Scott R. Smedley

Sodium Uptake by Puddling in a Moth

Male Lepidoptera commonly visit stands of water to drink, a behavior known as puddling. Males of the notodontid moth Gluphisia septentrionis routinely puddle for hours, imbibing hundreds of gut-loads and voiding the fluid as repetitive anal jets. Cationic analyses showed puddling to lead to systemic sodium gain, a potential benefit to Gluphisia, whose larval food plant is low in sodium. Male Gluphisia are specialized for puddling, possessing a wide oral slit and a highly expanded enteric surface. The acquired sodium is transferred to the female at mating, for eventual incorporation into the eggs. Sodium acquisition may be the primary function of puddling in Lepidoptera.

Pinoresinol: A lignol of plant origin serving for defense in a caterpillar

Pinoresinol, a lignan of wide distribution in plants, is found to occur as a minor component in the defensive secretion produced by glandular hairs of caterpillars of the cabbage butterfly, Pieris rapae. The compound or a derivative is appropriated by the larva from its normal food plant (the cabbage, Brassica oleracea). Pinoresinol was shown to be absent from the secretion if the larva was given a cabbage-free diet but present in the effluent if that diet was supplemented with pinoresinol. Pinoresinol is shown to be a feeding deterrent to ants (Formica exsectoides), indicating that it can complement the defensive action of the primary components of the secretion, a set of previously reported lipids called mayolenes. In the test with F. exsectoides, pinoresinol proved to be more potent than concomitantly tested mayolene-16.

Mayolenes: Labile defensive lipids from the glandular hairs of a caterpillar (Pieris rapae)

Larvae of the European cabbage butterfly, Pieris rapae (Pieridae), are beset with glandular hairs, bearing droplets of a clear oily secretion at their tip. The fluid consists primarily of a series of chemically labile, unsaturated lipids, the mayolenes, which are derived from 11-hydroxylinolenic acid. In bioassays with the ant Crematogaster lineolata, the secretion was shown to be potently deterrent, indicating that the fluid plays a defensive role in nature.

Firefly Toxicosis in Lizards

Ingestion of fireflies of the genus Photinus (Lampyridae) can be lethal to Australian lizards of the genus Pogona (Agamidae), probably because of the poisonous steroidal pyrones (lucibufagins) that these fireflies contain. One Photinus may suffice to kill a Pogona. Captive Pogona kept as pets need to be shielded from firefly ingestion. African chameleons (Chamaeleo; Chamaeleonidae) appear also to be vulnerable to Photinus toxicosis.

Defensive secretion of two notodontid caterpillars (Schizura unicornis, S. badia)

The cervical gland secretion of larvae ofSchizura unicornis andS. badia (Lepidoptera: Notodontidae) contains formic acid, acetic acid, and a mixture of lipophilic compounds, including 2-alkanones, 2-alkanols, and formates of the alkanols. InS. unicornis, the secretion also contains severalω-monounsaturated analogs of the alcohols, ketones, and formates. The absolute configuration of two of the alcohols (2-tridecanol and 2-pentadecanol) was established asS in both species. The larvae spray their secretion when physically disturbed, aiming it accurately in the direction of the offending agent.

Chemical defense of a rare mint plant.

SummaryAnalyses of leaf extracts ofDicerandra frutescens, a highly aromatic mint plant from central Florida listed as an endangered species, revealed presence of 12 closely related monoterpenes. The principal of these, (+)—trans-pulegol, is a new natural product, the synthesis of which is described. The terpenes are produced in glandular capsules that release their contents upon injury of the leaf. Data from bioassays with ants and cockroaches indicate that the terpenes serve for defense against insects.Dicerandra does, however, have a leaf-eating enemy, the caterpillar of a pyralid moth,Pyrausta panopealis. The discovery of a new natural product from an endangered species raises questions about the chemical implications of species extinction.

2D NMR-spectroscopic screening reveals polyketides in ladybugs

Small molecules of biological origin continue to yield the most promising leads for drug design, but systematic approaches for exploring nature’s cache of structural diversity are lacking. Here, we demonstrate the use of 2D NMR spectroscopy to screen a library of biorationally selected insect metabolite samples for partial structures indicating the presence of new chemical entities. This NMR-spectroscopic survey enabled detection of novel compounds in complex metabolite mixtures without prior fractionation or isolation. Our screen led to discovery and subsequent isolation of two families of tricyclic pyrones in Delphastus catalinae, a tiny ladybird beetle that is employed commercially as a biological pest control agent. The D. catalinae pyrones are based on 23-carbon polyketide chains forming 1,11-dioxo-2,6,10-trioxaanthracene and 4,8-dioxo-1,9,13-trioxaanthracene derivatives, representing ring systems not previously found in nature. This study highlights the utility of 2D NMR-spectroscopic screening for exploring nature’s structure space and suggests that insect metabolomes remain vastly underexplored.

ABSOLUTE CONFIGURATION OF INSECT-PRODUCED EPILACHNENE

Samples of (R) and (S)-epilachnene [(5Z)-11-propyl-12-azacyclotetradec-5-en-14-olide] were synthesized from (R) and (S)-norvaline. The diastereomericα-methoxy-α-trifluoromethylphenylacetyl amides of these synthetic samples, prepared using (S) α-methoxy-α-trifluoromethylphenylacetyl chloride, were well resolved by gas chromatography. Analogous derivatization and gas chromatographic analysis of a sample of epilachnene from the pupal secretion of the coccinellid beetle, Epilachna varivestis, established that the natural product is (S)-epilachnene.

Biosynthesis of epilachnene, a macrocyclic defensive alkaloid of the Mexican bean beetle ☆

Abstract The carbon skeleton of the azamacrolide epilachnene, the principal defensive alkaloid of Epilachna varivestis pupae, can be derived from oleic acid and serine. Analytical evidence from three experiments in which insects were fed [2H35]octadecanoic acid, (Z)-9-[11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,18-2H17]octadecenoic acid and (Z)-9-[11,11,12,12,13,13,14,14,16,16,17,17,18,18,18-2H15]octadecenoic acid, indicates that only the C-15 methylene group of oleic acid is involved in the mechanism leading to carbon-nitrogen bond formation in epilachnene. Support for this scheme is provided by the observation of an unusual ion at m z 170 in the electron-ionization mass spectrum of epilachnene, rationalized as CH2CHCOOCH2CH2NH+CHCH2CH2CH3.

Tocopheryl acetates from the pupal exocrine secretion of the squash beetle, Epilachna borealis (Coccinellidae).

The oily droplets on the pupal integumental hairs of the squash beetleEpilachna borealis contain a mixture of α-, β-, γ-, and δ-tocopheryl acetates as major constituents. In addition, the secretion contains a number of minor components that appear to be dehydrocongeners of the major components. This is the first report of the occurrence of acetate esters of any tocopherol in nature.