June, ’23 
mccolloch: hessian fly, resistant wheat 
297 
and Kanred Hybrids to 80 percent for Marquis and Kharkof. (3) 
There is practically no difference in the ability of the larvae to get down 
between the soft wheats as a class and the hard wheats. (4) In all 
cases, enough larvae succeeded in getting down to seriously injure the 
plant should they develop. 
This investigation of the migration of the larvae has failed to demon¬ 
strate any marked relation between resistance and morphological char¬ 
acters of the plant, although there is an apparent difference in the 
ability of the larvae to reach the base of the plant. Careful studies 
have been made of the structure of the leaf and the ligule, since these 
are closely associated with larval migration. With the exception of the 
height of the ligule there has been no correlation between gross morpho¬ 
logical characters and resistance. In some of the resistant strains it 
was found that the ligule was slightly higher than in the susceptible 
strains, and, therefore, offered a greater barrier. 
The next phase to be investigated was the ability of the larvae to 
develop after they had reached their normal feeding place. Experi¬ 
ments were conducted with a few resistant and susceptible varieties, and, 
while the number of tests was not as great as in the above experiment, 
they brought out several significant facts. Only 2.5 percent of the 
larvae developed on Dawson Golden Chaff; 13.4 percent on Illini Chief 
No. 2591, a resistant strain; and 62.6 percent on Illini Chief No. 3291, 
a susceptible strain. On the other hand, from 95 to 100 percent of the 
larvae developed on Kanred, Red Winter No. 2101 and No. 2132, 
Kharkof, and Zimmerman. It is of interest to note that Red Winter 
No. 2132, which has been consistently resistant under field conditions, 
has not been resistant when grown in cultural media. It was also 
found that in the case of the resistant varieties, when larval development 
did take place, it was usually high on the stem and not at the base of 
the plant. Growth of the larvae was slow on these varieties, and in 
some cases one-fourth grown larvae were still active and moving about 
instead of assuming the normal sedentary habit. Undeveloped larvae 
were generally found at the base where the leaf sheath has its origin. 
The results of these observations indicated that resistance was due 
to physiological conditions and was located at the base of the plant. 
Experiments were, therefore, outlined for the purpose of studying the 
various physiological characters of the wheat plant, and especially of the 
outer cells of the stem. This line of investigation presents many diffi¬ 
culties and necessitates the development of special technique, conse¬ 
quently progress has been rather slow. 
