Antifeedants to Armyworms, Spodoptera lituraand Pseudaletia separata,from Bitter Gourd Leaves, Momordica charantia

Bitter gourd, Momordica charantia, was less palatable to two species of armyworms, Spodoptera litura and Pseudaletia separata, than two other cucurbitaceous plants. A methanol extract of M. charantia leaves inhibited feeding of the armyworm larvae. The two most active fractions obtained by silica gel chromatography were purified by HPLC. Momordicine II, a triterpene monoglucoside, was identified as an antifeedant compound from the more active of these fractions. The second active fraction led to the isolation of a new triterpene diglucoside. Fresh leaves of M. charantia contained ca. 0.3% of momordicine II. Momordicine II showed significant antifeedant effects on P. separata at concentrations of 0.02, 0.1, and 0.5% in artificial diets. Momordicine II caused a significant feeding reduction in S. litura only at the highest concentration (0.5%) tested. The difference in feeding response of the two armyworms to momordicine II may be related to the diversity in their host range.     

Antitermitic Activities of Abietane-type Diterpenes from <Emphasis Type="Italic">Taxodium distichum</Emphasis> Cones

Eight known abietane-type diterpenes were isolated from the weak acidic fraction of the n-hexane extract from cones of Taxodium distichum, one of the extant, living fossil conifers. They were identified as 6,7-dehydroroyleanone (1), taxodal (2), taxodione (3), salvinolone (4), 14-deoxycoleon U (5), 5,6-dehydrosugiol (6), sandaracopimaric acid (7), and xanthoperol (8). The structures of these compounds were determined by comparison of NMR spectral data with published data. The antitermitic (termicidal and antifeedant) activities of the compounds 1–8 against the subterranean termite, Reticulitermes speratus Kolbe, were evaluated. Compounds 1 and 3 showed potent termicidal activity, and 5 and 8 showed potent antifeedant activity. Compound 1 was found to be one of the representative bioactive compounds in the n-hexane extract of T. distichum cones. Compounds 1–8, with the exception of 7, were oxides of ferruginol (9). Therefore, the presence of various oxidation forms of the abietane-type structure reflects their various bioactivities.     

Oviposition stimulants for the tropical swallowtail butterfly,Papilio polytes,feeding on a rutaceous plant,Toddalia asiatica

In nature, Papilio polytes utilizes a limited range of rutaceous plants as hosts. We isolated and identified oviposition stimulants for the butterfly from the foliage of its primary host plant Toddalia asiatica. Females readily deposited eggs in response to a methanolic extract of the plant. Partition of the extract with organic solvents revealed that chemicals responsible for eliciting egg-laying resided in a water-soluble fraction. Further bioassay-guided fractionation of the active fraction by column chromatography, preparative TLC, and HPLC led to the isolation of two oviposition stimulants. One was isolated from an amphoteric fraction and identified as trans-4-hydroxy-N-methyl-L-proline [(–)-(2S,4R)-4-hydroxy-1-methyl pyrrolidine-2-carboxylic acid; HMP]. The other, isolated from an acidic fraction, was identified as 2-C-methyl-D-erythronic acid [(–)-(2R,3R)-2-methyl-2,3,4-trihydroxybutanoic acid; MEA]. HMP alone evoked significant oviposition-stimulatory activity, although this was much lower than that of the original water-soluble fraction. MEA, on the other hand, alone did not elicit positive responses from females. However, HMP, when assayed in combination with MEA, markedly enhanced the female response, and the mixture was as active in stimulating oviposition as were the original water-soluble fraction and the plant foliage. We conclude that HMP is a substance crucial for host recognition by females, while MEA is a synergistic stimulant involved in host recognition and/or preference.     

