EXPERIMENT STATION BULLETINS. 



655 



were made and experimeuts conducted to learn the mode of hibernation 

 and the number of generations of the potato leafhopper under Michigan 

 conditions. 



HIBERNATION 



Considerable difference of opinion has been expressed in the 

 literature aj^ to the manner in wliich this leaflMupper ])ais'S'eis the 

 winter. Gillette^'' in Iowa, Lathrop^^ in New York, and Ackerman^- 



Fig. 9. Egg blisters of the i ose leafhopper (Empoa rosae) and apple leafhopper (Empoasca unicolor) on apple twig. (Enlarged.) 



(Photo.by Miss E. McDaniel.) 



in Pennsylvania, reported over-wintering adults, while Webster" 

 in Minnesota, was of the opinion that the insect passes the winter both 

 as an egg laid in apple twigs and as an adult. 



During the winter of 1019-20, six dozen apple twigs, varying in age 

 from one to seven years, were brought in from the college orchard and 

 placed in water in lantern-globe insect cages in the insectary of the 

 Entomology Department. These soon leaved out and leafhopper nymphs 

 hatched from eggs laid in crescent-shaped blisters, approximately 1/25 

 of an inch in length. (Fig. 9-10). The injury to the leaves which was 



