Caffeoyltartronic acid from catnip (Nepeta cataria): A precursor for catechol in lubber grasshopper (Romalea guttata) defensive secretions

Adults of the lubber grasshopper (Romalea guttata) secrete increased amounts of catechol from their defensive glands when fed diets containing only catnip leaves (Nepeta cataria). Model compound bioassays showed that these insects were able to sequester and biomagnify simple phenols, such as catechol and hydroquinone, in their defense gland secretions. Excessive catechol secretions from caffeic acid-fortified diets indicated metabolic pathways exist to perform efficiently more complex biochemical conversions. Reverse-phase HPLC of methanol extracts of catnip revealed only one major caffeoyl-polyphenol as a possible precursor for the observed elevated catechol secretions, when this plant is fed to lubbers. The compound was shown to be caffeoyltartronic acid (CTA). During analysis of CTA by probe-MS or gas chromatography (of its silylated derivative), CTA decomposed by loss of carbon dioxide to form caffeoylglycolic acid (CGA), making identification by these methods ambiguous. Only fast atom bombardment mass spectrometry (FAB-MS, negative mode) gave a true molecular weight. Groundivy (Glecoma hederacea), a relative of catnip, was also shown to contain CTA. The mung bean (Phaseolus radiatus=Vigna radiata), a species totally unrelated to catnip, is the only other reported plant source of CTA. Catnip leaves were found to contain about twice as much CTA as mung bean leaves.     

Identification and Function of Prothoracic Exocrine Gland Steroids of the Dytiscid Beetles Graphoderus cinereus and Laccophilus minutus

The chemical composition of the prothoracic defensive secretion of the water beetles Graphoderus cinereus and Laccophilus minutus was examined by gas chromatographic–mass spectrometric analysis of trimethylsilylated gland extracts. The main components are 3,11-dihydroxy-5-pregnan-20-one in G. cinereus and 3,12-dihydroxy-5-pregnan20-one in L. minutus. Fully saturated pregnanes have not been found in the prothoracic defensive glands of dytiscids before. Based on tests with synthetic compounds, their biological role was examined in a feeding assay with the minnow Phoxinus phoxinus. Agar pellets containing either steroid strongly deterred feeding.     

Defensive role ofAllium sulfur compounds for leek mothAcrolepiopsis assectella Z. (Lepidoptera) against generalist predators

It has been shown previously that sulfur volatiles produced byAllium plants affect the behavior of their specialist phytophages and of their specialist entomophages. The action of these compounds in protecting the leek mothAcrolepiopsis assectella against generalist entomophages was studied in comparison to the proposed original defensive role of these compounds against generalist herbivorous insects. Two ants species,Formica selysi andF. fusca, were used as generalist predators. Six behavioral criteria of the predatory behavior of the ants were studied in presence of the last-instar caterpillars (C₅). C₅ reared on artificial diets with or without leek components were tested, as well as C₅ soaked in frass of leek-reared caterpillars or disulfide solutions. In addition, the response of the ants to pure chemicals found in leek was studied using honey solutions with or without sulfur compounds. The sulfur allelochemicals ofAllium plants have a negative action on predatory ants. Interestingly, the nonvolatile precursors of sulfur volatiles ofAllium plants seem to have a protective role for their phytophagous insects against generalist entomophages.     

Effects of Quantitative Variation in Allelochemicals in <Emphasis Type="Italic">Plantago lanceolata</Emphasis> on Development of a Generalist and a Specialist Herbivore and their Endoparasitoids

