hyperparasites. 



Taylor (1937) is of opinion that the importance of secondary 

 parasites has been greatly exaggerated in some cases. He remarks, 

 " Many secondaries are wholly incapable of hindering extensively 

 the primaries which they attack, mainly because the percentage of 

 primary individuals which they succeed in finding increases 

 directly as the concentration of the primaries and the percentage 

 cannot approach 100 until the primaries are already sufficiently 

 plentiful to suppress the pest. In other cases, inferior egg- 

 capacity, or other factors of this nature, may ensure economic 

 negligibility in the secondaries. For these reasons it is unwise to 

 refrain from introducing a parasite which seems otherwise 

 desirable, and to search for another, merely because the former 

 is certain to be attacked by secondaries which are already present. 

 The elimination of the secondaries from the consignment of 

 primaries introduced is an obviously desirable and usually simple 

 precaution, but in many cases the introduction of the former 

 would not be harmful to an appreciable extent." 



The available facts lead to the conclusion that hyperparasitism 

 is most likely to supervene where parasite introductions are made 

 into continental areas, especially where a sequence involving 

 numerous species is aimed at. Increasing knowledge may to 

 some extent reduce the possibility of species liable to betray this 

 habit being introduced. On the other hand, in view of the 

 general behaviour and widespread activities of hyperparasites, a 



^ In the case of some of the primary parasites, the average mortality, over 

 a four-year period, was only from 5 to Hi per cent., while in others it ranged 

 from 44 to 84 per cent. 



