18 DEPAKTMENT BULLETIN 779. 



fields of small grain have been observed in which the adults aiwi, 

 nymphs averaged 4 or 5 to each head of grain. On several occasions 

 a quart of the insects was swept within a space of five minutes. 

 After the middle of July the numbers of each succeeding generation 

 are greatly reduced by the activities of parasites and predacious 

 enemies until at the end of the season it is sometimes very difiicult 

 to find specimens of the insects, or their eggs, in fields where they 

 were formerly abundant. 



HABITS OF NYMPHS. 



GREGARIOUSNESS AND POWERS OF LOCOMOTION. 



During the first instar the young nymphs are gregarious in habit 

 and seldom leave the proximity of their parent egg cluster. Soon 

 after the second instar is reached they may wander away singly in 

 search of food, but usually are found feeding very close together. 

 During the third and succeeding instars the nymphs become more 

 solitary in habit, but if the food supply is abundant the entire 

 progeny of one egg cluster may reach maturity within a few feet 

 from the place of their incubation, and under exceptional circum- 

 stances they sometimes complete their development on the same 

 plant. The nymphs are rather slow of movement and they lack the 

 power of flight, but in cases of necessity the larger nymphs may 

 crawl several hundred feet in search of food. 



FEEDING. 



The nymphs when feeding assume a position with the legs strongly 

 braced against the plant, the head upward or downward. The setse of 

 the mouth parts are inserted at right angles to the body and the liquid 

 contents of the host are removed by suction. In the case of small 

 grains the nymphs remove the entire contents of each kernel through 

 a single puncture, but when feeding on tender stems several punctures 

 are made within short distances of each other. Apparentl}^ the 

 nymphs can not pierce any plant tissue after its epidermis has become 

 hardened. 



In the early spring the nymphs of all stages feed upon Eussian 

 thistle but later in the season a large percentage of the fourth and 

 fifth instar nymphs feed, with the adults, on the tender stems and 

 developing heads of grain. The larger nymphs have also been ob- 

 served feeding on the tender stems and newly formed seeds of 

 alfalfa, but experiments demonstrated that the species could not be 

 reared from egg to adult on this plant. Throughout the season the 

 young nymphs of the first three instars appear to confine their atten- 

 tion almost exclusively to Eussian thistle, and when other food 

 plants are lacking the nymphs of the last two instars feed upon this 

 plant. 