Studies in crop species show that the effect of plant allelochemicals is not necessarily restricted to herbivores, but can extend to (positive as well as negative) effects on performance at higher trophic levels, including the predators and parasitoids of herbivores. We examined how quantitative variation in allelochemicals (iridoid glycosides) in ribwort plantain, Plantago lanceolata, affects the development of a specialist and a generalist herbivore and their respective specialist and generalist endoparasitoids. Plants were grown from two selection lines that differed ca. 5-fold in the concentration of leaf iridoid glycosides. Development time of the specialist herbivore, Melitaea cinxia, and its solitary endoparasitoid, Hyposoter horticola, proceeded most rapidly when reared on the high iridoid line, whereas pupal mass in M. cinxia and adult mass in H. horticola were unaffected by plant line. Cotesia melitaearum, a gregarious endoparasitoid of M. cinxia, performed equally well on hosts feeding on the two lines of P. lanceolata. In contrast, the pupal mass of the generalist herbivore, Spodoptera exigua, and the emerging adult mass of its solitary endoparasitoid, C. marginiventris, were significantly lower when reared on the high line, whereas development time was unaffected. The results are discussed with regards to (1) differences between specialist and generalist herbivores and their natural enemies to quantitative variation in plant secondary chemistry, and (2) potentially differing selection pressures on plant defense.     

Reduction in diet breadth results in sequestration of plant chemicals and increases efficacy of chemical defense in a generalist grasshopper

The lubber grasshopper,Romalea guttata, is a generalist feeding on a broad diet of many herbaceous plant species and has a metathoracic defensive secretion normally containing phenolics and quinones synthesized by the insect. When insects were reared on a restricted diet of wild onion, they sequestered sulfur volatiles from the plant into their defensive secretions. These compounds were not detected by gas chromatography-mass spectroscopy in secretions of insects on an artificial diet or a natural, generalist diet of 26 plants that included wild onion as a component, nor were they present in secretions from field-collected insects. Defensive secretions of insects reared on wild onion were significantly more deterrent, by as much as an order of magnitude, to two species of ant predators than secretions from insects on either of the other two diets, despite a reduction in the concentration of autogenous defensive chemicals in secretions of insects on the onion diet. Sequestration of plant chemicals that increased defensive efficacy occurred when diet breadth was reduced. We suggest that this occurs because under conditions of specialization, plant secondary metabolites are more likely to be ingested and bioaccumulated in sufficient concentrations to have biological activity against predators. What we define as casual bioaccumulation of bioactive plant chemicals following dietary specialization may lead to evolution of sequestered defense syndromes in insects, and this process may not necessarily require specific adaptation to or coevolution with a toxic host plant.     

Defensive secretions of three species ofAcilius (Coleoptera: Dytiscidae) and their seasonal variations as determined by high-pressure liquid chromatography

A rapid, sensitive, stable, and quantitative high-pressure liquid chromatographic technique was developed for the analysis of defensive secretions obtained from the pygidial and prothoracic glands of dytiscids. Methods were developed for both normal phase (Porasil) and reverse phase (Bondapak C₁₈) columns. The applicability of this technique was demonstrated when defensive compounds ofAcilius semiculcatus, A. sylvanus andA. mediatus were isolated, identified, and quantitated. No major differences were found in the composition of the defensive secretions between the three species. The seasonal defensive titer ofA. semisulcatus was determined from June through October 1977. The pygidial defensive agents (benzoic acid,p-hydroxybenzaldehyde, and methylp-hydroxybenzoate varied from 9.0 to 67.8 g and exhibited a maximum in July, and a steroid from the prothoracic gland varied from 7.1 to 33.2 g and was maximum in October.     

Larval exposure to oviposition deterrents alters subsequent oviposition behavior in generalist,Trichoplusia ni and specialist,Plutella xylostella moths

The present study was undertaken to determine the effects of larval feeding experience on subsequent oviposition behavior of the resulting moths. Larvae of the cabbage looper (Trichoplusia ni, Noctuidae) and the diamondback moth (Plutella xylostella, Plutellidae) were exposed to the phenylpropanoid allelochemical trans-anethole (at 100 ppm fw in artificial diet) or the limonoid allelochemical toosendanin (10 ppm sprayed on cabbage leaves). Both compounds had been shown to deter oviposition in naïve moths in previous choice tests. Moths developing from experienced larvae (both sexes) showed a decrease in oviposition deterrence response when given a choice between control and treated leaves, unlike naïve moths. This phenomenon, analogous to habituation to feeding deterrents in lepidopteran larva, occurred irrespective of duration of feeding on the deterrent compound. We also observed that F₁larvae resulting from experienced moths (previously exposed to toosendanin as larvae) grew as well on toosendanin-treated foliage as on control foliage. In contrast, growth of F₁larvae from naïve moths was significantly impaired by toosendanin. These results demonstrate that host-selection behavior in cabbage looper (a generalist) and diamondback moth (a specialist) may be shaped by feeding experience according to Hopkins' Host Selection Principle in addition to chemical legacy.     

