380 BIOLOGICAL CONTROL 



L. O. Howard, the work of parasite introduction has now gone on 

 for about twenty-five years, and after exploring European countries 

 Federal entomologists have also directed their attention to Japan. 

 Some 47 species of parasites and predators have been brought into 

 the United States, where many millions of individuals have been 

 reared and liberated (Burgess and Crossman, 1929). This vast 

 experiment is governed by the contention that only the strongest 

 possible sequence of enemies is likely to exercise any appreciable 

 influence over the pests in question now that they are so firmly 

 established. Continuous effort is consequently being made to 

 assemble all likely parasites from whatever country the hosts 

 inhabit. Up to 1929 fifteen species of introduced parasites had 

 become established in New England, and of these the following are 

 now abundant : the beetle Calosoma sycophanta L., a predator of the 

 larva? and pupa? ; the Tachinid parasites Compsilura concinnata 

 Meig. and Blepharipa scuteUata R.D., and the Braconid Ajxinteles 

 melanoscelus Ratz., which attack the larva; ; and the Chalcid 

 egg-parasites Anastatus hifasciatus Fonsc, and Schedius kuwance 

 How. It is extremely difficult to evaluate the effects of these 

 parasite introductions, owing to the existence of a number of other 

 controlling agencies. Among the latter climatic variations, wilt 

 disease, the reduction of favoured shade trees, arsenical spraying, 

 and the wholesale destruction of egg-clusters, all have to be taken 

 into account. It is noteworthy that the average collective 

 parasitism was at its highest in 1923, and in the summer of 1924 

 gipsy moth infestation reached its lowest level for twenty years. 

 Since then a decline in parasitism has been observed, and in several 

 parts of the infested area this has been followed by increased 

 abundance of the pest. Fluctuations of this character will most 

 likely recur periodically, and at present there is no reliable 

 indication as to whether the gipsy moth or its enemies will 

 ultimately gain control. Those who are inclined to believe that 

 parasite control has been a failure in this particular instance are 

 in the difficult position of having to prove that the infestation 

 to-day would not have gained materially, either in intensity or 

 distribution, if parasite introductions had not been made. 



The brown-tail moth, on the other hand, gives every indication 



