440 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1931 



plete success with imported parasites in Hawaii. But this case is 

 not typical of most introductions into the United States and else- 

 where, for the reason that parasites taken to Hawaii have no native 

 secondary enemies awaiting them, hence multiply with extraordinary 

 rapidity. 



Extensive attempts have been made with varying success to estab- 

 lish foreign parasites of imported pests in the United States. Cali- 

 fornia has always been a leading State in experiments with biological 

 control, and (4) " because of the spectacular results of the introduc- 

 tion of Vedalia the Australian ladybird, in the early days of Cali- 

 fornia horticulture, the general public was inclined to favor this 

 method of control to the exclusion of all others." The black scale 

 " is still the most important pest of citrus in the State," and effective 

 natural enemies are still being sought. 



From 1911 to 1913 (5) the cocoons of the parasite of the alfalfa 

 weevil were sent to Utah where alfalfa culture was damaged by 

 this snoutbeetle. By 1922 the parasite " was practically covering 

 the weevil territory," and parasitism sometimes reached 85 to 90 

 per cent or more. 



Generally, the appearance of a new insect pest of importance in 

 this country is a signal for the beginning of a search for its para- 

 sites. In the New England States thousands of acres of woodlands, 

 and shade and forest trees have been defoliated at various times since 

 1889 by the caterpillars of the gypsy and brown-tail moths, both of 

 which are of European origin. Than this there is no more extensive 

 instance of damage by introduced pests and there is scarcely an 

 example of a more far-reaching attempt to control such pests by its 

 introduced parasites. Since 1905 (6) " over 60 species of parasites " 

 of these enemies of trees, " including predacious bettles, have been 

 imported from Europe and Japan." Mr. Burgess indicates that 

 many attempts failed, for " of this number 16 species have become 

 established in New England. One-half of these have not become 

 very abundant and are probably of slight importance." The dam- 

 age, however, decreased " with more or less regularity until 1924, 

 when only a small number of localized areas were defoliated." Ob- 

 servations over many years indicate that the number of parasites 

 fluctuates with the result that occasional injury of more or less ex- 

 tent may be expected in the future. The same consequences will 

 normally result in the instance of any other pest for whose control 

 parasites are chiefly employed. The ideal of parasite importation 

 in this and other instances is perhaps to find and establish a series 

 of parasites, one or more attacking each stage of the host, and thus 

 developing a sequence that will strike the host at various seasons of 

 the year and perchance effect an adequate control in spite of varia- 