The “Raison D'être” of pyrrolizidine alkaloids inCynoglossum officinale: Deterrent effects against generalist herbivores

In this study we tested whether pyrrolizidine alkaloids (PAs) ofCynoglossum officinale serve as antifeedants against herbivores. Total PA N-oxide extracts of the leaves significantly deterred feeding by generalist herbivores. Specialist herbivores did not discriminate between food with high and low PA levels. Three PAs fromC. officinale, heliosupine, echinatine, and 3-acetylechinatine, equally deterred feeding by the polyphagous larvae ofSpodoptera exigua. Although the plants mainly contain PAs in their N-oxide form, reduced PAs deterred feeding byS. exigua more efficiently than PA N-oxides. On rosette plants, the monophagous weevilMogulones cruciger significantly consumed more of the youngest leaves, which had the highest PA level and the highest nitrogen percentage. Larvae ofEthmia bipunctella, which are oligophagous within the Boraginaceae, did not discriminate between leaves. All generalist herbivores tested significantly avoided the youngest leaves with the highest PA levels. In the field, the oldest leaves also were relatively more damaged by herbivores than the youngest leaves. It is hypothesized that the skewed distribution of PAs over the leaves of rosette plants reflects optimal defense distribution within the plant.     

Chemistry and Defensive Efficacy of Secretion of Burrowing Bug (Sehirus cinctus cinctus)

Adult Sehirus cinctus cinctus emit a volatile secretion from their metathoracic scent glands when tactually stimulated. We identified the volatile components by gas chromatography, high-performance liquid chromatography, and mass spectrometry. The secretion of both sexes contained (1R)-(+)--pinene, (1S)-(–)--pinene, -myrcene, (R)-(+)-limonene, and -terpinolene. Two additional compounds were found in only female secretions: (E)-2-hexenyl acetate and (E)-2-octenal. We also tested the defensive capability of this insect by offering it to various predators. Anoles, starlings, and a killdeer rejected S. c. cinctus after an initial sampling. These findings suggest that the secretion plays a defensive role.     

A long-range attractant kairomone for egg parasitoidTrissolcus basalis,isolated from defensive secretion of its host,Nezara viridula

A short-chain ,-unsaturated aldehyde, (E)-2-decenal, present in the defensive metathoracic gland ofNezara viridula (L.) (Heteroptera: Pentatomidae), stimulates a behavioral response in the egg parasitoidTrissolcus basalis (Woll.) (Hymenoptera: Scelionidae). Preliminary studies showed thatT. basalis are attracted to an area containing adultN. viridula, but we also found that femaleT. basalis would examine and probe glass beads coated with an acetone extract of the metathoracic gland from males or females. Using this bioassay, the kairomone was isolated by bioassay directed by preparative gas chromatography and identified by NMR and mass spectrometry as (E)-2-decenal. The biological activity of the identified aldehyde was compared with analogs to determine specificity. An unstable Z isomer was found to be more active but not present in detectable or behaviorly relevant levels in the host, based on the bell-shaped dose-response curve of the two isomers. An investigation was also designed to determine if theE isomer was also responsible for the egg recognition kairomone activity previously reported. However, no 2-decenal isomers were detected in host egg extracts and the chemical characteristics of the 2-decenal isomers differ from the unidentified egg recognition kairomone. The role of the (E)-2-decenal in attracting femaleT. basalts toN. viridula was demonstrated in a Y-tube olfactometer; this alk-2-enal appears to act as a long-range kairomone orientingT. basalis toNezara populations.     

