Cucurbit Genetics Cooperative Report 4:37-38 (article 20) 1981
Monitoring and Controlling Corn Rootworm Beetles with
Baits of Dried Bitter Cucurbita Hybrids
Metcalf, R. L., A. M. Rhodes and E. R. Metcalf*
Departments
of Entomology and Horticulture, University of Illinois,
Urbana-Champaign, IL 61801
Recently we reported (1) that fruits of two hybrid species
of Cucurbita, C. texana x C. pepo
and C. andreana x C. maxima combined the
genetic production of bitter cucurbitacin terpenoids (Cucs)
of the wild parents with the high yields of squash fruit
characteristic of the domestic cultivars. The fruit of the
former hybrid contained about 0.48 mg Cucs E, I and E glycosides
per g fresh weight and that of the latter about 1.25 mg
per g of Cucs B and D. These Cucs act as arrestants and
feeding stimulants for the corn rootworm beetles Diabrotica
virgifera, D. longicornis and D. undecimpunctata
in amounts as small as 1 ng (2).
During the 1979 season we investigated the use of cut fruits
of these bitter Cucurbita hybrids, poisoned with
methomyl or trichlorfon at 0.01 to 0.1% of fruit weight, for
monitoring and control of the adult corn rootworms. These
fresh baits remained attractive to the adult beetles for
at least 2 weeks and individual cut fruits killed several
thousand beetles (1, 3).
During the 1980 season we explored the use of dried and
ground fruits of these bitter Cucurbita hybrids,
poisoned with 0.1% methomyl or 0.01% fenvalerate or decamethrin
as broadcast, granular baits for the control of the corn
rootworm beetles. To our surprise these baits were highly
effective in killing the beetles when broadcast in sweetcorn
at dosages of 10, 30, and 100 kg per ha, containing 10 to 100
g methomyl or 1 to 10 g fenvalerate or decamethrin. The
C. texana x C. pepo fruits produced a somewhat
more effective bait than the C. andreana x C.
maxima bait, perhaps due to better physical properties
of the fibrous "zucchini' type fruit (1). The C.
texana x C. pepo bait at 30 kg ha (30 g methomyl)
killed an estimated 150000 beetles per ha within 20 hrs
after application or approximately 85% of the pretreatment
population. At a dosage of 10 kg ha (10 g methomyl), the
reduction was about 62% of the pretreatment count. Bitter
Cucurbita baits containing decamethrin killed large
numbers of corn rootworm beetles at dosage of insecticide
ranging from about 1 to 3 g/ha. The dried baits remained
effective in killing beetles for 2 weeks or longer.
These successful experiments suggest that the dried bitter
hybrid Cucurbita fruits may have practical value
in IPM programs for corn rootworms. Poisoned dried fruit
sections may be incorporated into simple traps for monitoring
beetle populations. Dried bitter fruits may be formed into
poisoned baits as indicated above or formulated into granular
or pelleted insecticides for control of adult beetles above
ground or corn rootworm larvae in the soil. We plan to investigate
higher yielding hybrids of bitter Cucurbita, refined
methods of bait formulation, and better methods of distribution,
during subsequent seasons.
Literature Cited
- Rhodes, A. M., R. L. Metcalf and E. R. Metcalf. 1980.
J. Amer. Soc. Hort. Sci. 105: 838-842.
- Metcalf, R. L., R. A. Metcalf and A. M. Rhodes. 1980.
Proc. Nat. Acad. Sci. USA 77: 3769-3772.
- Rhodes, A. M., R. L. Metcalf and E. R. Metcalf. 1980.
Cucurbit Genetics Coop. Rpt. 3:44.
*This research was supported in part by a grant form 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.