1-Cyano-2-Hydroxy-3-Butene, A Phytotoxin From Crambe (Crambe abyssinica) Seedmeal

Crambe (Crambe abyssinica) seedmeal was found to suppress seedling emergence and biomass accumulation when added to a sandy loam soil containing wheat (Triticum aestivum Cardinal) and hemp sesbania (Sesbania exahata) seeds. Hexane, CH₂Cl₂, MeOH, and water extracts of the seedmeal were prepared and bioassayed against wheat and velvetleaf (Abutilon theophrasti) radicle elongation. The CH₂Cl₂ extract was the most inhibitory, while the other extracts inhibited the bioassay species only slightly (MeOH) or not at all (hexane, water). Fractionation of the CH₂Cl₂ extract identified the major phytotoxin as l-cyano-2-hydroxy-3-butene (CHB), comprising 96.1% of the active CH₂Cl₂ fraction. Radicle elongation of wheat and velvetleaf were inhibited by CHB with I₅₀ values of 2.1 × 10^–4 M for wheat and 2.7 × l0^–3 M for velvetleaf.     

Baldcypress allelochemics and the inhibition of silkworm enteric microorganisms Some Ecological Considerations

Exposure ofBombyx mori larvae to 2-furaldehyde, a major volatile component of baldcypress heartwood,Taxodium distichum, resulted in in vivo inhibition of enteric microorganisms at concentrations (1–47 ppm) that were released naturally from heartwood. The 7 bacterial and 2 fungal enteric isolates were also inhibited in vitro at the same concentrations. It is suggested that inhibition of leaf surface micro-organisms or in vivo inhibition of silkworm enteric microflora, as a result of indirect or direct action of 2-furaldehyde, exacerbates the growth-inhibitory effects of this compound on larvae by reducing the microbial nutritional contribution. The ecological significance of insect enteric microbial inhibition by plant allelochemics is discussed.     

Components of Honeybee Royal Jelly as Deterrents of the Parasitic <Emphasis Type="Italic">Varroa</Emphasis> Mite, <Emphasis Type="Italic">Varroa destructor</Emphasis>

The parasitic mite Varroa destructor Anderson & Trueman reproduces on the immature stage of the honeybee, Apis mellifera L. Mites are found more often on drone brood than worker brood and only infrequently on queen brood. We investigated the chemical basis for the low incidence of mites on queen brood. V. destructor mites were deterred by a crude extract of royal jelly, a glandular secretion produced by nurse bees and fed to queen larvae. Bioassay-driven fractionation of the crude extract via column chromatography resulted in one active fraction that was as active as the crude extract. Compounds in the active fraction were identified using gas chromatography (GC) and coupled gas chromatography/mass spectrometry (GC-MS). Before injection, compounds were esterified with MeOH/sulfuric acid, followed by silylation of any hydroxyl groups present. The active fraction contained at least 22 compounds, all fatty acids, several of which contained an additional hydroxyl group on the alkyl chain. Synthesis of some of these compounds that are not commercially available is described. A synthetic mixture containing most of the compounds in the active fraction was as active as the active fraction in the bioassay.     

2-Furaldehyde from baldcypress

2-Furaldehyde was growth inhibitory and toxic to larvae ofBombyx mori at concentrations as low as 1 ppm. Baldcypress,Taxodium distichum, heartwood released this volatile at concentrations in excess of these levels. The adverse effect of this chemical on silkworms may partially account for the demise of the Georgia silkworm industry (circa 1765), after the construction of a baldcypress rearing facility.     

Cardenolides fromErysimum cheiranthoides: Feeding deterrents toPieris rapae larvae

Larvae of the cabbage butterfly,Pieris rapae, refuse to feed on the wild mustard,Erysimum cheiranthoides, due to the presence of alcoholextractable deterrents. The active components were extracted inton-BuOH, and this extract was separated into four fractions (I–IV) by reverse-phase HPLC. Fractions III and IV retained the feeding deterrent activity. The activity of fraction III was found to be due to the cardenolide diglycosides 1 and 2, which were previously reported as oviposition deterrents for gravidP. rapae butterflies. Three active compounds were isolated from fraction IV by column chromatography on silica gel followed by reverse-phase HPLC. These compounds were identified as a monoglycoside, digitoxigenin 3-O--D-glucoside (4), and two diglycosides, glucodigigulomethyloside (5) and glucodigifucoside (6). An additional cardenolide isolated from fraction II was identified as cheirotoxin (7). All compounds were identified by UV, NMR (¹H and¹³C), and mass spectrometry, as well as hydrolysis experiments. The feeding deterrent activity of these compounds was compared with that of related commercially available chemicals and other compounds isolated fromE. cheiranthoides.     