(6Z,9Z-3R,4S)-Epoxy-heptadecadiene: major sex pheromone component of the larch looper,Semiothisa sexmaculata (Packard) (Lepidoptera: Geometridae)

Gas chromatographic-electroantennographic analysis (GC-EAD) of female larch looper,Semiothisa sexmaculata (Packard), gland extracts revealed two EAD-active compounds. Retention index calculations, GC-mass spectroscopy in selected ion monitoring mode, and GC-EAD analysis of authentic standards identified the compounds as (3Z,6Z,9Z)-heptadecatriene (3Z,6Z,9Z-17H) and (6Z,9Z)-cis-3,4-epoxy-heptadecadiene (6Z,9Z-cis-3,4-epoxy-17H). Chirality determination of the monoepoxydiene in gland extracts was impeded by small quantities, but field experiments indicated that maleS. sexmaculata were most strongly attracted to enantiomerically enriched 6Z,9Z-3R,4S-epoxy-17H (69% ee), while maleS. neptaria (Guenée) responded well to various blends of theR,S- and S,R-epoxide enantiomers. Binary combinations of theR,S-epoxide enantiomer with 3Z,6Z,9Z-17H significantly inhibited response by maleS. sexmaculata, but strongly enhanced attraction of sympatric maleS. marmorata Ferguson. Enantiomerically enriched 6Z,9Z-3R,4S-epoxy-17H can be used as a trap bait to monitor populations of the larch-defoliatingS. sexmaculata. Whether 6Z,9Z-3R,4S-epoxy-17H serves as single component sex pheromone inS. sexmaculata or small amounts of 6Z,9Z-3S,4R-epoxy-17H synergize or suppress optimal attraction, will be tested as chirally pure monoepoxydienes become available.     

The Iridoid Glucoside,Antirrhinoside, from <Emphasis Type="Italic">Antirrhinum majus</Emphasis> L. has Differential Effects on Two Generalist Insect Herbivores

The iridoid glucoside, antirrhinoside, is constitutively distributed throughout Antirrhinum majus L. in a manner consistent with its possible role as an allelochemical, but there is no evidence that it has a defensive function with respect to insect herbivory. To address this question, two generalist herbivores, Lymantria dispar L. (gypsy moth) and Trichoplusia ni Hübner (cabbage looper) were chosen for feeding trials on excised whole leaves of A. majus and in artificial diet assays. In leaf excision feeding trials, fourth instar gypsy moth rejected, without sampling, the leaves of A. majus regardless of what node the leaf was excised from. In contrast, fourth instar cabbage looper readily fed on the excised leaves, and antirrhinoside was not found in their bodies or feces (frass) as determined by thin layer and high-pressure liquid chromatography. In the leaf and diet assays, a second major leaf iridoid in A. majus, antirrhide, was found in both cabbage looper and gypsy moth frass. In diet feeding assays, the growth of gypsy moth and cabbage looper were not inhibited by methanol extracts, iridoid fractions, or pure antirrhinoside at concentrations of 0.6% in diet, but cabbage looper growth was enhanced. At an antirrhinoside concentration of 3.3% in diet, gypsy moth growth was reduced, whereas cabbage looper growth again increased significantly relative to the control. It is likely that antirrhinoside functions as defense against herbivory for one generalist insect herbivore but also, at low concentrations, enhances the growth of another.     

Homogeneous asymmetric hydrogenation ofo-chloroacetophenone to enantiomerically pureo-chloro-(1-phenyl)ethanol catalyzed by BINAP-Ru(II) complex

The BINAP-Ru(II) catalyst (2,2-bis(diphenylphosphino)-1,1-binaphthyl)chloro(p-cymene)rutheniun chloride is found to be highly active and enantioselective for homogeneous asymmetric hydrogenation of o-chloroacetophenone to optically pureo-chloro-(1-phenyl)ethanol. In contrast to results of Noyori and coworkers, no organic and inorganic bases are required to obtain high activities and enantioselectivities     

The influence of a queen-produced substance, 9HDA,on swarm clustering behavior in the honeybeeApis mellifera L.

