As anexample of misinformation on varieties 
resistant to insects, the following is quoted 
from one of the most widely used texts and 
reference books on economic entomology by 
Metcalf, Flint, and Metcalf, ''Destructive and 
Useful Insects,'' 4th edition, 1962, page 535; 
"Some varieties of wheat have been found 
resistant to Hessian fly, but up to the present 
time, no varieties have been found sufficiently 
resistant to attacks of this insect, and having 
other desirable qualities, to warrant recom- 
mending them generally in any of the large 
wheat growing areas," 
Let us look at the facts, Four years before 
this book was published, six varieties of wheat 
had been listed (Painter, 1958) as having been 
recommended by 10 State experiment stations 
as resistant to the Hessian fly and also 
satisfactory in other respects. One, the variety 
Pawnee, became the leading wheat in acreage 
in 1949 in the United States--strong evidence 
of "having other desirable qualities." At the 
time, Pawnee was recommended and occupied 
nearly 6 million acres in Kansas alone and 
over 11 million acres in the United States 
(Clark and Bayles, 1951). Six million acres 
certainly qualify as a "large wheat growing 
area," 
Another wheat variety, Big Club 43, from 
soon after its distribution and since, has oc- 
cupied about 98 percent of the acreage in 
California formerly infested by the Hessian fly. 
It was so successful in virtually eliminating 
the Hessian fly in that area that no more re- 
search could be done, and the U.S. Department 
of Agriculture experiment station concerned 
with this insect in California was closed. This 
level of control of an insect has rarely been 
obtained by other methods. 
In the 1961-62 wheat crop, Gallun (1962, 1965) 
reported that 17 wheat varieties resistant to the 
Hessian fly occupied up to 72 percent of the 
wheat acreage in 25 States. The varieties in- 
clude five genetic sources of resistance, and 
then occupied a total of 4 1/2 million acres. 
This recent increase in Hessian fly-resistant 
wheat varieties reflects in particular the long- 
time studies at the Indiana Agricultural Ex- 
periment Station in cooperation with the U.S, 
Department of Agriculture, in addition to the 
research at the Kansas Agricultural Experi- 
ment Station. It also reflects recently expanded 
139 
interest in noninsecticidal methods of insect 
control, 
In contrast to the text book statement quoted, 
there now is no Hessian fly-infested major 
wheat growing area where at least one adapted 
Hessian fly-resistant wheat variety cannot be 
grown. There is now no need of loss because 
of the Hessian fly. Control can be achieved 
without extra cost except perhaps for new seed, 
which may also give other benefits. This can 
be said of no other method of control for a 
widespread insect. 
No information on well-documented and suc- 
cessful instances of insect control by host plant 
resistance is given in any general textbook of 
applied entomology. Examples are readily 
available. The classical example of control of 
the grape phylloxera by such means (Howard, 
1930) should be as well known to students of 
entomology as control of the cottony-cushion 
scale by the vedalia lady beetle. But it is not. 
With such misleading or lack of information 
in textbooks, an appreciation and knowledge of 
plant resistance as a method of insect control 
cannot be expected of many entomology gradu- 
ates. 
I now wish to comment on procedures and 
principles involved in developing host plant 
resistance and on the present status of some 
research projects dealing with the subject. 
Plants that are inherently less damaged or 
less infested than others under comparable 
environments in the field may be called 
resistant, 
The first step in any resistance program is 
to find genetic factors for resistance. The 
chance of finding resistance is more or less 
proportional to the number and diversity of the 
plants and varieties of a crop species that can 
be studied, and to the control of the infesting 
population of insects used during the period of 
search. The best insect population to be used 
for infestation is not always the highest pos- 
sible population of insects, but rather the level 
of population that gives the maximum dif- 
ference between resistant and susceptible 
plants. Thus far, genetic factors for resistance 
have been found wherever adequate search has 
been made, 
For example, in a search for Hessian fly 
resistance, tests on about 3,000 foreign and 
domestic wheat varieties were reported at 
