Oviposition stimulants of aCitrus-feeding swallowtail butterfly,Papilio xuthus L

Genome-Wide Analysis of Odorant-Binding Proteins in Papilio xuthus with Focus on the Perception of Two PxutGOBPs to Host Odorants and Insecticides

In this study, we annotated 49 odorant-binding proteins (OBPs) in Papilio xuthus, with four novel genes and seven improved sequences. Expression profiles identified numerous OBPs in antennae or reproductive tissues. Using two antenna-enriched general OBPs (PxutGOBP1 and PxutGOBP2) as targets, we screened three key compounds by a reverse chemical ecology strategy. Of these, an oviposition stimulant vicenin-2 could strongly interact with PxutGOBP1, representing a dissociation constant (K_i) value of 10.34 ± 0.07 μM. Molecular simulations and site-directed mutagenesis revealed the importance of His66, Thr73, and Phe118 between PxutGOBP1 and vicenin-2 interactions. Two other compounds, an ordinary floral scent β-ionone and a widely used insecticide chlorpyrifos, exhibited high affinities to PxutGOBPs (K_i < 13 μM). Furthermore, two mutations His66Ala and Thr73Ala of PxutGOBP1 significantly reduced the binding to chlorpyrifos. Our study provides insights into the putative roles of PxutGOBPs in odorant perception and identifies key binding sites of PxutGOBP1 to vicenin-2 and chlorpyrifos.

Swallowtail Butterflies Use Multiple Visual Cues to Select Oviposition Sites

Simple Summary

Butterflies must not only identify host plants on which to lay their eggs—which they achieve using chemical cues—but also select suitable leaves on that plant that will support the growth of their larval offspring. Here, we asked whether swallowtail butterflies lay eggs on particular leaves of a Citrus tree and, if so, which cues they use to select the leaves. We first observed that butterflies indeed select just a few leaves on which to lay eggs. These leaf preferences were observed across many individuals, implying that they were not idiosyncratic, and the butterflies descended directly towards the leaves from some distance, suggesting that they were using visual rather than chemical cues. We then investigated which visual cues are used by the butterflies, and found that the number of eggs laid upon a leaf was correlated with its height on the tree, flatness, green reflectance, brightness, and degree of polarization. These five features may be important both for selecting young leaves and those which are situated well for egg-laying. An outstanding question for future study is how visual and chemical cues interact in this context.

Abstract

Flower-foraging Japanese yellow swallowtail butterflies, Papilio xuthus, exhibit sophisticated visual abilities. When ovipositing, females presumably attempt to select suitable leaves to support the growth of their larval offspring. We first established that butterflies indeed select particular leaves on which to lay eggs; when presented with a single Citrus tree, butterflies significantly favored two out of 102 leaves for oviposition. These preferences were observed across many individuals, implying that they were not merely idiosyncratic, but rather based on properties of the leaves in question. Because the butterflies descended towards the leaves rather directly from a distance, we hypothesized that they base their selection on visual cues. We measured five morphological properties (height, orientation, flatness, roundness, and size) and four reflective features (green reflectance, brightness, and degree and angle of linear polarization). We found that the number of eggs laid upon a leaf was positively correlated with its height, flatness, green reflectance, and brightness, and negatively correlated with its degree of polarization, indicating that these features may serve as cues for leaf selection. Considering that other studies report ovipositing butterflies’ preference for green color and horizontally polarized light, butterflies likely use multiple visual features to select egg-laying sites on the host plant.

Evolution of Gustatory Receptor Gene Family Provides Insights into Adaptation to Diverse Host Plants in Nymphalid Butterflies

The host plant range of herbivorous insects is a major aspect of insect–plant interaction, but the genetic basis of host range expansion in insects is poorly understood. In butterflies, gustatory receptor genes (GRs) play important roles in host plant selection by ovipositing females. Since several studies have shown associations between the repertoire sizes of chemosensory gene families and the diversity of resource use, we hypothesized that the increase in the number of genes in the GR family is associated with host range expansion in butterflies. Here, we analyzed the evolutionary dynamics of GRs among related species, including the host generalist Vanessa cardui and three specialists. Although the increase of the GR repertoire itself was not observed, we found that the gene birth rate of GRs was the highest in the lineage leading to V. cardui compared with other specialist lineages. We also identified two taxon-specific subfamilies of GRs, characterized by frequent lineage-specific duplications and higher non-synonymous substitution rates. Together, our results suggest that frequent gene duplications in GRs, which might be involved in the detection of plant secondary metabolites, were associated with host range expansion in the V. cardui lineage. These evolutionary patterns imply that the capability to perceive various compounds during host selection was favored during adaptation to diverse host plants.

