Jan. 15. 1915 



Tliree-Cornered Alfalfa Hopper 



357 



to four generations annually. During 191 2 the writer observed three 

 and a partial fourth, and during 1913 Mr. T. Scott Wilson observed the 

 same number. The species reaches its greatest numbers during Septem- 

 ber, when adults of the third generation are appearing. Immediately 

 following the first of November the adults begin disappearing quite 

 rapidly. Many doubtless deposit their complement of eggs and die a 

 natural death, others are killed by the approach of cold weather, and the 

 rest go into hibernation. Of the immense numbers that go into hiberna- 

 tion but few appear in the spring. This heavy mortality is doubtless due 

 to the varying temperature. A week of warm days appears. The 

 insects, thinking spring has come, desert their protected places and begin 

 feeding. Then, if the night temperature suddenly drops to freezing or 

 below, a great man)' of them succumb. 



The actual dates for the different generations as observed in cages are 

 given in Table VII. Under field conditions it is quite probable that there 

 would be considerable variation from these dates, but they can be con- 

 sidered as an average for the different conditions. 



Table VII. — Periods of generations of the three-cornered alfalfa hopper in Arizona in 



IQ12 and IQ13 



DAMAGE TO ALFALFA 



INJURY TO THE PLANT 



The damage to alfalfa and other plants comes as a result of the sucking 

 up of the plant juices for food by the adults and nymphs. The sharp- 

 pointed proboscis-like mouthparts or beak is thrust into the plant and the 

 juice extracted, leaving the plant wilting and often in a dying condition. 

 Both the adults and the young have two methods of feeding. One is a 

 promiscuous puncturing of the stems, while the other is the puncturing 

 in a regular and continuous line which takes the form of a ring or girdle 

 aroimd the stem (PI. XLllI, fig. 7, a). At first it was suspected that this 

 girdling had something to do with egg deposition, since the eggs, being 

 deposited below the girdle which had stopped the circulation of plant 

 fluids, were safe from injury by plant growth. Soon, however, it was 

 noticed that nymphs were more often responsible for the ringing than 

 adults and that girdling from adults had no relation whatever to oviposi- 

 tion. 



It is from these girdling punctures that the greatest damage results; 

 for in addition to the loss of plant juices, the stems are weakened, a 

 gall (PI. XLIII, fig. 7, b) usually develops, circulation is cut off from the 

 upper portion of the plant, and a great many of the plants break off", be- 

 come yellow, and die. It is interesting to note here that the nymphs do 

 more damage than the adults. They seem to be much more hearty 

 69733°— 15 G 



