SEASONAL HISTORY. 43 



adult. The plowing which the land receives at this time can hardly 

 be called a plowing, but the ground is torn up to a dejith of from 6 

 to 12 inches. As the soil is dry, that disturbed is for the most part 

 in large clods, so there is little chance that many pupae or adults 

 will be disturbed. 



Those which by chance are disturbed are either killed outright or 

 have to live under changed conditions until spring. If they happen 

 to be pupae the chances must be very much against them, and they 

 will probably either be injured by the sharp particles of dirt or will 

 dry out. If the insects are in the adult stage they will have a better 

 chance of survival, but here also they may be compacted into the 

 soil and killed, or be eaten by birds, since, living under unnatural 

 conditions, they are obliged to appear earlier in the spring than they 

 would otherwise. Even when kept under laboratory conditions 

 many of those disturbed in the fall can not live till the normal time 

 of their appearance. 



Hibernation. 



The adults pass the severest part of the winter in the soil. If 

 disturbed they mnter in their pupal cells, where they are well pro- 

 tected, as these are on the average about 6 inches below the surface. 

 This tempers the winter for them very well, and moisture can reach 

 them only after heavy rains, and these seldom if ever occur except 

 at the latter part of the hibernating period. When the beetles are 

 disturbed in the fall they dig down into the soil for shelter. The 

 depth to which they go varies. In some cases, where the soil is 

 powdery, they go down only about from 1^ to 3 inches, but when 

 the soil is partially made up of clods and full of cracks they are 

 sometimes found from 4 to 6 inches below the surface. 



Mortality During Hibernation. 



• 



Under ordinary circumstances and where the pupal cells are undis- 

 turbed, a large percentage of the beetles emerge safely — at least this 

 is so under laboratory conditions. One cage was watered and kept 

 outdoors so that the beetles were subjected to conditions as severe 

 as the ordinary field conditions, yet all came through safely. Of 

 those disturbed in the fall, not enough have been tested to give 

 representative figures, but thus far almost a third of those treated 

 in this way have died during hibernation. 



Gradual Emergence from Hibernation. 



The time of the appearance of the beetles in the spring is influenced 

 to a large extent by artificial agencies, the most important of which 

 is spring plowing. This plowing, which takes place as soon as possible 