Changing the content of phenolic compounds as the response of blackcurrant (Ribes nigrum L.) leaves after blackcurrant leaf midge (Dasineura tetensi Rübs.) infestation

Blackcurrant leaf midge (Dasineura tetensi) is one of the most common pests of blackcurrant (Ribes nigrum). The aim of this study was to investigate changes in the content of phenolic compounds in the leaves damaged by the larvae of this pest. Additionally, susceptibility of different blackcurrant cultivars to the midge attack was investigated. Qualitative and quantitative analyses of control and pest-infested blackcurrant leaves were performed using LC-PDA-QTOF/MS and UPLC-PDA-FL systems. A total of 39 types of phenolic compounds were identified in blackcurrant leaf extracts and they included 3 flavan-3-ols, 14 hydroxycinnamic acid derivatives, and 22 flavonols. Feeding of blackcurrant leaf midge on blackcurrant leaves lowered the content of leaf polyphenolic compounds. The greatest differences in polyphenolics between control and infected leaves were observed in 'Ruben', 'Fariegh', 'Foxendown', 'Ores', 'Ben Hope', 'Ben Connan' and 'Tisel' cultivars that were probably highly susceptible to the pest attack. In the other cultivars: 'Ben Finlay', 'Polares', 'Tiben', and 'Gofert' the differences in phenolics content were less pronounced, so they were probably less susceptible to D. tetensi attack. Plant polyphenolic compounds was strongly involved in pathogen-plant interaction, and their accumulation significantly decreased as a result of the pathogen attack.

Opposing Roles of Foliar and Glandular Trichome Volatile Components in Cultivated Nightshade Interaction with a Specialist Herbivore

Plant chemistry is an important contributor to the interaction with herbivores. Here, we report on a previously unknown role for foliar and glandular trichome volatiles in their interaction with the specialist herbivore of solanaceous plants, the tomato red spider mite Tetranychus evansi. We used various bioassays and chemical analyses including coupled gas chromatography-mass spectrometry (GC/MS) and liquid chromatography coupled to quadrupole time of flight mass spectrometry (LC-QToF-MS) to investigate this interaction between cultivated African nightshades and T. evansi. We show that, whereas morphologically different cultivated African nightshade species released similar foliar volatile organic compounds (VOCs) that attracted T. evansi, VOCs released from exudates of ruptured glandular trichomes of one nightshade species influenced local defense on the leaf surface. VOCs from ruptured glandular trichomes comprising mainly saturated and unsaturated fatty acids deterred T. evansi oviposition. Of the fatty acids, the unsaturated fatty acids accounted for >40% of the oviposition deterrent activity. Our findings point to a defense strategy in a plant, based on opposing roles for volatiles released by foliar and glandular trichomes in response to attack by a specialist herbivore.

Essential Oil Variation from Twenty Two Genotypes of Citrus in Brazil-Chemometric Approach and Repellency Against Diaphorina citri Kuwayama

The chemical composition of volatile oils from 22 genotypes of Citrus and related genera was poorly differentiated, but chemometric techniques have clarified the relationships between the 22 genotypes, and allowed us to understand their resistance to D. citri. The most convincing similarities include the synthesis of (Z)-β-ocimene and (E)-caryophyllene for all 11 genotypes of group A. Genotypes of group B are not uniformly characterized by essential oil compounds. When stimulated with odor sources of 22 genotypes in a Y-tube olfactometer D. citri preferentially entered the arm containing the volatile oils of Murraya paniculata, confirming orange jasmine as its best host. C. reticulata × C. sinensis was the least preferred genotype, and is characterized by the presence of phytol, (Z)-β-ocimene, and β-elemene, which were not found in the most preferred genotype. We speculate that these three compounds may act as a repellent, making these oils less attractive to D. citri.

Feeding stimulants for larvae of Graphium sarpedon nipponum (Lepidoptera: Papilionidae) from Cinnamomum camphora

The feeding response of larvae of the swallowtail butterfly, Graphium sarpedon nipponum (Lepidoptera: Papilionidae), is elicited by a methanolic extract from camphor tree (Cinnamomum camphora) leaves. Based on bioassay-guided fractionation, three compounds, isolated from the methanolic extract of fresh leaves of the camphor tree, were revealed to be involved in a multi-component system of feeding stimulants. Structures of these feeding stimulants were identified as sucrose, 5-O-caffeoylquinic acid and quercetin 3-O-β-glucopyranoside by NMR and LC-MS.

