INSECTS AND MANKIND 423 



which co-operation and team-work become increasingly 

 necessary to success. 



Of special interest from the biological point of view are 

 the many cases in which some insect deliberately or un- 

 wittingly introduced by human agency into a new country, 

 has there become a serious pest on the farm or in the orchard 

 or forest, and the subsequent attempts to naturalise in the 

 invaded territory some imported natural enemy of the 

 destructive insect so as to bring about the reduction or 

 extermination of the latter. The classical example of this 

 line of practice is afforded by the introduction forty years 

 ago into California of a mealy-bug or '' fluted scale '* 

 {Icerya purchasi) which increased and multiplied and 

 attacked citrus groves so violently as to threaten destruction 

 to an important industry. When the native country of the 

 Icerya had been determined as Australia, a study of the 

 insects of that region which prey on it in its homeland 

 was inaugurated under the direction of C. V. Riley (1888), 

 with the result that a ladybird-beetle {Vedalia cardinalts), 

 selected for importation in quantity to California, extermi- 

 nated the noxious fluted scale. 



Among the injurious insects taken into North America 

 from Europe the " Gipsy " Moth {Porthetria dispar) has 

 become famous. Specimens were imported into Massa- 

 chusetts in 1868 with the intention of using industrially 

 the silk spun by the caterpillars. A number of insects 

 escaped into the open country and the species, being easily 

 spread by flight of the moths and wind-carriage of the young 

 hairy larvae, has become a serious pest in the parks and 

 gardens of New England. Much attention has been paid 

 by American entomologists to the Hymenoptera and other 

 insects that live as parasites on the " Gipsy " caterpillars, 

 and many of these have been imported into New England 

 in the hope, as yet unfulfilled, that some of them might ex- 

 terminate the American colony of Porthetria dispar. But 

 partially successful economically, this efl"ort has added largely 

 to our knowledge of the relations between the " Gipsy '* 

 and its predaceous and parasitic enemies (L. O. Howard 



