THIRD ANNUAL REPORT OF STATE ENTOMOLOGIST. 189 



animals reproductively active. The degrees of normal mean daily 

 heat in excess of the minimum stated were added together for each 

 station beginning when the normal mean daily temperature went 

 higher than 60 degrees C in the spring and ceasing when it fell to 

 the same point in the fall. Connecting by isotherms the points in 

 the United States thus obtained it was found that the isotherms 

 conformed very closely with the northern boundary of the several 

 life zones. In determining the southern limits for experimental 

 purposes the mean normal temperature of the six hottest consecu- 

 tive weeks was arbitrarily chosen and platted. When drawn, the 

 isothermal lines conformed so closely with the southern boundaries 

 of the boreal, transition, and the upper austral zones that the matter 

 was not carried further. 



Three of the life zones thus determined occur in Montana, viz: 

 the boreal, transition and upper austral. The accompaning outline 

 map of Montana, figure i, shows the territory covered by these 

 life zones in this state. This map was drawn from Prof. Merriam'st 

 bulletin above referred to (Bulletin 10, Division of Biological Sur- 

 vey, U. S. Department of Agriculture, 1898). The black circles 

 indicate the location of the colonies of the codling moth and are 

 based on notes in the Entomologist's office. It may be seen that 

 all the colonies are in the transition and upper austral zones. The 

 upper austral zone has the mildest climate of the state and is much 

 more favorable to the development of the codling moth as well as 

 to the growth of apples. It may be expected, therefore, that when 

 Montana's orchards have come more fully into b^:aring and the 

 codling moth has become more widely disseminated this part of the 

 state in the southeastern corner will have a higher percentage of 

 damage than the western portion. 



The boreal zone does not permit of the growth of apples on 

 account of its higher altitude and colder climate. 



MEANS BY WHICH THE CODLING MOTH SPREADS. 



Over long distances the most common means by which the 

 moth spreads is undoubtedly in fruit packages sent to supply com- 

 mercial demands. It is not strange that by this means the moth has 

 extended itself to almost every fruit growing region in the world 

 for, when we analyze horticultural and commercial practices we find 

 a chain of conditions almost perfectly adapted to that end: 



