- 308 
Tab le_. 8 Summary of the length of the li'mDhal period 
for Jfew Mesdco. Texas, and Colorado^ in 1939 
State : 
Pirst hatch 
Pirst adults 
Length of 
nymphal period 
Days 
New Mexico - : — \ 
April 21 
, June 5 
45, 
Texas -f 
April 22 
June 5 
44' 
Colorado - - - -j 
May 2 
June 15 
44 
” D. longiueimis persisted in bands throughout the nymphal period, 
except in cases where populations were too low (either originally or as a 
result of control) to become gregarious. Populations of less than 5 per 
square yard were not observed to band together in Texas and New Mexico, 
whereas in Colorado populations of less than 20 per square yard were not 
observed to band together. This discrepancy probably represents the popu- 
lation range wherein D. longinennis may or may not become gregarious, depend- 
ing on such factors as nymphal size, vegetation, topography, or weather, 
Pirst-instar nymphs occurred in bands averaging 500 per square yard but 
sometimes noambering as many as 2,000 per square yard, A gradual dispersal 
and thinning in numbers took place during the whole of the nymphal period 
until the last instar, when the average per square yard ranged from less 
than 50 to 150, Nymphs remained on their hatching groamds more than a 
week in some cases, and on other beds left immediately after hatching. 
Usually migration began near the end of the first week of hatching, and 
the spread was rapid, Pirst-instar nymphs traveled about 3 feet per 
minute, third-instar nymphs from 6 to 12 feet per minute, and the late 
instars 10 feet or more per minute. Bands of nymphs could be found mov- 
ing in all directions during a single day and often within one locality. 
Because of repeated changes in direction, bands did not attain great dis- 
tances, but some were known to have reached a distance of 2 to 3 miles 
from the place of hatching. Very often by the end of a week or 10 days 
after hatching began, nymphal bands occupied 10 times the area of their 
egg beds. Nymphs from a l/2 acre bed in Texas spread over 30 acres in 
less than 2 weeks. Notwithstanding good control,' the last-instar nymphs 
in Colofadd were estimated to cover 5 times as much area as the original 
egg beds, and in parts of Nev/ Mexico fif-th-ihstar nymphs covered nearly 
10 times the area of the egg beds, ^ " 
•'The first adults D. longinennis in 1939 were found on J\ine 5 in 
New Mexico and Texas, and on June 15 in Colorado, By July 1, in the first 
two States and by July 15 in Colorado, populations were more than 98 per- 
cent adult. New areas became infested as the moving bands of nymphs be- 
came adults. Nymphs in the process of molting were left scattered behind 
the bands and the newly emerged adults soon flew away. During the month 
following the first adult emergence, D. longinennis adults showed no evi- 
dence of the gregariousness exhibited by the nymphs, and dispersed on wing. 
