1920] Ball: Life Cycle in Ilemiptera 147 



ordinary circumstances would tend to throw the first generation 

 later than the one that wintered in the egg stage. 



The writer's experience in the arid region and especially in 

 the Imperial Valley indicates that this early starting is an almost 

 uniform adaptation. Insects , develop abnormally early in the 

 spring before ordinary temperatures are reached and their life 

 cycle is practically completed before the drying up of the .veg- 

 etation by the excessive heat of the fall so that only those stages 

 that are developed to resist adverse conditions remain in any 

 numbers. This will be brought out again in the case of the 

 grape leafhopper. 



The CiCADELLiD^ or leafhoppers, have more economic 

 species and have received more study than any other family in 

 the group. On the other hand the Fulgorid^, called lantern 

 flies, or more commonly leafhoppers have probably received less 

 attention. Both groups of these leafhoppers appear to have 

 about the same variation in their life cycles and will be treated 

 together. These leafhoppers feed on all types of vegetation, 

 trees, shrubs, perennials, biennials, and annuals, under every 

 condition of humidity, moisture, and temperature, and yet the 

 writer has never been able to find a single example in which it' 

 could be demonstrated that more than two generations a year 

 occurred nor on the other hand one in which there was less than 

 one generation per season. This is a very limited range and yet, 

 in almost every case investigated, a definite and sufficient 

 reason could be found for the limitation in generations and that 

 reason was almost invariably its adaptation to some period in 

 the growth of its food plant. 



The leafhoppers with a single annual generation may be 

 roughly divided into three groups, depending upon whether they 

 pass the winter as eggs, nymphs or adults. In general passing the 

 winter in the egg stage will result in the earliest development in 

 the spring, and in this class we find Empoasca unicolor, the real 

 apple leafhopper. This species has been worked out by Lathrop 

 in New York, Brittain, in Nova Scotia, and Fenton in Iowa, 

 and all of them find an early nymphal period in May and June, 

 with adults from that time on throughout the season, egg 

 laying occurring late and these eggs going over winter. This, 

 as explained previously, is the adaptation to the short period of 

 growth of the mature apple tree and is a general type of adapta- 



