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Cucurbit Genetics Cooperative Report 5:42-43 (article 21) 1982

Cucurbitacins of Cotyledons of Cucurbitaceae Cultivars as Related to Diabroticite Beetle Attack

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

Departments of Entomology and Horticulture, University of Illinois, Urbana, Champaign

The worldwide culture of many species and varieties of Cucurbitaceae is complicated by the feeding of many species of rootworms, cucumber beetles, pumpkin beetles, of the order Coleoptera, family Chrysomelidae, tribe Luperini. A common feature of the preference of this group of beetles for cucurbits is the presence of the oxygenated tetracyclic triterpenoid cucurbitacins that act as kairomones promoting arrest and compulsive feeding. In the United States cucurbit seedlings are especially severely attacked and often defoliated by the spotted cucumber beetles Diabrotica undecimpunctata undecimpunctata Mannerheim and D. u. howardi Barber, by the banded cucumber beetle D. balteata LeConte and by the striped cucumber beetles Acalymma vittata Fabricius, and A. trivittata (Mannerheim).

The cucurbitacins seem clearly to have arisen by coevolutionary selection as intensely bitter substances effective as feeding deterrents to herbivores. Their presence renders cucurbitaceous fruits completely unpalatable to man and our present cultivars selected over thousands of years for palatability, are essentially devoid of Cucs (1, 2). However, the extent of Diabroticite feeding on the cotyledons of many varieties of Cucurbita, Cucumis, and Citrullus suggests that substantial amounts of Cucs are present. Cuc synthesis in these genera is initiated by a single dominant gene B1 (3) but non-bitter fruit may develop from bitter seedlings in the presence of a modifier suppressing Cuc synthesis in the fruit.

We have investigated the Cuc content of the cotyledons of 19 species and 47 cultivars of Cucurbita, Cucumis, and Citrullus by extracting the Cucs, separating them by thin-layer chromatography, and localizing them by the feeding spots produced after exposure to adult D. undecimpunctata and D. balteata. Some cultivars have also been characterized by high pressure liquid chromatography. Substantial amounts of Cucs were found in 30 of 47 cultivars (Table 1) and 10 of 11 wild species examined (Citrullus colocynthis, Cucumis hardwickii, Cucurbita andreanna, C. ficifolia, C. Foetidissima, G. lundelliana, C. martinezii, C. okeechobeensis, C. palmeri, and C. texana). Cotyledonary Cuc content was found to be directly related to seedling beetle damage on the field but unrelated to fruit or leaf beetle damage.

Although other factors may be involved in Diabroticite feeding on Cucurbit cultivars, they are negligible in the presence of the powerful kairomones, the cucurbitacins. The screening of Cucurbits in the seedling stage is paramount in developing non-Cuc containing cultivars for incorporation into PIM programs to lessen Diabroticite attack upon the Cucurbitaceae.

Table 1. Cucurbitacin content of cotyledons of Cucurbitaceae cultivars as estimated by Diabroticite feeding on TLC plates developed from standard chloroform extracts. Species abbreviations and characteristic major Cucs: Cuc E and Cuc-glycosides - LAN = Citrullus lanatus; Cuc C - SAT = Cucumis sativus; Cuc B-ANG = Cucumis anguria, MELO - Cucumis melo, MAX = Cucurbita maxima, MIX = C. mixta, MOS = C. moschata, PEPO = C. pepo.

Cucurbitacin Content* : Species - Cultivar
Large Moderate None detected
LAN LAN MELO

Charleston Gray

New Hampshire

Early Dawn

Iopride

MELO

Gold Star

Sugar Baby

Golden Rind

SAT

Yellow Doll

Honey Mist

Saticoy

ANG SAT MIX

West Indian Gherkin

Marketmore

Gold Striped Cushaw

SAT

Pot Luck

MOS

Liberty Hybrid

Wis. SMR-18

Dickinson Field

Palomar

MAX

Early Butternut

MAX

Boston Marrow

PEPO

Mammoth Gold

Golden Hubbard

Bush Table King

MOS

Pink Banana Jumbo

Crookneck

Tahiti

PEPO

Early White Squash

PEPO

Blackjack

Goldbar

Ambassador

Caserta

Goldneck

Black

Greyzini

Patty Green Tint

Diplomat

Seneca Butterbar

Scottsdale

Gourmet Globe

 

Seneca Prolific

Greenbay

 

St. Pat Scallop

Cocozelle

 

Straightneck

Scallopini

   

Storr's Green

   

Striato Striped

   

*Cuc content verified by HPLC Iopride (large) = 39.3 μg Cuc E/g fwt cotyledons; Black (large) = 23.0 μg Cuc B/g fwt; Blackjack (moderate) = 10.8 μg Cuc B/g fwt; and Goldbar (none detected), 0.25 μg fwt.

Literature Cited

  1. Metcalf, R.L., R.A. Metcalf and A.M. Rhodes, 1980. Cucurbitacins as kairomones for diabroticite beetles. Proc. Nat. Aca. Sci. 77: 3769-3772.
  2. Metcalf, R.L., A.M. Rhodes, R.A. Metcalf, Jane Ferguson, Esther R. Metcalf and Po-Young Lu, 1982. Cucurbitacin contents and Diabroticite feeding upon Cucurbita spp. In Press. Env. Entom.
  3. Robinson, R.W., H.M. Munger, T.W. Whitaker and G.W. Bohn, 1976. Genes of the Cucurbitaceae, Hort. Scoi. 11(6):554-568.
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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