The degree of tolerance of maize (Zea mays L.) to corn rootworm (Diabr
otica spp.) larval feeding may be affected by root system growth after
insect feeding damage. This study evaluated the change in root pull r
esistance (DELTARPR; as determined by the subtracting the root pull re
sistance at the time of maximum larval feeding damage from the root pu
ll resistance measured 17 days later) caused by western corn rootworm
(D. virgifera virgifera LeConte) larval feeding damage in single-cross
maize hybrids which were popular with corn producers during three suc
cessive 10-yr eras. The 2-yr field study was conducted as a split-spli
t plot with plant population as main plot treatments, rootworm infesta
tion levelas subplot treatments, and plant hybrid as sub-subplot treat
ments. Increased plaNt populations reduced vertical root pull resistan
ce and delayed root development (as measured by the number of nodes pr
oducing root axes). Under dry soil conditions, there was a significant
plant population x infestation level x hybrid interaction because inc
reased rootworm larval feeding damage and plant population reduced DEL
TARPR to a great extent in 1960-era hybrids, while the 1980 and 1970-e
ra hybrids were relatively unaffected. Under wet soil conditions, ther
e was no significant effect of infestation level or plant population o
n DELTARPR, and no significant 3-way interaction. However, DELTARPR of
1980 and 1970-era hybrids was greater than that of 1960-era hybrids.
When the change in root pull resistance after rootworm larval feeding
is considered, maize hybrids popular in the 1970's and 1980's were mor
e tolerant than the 1960-era hybrids under high plant populations and
dry growing conditions.