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Cucurbit Genetics Cooperative Report 2:38 (article 23) 1979

Bitter Cucurbita spp. as Attractants for Diabroticite Beetles

R. L. Metcalf, A. M. Rhodes, Jane E. Ferguson and Esther R. Metcalf

University of Illinois, Urbana-Champaign, Urbana, IL 61801

The attacks of the striped cucumber beetle, Acalymma vittata, and the spotted cucumber beetle or southern corn rootworm, Diabrotica undecimpunctata howardi, on cultivated Cucurbitaceae and of the corn rootworm, D. u. howardi, northern corn rootworm D. longicornis, and western corn rootworm D. virgifera on corn in the Midwest are conservatively estimated to cause damage and expenditures for control aggregating hundreds of millions of dollars annually. Approximately 40 million A (16 million ha) of corn are treated each year with soil insecticides and more than 10 million A (4 million ha) are sprayed to control the adult beetles.

There is need for a satisfactory monitoring and trapping system to determine population densities of adult Diabroticites in order to schedule insecticide treatments and develop integrated pest management programs. Such a system, if effective, could be used to control the beetle populations in small garden plots and in limited acreages of row crops. It is well known that several species of Diabroticite beetles are attracted by the tetracyclic triterpene cucurbitacins (1, 2, 3). These cucurbitacin "bitter substances" are specific kairomones for the Diabroticite beetles, acting as arrestants and feeding stimulants. The attacks of these beetles on the foliage and fruits of 18 species of Cucurbita were found to be directly related to the amounts of cucurbitacins B and E present. The cucurbitacin content may range up to 0.3% fresh weight in the fruit and roots of certain wild Cucurbita species.

The fruits of C. andreana, containing large amounts of cucurbitacin B, and C. texana, containing large amounts of cucurbitacin E glycoside, were found to be particularly suitable as trap crops or for attractant preparations for the Diabroticite beetles. In our preliminary experiments, approximately 100 g of squash fruit were homogenized in 500 ml of water to make a thick paste. This was poured into 10 inch (25 cm) paper pie plates so that each plate contained about 15 g of homogenate. In a typical experiment using C. texana fruit and three replicate traps placed around the perimeter of a planting of about 400 sq ft of C. andreana, the following average numbers of Diabroticite beetles were attracted:

Minutes of exposure

Average number of beetles

5

16

10

21

20

75

30

154

60

197

120

355

In these traps, the beetles, largely D. undecimpunctata with some D. virgifera and A. vittata compulsively ate the squash homogenate until it was totally consumed in about 5 hrs. The effectiveness of such traps was greatly improved by adding from 0.01 to 0.1% (w/v) of the contact insecticides trichlorfon or methomyl. These poisoned traps killed the feeding beetles within 5 minutes and up to 1,000 beetles within 4 hours. We estimate the cost of the individual traps at less than $0.10. Cucurbita texana and C. andreana produce large numbers of fruits under Illinois conditions and sufficient quantities will be grown to explore the practicality of trapping Diabroticites to protect home gardens and to determine population densities in corn plantings.

Literature Cited

  1. Chambliss, 0. L. and C. M. Jones. 1966, Chemical and genetic basis for insect resistance in cucurbits. Proc. Amer. Soc. Hort. Sci. 89:394.
  2. DaCosta, C. P. and C. M. Jones. 1971. Resistance in cucumber Cucumis sativus L. to three species of cucumber beetles. HortScience 6:340.
  3. Howe, W. L., J. R. Sanborn, and A. M. Rhodes. 1976. Western corn rootworm adult and spotted cucumber beetle associations with Cucurbita and cucurbitacins. Environ. Entomol. 5:1042.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 23 October, 2009