(Z)-oxacyclotridec-10-en-2-one does not appear to be responsible for resistance to adult alfalfa weevil feeding exhibited byMedicago rugosa

Steam distillate prepared from leaves ofMedicago rugosa Desr. could inhibit feeding by adult alfalfa weevils (Hypera postica (Gyll.) on membrane filters, whereas an equivalent amount of steam distillate prepared usingM. sativa L. had no effect on weevil feeding. Earlier work established that a 12-carbon lactone, (Z)-oxacyclotridec-10-en-2-one, was responsible for the feeding deterrent properties of the steam distillate fromM. rugosa. The concentration of this volatile varied with plant age and leaf position. The maximum concentration in leaves ofM. rugosa (area basis) was estimated, on the basis of tests using an inert substrate, to be too low to cause a detectable inhibition of feeding. No correlation between lactone content and weevil feeding was detected when leaves from similar positions on plants of different ages were used in a multiple choice bioassay. Although small amounts (< 12.5g) of (Z)-oxacyclotridec-10-en-2-one can inhibit adult alfalfa weevil feeding on 13-mm-diameter membrane filters, because leaf concentrations (area basis) of this compound are lower than required to cause a detectable inhibition of feeding on the inert substrate, and because concentrations do not correlate with weevil feeding, it is unlikely that this lactone is responsible for resistance to adult alfalfa weevil feeding exhibited byM. rugosa.Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the USDA and does not imply approval to the exclusion of other products or vendors that may also be suitable.Technical paper No. 9416 of the Agricultural Experiment Station, Oregon State University, Corvallis, Oregon 97331.     

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.     

Technique for injecting intact glands for analysis of sex pheromones of Lepidoptera by capillary gas chromatography

The structure elucidation of sex pheromones of Lepidoptera by a solid-sample injection technique in conjunction with capillary gas chromatography is described. The applicability of this method in GC and GC-MS modes was demonstrated by reanalyzing the sex attractants of females ofOstrinia nubilalis andBombyx mori. The pheromone complex ofMamestra brassicae was reinvestigated and (Z)-9-hexadecenyl acetate and (Z)-11-hexadecenol were found in addition to already known pheromone components of this species. By using the solid-sample injection, the exact site of pheromone release could be determined inM. brassicae.Pheromones 52. Pheromones, 51: Bestmann, H.J., and Schmidt, M. 1985.Tetrahedron Lett 26:6171–6174.     

Nerolidol: An antifeeding sesquiterpene alcohol for gypsy moth larvae fromMelaleuca leucadendron

A systematic procedure is reported for the isolation of a feeding deterrent, (E,S)-nerolidol (I), fromMelaleuca leucadendron leaves for the gypsy moth larvae. Testing of the related alcohols, farnesol (II) and geraniol (III) showed them to be deterrent, but the simpler isoprene-related compounds, 2-methyl-3-buten-2-ol andt-amyl alcohol were inactive.     

Neonate Silkworm (<Emphasis Type="Italic">Bombyx mori</Emphasis>) Larvae Are Attracted to Mulberry (<Emphasis Type="Italic">Morus alba</Emphasis>) Leaves with Conspecific Feeding Damage

The silkworm Bombyx mori is a molecular genetic model for the Lepidoptera. Its odorant receptor genes have been described, and preliminary studies suggest that several are expressed specifically in the larval caterpillar stage. This study was undertaken to identify olfactory behaviors specific to the larvae. A two-choice leaf disk bioassay with naive neonate larvae was used to evaluate the attractiveness of three types of mulberry leaf (Morus alba): newly flushed leaves from branch tips, mature leaves, and mature leaves with feeding damage caused by conspecific larvae. Mature leaves with feeding damage were the most attractive, newly flushed leaves were moderately favored, and undamaged mature leaves were the least attractive. Volatile odors collected from whole mulberry leaves by using solid-phase microextraction fibers were analyzed by gas chromatography-mass spectrometry. The volatile profile of newly flushed leaves and mature leaves damaged by conspecific larvae was more complex compared to undamaged mature leaves. By comparing the volatile makeup of each leaf type, a list of 22 candidate odors responsible for attracting the neonate larvae was generated; α-farnesene was particularly notable as a herbivore-induced volatile. These odors will be used in future in vitro studies to determine whether they activate larval-specific odorant receptors. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

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.     