Chemicals Used for Host Recognition by the Granary Weevil Parasitoid Lariophagus distinguendus

In order to develop methods for mass rearing of the parasitic wasp Lariophagus distinguendus, we characterized and identified chemicals used by this parasitoid to recognize wheat grains infested by its host, larvae of the granary weevil, Sitophilus granarius, a major pest of stored grain worldwide. Bioassays revealed that drumming and drilling behavior of the parasitoids on grain models of filter paper treated with host feces was as intense as on host-infested grains. Thus, chemicals from feces are highly important to recognize infested grains. Extracts of the feces with hexane or dichloromethane applied on grain models were able to provoke drumming and drilling activity. Hexane extract of feces was as active as infested grain itself. Subsequent fractionation of the hexane extract by adsorption chromatography revealed that highest activity was recovered in the dichloromethane fraction. This fraction was characterized by the presence of -tocopherol, -tocopherol, -tocotrienol, cholesterol, ergostenol, and -sitosterol. Synthetic chemicals in proportions found in the active dichloromethane fraction stimulated drumming behavior in bioassays. The significance of these results with respect to the mass propagation of L. distinguendus as natural enemies for the control of the granary weevil is discussed.     

(Z)-8-heptadecene from infested cells reduces the reproduction of Varroa destructor under laboratory conditions

The parasitic mite Varroa destructor Anderson and Trueman, the most serious threat to apiculture in many countries of the world, reproduces inside honeybee brood cells. Previous research, using artificial cells for rearing the mite on an Apis mellifera larva, indicated that semiochemicals affecting the reproduction of Varroa destructor are released into such cells. In order to isolate these semiochemicals, infested artificial cells were extracted with hexane and the extract fractionated twice. Several unsaturated hydrocarbons were identified in the active fraction; some of them were released in higher amounts in case of infestation and were, therefore, bioassayed for their effect on the mite's reproduction. Of five alkenes tested under laboratory conditions, (Z)-8-heptadecene, caused a 30% reduction in the mean number of offspring of mites reared in cells treated with this compound.     

Evidence for trail-pheromone precursor in termiteReticulitermes speratus (Kolbe) (Rhinotermitidae: Isoptera)

Whole body extracts of the termite,Reticulitermes speratus, were subjected to various chemical operations and bioassays to examine the presence of trail-pheromone precursor. Fractions that mainly contained fatty acid esters were obtained from hexane extracts by means of silica gel column chromatography. Trail-following activity of the fractions was activated by alkaline hydrolysis, while the original fractions did not show any conspicuous activity. Bioassay showed that the activity of hydrolyzed product was approximately 20 times as high as the original hexane extract. This suggests that the precursor candidate could be stored in termite bodies as an esterified form. Chemical analyses revealed that the complete structure of the hydrolyzed product was coincident with that of the native pheromone ((Z,Z,E)-3,6,8-dodecatrien-1-ol).     

Antioxidant effect of the constituents of susabinori (Porphyra yezoensis)

The antioxidant activities of several extracts from Susabinori (Porphyra yezoensis) were measured by the ferric thiocyanate method and the thiobarbituric acid method. The methanol, acetone, ethyl acetate, and hexane extracts, and the chloroform-soluble and water-soluble fractions from the chloroform-methanol extract exhibited higher activities than α-tocopherol. The hot water extract showed little activity. Thin-layer chromatography analysis of the active extracts suggested the existence of several antioxidants. The activity of the chloroform soluble fraction was due to chlorophyll analogs. A strong antioxidant was isolated from the methanol extract, accompanied by several amino acids such as leucine and phenylalanine. This compound was identified as usujilene, a kind of mycosporine-glycine like amino acid.     