The effect of enantiomers of the queen-produced substance, 9-hydroxy-(E)-2-decenoic acid (9HDA) on swarm clustering behavior of the honeybeeApis mellifera was studied. Caged queens were removed from the swarms at the start of each test and were replaced with small Petri dishes containing one of the following treatments: 100 gS(+) enantiomer of 9HDA, 100 gR(-) enantiomer of 9HDA, 200 g racemic (R, S) 9HDA, and a vehicle-treated control. Each swarm was considered to have dispersed when it had lost 50% of its starting weight. All treatments with 9HDA resulted in significantly longer swarm aggregation when compared with the control. Enantiomers were not shown to have different effects at theP 0.05 level of significance. However, observations on swarm behavior indicated that theR(-) enantiomer was the most active in retarding swarm dispersal.     

Effects of diet breadth on autogenous chemical defense of a generalist grasshopper

The lubber grasshopper,Romalea guttata, produces a metathoracic defensive secretion containing primarily phenolics and quinones. This insect feeds on a wide range of plant species. Insects reared on an artificial diet and a diet of onion,Allium canadense, had secretions that contained fewer compounds, lower concentrations of compounds, and markedly altered relative composition of components compared to insects reared on a varied diet of 26 plant species that included onion. The study demonstrates that diet breadth has a major effect on the quality and quantity of the autogenous defensive secretion of this generalist herbivore. The results are compared to diet effects known in chemically defended specialists. Two possible mechanisms explaining the effects of diet breadth are proposed: one involves changes in precursor availability with changing diet breadth; the other suggests that physiological stress due to diet restriction changes allocation of resources to chemical defense.     

Volatile glandular secretions of three species of new world army ants,Eciton burchelli,Labidus coecus,andLabidus praedator

The Dufour glands of workers ofEciton burchelli contain a mixture of small quantities of oxygenated compounds, some of which are derived from terpenes, and C₁₇-C₂₅ hydrocarbons. The secretion of the Dufour glands of soldiers was either similar to that of workers, with geranylacetone a significant component, or they contained geranyllinalool in large amounts. The glands of workers and soldiers ofLabidus praedator andLabidus coecus contained (E)--ocimene, a new substance for the Dufour glands of ants. 4-Methyl-3-heptanone was the dominant compound in the mandibular glands ofE. burchelli andL. coecus. Skatole and indole were found in the gasters ofL. praedator, and skatole was present in the venom glands of some soldiers ofE. burchelli.     

Microsomal oxidation of allelochemicals in generalist (Spodoptera frugiperda) and semispecialist (Anticarsia gemmatalis) insect

Midgut microsomes prepared from larvae of the fall armyworm [Spodoptera frugiperda (J.E Smith)], a generalist insect, and the velvetbean caterpillar (Anticarsia gemmatalis Hubner), a semispecialist, were used to study their oxidative activity toward a variety of allelochemicals. Allelochemicals such as terpenoids, alkaloids, indoles, glucosinolates, flavonoids, coumarins, cardenolides, phenylpropenes, and a ketohydrocarbon were all metabolized by the microsomal cytochrome P-450 monooxygenases in both species. Fall armyworm microsomes oxidized monoterpenes more favorably than other types of terpenes, indicating a preference for these compounds. In all instances, the oxidative metabolism of these allelochemicals can be induced by dietary allelochemicals such as indole 3-carbinol, indole 3-acetonitrile, menthol, flavone, or peppermint oil ranging from 1.3- to 9.5-fold. In the case of certain triterpenes, tetraterpene, alkaloid, coumarin, and cardenolides, metabolic activity can only be observed after induction. The monooxygenase activities toward these allelochemicals were generally higher in the generalist than in the semispecialist. These findings provide strong evidence that microsomal monooxygenases play an important role in the detoxification of plant toxins and hence host-plant selections in herbivorous insects.     

