Cucurbit Genetics Cooperative Report 3:44 (article 25) 1980
Bitter Cucurbita Hybrids as Baits for Diabroticite Beetle
A. M., Rhodes, R. L. Metcalf, and E. R. Metcalf
of Illinois at Urbana-Champaign, Urbana, IL 61801
We reported previously (1) that the leaves and fruits of
bitter Cucurbita spp., e.g. C. andreana
containing up to 0.3% cucurbitacins B and D and C. texana
containing up to 0.1% cucurbitacin E-glycoside, were very
attractive to adult cucumber beetles Diabrotica undecimpunctata
and Acalymma vittata and to the western corn
rootworm D. virgifera. The cucurbitacins acted
as kairomones, arresting the beetles and stimulating them
to compulsive feeding at quantities as low as 1 ng. There
is evidence that the nonvolatile cucurbitacins co-distill
from bruised leaves or damaged fruits and can be detected
by the beetles over a distance of several meters. The effectiveness
of cut fruits or homogenates was greatly improved by treating
them with the rapidly acting contact insecticides trichlorfon
or methomyl at concentrations of 0.01-0.1% of fruit weight.
Such preparations killed feeding beetles within 2-5 min and
prevented them from rapidly consuming the baits. Ten cut
fruit of C. andreana each sprinkled with about
0.1 g or methomyl killed an average of 437 D. undecimpunctata
and D. virgifera beetles over three days,
compared with an average of 381 beetles for C. texana
fruits. Such baits continued to kill the beetles for at
least two weeks, individually treated fruits killing thousands
However, these wild bitter Cucurbita spp. are
not dependable sources of cucurbitacins under Midwest growing
conditions. Fruiting is generally dependent upon photoperiod,
yields are low and often erratic. Therefore, a number of
interspecific hybrids were grown and evaluated for beetle
attraction in the field and the cucurbitacin contents determined.
Hybrids of C. andreana x C. maxima and
of C. texana x C. pepo were the most promising
from the standpoint of high cucurbitacin content, high yield,
and ease of culture. They were grown in acre-sized plots
in 1979. The C. andreana x C. maxima hybrid
fruits contained about 0.13% cucurbitacin B and D and yielded
about 30,000 lbs/A. The C. texana x C.
pepo hybrid fruits contained about 0.06% Cu E and its
glycoside and yielded about 15,000 lbs/A.
The leaves, fruits, and blossoms of these hybrid bitter
squash were evaluated for feeding preferences by the Diabroticite
beetles and for cucurbitacin contents. In general, the hybrids
plants were fully as attractive as baits as the parent bitter
squash, although the cucurbitacin contents were slightly
lower. Therefore, we now have a dependable source of highly
attractive bitter fruits. The hybrids will be further selected
for high cucurbitacin yield during the 1980 season and will
be extensively evaluated as trap crops and as poisoned baits
for Diabroticite pest management using cut fruits and granular
and pelleted baits.
This research was supported in part by a grant from the
USDA, SEA, Competitive Research Grants Office, 5901-0410-8-0067-0.
Any opinions, findings, and conclusions are those of the
authors and do not necessarily reflect the views of USDA.
- Metcalf, R. L., A. M. Rhodes, J. E. Ferguson, and E.
R. Metcalf. 1979. Bitter Cucurbita spp. as attractants
for Diabroticite beetles. Cucurbit Genetics Coop.