A neolignoid feeding deterrent againstLuehdorfia puziloi larvae (lepidoptera: Papilionidae) fromHeterotropa aspera,a host plant of sibling species,L. japonica

A feeding deterrent against larvae of a papilionid butterfly,Luehdorfia puziloi (Parnassiinae), a specialist onAsiasarum plants (Aristolochiaceae), was isolated from another aristolochiaceous plant,Heterotropa aspera. Antifeedant activity was exhibited by then-hexane-soluble fraction that proved to contain at least two active components. One of the deterrents was identified as a neolignan compound, asatone. The concentration of asatone inH. aspera was estimated at approximately 225 ppm, and larval feeding ofL. puziloi was significantly deterred at concentrations over 90 ppm. By contrast, asatone was not detectable (< 1 ppm, if any) in its host plant,Asiasarum sieboldii.     

Antitermitic activity ofLonchocarpus castilloi flavonoids and heartwood extracts

The heartwood of the tropical treeLonchocarpus castilloi Standley (Leguminosae) is highly resistant to attack by the drywood termitesCryptotermes brevis (Walker); nevertheless successive extraction with hexane, diethyl ether, acetone, methanol, and water reduced its resistance to these organisms. Antitermitic properties of the extracts were bioassayed using impregnated filter paper disks. Although the five extracts reduced both feeding and survival ofC. brevis, no significant differences among them were detected. Choice feeding tests showed that termites avoided eating the paper treated with the extracts. Two flavonoid compounds isolated from the heartwood, castillen D and castillen E, impregnated into filter paper showed concentration-dependent feeding deterrent activity, but were not toxic toC. brevis.     

Chemical constituents of an unacceptable crucifer,Erysimum cheiranthoides,deter feeding byPieris rapae

The wild cruciferErysimum cheiranthoides was found to contain extractable constituents that deterred feeding by larvae of the crucifer specialistPieris rapae when applied to cabbage leaf disks in both choice and nochoice bioassays. High-performance liquid chromatography was used to separate the extract into several fractions, two of which retained the feeding deterrent activity of the extract. UV-absorption spectra of the fractions suggested that one contained cardenolides similar or identical to those reported to deter oviposition byP. rapae onE. cheiranthoides. The other active fraction evidently contains a compound that deters larval feeding but not adult oviposition. The results suggest that the chemical defense ofE. cheiranthoides depends on two types of compounds acting on separate developmental stages of the insect.     

Using wood extracts to determine the feeding preferences of the western drywood termite,Incisitermes minor (Hagen)

Nymphs of the western drywood termite,Incisitermes minor (Hagen), were tested for their feeding preferences on wood and extracts of 11 tree species. The amount of wood consumed was inversely proportional to its specific gravity, but methanol extracts of least preferred woods were also least preferred when termites were confined to paper treated with extracts. In choice tests, only paper treated with extract of wood from which the colony developed and untreated and methanol-treated controls were significantly fed upon. Ponderosa pine extract applied to Douglas fir and sugar pine significantly decreased the amount of wood consumed. Resistance to termite feeding appeared to depend on the presence of repellent chemicals in the wood.     

Evidence for a multicomponent sex pheromone in the yellowheaded spruce sawfly

The existence of a female-produced sex pheromone in the yellowheaded spruce sawfly,Pikonema alaskensis (Rohwer) (Hymenoptera: Tenthredinidae) was demonstrated by field and greenhouse bioassays. Virgin females, their empty cocoons (with which they were confined during handling procedures), and the hexane extract of these cocoons were attractive in the field. The only Florisil fraction of this extract consistently attractive by itself was that eluted with hexane, but three, more polar fractions (eluted with 5%, 25%, and 50% ether in hexane) each synergized the hexane fraction, increasing bioassay responses 10–30 times. Fractions derived directly from virgin females yielded comparable results. The greenhouse data corroborated the field data, except that the 5% ether-hexane fraction, while very synergistic in the field, was consistently inactive in the greenhouse.     

