1920] Ball: Life Cycle in Hemiptera 149 



of that region. Starting as early as the first leaves appear this 

 species has a generation on rose the adults of which fly to the 

 apple, producing there a second brood which in turn flies back 

 to the rose to deposit eggs to pass the winter. 



In sharp contrast with this extended life history period the 

 potato leafhopper Empoasco mali as worked out by Lathrop in 

 New York and Fenton and Hartzell in Iowa, shows a very 

 restricted developmental period. The adults hibernate and as 

 usual with such species appear late in the spring, feed on weeds 

 through May, and fly to the potatoes in June. This year they 

 appeared suddenly on potato June 6th, where they laid eggs for 

 nearly two months. The first generation was produced on the 

 early potatoes but the adults did not lay eggs there as they 

 appeared. Instead they waited until after the summer migra- 

 tion which was mostly to the late potatoes and deposited their 

 eggs there for a second generation in the fall. Adults of this 

 generation did not become sexually mature that season. The 

 two periods of development of hopperburn coincided with the 

 development period of the two generations of nymphs. This 

 species has previously been credited with four generations in 

 Minnesota, five in Iowa, while one enthusiast, not to be outdone, 

 announced six for Mississippi, although there is not a single sug- 

 gestion that any continuous breeding work from generation to 

 generation had been done to verify these preposterous state- 

 ments. By reference to the charts it will be seen that there 

 would be adults, eggs, and nymphs present on the vines in 

 numbers continuously from the middle of June until frost and 

 this was apparently the only justification for the use of the 

 mathematical method. 



The most carefully worked out study of the life history of a 

 leafhopper ever published was made by Fred Johnson on the 

 shores of Lake Erie in 1912. Johnson succeeded in keeping the 

 grape leafhopper, which winters as an adult, alive in cages 

 through the summer and on into September and obtained from 

 115 to 140 eggs apiece deposited through a period of more than 

 60 days. He found a single complete generation of nymphs 

 extending from June to October, a period long enough so that 

 three individuals could have successfully matured. Only the 

 very earliest adults of the developing brood appearing in July 

 ever mated and the resulting production of nymphs of a partial 

 second generation was so small as to be almost negligible. Con- 



