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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

  1. Rhodes, A. M., R. L. Metcalf and E. R. Metcalf. 1980. J. Amer. Soc. Hort. Sci. 105: 838-842.
  2. Metcalf, R. L., R. A. Metcalf and A. M. Rhodes. 1980. Proc. Nat. Acad. Sci. USA 77: 3769-3772.
  3. 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.

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