Identification of sex pheromones from cowpea weevil,Callosobruchus maculatus,and related studies withC. analis (coleoptera: Bruchidae)

Female cowpea weevils,Callosobruchus maculatus, produce a sex pheromone that elicits orientation and sexual behavior in males. Bioassay-directed isolation of the sex pheromone was conducted and compounds in the active fraction were identified and synthesized. Volatiles were collected from individual virgin females by adsorption on filter paper dises and hexane extraction. A bioassay was used in which the locomotory response of single males in glass vials was recorded upon exposure to treatments or controls. Crude extracts were subjected to silica gel column chromatography with solvents of increasing polarity; all activity eluted with methanol. Activity in the highly polar methanol fraction suggested a carboxylic acid or a compound with multiple polar functionality. Acid-base partitioning of the crude extract isolated all activity in the acid fraction, confirming that the pheromone was a carboxylic acid. The acid fraction was further fractionated by preparative GC with a Carbowax column. The most active GC fraction contained the following five 8-carbon acids identified by GC-MS and comparison with synthetic candidates: 3-methyleneheptanoic acid, (Z)-3-methyl-3-heptenoic acid, (E)-3-methyl-3-heptenoic acid, (Z)-3-methyl-2-heptenoic acid, and (E)-3-methyl-2-heptenoic acid. Each of the synthetic acids was active individually for males, and combinations of two or more of the acid pheromones had an additive effect. Upwind flight responses to natural and synthetic pheromones were observed in a flight tunnel. (Z)-3-Methyl-2-heptenoic acid was previously identified as the sex pheromone for the relatedC. analis, but this and the other four acid pheromones fromC. maculatus were inactive for maleC. analis. There was no cross-attraction betweenC. maculatus andC. analis in reciprocal studies using extracted volatiles from females of both species, GC-MS analysis ofC. analis female volatiles failed to detect any of theC. maculatus compounds but did find an unidentified C-8 acid with a GC retention time different from any of theC. maculatus pheromones.This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or a recommendation for its use by USDA.     

Leaf surface extracts ofSolanum berthaultii hawkes deter colorado potato beetle feeding

Leaf rinses ofS. berthaultii PI 473334 with methylene chloride were deterrent to feeding by the Colorado potato beetle when applied toS. tuberosum tuber and leaf disks. When the leaf rinse was separated into its nonvolatile and volatile fractions and applied to tuber disks, the nonvolatile fraction was highly deterrent, while the volatile fraction reduced consumption, but not significantly compared to the controls. A hexane leaf rinse was not deterrent to feeding, while an acetone rinse was approximately twofold more deterrent than the methylene chloride rinse when applied to leaf disks. Three cycles of bioassay-guided, reversed-phase open-column fractionation of an acetone leaf rinse yielded a relatively polar fraction with low deterrent activity, and two nonpolar fractions exhibiting higher specific activity. Reversed-phase preparative HPLC of these fractions yielded seven active fractions among the 10 assayed. Subsequent analytical HPLC indicated that two fractions each contained a single UV-absorbing compound, while another represented a mixture of at least four compounds. The remaining fractions were composed of complex mixtures of possibly ionic or polymeric compounds that were poorly resolved by HPLC.     

Chemical induction of feeding in California spiny lobster,Panulirus interruptus (Randall):

Molecular weight fractions of abalone muscle were tested for the ability to induce appetitive feeding and locomotor behavior in the spiny lobster,Panulirus interruptus. Fractions of <1000, 1000–10,000 and >10,000 daltons were isolated by ultrafiltrations and gel chromatography from a seawater extract of abalone muscle. The two lower-molecular-weight fractions (<1000, 1000–10,000) were the least stimulatory of the three fractions tested, and both were ineffective as feeding stimulants. Solutions combining any two of the three isolated fractions produced behavioral activity equal to that caused by whole extract; thus, no single fraction was essential to the stimulatory capacity of abalone. The >1000-dalton fraction was also highly stimulatory, meaning that large and not small molecules were essential in initiating feeding. Finally, a 75% ethanol-insoluble component of the <10,000 fraction was effective, while the ethanol-soluble portion was not. Since the insoluble material consisted predominantly of peptides and polypeptides, it is probable that these molecules act as principal stimulants in abalone muscle.