Disposition and fate of cucurbitacin B in five species of diabroticites

Abstract

Five species of diabroticites with different host-plant preferences produced an essentially identical array of metabolites when fed radiolabeled cucurbitacin B synthesized in vivo and purified fromCucurbita maxima Duchesne seedlings. All species excreted the bulk of the cucurbitacin (67,17-94.59% total dpm), permanently sequestered a small proportion of a cucurbitacin conjugate in the hemolymph (0.98-2.76%), and apportioned the remainder between the gut, the body, and the eggs (when present). Markedly different ratios between the excretory metabolites (i.e., polar vs. unmetabolized cuc) suggest thatDibrotica virgifera virgifera, a grass specialist, andAcalymma vittatum, a cucurbit specialist, have lower rates of metabolic alteration than the polyphagousD. undecimpunctata howardi, D. balteata, andD. cristata, which is associated with relict prairies. Mean life-spans ofD. balteata and D. v. virgifera and maleA. vittatum decreased significantly with continuous feeding onCucurbita fruit containing cucurbitacins (vs. fruit devoid of cucs). The longevity of femaleA. vittatum, however, was unaffected by the presence of cucurbitacins.

Sequestration of cucurbitacin analogs by New and Old World chrysomelid leaf beetles in the tribe Luperini

“…Howe et al (1976) suggested a possible defense mechanism in cucurbitacin-associated diabroticite beetles against birds or other insect-feeding vertebrates. Ferguson & Metcalf (1985) have clearly shown the defensive effect against a praying mantis, Tenodera aridifolia sinensis Saussure, using diabroticite beetles which fed on bitter squashes. Out results indicated the effectiveness of cucurbitacins to a vertebrate predator.…”

“…It has been suggested that the powerful feeding response by adults of the polyphagous diabroticites to cucurbitacins may be a relic feature of their ancestral association with the Cucurbitaceae (Metcalf 1979). On the other hand, it has been suggested that the phagostimulant activity of cucurbitacins may be associated with chemical defense mechanism against predators by sequestering bitter principles in the bodies of insects (Howe et al 1976;Gould & Massey 1984;Ferguson & Metcalf 1985;Nishida et al 1986). have extensively studied the fate of cucurbitacin B in diabroticite adults.…”

Chemical egg defense in Photuris firefly "femmes fatales"

“…The coleopteran examples include Coccinellidae (Pasteels et al 1973), Pyrochroidae (Eisner et al 1996b;Holz et al 1994), Meloidae (McCormick andCarrel 1987), Oedemeridae (Holz et al 1994), and Chrysomelidae. Interestingly, some chrysomelids protect their eggs exclusively with compounds of seemingly endogenous origin (Daloze & Pasteels 1979, Hilker & Schulz 1991, Howard et al 1982, Pasteels & Daloze 1977, Pasteels et al 1986), while others do so with chemicals acquired from the diet (Ferguson et al 1985, Pasteels et al 1986). Moreover, several species of Chrysomela, and a species of Phratora (P. 6itellinae), protect their eggs with a combination of dietary salicin, and isoxazolinone glucosides that they themselves produce (Pasteels et al 1986).…”

Ultramicrochemistry of insect semiochemicals

“…The Luperini beetles have maxillary chemoreceptors specifically attuned to respond to ultramicro quantities of cucs by signalling arcest and phagostimulation; thus delineating suitable host plants. Further evolution has resulted in the development of pharmacophagy whereby the Luperini sequester microgram quantities of cucs B and E in hemolymph and fatty tissues; and these serve as allomones protecting the beetles from predation [39,40].…”