OUR FRIENDS THE INSECTS BALDUF 441 



tions in factors governing host and parasite abundance. However, 

 this point of view has been criticized, and certain other plans may be 

 more effective. 



While the gypsy and brown-tail moths were the occasions for the 

 first large-scale biological control project of the United States Bu- 

 reau of Entomology, others of large dimensions have since been in- 

 stituted. The Japanese beetle is a relative of our common May 

 beetles or white grubs. It was first seen in this country in New 

 Jersey in 1916 and the grubs in the soil wrought havoc on lawns, 

 meadows and golf courses since that date, while the adults have done 

 likewise to foliage, flowers, and fruits in general. In 1920, the 

 study of its natural enemies, including parasites, was begun in Japan 

 (7), and up to January, 1927, nine species of parasites were found 

 there and in Chosen (Korea). One of the three tachinid flies para- 

 sitizing the adult beetle frequently destroys from 50 to 100 per cent 

 of its host and this species, among other parasites, has been intro- 

 duced into this country. Six other species attack the host in the 

 larval stage. 



Among other pests of primary importance are the Mexican bean 

 beetle, the Oriental fruit moth, and the European corn borer, all of 

 which have occasioned the investigation of their native parasites, but 

 those of the corn borer, the worst threat we ever had on our corn 

 crop, deserve special mention. Although six two-winged (Diptera) 

 parasites and seventeen wasplike species (Hymenoptera), all native, 

 have been found attacking the eggs, larvae, and pupae here, "the 

 combined parasitism " by these species " has totaled less than one per 

 cent of the larvae and jDupae collected each year" (8). The native 

 parasites are therefore " practically negligible except in the case of 

 the sporadic egg parasite, Tricho gramma minutum Riley" (8). 

 Eight species of Diptera and Hymenoptera that parasitize the corn 

 borer in Europe had been liberated in the infested area of the United 

 States up to February, 1927. Two of these {Microgaster tibialis Nees 

 and Exeristes roborator) had been recovered incidentally at that time. 

 It can not be predicted what the status of the imported species will 

 be in the future. Ten years or more are sometimes necessary for a 

 normal adjustment of parasites to their new surroundings and to 

 reach their maximum efficiency, providing they become established 

 at all. It is generally believed that parasites of the corn borer can 

 not be expected to become an adequate check alone on this pest, the 

 chief factor operating against a high proportion of mortality seem- 

 ing to be the habit of the host of feeding sheltered within the corn 

 stalk most of the time during the stages susceptible to attack. 



The amount of hope to be placed in the method of control by the 

 use of entomogenous insect parasites is obviously various, according 



