434 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol 14 



flight of the pale green adults into the cultivated regions during 1919, 

 the niunber of generations was again ascertained. Various phases of 

 the life historv- determined in cages were checked up in the cultivated 

 area and on the plains and foothills for a period of four years. 



The egg period was determined twice during each month from Feb- 

 ruary to October. The incubation periodss varied from 11-55 days, the 

 shortest egg periods occuring from July to September. Eggs deposited 

 from November 1 to January 15, failed to hatch or the nymphs died 

 out-of-doors during the winter. The eggs do not develop without ferti- 

 lization. 



Tem.perature plays an im.portant role on the duration of the egg period. 

 The mean tem.perature was S°F. higher in the case of an egg stage requir- 

 ing 44 days and extending from, the winter into the spring, than the in- 

 cubation period of 28 days in the autiim.n. The low winter tem.perature 

 and hum.idity prolong the egg period but the rate of developm.ent is 

 increased during the spring, whereas the high early autumn temperature 

 increases the rate of early embryonic development and results in a 

 shorter egg stage even with a lowering of the temperature later in the fall. 



The nymphal periods of the first brood varied from 23-37 days from 

 April to October. The egg and nym.phal periods varied from 37-99 days. 

 During the A\nnter a high mortality of the n^miphs occurred which hatch- 

 ed from, eggs deposited during Septem-ber and October. 



Stahl^ experienced many difficulties in determining the maximum 

 number of eggs deposited by a single female and records the deposition of 

 237 eggs by one female at Ppreckels and 247 eggs by another female at 

 Riverside. To determine the num.ber of eggs which a single female of 

 the first brood deposits during her life, a m.ale and female were confined 

 in a cage enclosing a sugar beet. The male acquired the winged stage 

 on May 8 and the female on May 9. The eggs were allowed to hatch 

 and the total nimiber of n\TP.phs rem.oved from the cage would equal the 

 egg-laying capacity providing all of the eggs hatched. A total of 328 

 nymphs were removed twice during each month from June 15 to August 

 16. The female died on November 20. 



Four generations were bred from the dark females which wintered over 

 in the cultivated area. After the flight of the first brood from the plains 

 and foothills into the cultivated area, four more generations were bred or 

 a total of five broods. The months of m.aximum emergence of the first 

 to the fourth broods bred from the dark females which wintered over in 



^Stahl, C. F., 1920. Studies on the Life History and Habits of the Beet Leafhop- 

 per. Jour Agr. Research, XX, No. 4, pp. 24.5-252. 