Feeding response of the silkworm,Bombyx mori,to UV irradiation of mulberry leaves

Ultraviolet irradiation of mulberry leaves caused a reduced feeding response inBombyx mori larvae (ca. 22% reduction in consumption as compared with control). Sucrose content of the foliage decreased after exposure to UV irradiation (0.5 mW/cm² for 1 hr. Electrophysiological responses of the sensilla styloconica-I to sucrose concentration (ca. 0–80 mg/g) showed a reduced response to UV-irradiated foliage when compared with the control. From feeding, gustatory, and electrophysiological responses, as well as the measurement of sucrose contents of the leaves, we concluded that the reduced feeding response to UV-irradiated leaves is due to the reduced sucrose content of the mulberry leaves, thus reducing pleogostimulatory levels.     

Vestitol: A phytoalexin with insect feeding-deterrent activity

A major feeding deterrent forCostelytra zealandica larvae was isolated from the root of the resistant pasture legumeLotus pedunculatus and was identified as 3R-(—)-vestitol. This compound was also identified in feeding deterrent-activeL. pedunculatus leaf extracts. (—)-Vestitol and a secondLotus isoflavan, sativan, have been reported to have phytoalexin activity, and the implications of this for the study and understanding of insect resistance are briefly discussed.     

Hydroxamic acid glucosides in honeydew of aphids feeding on wheat

DIMBOA glucoside (2-O-/gb-D-glucopyranosyl-4-hydroxy-7-meth-oxy-1,4-benzoxazin-3-one), the main hydroxamic acid (Hx) in intact wheat plants, was detected in the honey dew ofRhopalosiphum padi feeding on seedlings of six wheat cultivars that differed in their concentration of Hx, suggesting that the chemical circulates in the phloem. Neither the aglucone (DIMBOA) nor its main breakdown product were found in any of the honeydew samples. Honey dew production by aphids caged on seedlings of the wheat cultivars and DIMBOA glucoside concentrations in the honeydew followed biphasic curves when plotted against Hx concentration, suggesting passive ingestion of the chemical from the phloem at low Hx concentrations and limited ingestion due to feeding deterrency by Hx in mesophyll cells at high Hx concentrations. The presence of plant toxins such as Hx glucosides in the phloem sap, the main ingesta of aphids, and in the mesophyll cells, has major implications for plant defense, through a feeding deterrent effect during stylet penetration, and deterrency (antixenosis) along with antibiosis during feeding.     

Long-Term Effects on Food Choice of Land Snail Arianta arbustorum Mediated by Petasin and Furanopetasin, Two Sesquiterpenes from Petasites hybridus

Sesquiterpenes (STs) from the Senecioneae have been found to be potent snail repellents. We investigated the range of activity of the STs petasin, isopetasin, furanopetasin, kablicin, and cacalol, which were isolated from Petasites hybridus, P. kablikianus, and Adenostyles alpina. We found the petasin content of leaves of P. hybridus to lie within the range of deterrence of the isolated compound. Furthermore, leaf extracts containing petasin proved to be deterrent, and leaf discs with low petasin content were preferred over discs with higher petasin content. The cacalol-containing fraction of a leaf extract of A. alpina was not deterrent to the snails. When the snails had experience with the relevant ST one week before a choice test, their sensitivity towards petasine and furanopetasine increased whereas for the other ST it remained at the same level. We speculate that this sensitivity increase could be the result of a rapid long-term associative learning process, but there is also the possibility that these STs are directly interfering with the feeding motor program of the snails, thereby eliciting a direct neurophysiological sensitization reaction which prevents them from further feeding.     

