412 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
But even all the trained entomologists did not see clearly: The 
great master, David Sharp, of England, when I met him one day, in 
1902, in the British Museum, told me that in his opinion the eco- 
nomic entomologists should abandon every other kind of work and 
devote themselves exclusively to the parasites and predators. Even 
Doctor Sharp’s brilliant son-in-law, Frederick Muir, in spite of his 
remarkable successes in Hawaii, would not have made so sweeping 
a statement. 
While it is true that the introductions of NVovius cardinalis into 
California and other parts of the world have been followed by 
almost immediate results of enormous value, and while it is true 
that some of the Hawaiian work has given speedy and striking 
results, and that both of these instances did much to start and 
encourage the prosecution of the biological control idea, it is almost 
unfortunate that these results were so speedy and so perfect, since 
it has encouraged many people to expect equally speedy and perfect 
results in all cases. In fact, many people are disappointed and 
discouraged when work of this kind is not successful almost im- 
mediately. 
As a matter of fact, complete control by parasites and predators 
is rarely gained by such work. Thé success of the Australian 
Novius is almost unique. Only the success of the sugar cane leaf- 
hopper parasite in Hawaii and that of the parasites of the sugar 
cane borer in the same islands approach it in simplicity, efficiency, 
and speed. Immediately following these comes the introduction of 
Prospaltella berleset from America into Italy, where, after a few 
years, it virtually controlled the mulberry scale. And at the pres- 
ent time there is reason to hope that Aphelinus mali will approxi- 
mate this record in the control of the woolly apple aphis in New 
Zealand and parts of Australia, although the same insect in France, 
Italy, and South Africa seems to be less efficient. 
As opposed to these speedy beneficial results, we must remember 
the rapidly growing list, not of failures, but of parasitic insects 
of slow establishment and of only partial control of the crop pest. 
Many differing conditions in different countries operate favorably 
or unfavorably on introduced species, and these species themselves 
vary in their susceptibility to different conditions. 
With many species of parasites the normal environment is com- 
plicated. Years ago, in discussing the spread of land species by 
the agency of man and the lability of an introduced species. to 
accommodate itself to a foreign territory, I formulated the idea 
that “It is upon the degree of simplicity of its life—the degree of 
simplicity of its normal environment as a whole—that the capacity 
of a species for transportation and acclimatization, even in a parallel 
life zone, depends.” JI had in mind when I wrote this only in- 
