INFLUENCE OF PRECIPITATION. 66 
have more definite grounds upon which to base our studies of meteoro- 
logical influences. Thus applied, the terms wet or dry seasons would 
include within them the two breeding periods of the chinch bug, at least 
largely so, north of latitude 30° N. Hut the history of this species has 
shown that there may be an excess of rainfall during this critical period 
and that still a sufficient number of insects may develop to work serious 
injury over considerable areas of country. This is due to two, and 
Fiq. 8.— Map showing distribution of chinch bag in Ohio In l Si>7. 
perhaps more, causes. In the first place, an unusually heavy rainfall 
at long intervals, while bringing up the total for a given period, may 
have but little effect in reducing the number of chinch bugs, while even 
a less amount of precipitation coming at short intervals and in the midst 
of the hatching season would cause a far greater mortality among the 
young. And, in the second place, the precipitation may come at the 
beginning or even before the commencement of this breeding season or 
0008— No. 15 3 