Chemical aspects of host-plant specificity in threeLarrea-feeding grasshoppers

The host-selection behavior of three species of grasshopper feeding on creosote bush,Larrea tridentata, in southern California was investigated. The species wereBootettix argentatus, which is monophagous;Ligurotettix coquilletti, oligophagous; andCibolacris parviceps, polyphagous. The monophagous species is stimulated to bite by nordihydroguaiaretic acid (NDGA), a compound that is characteristic of the host plant and that may comprise up to 10% of the dry weight of the leaf. Host specificity ofB. argentatus is enhanced by deterrent responses to compounds present in the surface waxes of all non-host-plant species. Both the oligophagous and polyphagous species are deterred by NDGA at naturally occurring concentrations. Their association withLarrea is probably based on tolerance of the plant chemicals rather than on dependence on specific chemicals. Factors other than the chemistry of the plant probably also contribute to the specificity ofB. argentatus andL. coquilletti.     

Patterns of Bioactivity and Herbivory on Nothofagus Species from Chile and New Zealand

Nothofagus species from Chile and New Zealand were surveyed in the field for invertebrate abundance and leaf feeding damage and in the laboratory for antifeedant activity against leafrollers (Ctenopsteustis obliquana, Epiphyas postvittana), deterrent activity against pea aphid (Acyrthosiphon pisum), insect growth regulatory activity (Oncopeltus fasciatus), nematicidal activity (Caenorhabditis elegans), antibiotic activity (Pseudomonas solanaciarium), and general toxicity. A data matrix indicated that N. alessandri and N. pumilio most likely have a chemical barrier to insect attack as leaves showed low faunal abundance, low herbivory, and activity in the leafroller antifeedant, aphid deterrent, and nematicidal assays. A chemical examination of N. alessandri that used the leafroller antifeedant test to guide the separation yielded an active fraction containing the flavonoid, galangin, and the stilbene, pinosylvin, which appear to act in concert to deter leafroller feeding. The discovery of the phytoalexin, pinosylvin, in the leaves, raises the possibility that Nothofagus in general, and N. alessandri in particular, may have induced chemical defense mechanisms.     

Developmental profile of sinalbin (p-hydroxybenzyl glucosinolate) in mustard seedlings,Sinapis alba L., and its relationship to insect resistance

Sinalbin was identified as a chemical component of insect anti-xenosis and antibiosis resistance mechanisms in seedlings ofSinapis alba by DEAE-Sephadex chromatography, HPLC, treatment with sulfatase and myrosinase, various feeding tests using artificial and natural substrates, and by measuring sinalbin concentrations in cotyledons and leaves during seedling development. The effects of sinaibin on feeding were dependent upon the insect species and upon the rapidly changing profile of sinaibin concentrations in the developing seedling. The high concentrations of sinalbin found in young cotyledons (up to 20 mM) and leaves (up to 10 mM) deterred the feeding of the flea beetle,Phyllotreta cruciferae Goeze and larvae of the bertha armyworm,Mamestra configurata Walker. The protection that sinalbin confers upon the vulnerable, newly emerged seedling (and upon tiny, young leaves) appears critical for the first few days of survival ofS. alba under feeding pressure from flea beetles in the field. The lower concentrations of sinaibin found in older cotyledons and leaves (2–3 mM) offer little or no protection againstP. cruciferae and may actually stimulate the feeding of this crucifer specialist. These concentrations of sinaibin, however, are still effective in reducing the level of feeding by larvae of the more generalist feederM. configurata.     

Sequestration of Furostanol Saponins by <Emphasis Type="Italic">Monophadnus</Emphasis> Sawfly Larvae

