INSECT ENEMIES OF INSECTS — CLAUSEN 361 



that without it considerable damage would have been done to various 

 crops. This parasite seemed to be the solution of our problem here 

 in the United States. It was capable of effecting a very high per- 

 centage of parasitization in the field, it destroyed the beetles before 

 they were able to deposit their eggs, and, where the host population 

 was reasonably uniform, it maintained a nearly constant status year 

 after year. Centeter was shipped from Japan to the United States in 

 large numbers and the first liberations were made in New Jersey 

 about 10 years ago. It quickly became established and additional 

 colonies from Japan have reinforced the original colonies each year. 

 Yet the condition of the parasite infestation at the present time, 10 

 3^ears after the first importation, reveals a very disappointing state 

 of affairs. The fly has apparently reacted to the changed conditions 

 in a different way from that of the beetle. In Japan the flies emerge 

 each year shortly before the beetles and are present during the entire 

 period of beetle emergence. Here in the United States, however, the 

 flies emerge about one month in advance of the beetles and many die 

 before they can find any of the beetles upon which to deposit their 

 eggs. The remainder attack the first beetles which appear and all of 

 them are dead before the peak of beetle emergence is reached. Ow- 

 ing to this failure to synchronize its time of appearance with that 

 of the host, the parasite has not been able to increase its numbers. 

 It is possible that this difficulty will adjust itself in time. With its 

 present habits in the United States, however, the parasite can be 

 of very little value in controlling this destructive beetle. 



Probably the most extensive parasite-introduction project devel- 

 oped by the Bureau of Entomology is that upon the European corn 

 borer, which is now widely distributed in the United States. Mil- 

 lions of parasites, representing a large number of species, have been 

 imported from Europe and the Far East. Several species show 

 considerable promise, though it is yet too early to estimate their 

 value in reducing this pest. 



The most recent work of the department along parasite-introduc- 

 tion lines has been that against the citrus black fly. This insect 

 belongs in a family closely related to that of the scale insects. It 

 is ver}'- minute, and develops in vast numbers on the leaves, often 

 causing an almost complete loss of the crop. This black fly is a 

 native of tropical Asia, but has become established in Cuba and 

 other islands of the West Indies and in Central America. It does 

 not occur as yet in the United States, but because of the wide 

 variety of plants which it attacks and its very rapid spread, there 

 is a real possibility that it will eventually reach the Gulf States. 

 For this reason the department entered into a cooperative arrange- 

 ment with the department of agriculture and commerce of Cuba for 

 the importation of its natural enemies. Some years previous to this 



