1920] Ball: Life Cycle in Hemiptera 145- 



he will not) he would find that no one has ever carried a single 

 species of the higher Homoptera through as many as three 

 complete generations in a season. 



There are two fundamental fallacies embodied in all calcula- 

 tions of this kind. The first and most important being that 

 Nature is trying to see how many generations she can produce 

 annually. She is not — in Hemiptera or Orthoptera at least — but 

 rather trying to see how perfectly she can adjust the distribution 

 of the one or two generations to the optimum conditions for 

 development in the variable seasons. The tree hopper might 

 have three generations as far as the time factor was concerned 

 but it can have tender twigs for only one and one it conse- 

 quently has. The little black calva might have three and our- 

 mathematical optimist would say four generations but it could 

 not have the rich food destined for the forming seeds in more 

 than one and so it is content with one. 



The second common fallacy is that the time from egg to 

 adult is the measure of a generation — it is instead only about 

 half of the period. In the Hemiptera the adult emerges with eggs 

 undeveloped and they must feed and develop them before egg 

 laying begins. Somewhere in this period mating takes place. 

 Funkhouser shows mating 10 or 15 days after the adults appear- 

 in Vanduzea. Johnson states that the grape leafhopper fed 10 

 days before mating, Childs shows a longer period for the rose 

 leafhopper, while Fenton and Hartzell show a still longer 

 period for the potato leafhopper before egg laying began. In 

 some cases the mating appears to be near the beginning and in 

 other cases near the end of the period, but in all cases it must of 

 course precede egg laying. The total time therefore between 

 adult emergence and egg laying appears to be from 10 to 25 days.- 



Hemipterous insects rarely if ever lay all their eggs at one 

 time. Instead the Homoptera as a rule lay a few at a time 

 through long periods. Hodgkiss found Stictocephala laying as 

 many as 250 eggs through a two-month period. Johnson found 

 the grape leafhopper laying 115-140 eggs through a 70-day 

 period. Ball found the beet leafhopper laying eggs for two and 

 a half months. Fenton and Hartzell found the potato leafhopper 

 laying eggs for 50 days. In all life history studies made, this 

 period has been shown to be longer than the time required from 

 egg to adult and often two or more times as long. This period,. 



