Bugs and Things 17 



able fruit-culture may be determined more or less by the 

 parasite factor. A moment's reflection will show, however, 

 that the geographical distribution of the parasite is deter- 

 mined primarily by climate and by the distribution of its 

 host-plants; so that, on the one hand, the climatal limit 

 of the cultivation of the fruit may be approximately the 

 climatal distribution of the pest, and, on the other hand, 

 the parasite may be local or cosmopolitan according as the 

 fruit is either local or widely grown. 



Many of the common pests are restricted in range 

 because they have not yet reached the full limit of their 

 distribution. An excellent illustration of this fact is the 

 codlin-moth. Once Michigan was represented to be the 

 Eutopia of the apple-grower because of the absence of 

 this pest, and in our own day similar recommendations 

 have been made of far western states. To the naturalist, 

 however, it was evident from the first that the insect was 

 following closely behind the apple frontier, as a storm 

 follows an area of high pressure. 



In practice, the energetic and intelligent fruit-grower 

 .will think last of the parasite factor when locating his 

 plantation, for this factor is variable and migratory, and, 

 moreover, there are means of keeping most fruit pests 

 under control. Insects and fungi are of course to be 

 reckoned with, and for this reason they are the direct and 

 perhaps the most effective means of keeping the farmer hi 

 a state of mental alertness. There are a few cases, of 

 course, to which these remarks will not well apply, but 

 they are clearly exceptions. One of these is the dreaded 

 nematode root-knot of the southern states, and one might 

 hesitate in planting peaches on certain land where it 

 does not freeze deep enough to destroy the pest. The pro- 

 fessional experimenters can determine the course of the 

 B 