Sawfly larvae of the tribe Phymatocerini (Hymenoptera: Tenthredinidae), which are specialized on toxic plants in the orders Liliales and Ranunculales, exude a droplet of deterrent hemolymph upon attack by a predator. We investigated whether secondary plant metabolites from Ranunculaceae leaves are sequestered by phymatocerine Monophadnus species, i.e., Monophadnus alpicola feeding upon Pulsatilla alpina and Monophadnus monticola feeding upon Ranunculus lanuginosus. Moreover, two undescribed Monophadnus species were studied: species A collected from Helleborus foetidus and species B collected from Helleborus viridis. Comparative high-performance liquid chromatographic–photodiode array detection–electrospray ionization–mass spectrometric analyses of plant leaf and insect hemolymph extracts revealed the presence of furostanol saponins in all samples. Larvae of species A and B actively sequestered (25R)-26-[(α-l-rhamnopyranosyl)oxy]-22α-methoxyfurost-5-en-3β-yl O-β-d-glucopyranosyl-(1→3)-O-[6-acetyl-β-d-glucopyranosyl-(1→3)]-O-β-d-glucopyranoside (compound 1). This compound occurred at a 65- to 200-fold higher concentration in the hemolymph of the two species (1.6 and 17.5 μmol/g FW, respectively) than in their host plant (0.008 and 0.268 μmol/g FW, respectively). In M. monticola, compound 1 was found at a concentration (1.2 μmol/g FW) similar to that in the host plant (1.36 μmol/g FW). The compound could not be detected consistently in M. alpicola larvae where, however, a related saponin may be present. Additional furostanol saponins were found in H. foetidus and H. viridis, but not in the two Monophadnus species feeding on them, indicating that sequestration of compound 1 is a highly specific process. In laboratory bioassays, crude hemolymph of three Monophadnus species showed a significant feeding deterrent activity against a potential predator, Myrmica rubra ant workers. Isolated furostanol saponins were also active against the ants, at a concentration range similar to that found in the hemolymph. Thus, these compounds seem to play a major role for chemical defense of Monophadnus larvae, although other plant secondary metabolites (glycosylated ecdysteroids) were also detected in their hemolymph. Physiological and ecological implications of the sequestered furostanol saponins are discussed. Dedicated to the memory of Professor Ivano Morelli (1940–2005)     

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.     

Systemic induction of feeding deterrents in cotton plants by feeding ofSpodoptera SPP. Larvae

Cotton,Gossypium hirsutum L., has been shown to exhibit systemic induced resistance to arthropods under certain conditions. We conducted experiments to determine the effects of previous feeding ofSpodoptera exigua Hübner andSpodoptera littoralis (Boisd.) larvae on feeding behavior, growth, and survival of larvae subsequently feeding on cotton. In one feeding choice test,S. exigua larvae preferred young leaves from undamaged control plants to undamaged young leaves from a previously damaged plant. Feeding deterrence was noticeable after only 6 hr of initial feeding damage by larvae, and there was almost complete deterrence after 30 and 54 hr of continuous feeding. In a second feeding choice test,S. littoralis larvae fed more on mature leaves from undamaged control plants than on undamaged mature leaves from previously damaged plants. In no-choice tests, third instars ofS. littoralis fed undamaged young leaves from damaged plants did not gain weight and died by the seventh day, whereas larvae fed young leaves from undamaged control plants gained weight and pupated within 11 days. Sixth instars ofS. littoralis fed either old damaged leaves, old undamaged leaves, or young undamaged leaves all from previously damaged plants gained weight slowly and took more than 12 days to pupate, whereas larvae fed young leaves from undamaged plants gained weight rapidly and pupated within five days of the beginning of the experiment.     

Chemical and experiential basis for rejection ofTropaeolum majus byPieris rapae larvae

Rejection of nasturtium,Tropaeolum majus, by cabbage-reared larvae ofPieris rapae has been explained by the presence of feeding deterrents in the nastrutium foliage. Sensitivity to the deterrents develops as neonate larvae feed on cabbage. The most prominent deterrent compound, which is present in nasturtium at a concentration of 40 mg/100 g fresh leaves, was identified as chlorogenic acid. When neonate larvae were fed on a cabbage leaf treated with high concentrations of deterrent-containing extracts of nasturtium foliage, they remained insensitive to the deterrents, so they accepted nasturtium when transferred as second instars. When neonate larvae were reared on a cabbage leaf treated with 0.1 mg chlorogenic acid, ca. 35% of the second instars accepted nasturtium. Similar dietary exposure of neonates to the subunits of chlorogenic acid, caffeic acid and quinic, acid resulted in much less or no effect on the rejection behavior of second instars. The results suggest that the combined effects of specific chemical constituents of nasturtium can explain the rejection of this plant by larvae ofP. rapae, but if larvae are continuously exposed to these compounds immediately after hatching, they apparently become habituated to the feeding deterrents. The lack of activity of the subunits of chlorogenic acid suggests that specific structural features are necessary for a dietary constituent to cause such habituation or suppression of sensitivity development.     

