288 THE PRACTICAL APPLICATION OF ECOLOGY 



is notably polyphagous, but, in Europe, it chiefly attacks maize in 

 regions favourable to the cultivation of that crop ; in regions 

 north of the maize-growing areas it mainly attacks weeds and 

 more especially Artemisia vulgaris. In some regions, however, 

 it attacks both maize and Artemisia, but in others it favours only 

 one of these two hosts. Thus in the Department of Gers, in 

 south-western France, maize is practically its only food-plant, 

 while around Paris it lives principally upon Artemisia, and has no 

 opportunity of attacking maize owing to the absence of that crop. 

 It appeared likely, therefore, that material from these two areas, 

 where the conditions have remained relatively stable for a long 

 period of time, would be specially suitable for the study of the 

 host-selection principle. The conclusions derived from these 

 experiments show that, notwithstanding the long association of 

 the corn borer with Artemisia, which may indeed be its original 

 host, it exhibits no marked preference for this plant and laid the 

 majority of its eggs upon maize. In fact, the latter host is the 

 favoured one both by the Artemisia and maize strains of the insect, 

 as is shown by the following records of oviposition (in percentages) : 



It would appear, therefore, that the corn borer is a species 

 having a strong innate preference for maize, and that the Artemisia 

 strain exhibited a greater attraction for that host than for its 

 original host. It is true that this strain exhibited a stronger 

 preference for Artemisia than was evidenced by the maize strain — 

 in the latter case, in fact, the preference does not appear to be 

 significant, since even more eggs were deposited away from any 

 specific food-plant than upon Artemisia. 



Experiments by Thorpe (1929, 1931), with the moth 

 Hyponomeuta padella, indicate that this insect is divisible into 

 two biological races which were formerly regarded as separate 



