OTHER PROBLEMS IN UNITED STATES 383 



of the corn-borer in different zones or areas, and in a bulletin 

 written in conjunction with H. L. Parker (1928) he remarks as 

 follows : " Since control in any given region results from the 

 action of all the factors working together, it seems reasonable to 

 assume that the absence of any constant cause of mortality will 

 ordinarily disturb the natural equilibrium, and permit an 

 inevitable, though perhaps gradual, increase in numbers from 

 generation to generation until great economic injury results." 

 The introduction of parasites of the corn-borer has been in 

 progress since 1920. European shipments are received at the 

 special laboratory located at Arlington (Mass.), where stocks are 

 bred up in sufficient numbers prior to liberation. At the present 

 time no imported parasite is sufficiently numerous in the field to 

 be an appreciable factor in corn-borer control, but in view of the 

 magnitude of the area to be covered a more optimistic result would 

 be a premature expectation. It is evident, however, that from 

 among about twenty introduced species of parasites two are of 

 special importance, viz., the Ichneumonid Inareolata jmnctoria 

 and the Tachinid Lydela stahulans (Masicera senilis). These latter 

 show considerable promise as controlling agencies, but success in 

 a project of this kind is a matter of continued efforts spread over 

 what will probably prove to be a very considerable length of time. 

 The Oriental Fruit Moth Cydia {Grapholitha) molesta Busek. as 

 a larva bores into the shoots and later the fruit of especially the 

 peach. It was probably an accidental immigrant into the United 

 States from Japan about 1913. First detected in the environs of 

 Washington city, it has spread to every peach-growing district in 

 the eastern states and also further west. It is common in the 

 Ontario province of Canada and appears to be still extending its 

 range in America. In the absence of uniformly satisfactory 

 artificial measures of repression, biological means of control have 

 come to the fore in recent years in regard to this pest. Notwith- 

 standing the importation of foreign parasites, the most effective 

 natural agent has proved to be the Braconid Macrocentrus 

 ancylivorus — an indigenous parasite which had been previously 

 known to utilise the strawberry leaf-roller as its host. The 

 Macrocentrus can be bred in large numbers and liberated where 



