152 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



the beet leaf hopper, is yet to be worked out, but in any case, its relation 

 to the potato leafhopper seems to be a specific one. 



Life-History of the Leafhopper on Potatoes 



The life-history of this species has been studied mainly in connection 

 with its work as a nursery pest and reported under the name of the 

 apple leafhopper.^ Washburn, Webster and others have reported it 

 as having from four to six generations per year. In practically all of 

 this work the three species of leafhoppers commonly found on apples 

 have apparently been confused. 



Parrott was the first to clear this matter up and Lathrop,^ working 

 at Geneva, first differentiated the life-histories of the three species. 

 He showed that the rose leafhopper (Empoa roscc) wintered as an egg, 

 mainly on roses, produced two generations, the second one on apples; 

 that Empoasca unicolor Gill, the true apple leafhopper, spent its whole 

 life on apples, wintering as an egg under the bark and producing a 

 single generation a year; while Empoasca mali LeB., hereafter to be 

 called the potato leafhopper, wintered as an adult and produced two 

 broods during the season. 



The writer's observations during 1918 indicated that two generations 

 were produced on potatoes. The adults fljang in the spring- at the 

 time the early potatoes come up, laid their eggs in the stems and 

 midribs of the leaves (fig. 7, 2, 3, 4.) These hatched into nymphs 

 (fig. 7, Ic) that fed on the under sides of the leaves, remaining on 

 the single leaf, as shown by the successive cast skins, unless disturbed 

 or, in case there were several on the leaf, until it died when thej^ would 

 migrate to another. During July and early August the first generation 

 changed to adults and deposited eggs again or flew to the late potatoes 

 to start the second generation there. 



Proof That the Leafhopper Caused the Hopperburn 



That the burned condition of the potato leaves observed in 1918 was 

 due to the attack of the leafhopper seems to the writer to be well estab- 

 lished by the following summary of proof : 



First: Cage experiments showed that the leafhoppers could burn 

 and roll the leaves in three days and that plants from which leafhoppers 

 were all removed grew rapidly without sign of hopperburn. 



Second: All burned leaves showed on theii'* under surface, either 

 the leafhoppers, their cast skins or egg scars; often all three, while green 

 leaves showed no traces of these. Injury was proportional to the num- 

 ber of leafhoppers. 



^ A more extended discussion together with a complete bibliography wUl be found 

 in the "Second Biennial Report of the State Entomologist of Wisconsin, 1919." 

 2 Journal of Economic Entomology, Vol. II, p. 144, February, 1918. 



