Redalyc.Sesquiterpene Lactone Sequestration by the Tortoise Beetle Physonota Arizonae (Cassidinae)
Total Page：16
File Type：pdf, Size：1020Kb
Journal of the Mexican Chemical Society ISSN: 1870-249X [email protected] Sociedad Química de México México Aregullín, Manuel; Rodríguez, Eloy Sesquiterpene Lactone Sequestration by the Tortoise Beetle Physonota arizonae (Cassidinae) Journal of the Mexican Chemical Society, vol. 47, núm. 2, abril-junio, 2003, pp. 143-145 Sociedad Química de México Distrito Federal, México Available in: http://www.redalyc.org/articulo.oa?id=47547211 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Revista de la Sociedad Química de México, Vol. 47, Núm. 2 (2003) 143-145 Investigación Sesquiterpene Lactone Sequestration by the Tortoise Beetle Physonota arizonae (Cassidinae) Manuel Aregullín and Eloy Rodríguez* Natural Products Laboratory, Biotechnology 259, College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853-4301, USA In honor of Dr. Alfonso Romo de Vivar for his contributions to the field of phytochemistry the chemistry of sesquiterpene lactones Recibido el 24 de marzo del 2003; aceptado el 28 de mayo del 2003 Abstract. The phenomenon of sequestration of plant secondary Resumen. El fenómeno de secuestro de metabolitos secundarios de metabolites by herbivorous arthropods and its importance as an plantas por artrópodos hervíboros, y su importancia como estrategia arthropod defense strategy is well documented in chemical ecology de defensa artrópoda, se encuentra bien documentado en estudios de studies. Damsin (1), and the related terpene damsinic acid (2), are ecología química. Damsina (1), y el terpeno ácido damsinico (2), son sesquiterpene lactones sequestered by the tortoise beetle Physonota sesquiterpen lactonas secuestradas por el escarabajo tortuga Physo- arizonae (Cassidinae) from its host plant Ambrosia ambrosioides nota arizonae (Cassidinae) de su planta anfitrión Ambrosia ambro- (Asteraceae) for possible chemical protection. sioides (Asteraceae) para su posible protección química. Keywords: Sequestration, sesquiterpene lactones, Asteraceae, Am- Palabras clave: Secuestro, sesquiterpen lactonas, Asteraceae, Am- brosia ambrosioides, Cassidinae, Physonota arizonae, Coleoptera, brosia ambrosioides, Cassidinae, Physonota arizonae, Coleoptera, tortoise beetles. escarabajos tortuga. Introducción Because of the external adult morphology (i.e., analogous to the reptilian Chelonia), the beetles in the family Cassidinae The phenomenon of sequestration of natural products is a well are commonly referred to as tortoise beetles (Fig. 1a). The documented biological event occurring extensively in the pronotum and elytra in these beetles extend to cover complete- Arthropoda [1, 2]. The uptake of toxic substances of exoge- ly the margins of the body, and is an excellent example of nous origin, for purposes of defense, has been dramatically mechanical defense for the adult life stage. However, the demonstrated in several plant-insect interactions [3, 4]. In the nymphal stages possess a very different morphology (i.e., class Insecta, plant-derived chemicals are often stored inter- platyform with lateral segmental appendages) that cannot be nally in the hemolymph or in specialized glands, and used in used effectively for protection. The nymphal stages possess a acts of reflex bleeding or active secretion triggered by the caudal bifurcated process (i.e., urogomphi) where exuvia are encounter with a potential predatorial threat [1]. accumulated, as the beetle develops, and covered with fecal However, less common are the cases of sequestration in matter, this assemblage can be best described as a small green which the toxic chemicals are stored externally (i.e., appen- caudal globe that can represent from 1 / 5 to 1 / 3 of the over- dages or whole body coatings). The possible advantage of all size of the beetle (Fig. 1b). Because the urogomphi are such a defense posture is its utilization as visual or olfactory articulated with muscles, the beetle can raise this caudal globe warning of chemical protection. It is only recently that the over the body in an umbrella or shield like fashion and con- chemistry of these defense strategies or “shields” has been spicuously display it. Moreover, in the event of a threat, this recognized [5-7]. display is accompanied by a typical defensive behavior in In this study, we investigated the chemistry of an interest- which the caudal globe is actually pointed in the direction of ing case of external sequestration in the family Cassidinae the threat (scorpion syndrome). Thus, we propose that the within the Coleoptera. nymphal stages are protected chemically by these accumula- One such tortoise beetle