Pentatomid natural products

In addition to the primarily defensive metathoracic glands, adult Pentatomoidea possess a pair of active exocrine glands that open between the III and IV abdominal tergites. In the southern green stink bug,Nezara viridula, and other phytophagous species examined, the glands are small (< 10 g secretion/individual) and of approximately equal size in both sexes. In some, but not all, of the predaceous pentatomids (Asopinae), the III-IV dorsal abdominal glands are small in females (< 10 g secretion/individual) and extremely large in males (>500 g secretion/individual). Using a GC-MS system, the secretion from both males and females ofN. viridula (Pentatominae) was found to contain (E)-2-hexenal, hexanal, 1-hexanol, andn-tridecane. Females contained about three times moren-tridecane than males. The capacious glands ofPodisus maculiventris (Asopinae) males produce (E)-2-hexenal, benzyl alcohol, -terpineol, linalool, terpinen-4-ol, andcis-piperitol. The composition of the previously unanalyzed secretions from the adult III-IV dorsal abdominal glands is compared and contrasted to that of secretions from the metathoricic gland, and the role of coexisting exocrine glands in adult Heteroptera is discussed.     

Sticky secretion from two pairs of defensive glands of rove beetleDeleaster dichrous (Grav.) (Coleoptera: Staphylinidae)

The phylogenetically primitive rove beetleDeleaster dichrous (Grav.) (Oxytelinae) has been shown for the first time to possess two pairs of neighboring abdominal glands which are depleted simultaneously on molestation. The morphology of these glands is described. The defensive constituents of theDeleaster glands were elucidated directly from the mixtures by gas chromatographic-mass spectroscopic methods and microchemical reactions. The paired whitish glands secrete iridodial, which polymerizes on exposure to air to form an adhesive that probably deters small predatory arthropods. The red gland system ofD. dichrous contains the toxicp-toluquinone and a variety of isopropyl andsec-butyl esters. Artificial quinoid ester mixtures simulating the secretion ofD. dichrous showed only weak effects on mortality ofLucilia larvae in comparison with more effective secretions of phyiogenetically derived Oxytelinae. The secretion of the primitive genusDeleaster is characterized chemotaxonomically by , -unsaturated C₁₂ acids and esters, which are postulated as precursors for the characteristic defensive compounds of the derived species, thus indicating a clear evolutionary trend at the micromolecular level.     

Iridoid glycoside sequestration byThessalia leanira (Lepidoptera: Nymphalidae) feeding onCastilleja integra (Scrophulariaceae)

A small population of a polyvoltine checkerspot butterfly,Thessalia leanira fulvia (also known asChlosyne leanira ssp.fulvia), was found to useCastilleja integra as a larval food plant at a localized site (Burnt Mill) southwest of Pueblo, Colorado. Field-captured adult butterflies contained the major iridoid glycosides (catalpol and macfadienoside) of theCastilleja. The content of a third iridoid glycoside, methyl shanzhiside, was also relatively high in the collected butterflies even though most individualCastilleja plants at Burnt Mill contained little or no methyl shanzhiside. Only a few plants, restricted to a small area, did contain appreciable methyl shanzhiside. Most of the plants that lacked the ester methyl shanzhiside contained shanzhiside, the corresponding free carboxylic acid.Thessalia larvae did not normally methylate the acid to produce methyl shanzhiside. Larvae that stopped feeding at an early instar, but yet survived several weeks, did contain major amounts of methyl shanzhiside. It is suggested that only larvae that overwinter or otherwise enter diapause convert shanzhiside to methyl shanzhiside. TheCastilleja food plant also contained iridoids other than catalpol and macfadienoside, sometimes in major amounts, but these were never found in larvae, pupae, or butterflies.Paper 27 in the series Chemistry of the Scrophulariaceae. Paper 26: Stermitz, F.R., Foderaro, T.A., and Li, Y.-X., 1993.Phytochemistry 32:1151