Lucibufagins: Defensive steroids from the fireflies Photinus ignitus and P. marginellus (Coleoptera: Lampyridae)

Abstract

Feeding tests with thrushes (Hylocichia spp.) led to the isolation of three novel steroid pyrones from fireflies (Photinus ignitus and P. marginellus) responsible, in part at least, for the unpalatability of these insects to the birds. The term lucibufagin is coined for these steroidal pyrones. The closest known relatives of lucibufagins are the familiar cardiotonic bufadienolides, found in certain toads and plants. It had previously been suspected that fireflies-the familiar luminescent beetles of the family Lampyridae-contain noxious substances that protect them against vertebrate predators. A diversity of lizards, birds, and mammals was said to reject these insects, but the defensive substances responsible, presumed to be present in the blood and tissues of the beetles, had not been characterized (2-4).Pursuant to our finding that fireflies of the genus Photinus are rejected by birds (thrushes of the genus Hylocichla), we developed a bioassay with these predators by which the feeding deterrency of extracts of Photinus, and that of fractions of the extracts, could be evaluated. The procedure led to the isolation of three novel steroidal pyrones, deterrent to the birds, and present in the beetles at defensively effective concentrations. We here describe the isolation and partial characterization of these compounds, for which we propose the term lucibufagins. Steroidal pyrones, or bufadienolides, are of restricted occurrence in nature. They have been found in some well-known toad venoms as well as in a small group of plants (ref. 5, pp. 469-476). However, no examples have been reported from invertebrates. MATERIALS AND METHODSThe two species of Photinus studied, P. ignitus and P. marginellus, are common in the northeastern United States. They were collected at night with nets in the environs of Ithaca, New York, and immediately brought to the laboratory for feeding tests or chemical extractions. Because the fireflies were taken in flight, they can be assumed to be virtually all males. Thrushes were chosen for the feeding tests because they adapted well to captivity and were known to be broadly insectivorous in their habits. A single Swainson's thrush (Hylocichla ustulata, male) and five hermit thrushes (H. guttata, three females and two males) were used. All had been taken months beforehand in mist nets during the migratory season. They were caged singly in the laboratory and were "experienced" at the time of experimentation, having previously been offered palatable and unpalatable insects in connection with other studies. They were sexed at autopsy.The initial tests with the single Swainson's thrush were in-The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. 905tended to provide preliminary data on the food preferences of such a bird. These tests extended over a period of 23 days, during which the thrush was offered, in daily feedi...

Lampyridae (Coleoptera): A plethora of mollicute associations

“…Eisner et al [15] postulated that lampyrids produce these steroid-related molecules from ingested cholesterol, a nutrient required for growth ofspiroplasmas and mycoplasmas. Spiroplasmas are frequently present in other insects [ 19] that possess cardenolides (e.g., danaid butterflies and chrysomelid beetles [ 15]) or that have cholesterol-rich diets (e.g., tabanid flies, mosquitoes, and ticks). Determination of a causative relationship between this added sterol dependence and the high frequency of associations of these insects with spiroplasmas and mycoplasmas would be important to our understanding of the role of these microbes in nature.…”

“…Many members exhibit unique physiological characteristics, including luminescence. They also release large amounts of steroid related cardenolides (lucibufagins [15,17,28]) by reflex bleeding [2].…”

The Terrestrial Bioluminescent Animals of Japan

“…In the Lampyridae, many species exhibit reflex bleeding, and the excreted fluid is stinky, distasteful and repellent to predators (Lloyd, 1973;Ohba and Hidaka, 2002). Eisner et al (1978) demonstrated that fireflies possess defensive steroids in effective quantities to deter predation. Lizards, birds and mice quickly learn to associate bioluminescence with a distasteful organism (Underwood et al, 1997;Matthysen, 1999, 2003;Knight et al, 1999).…”

The chemistry of phyletic dominance.

“…This bug discharges a mixture of pregnanes in which desoxycorticosterone is the main component (12). A family of much more highly functionalized steroids, the lucibufagins, serves to render some species of firefly (lampyrid beetles) unpalatable to predatory spiders and birds (13)(14)(15) …”