374 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



is generally conceded by entomologists to be extraordinary and not 

 to be expected except in rare instances. 



3. Ordinarily it may be expected that it will require several years 

 for an introduced beneficial insect to become effective over a large 

 extent of territory. 



4. Many attempts may be necessary before the successful intro- 

 duction of a beneficial insect is accomplished. 



5. There are instances of complete failures of repeated attempts 

 to introduce beneficial insects into new regions, the reasons not being 

 definitely known, but presumed to be due to the differences in climatic 

 •conditions. 



6. Parasitic or predatory insect enemies may appear to accomphsh 

 the complete control of an insect in its native home and prove of little 

 <^ommcrcial importance against the same insect pest when introduced 

 into another region. 



7. There is a danger of native hyperparasitic insects attacking the 

 introduced beneficial species and preventing its multiplying rapidly 

 enough to become useful. 



8. The apparent control maintained by a beneficial insect and 

 observed by foreign explorers may be due to characteristics of the 

 food plant of the insect pest. The food plants in the native home may 

 have become adapted to resist the injurious effects of the insect and 

 the predaceous or parasitic enemies may consequently appear effective 

 when in reality such enemies would be ineffective without these plant 

 adaptations.^ 



9. Notwithstanding the preponderance of unfavorable probabilities 

 and possibilities, the importance of making every effort to secure 

 successful natural enemies, or enemies which will contribute to a 

 condition of successful natural control of serious insect pests is second 

 only to the importance of taking immediate steps to control such pests 

 by the means at hand.^ 



1 This conclusion is suggested by a memoir of Prof. Paul Marchal (English trans- 

 lation in Popular Science Monthly, Vol. LXXII, page 417) and appears to the writer 

 as well within the range of possibilities in the case of the citrus whitefly. The discus- 

 sion of the food plant adaptations of this species by the present writer and Dr. E. A. 

 Back in a recent publication shows that the pomelo or grape fruit possesses certain 

 characteristics which are decidedly unfavorable to the multiplication of the insect 

 to an injurious extent. The foliage, of the orange in the native home of the whitefly 

 therefore, would have only to adapt itself so as to possess the same or similar charac- 

 teristics as exist in the foliage of the Florida types of grape fruit in order to become 

 nearly immune to the insect. 



2 The words of Prof. Marchal may be aptly quoted in this connection {Popular 

 Science Monthly, Vol. LXXII, page 419): "Confidence in the assistance we can get 

 occasionally from parasites and predaceous insects should not make us lose all pru- 

 dence nor prevent us from seeking a guard against the perils that surround us, in 

 organizing at our large ports an inspection and disinfection serv-ice — -and in a gen- 

 eral way taking every measure possible to protect our crops. " 