Metatranscriptome Analysis of Fig Flowers Provides Insights into Potential Mechanisms for Mutualism Stability and Gall Induction

A striking property of the mutualism between figs and their pollinating wasps is that wasps consistently oviposit in the inner flowers of the fig syconium, which develop into galls that house developing larvae. Wasps typically do not use the outer ring of flowers, which develop into seeds. To better understand differences between gall and seed flowers, we used a metatranscriptomic approach to analyze eukaryotic gene expression within fig flowers at the time of oviposition choice and early gall development. Consistent with the unbeatable seed hypothesis, we found significant differences in gene expression between gall- and seed flowers in receptive syconia prior to oviposition. In particular, transcripts assigned to flavonoids and carbohydrate metabolism were significantly up-regulated in gall flowers relative to seed flowers. In response to oviposition, gall flowers significantly up-regulated the expression of chalcone synthase, which previously has been connected to gall formation in other plants. We propose several genes encoding proteins with signal peptides or associations with venom of other Hymenoptera as candidate genes for gall initiation or growth. This study simultaneously evaluates the gene expression profile of both mutualistic partners in a plant-insect mutualism and provides insight into a possible stability mechanism in the ancient fig-fig wasp association.

Chemical ecology of insect-plant interactions: ecological significance of plant secondary metabolites

Plants produce a diverse array of secondary metabolites as chemical barriers against herbivores. Many phytophagous insects are highly adapted to these allelochemicals and use such unique substances as the specific host-finding cues, defensive substances of their own, and even as sex pheromones or their precursors by selectively sensing, incorporating, and/or processing these phytochemicals. Insects also serve as pollinators often effectively guided by specific floral fragrances. This review demonstrates the ecological significance of such plant secondary metabolites in the highly diverse interactions between insects and plants.

Specific volatile compounds from mango elicit oviposition in gravid Bactrocera dorsalis females

Selecting a suitable oviposition site is crucial to the fitness of female insects because it determines the successful development of their offspring. During the oviposition process, an insect must use cues from the external environment to make an appropriate choice of where to lay eggs. Generalist insects can detect and react to a plethora of cues, but are under selection pressure to adopt the most reliable ones to override noise and increase efficiency in finding hosts. The oriental fruit fly, Bactrocera dorsalis (Hendel), is a generalist that utilizes a multitude of fruits as oviposition sites. However, the identity and nature of oviposition stimulants for B. dorsalis is not well known. Recently, we identified a volatile compound γ-octalactone that elicits an innate oviposition response in B. dorsalis. We screened 21 EAD-active volatiles, identified from mango, for their oviposition stimulant activity. 1-Octen-3-ol, ethyl tiglate, and benzothiazole instigated oviposition in gravid B. dorsalis females. Flies deposited most of their eggs into pulp discs with oviposition-stimulants, and only a small fraction of eggs were laid into control discs. In a binary choice oviposition assay, 95.1, 93.7, and 65.6 % of eggs were laid in discs treated with 1-octen-3-ol, ethyl tiglate, and benzothiazole, respectively. Single plate two-choice assays proved that oviposition-stimulants were crucial in oviposition site selection by gravid female B. dorsalis. In simulated semi-natural assays, gravid B. dorsalis females accurately differentiated between fruits with and without 1-octen-3-ol, ethyl tiglate, and γ-octalactone by laying more eggs on the treated fruit. However, benzothiazole did not elicit an increase in oviposition when presented in this context. Our results suggest that the identified oviposition-stimulants are 'key' compounds, which the flies associate with suitable oviposition sites.

Identification of host-plant chemicals stimulating oviposition by swallowtail butterfly,Papilio protenor

The ovipositional response of a Rutaceae-feeding papilionid butterfly,Papilio protenor, toCitrus host plants was evoked by the synergistic action ofL-(-)-stachydrine,D-(-)-quinic acid, (-)-synephrine, andL-(-)-proline that characterize the chemical compositions of the leaves and epicarp ofCitrus plants (C. natsudaidai andC. unshiu). The stimulatory activity of their mixture was enhanced by the addition of flavanone glycosides, naringin and hesperidin, which coexist in these plants and have previously been demonstrated to serve as oviposition stimulants. However, sugars such as sucrose, glucose, and inositols, which abound in plant tissues, exerted no effect on egg-laying by the females. On the other hand, chlorogenic acid present in the leaves of another host plant,Fagara ailanthoides, was found to act as an excellent synergist. However, there existed significant qualitative dissimilarities between the chemical compositions of the leaves ofC. unshiu andF. ailanthoides. This strongly suggests thatP. protenor is likely to utilize different categories of compounds as chemical cues in recognizing each plant as a host.

