GIPSY AND BROWN-TAIL MOTHS 379 



conditions, the necessary phases of the host are not available for 

 many months, and the parasite consequently becomes scarce. 

 After a few years, wherein this parasite effected marked control of 

 its host, its activities became largely neutralised by the secondary 

 parasite Quylea whittieri. Notwithstanding the combined activities 

 of the entomophagous insects already mentioned, together with 

 others of lesser importance, the black scale maintains its rank as 

 the worst of citrus pests. 



The red scale (Chrysomphalus aurantii) and the purple scale 

 {Lepidosaphes beckii) likewise have not so far been subject to 

 satisfactory biological control. In 1925 a search for further 

 parasites of the first-mentioned species was undertaken on behalf 

 of the State by F. Silvestri in China. Various new parasites and 

 predators were located, and shipments made to California, but 

 owing to the civil war and other circumstances work in the Orient 

 has had to be discontinued for the time being. 



For detailed information respecting the application of biological 

 control in California, and the various hosts and their parasites 

 that are involved, reference should be made to the work by Essig 

 (1931). 



The Gipsy and Brown-tail Moths in New England. The most 

 prolonged and extensive campaign of biological control so far 

 waged in any quarter of the globe is that centred round the 

 gipsy moth {Porthetria dispar L.) and the brown-tail moth 

 {Euproctis chrysorrhoea L.) in New England. Both insects came 

 originally from Europe, and appeared first in Massachusetts ; the 

 gipsy moth in 1867 and the brown-tail in 1897. Some twenty 

 years elapsed before the gipsy moth developed into a serious pest, 

 and it was not until 1905 that any campaign was formulated for 

 introducing natural enemies of either of these insects. Previous 

 observations had shown that the aggregate effectiveness of 

 indigenous parasites in controlling these species was wholly 

 insignificant. On the other hand, both species were found to be 

 heavily parasitised in Europe, and it seemed further evident that 

 whatever degree of restraint is exercised by natural enemies in 

 Europe, it is the result of a sequence of species attacking the 

 eggs, larvae and pupae respectively. Through efforts initiated by 