species, Physonota arizonae [8], is tions of fecal matter in combination with a behavioral respon- endemic to the southwest United States and northern Mexico se, and that this protection represents a case of external se- and it uses as host plant a commonly occurring shrub from the questration of plant derived chemicals. family Asteraceae, Ambrosia ambrosioides (canyon ragweed). We have now shown that P. arizonae covers its exuvia with We became very interested in learning the chemical com- resinous fecal deposits that comprise up to 90 % (w/w) of a mix- position of the caudal globe the nymphal stages carry, in an ture of two sesquiterpene lactones, Damsin (1) and Damsinic attempt to infer from this composition any potential defensive acid (2), sequestered from A. ambrosioides. Flavonoids were value. also present in the mixture but were not characterized. 144 Rev. Soc. Quím. Méx. Vol. 47, Núm. 2 (2003) Manuel Aregullin and Eloy Rodriguez Fig. 1. 1a (left) Adult tortoise beetle Physonota arizonae with typical Cassidinae morphology. 1b (right) Larval stages of Physonota arizonae feeding on host plant Ambrosia ambrosioides and displaying defensive fecal shields (FS). Experimental evaporated to dryness in a rotavapor under vacuum. The residue was redissolved in methanol, the insoluble fraction Collection of Plant Material and Beetles. Ambrosia ambro- was discarded, and the filtrate evaporated to dryness to yield a sioides leaf material containing feeding Physonota arizonae gummy residue. beetles were collected from wild populations in washes, in the The residue was dissolved in methanol and applied to a Coyote Mountains off of Hwy 86, approximately 20 mi. west Sephadex LH-20 chromatographic column and eluted with of Tucson, Arizona during the months of July and August. methanol. Several fractions from the column were collected The leaf plant material was brought to the laboratory, and the according to their different fluorescence under longwave ul- beetles were removed manually and processed separately. The traviolet light. Two fractions showed to contain each one a leaf plant material was air-dried and ground prior to solvent discrete sesquiterpene lactone that upon spectral analysis were extraction, and from the beetles the exuviae and its resinous shown to be Damsin (1) and Damsinic acid (2). The structures coating were collected and extracted fresh with organic sol- of (1) and (2) were established by spectroscopic analysis and vents. comparison with authentic samples. Ambrosia ambrosioides Extraction and Chemical Analysis. Dried and ground leaf plant material (250 g) was extracted Results and discussion with 1500 mL of chloroform and magnetic stirring overnight. The chloroformic extract was filtered and the solvent evapo- Field observations have revealed the occurrence of the tortoise rated to dryness in a rotavapor under vacuum. The residue was beetle Physonota arizonae on wild populations of canyon rag- retaken in methanol to remove most of the hydrocarbons and weed (Ambrosia ambrosioides), suggesting high host-plant filtered. The filtrate was evaporated to dryness to yield 24 g specificity for this Asteraceae. All four life stages of the beetle (9.6 %) of methanol soluble crude extract. (i.e., eggs, larvae, pupae and adults) were present on the host The crude extract was dissolved in methanol and applied plant. Field observations also suggested that the appearance of to a Sephadex LH-20 chromatographic column and eluted the beetle on the plant is closely associated with the initiation with methanol. Fractions from the column were collected of the regional monsoon season that usually starts in July- according to their fluorescence under longwave light from a August [9]. We suspected that the highly conspicuous accumu- portable ultraviolet lamp. Fractions 1 and 2 showed to contain lation of fecal matter (primarily derived from plant material), a mixture of hydrocarbons that was not further characterized. in combination with a discrete defensive behavior by the Fraction 5 was shown to contain the sesquiterpene lactone nymphal stages, could be implicated in the chemical protection Damsin (1). Fraction 6 was shown to contain the sesquiter- of the beetle from potential predators (i.e., birds, lizards, etc.). pene lactone Damsinic acid (2). The structures of the two P. arizonae larvae, feeding on the plants, were collected sesquiterpene lactones were established by spectroscopic from wild populations of A. ambrosioides to obtain enough methods (i.e., UV, IR, 1H-NMR and 13H-NMR, and MS), and material for chemical analysis. It was found that the fecal comparison with authentic samples. Fractions 7-10 were excretions covering the urogomphi were essentially lipophilic shown