Oviposition stimulants for the black swallowtail butterfly: Identification of electrophysiologically active compounds in carrot volatiles

Headspace volatiles were collected from undamaged foliage of carrot,Daucus carota, a host-plant species of the black swallowtail butterfly,Papilio polyxenes. The volatiles were fractionated over silica on an open column, and the fractions were tested in behavioral assays withP. polyxenes females in laboratory experiments. The polar fractions, as well as the total mixture of volatiles, increased the landing frequency and the number of eggs laid on model plants with leaves bearing contact-oviposition stimulants. The nonpolar fraction, containing the most abundant compounds in carrot odor, was not stimulatory. Gas Chromatographic (GC) separation of the fractions was coupled with electroantennogram (EAG) recordings to identify the compounds perceived byP. polyxenes females. The EAG activity corresponded to the behavioral activity of the fractions. None of the nonpolar compounds, identified as various monoterpenes, evoked a major EAG response, but several constituents of the polar fractions elicited high EAG responses. Sabinene hydrate (both stereoisomers), 4-terpineol, bomyl acetate, and (Z)-3-hexenyl acetate were identified by GC-MS as active compounds.

Larval feeding stimulants for a rutaceae-feeding swallowtail butterfly, Papilio xuthus L. in Citrus unshiu leaves

Larvae of a swallowtail butterfly, Papilio xuthus L., feed exclusively on plants of the family Rutaceae, including various Citrus crops. Larvae were strongly stimulated to feed on paper strips impregnated with ethanolic extracts of host-plant leaves. Stimulation of feeding on extracts of Citrus unshiu leaves required a mixture of chemicals including sugars (D: -glucose, D: -fructose, and D: -sucrose), a betaine [(-)-stachydrine], a cyclic peptide (citrusin I), a polymethoxyflavone (isosinensetin), and the lipids 1-linolenoylglycerol, 1-linoleoylglycerol, 1-octadecenoylglycerol, 1-stearoylglycerol, and 1,2-dilinolenoyl-3-galactosyl-sn-glycerol. When these compounds were assayed individually, few larvae consumed test strips. However, larvae readily chewed the test strips treated with a mixture of all compounds, indicating that host recognition by P. xuthus larvae is mediated by a specific combination of both primary and secondary substances. Comparison of 11 stimulant components with 10 compounds from C. unshiu leaves previously reported as stimulant components for oviposition by P. xuthus adult females revealed only one compound, stachydrine, as an ingredient in common. While the larval feeding-stimulant mixture is dominated by nutrients and other compounds of general significance for primary metabolism, the component oviposition stimulants are mostly secondary substances, including flavonoid glycosides, protoalkaloids, a cyclitol, and a betaine, that have restricted distributions in plants. Reliance by adult females on unique profiles of secondary compounds presumably reflects the need to locate and recognize specific host-plant species within a diverse flora. Since the initial host choice for the larvae is made typically by the ovipositing female, however, unique secondary compounds may be less important for larval feeding than are compounds useful for indicating food and microhabitat quality once on the host plant.

Identification of cytochrome P450 and glutathione-S-transferase genes preferentially expressed in chemosensory organs of the swallowtail butterfly, Papilio xuthus L

The swallowtail butterfly, Papilio xuthus L., feeds exclusively on members of the plant family, Rutaceae. Female butterflies lay eggs in response to specific chemicals contained in their host plants. They perceive a variety of polar compounds as oviposition stimulants through the tarsal chemosensilla of the foreleg by drumming upon the leaf surface. We undertook an expressed sequence tag (EST) analysis to identify the chemosensory-related genes that are expressed in chemosensilla on the tarsus of P. xuthus. Several genes that showed similarity with biotransformation enzymes were identified from the ESTs. Among them, a cytochrome P450 and a glutathione-S-transferase (GST) were preferentially expressed in the chemosensory organs. We have determined the structure of both cDNA and genomic sequences encoding these enzymes and designated the P450 as CYP341A2, a novel member of CYP341A subfamily, and the GST as GST-pxcs1, respectively. We observed a localized expression of CYP341A2 at the base of tarsal chemosensilla by in situ hybridization. These results suggest that these degrading enzymes play a role in the chemosensory reception for host plant recognition.

