February, '21] hartzell: potato leafhopper 63 



Dr. F. A. Fenton to whom the writer is indebted for suggestions and 

 criticisms. Air. I. L. Ressler and Mr. Carl Knapp assisted in conducting 

 some of the experiments. . 



Methods 



Because of its small size, protective coloration and activity, the potato 

 leafhopper required the development of special technique in order to 

 keep the insect under observation for a sufficient length of time to 

 determine its life, cycle. The cage that proved most successful in our 

 work consisted of a large lantern globe with the top covered by means 

 of a very fine screen (20 meshes to the inch) soldered on a galvanized 

 collar made to fit tightly against the top of the globe. By plugging the 

 rixn with cotton a very tight and serviceable cage could be had and since 

 the cage was large enough to cover a whole potato stalk it approximated 

 field conditions better than any other device we were able to use. The 

 lantern cages were placed in an out-door shelter which was similar to 

 those used generally in life histor}^ work and the results checked up with 

 field observations and experiments. 



As the adults are very small and active, difficulty was experienced in 

 transferring them from one cage to another in order to supply them 

 with fresh food plants. To alleviate this a special dark room was built 

 provided with a small window tighth' screened. In order to make the 

 darkness more intense the walls were painted black. If lost in 

 transferring, the adults could be recovered because they are positive 

 photo trophic. By means of this device it was possible to make frequent 

 transfers without undue loss of time and the minimum danger of the 

 adults escaping. 



Climatic Factors 



The season of 1920 was unusual in that the average temperature was 

 considerably lower than normal. The maximum temperature at no 

 time exceeded 95 degrees F. at Ames, while during the previous siimmer 

 a constant high average was maintained from the middle of June until 

 the first week in August with the maximum reaching as high as 100 

 degrees F. The stimmer of 1919 was dry and hot as contrasted with a 

 cool, late season this year. The fore part of the season was at least 

 three weeks later than last year and the low average temperature was 

 unfavorable for the development of the leaf hoppers. That the insect 

 reaches its optimum development during hot, dry weather has been 

 noted by other workers and was in evidence this season by the large 

 number of adults and nvTnphs appearing during the last week in Juh'. 



vSeasonal History 

 The potato leafhopper overwintered in the adult stage. A few 

 females were found earlv in Mav on curlv dock and other weeds. In 