The Chlorophyll Catabolite,Pheophorbide <Emphasis Type="Italic">a</Emphasis>, Confers Predation Resistance in a Larval Tortoise Beetle Shield Defense

Larval insect herbivores feeding externally on leaves are vulnerable to numerous and varied enemies. Larvae of the Neotropical herbivore, Chelymorpha alternans (Chrysomelidae:Cassidinae), possess shields made of cast skins and feces, which can be aimed and waved at attacking enemies. Prior work with C. alternans feeding on Merremia umbellata (Convolvulaceae) showed that shields offered protection from generalist predators, and polar compounds were implicated. This study used a ubiquitous ant predator, Azteca lacrymosa, in field bioassays to determine the chemical constitution of the defense. We confirmed that intact shields do protect larvae and that methanol-water leaching significantly reduced shield effectiveness. Liquid chromatography-mass spectrometry (LC-MS) of the methanolic shield extract revealed two peaks at 20.18 min and 21.97 min, both with a molecular ion at m/z 593.4, and a strong UV absorption around 409 nm, suggesting a porphyrin-type compound. LC-MS analysis of a commercial standard confirmed pheophorbide a (Pha) identity. C. alternans shields contained more than 100 μg Pha per shield. Shields leached with methanol-water did not deter ants. Methanol-water-leached shields enhanced with 3 μg of Pha were more deterrent than larvae with solvent-leached shields, while those with 5 μg additional Pha provided slightly less deterrence than larvae with intact shields. Solvent-leached shields with 10 μg added Pha were comparable to intact shields, even though the Pha concentration was less than 10% of its natural concentration. Our findings are the first to assign an ecological role for a chlorophyll catabolite as a deterrent in an insect defense.     

Isolation of feeding deterrents against argentine stem weevil from ryegrass infected with the endophyteAcremonium loliae

Infection of ryegrass (Lolium perenne) by an endophytic fungus (Acremonium loliae) confers resistance against the Argentine stem weevil (Listronotus bonariensis). Extracts from ryegrass clones, infected and uninfected withA. loliae, were compared in a feeding choice bioassay, and several fractions were identified which affected stem weevil feeding behavior. One stem weevil feeding deterrent, peramine C₁₂H₁₇N₅O, has been isolated from infected ryegrass and partially characterized as a basic indole derivative. Extracts from culturedA. loliae had no effect on stem weevil feeding behavior nor was peramine detected in the fungal cultures examined. Peramine and the other active substances are hydrophilic in contrast to the lipophilic properties reported for the neurotoxic lolitrems also isolated from ryegrass infected withA. loliae and associated with causing ryegrass staggers disorder in livestock. It is suggested that ryegrass staggers and stem weevil feeding deterrency may arise by different biochemical mechanisms.     

Aphid feeding deterrents in sorghum

Improvements in a synthetic diet for use in a bioassay to screen for feeding deterrents againstSchizaphis graminum, greenbug, are reported. Feeding on the synthetic diet was highly pH dependent with maximum feeding occurring at about pH 8.0. The bioassay was used as a guide in the isolation of feeding deterrent substances from aphid-resistant lines of sorghum (Sorghum bicolor). The major greenbug feeding deterrents isolated from sorghum leaves wereP-hydroxybenzaldehyde (ED₅₀ 0.13%), dhurrin (ED₅₀ 0.16%), and procyanidin (ED₅₀ 0.08%).Reference to a company and/or product named by the department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.