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INSECTS AND HUMAN WELFARE 



live, presumably on account of more efficient control by para- 

 sites. Since parasites capable of attacking the moth were 

 practically absent in the American fauna, an extensive at- 

 tempt has been made to colonize the Eurasian parasites on 

 this continent. This work has been well under way for about 

 ten years, and after numerous technical difficulties, a series 



FIG. 35. Chart illustrating the way in which parasitic insects aid in the control of an insect pest. 

 The sixteen species mentioned are some of the most important parasites of the gipsy moth in Eu- 

 rope and Japan where this insect is native. Of the large series introduced into the United States, 

 they are the most promising enemies of the gipsy moth as they appear to have become most readily 

 acclimated and to have multiplied most satisfactorily. Two species attack the moth eggs, eleven 

 attack the caterpillars and three the chrysalids. The light lines indicate the stages of the host during 

 which the parasites attack it and deposit their eggs, while the heavy lines indicate the ages of the 

 host during which the parasitic insects may live within its body. A series or sequence of parasites 

 acts as a much more efficient hindrance to the multiplication of an insect pest than any single 

 parasite, no matter how abundant. (Modified from Howard.) 



of the parasites were successfully imported and liberated 

 (Fig. 35). Some of these bid fair to become of great value, 

 and they have a great advantage over arsenical sprays and 

 other methods of control, in that they maintain themselves 

 when once established, and do not require repeated human 

 effort with a lavish expenditure of money from year to year. 

 Efforts are also being made to foster certain diseases of 

 the gipsy moth which cause a high mortality among the 



