Cucurbit Genetics Cooperative Report 3:44 (article 25) 1980
A. M. Rhodes, R. L. Metcalf, and E. R. Metcalf
University 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 of insects.
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.
Literature Cited
- 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. Rpt. 2:38-39.