August, '19] SEVERIN: BEET LEAFHOPPER 325 



certainty under both cultivated and natural conditions during the 

 autumn and winter. 



During September the dark adults gradually increased from 7-44 

 per cent. Before the return flight to the natural breeding area 86-98 

 per cent of the beet leafhoppers were dark and in December 90-98 

 per cent of the stragglers which remained behind in the cultivated 

 regions were dark. In the natural breeding area 92-100 per cent of 

 the leafhoppers were dark from October to December. 



Do the yellowish beet leafhoppers assume the dark shades during 

 autumn or winter? On September 5, 150 cream colored adults were 

 captured in a beet field at Manteca, and were placed in a cage enclosing 

 a sugar beet under field conditions at Berkeley. The hoppers were 

 transferred to a new beet on November 8, and it was found that 75 had 

 died. On December 19, the insects were again transferred and only 

 6 light forms survived and these were still alive in January. Evidently 

 most of the light forms were near the end of their natural life and only 

 a small percentage wintered over, possibly only those of the preceding 

 generation which reached the adult stage late. 



Do the nymphs in late summer, autumn and winter give rise to light 

 adults? On September 5, 200 nymphs were captured in a beet field at 

 Manteca and were placed in a cage enclosing a sugar beet under field 

 conditions, and a similar experiment was conducted at Berkeley. 

 The adults reared were all dark. In November and December nymphs 

 were collected on the foothills and all of the adults bred were dark. 



Incomplete Hibernation 



E. tenella does not undergo a complete hibernation in the San Joa- 

 quin Valley, understanding by that term the passing of the winter in a 

 torpid state without food. The bugs are torpid during cold weather, 

 but when the sun warms the foothills during the winter, they become 

 active. On cokl days the hoppers were rarely captured in an insect- 

 net; such specimens as were caught, sometimes displayed a torpid con- 

 dition and could be rolled about in a net without showing a trace of 

 Hfe. When the leafhoppers were not taken by sweeping with a net, 

 the adults were often collected by moving the hand among the Filaree, 

 and the disturbance would sometimes cause them to make short leaps. 



Experiments were conducted to determine whether the leafhoppers 

 require food during the winter. The hoppers were captured on the 

 foothills and were placed in cages without food. To prevent seeds 

 from germinating within the cages, a hole was dug in the soil and filled 

 with about six inches of moist sand. In one cage stones and blocks of 

 wood were placed to shelter the insects from rains. The results 

 obtained during November and December are indicated in Table IV: 



