intervals at each of the two places are listed in table 12. These columns of 
figures now become column 3 of the prediction tables 7a and 8a, depending on 
which column fits the more closely. 
From the middle of April on one can readily see that the average daily 
maximum temperature pattern or trend for Circle, Mont., 1939 fits the average 
maximum temperatures shown in column 2, table 7a, and that for Carson, N. Dak., 
1945 fits those in column 2, table 8a. Therefore, in the last columns, tables 
13 and 14, are the computations for the prediction of the hatching period. 
The prediction in table 13 for the early hatch of sanguinipes from the 
start does not vary much from the actual hatching period. In table 14, however, 
the prediction for late hatching on April 5 begins with the average dates June 7- 
26 and gets later and later with each 5-day interval until on June Lit te. duly, 
8-27, or 6 days later than the actual. Then 5 days later on June 9, the limit 
of the table, the prediction drops back to July 3-22 as compared with the actual 
July 2-23. 
It is not practical to use the O to 100 percent hatch, as there is a much 
greater variability in the first and last 10 percent of the hatch than any 10 
percent between 10 and 90. Hatching is prolonged more for the first and last 
10 percent. 
Summary 
The earliness or lateness of the hatching period of grasshoppers affects the 
type and amount of damage to the crop and the timing of control measures. Labora- 
tory experiments substantiated by field observations have shown the significant 
effect that temperature has on the rate of embryonic development and the subse- 
quent hatching period. The average daily maximum air temperatures for unit 
intervals of 5 days each were used in the development of a method for currently 
predicting the hatching period of four economically important species of grass- 
hoppers--Melanoplus sanguinipes (F.), M. bivittatus (Say), M. differentialis 
(Thomas), and M. femurrubrum (De Geer). These units became the independent 
variables affecting a hatching date, the dependent variable given as the number 
of days after April 30 when 70 percent of the end infestation had hatched. The 
term "end infestation" applies to the surviving infestation made up of those 
grasshoppers that have survived all the natural factors that tend to destroy 
early instar nymphs. It is not the true hatching period for all the infestation, 
but it is the one that concerns the farmer and the control supervisor. 
A method is described for obtaining figures for the dependent variables, 
based on grasshopper collections made during the nymphal development period and 
a knowledge of the average number of days in each instar. Thus the requirements 
for orthogonality were met and the computations of multipliers and regression 
coefficients carried out. 
Laboratory tests in the hatching of eggs at controlled temperatures had 
already proved that heat had an additive effect on the rate of embryonic develop- 
ment. This permitted an assumption that the effect of heat on hatching at any 
time is independent of the amount of heat occurring at any other time. A regres- 
sion curve was developed for each of the four species. It showed the average 
effect of a unit change of 1 degree of average daily maximum temperature for a 
5-day interval on the number of days after April 30 when 70 percent of the end 
infestation had hatched. 
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