Identification of amine receptors from a swallowtail butterfly, Papilio xuthus L.: cloning and mRNA localization in foreleg chemosensory organ for recognition of host plants

The swallowtail butterfly, Papilio xuthus L., feeds exclusively on members of the plant family, Rutaceae. Female butterflies lay eggs in response to specific chemicals contained in their host plants. They perceive a variety of polar compounds as oviposition stimulants through the tarsal chemosensilla of the foreleg by drumming upon the leaf surface. Some biogenic amine analogs have been characterized as oviposition stimulants. We have cloned three amine receptors, serotonin, tyramine, and dopamine, from cDNA derived from foreleg tarsus of P. xuthus, and determined structures of both cDNA and genomic genes. The phenylethylamine (tyramine and dopamine) receptors were expressed preferentially in brain and chemosensory organs. Moreover, we observed the localized expression of dopamine receptors at the base of tarsal chemosensilla by in situ hybridization. These results suggest that amine receptors in tarsal chemosensilla have a functional role in chemoreception for host plant recognition.

Flavonoid function and activity to plants and other organisms

Flavonoid compounds distribute widely in vascular plants and Bryophytes, and ca. 5,000 kinds have been reported as naturally occurring substances. Many biological activities of the flavonoids were found until now. They include pollinator attractants, oviposition stimulants, feeding attractants and deterrents, allelopathy and phytoalexins. This paper reviews function and activity of flavonoids against plants and other organisms.

Role of endogenous flavonoids in resistance mechanism of Vigna to aphids

Cultivated and wild species of the genus Vigna were screened for their flavonoid content. Flavonoid HPLC analyses clearly showed that cultivated lines of cowpea (Vigna unguiculata L. Walp.) are very similar from a qualitative point of view, always showing three flavonoid aglycons: quercetin, kaempferol, and isorhamnetin. In addition, a positive relationship between resistance/susceptibility characteristics against aphids and flavonoid glycoside content of cowpea lines was found. The resistant lines showed a flavonoid content higher than that of susceptible ones. In vitro bioassays proved that, among endogenous flavonoids, quercetin and isorhamnetin possess a good inhibitory aphid reproduction rate. Flavonoid HPLC analyses of wild Vigna species supported evidence for the existence of different flavonoid chemotypes in some species of section Vigna. There are kaempferol chemotypes, kaempferol being the main aglycon detected, quercetin chemotypes, containing quercetin glycosides only, and two isorhamnetin chemotypes. When the resistance characteristics to aphids in different chemotypes of the same species were tested, it became evident that quercetin or isorhamnetin chemotypes showed a higher level of resistance compared to kaempferol chemotypes in the same species, thus demonstrating a direct involvement of quercetin or isorhamnetin in the resistance mechanism. These results can provide useful information for further studies on gene expression of resistance factors.

Oviposition stimulants for the monarch butterfly: flavonol glycosides from Asclepias curassavica

The monarch butterfly, Danaus plexippus oviposits on milkweed plants, primarily within the Asclepiadaceae. Oviposition stimulants responsible for host plant recognition were isolated from Asclepias curassavica. Six flavonoid glycosides-quercetin 3-O-(2",6"-alpha-L-dirhamnopyranosyl)-beta-D-galactopyranoside, quercetin 3-O-beta-D-glucopyranosyl-(1-->6)-beta-D-galactopyranoside, quercetin 3-O-(2"-O-alpha-L-rhamnopyranosyl)-beta-D-galactopyranoside, quercetin 3-O-alpha-L-rhamnopyranosyl-(1-->6)-beta-D-glucopyranoside, quercetin 3-O-beta-D-galactopyranoside, quercetin 3-O-beta-D-glucopyranoside, and an unidentified flavonoid mixture were isolated and characterized from this plant. An additional glycoside, possibly quercetin 3-O-(2",6"-alpha-L-dirhamnopyranosyl)-beta-D-glucopyranoside, which could not be separated from the first triglycoside, was also found in some batches of plant extract. The two dirhamnosyl glycosides, the glucosylgalactose and the rutinoside were found to be active as oviposition stimulants at 0.5 g leaf equivalents.

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.

Oviposition stimulant of a Zeryntiine swallowtail butterfly, Luehdorfia japonica

Luehdorfia japonica Leech (Papilionidae, tribe Zerynthiini) is a swallowtail butterfly whose larvae feed exclusively on the plant genus Heterotropa (Aristolochiaceae). Luehdorfia japonica females were strongly stimulated to lay eggs on filter paper treated with a methanolic extract of the host plant leaves. The oviposition stimulant factor was composed of several water-soluble components. One of the oviposition stimulants was isolated from the leaves of Heterotropa aspera and identified as isorhamnetin 3-O-glucosyl-(1-->6)-galactoside-7-O-glucoside. This compound was inactive alone but induced the specific oviposition response from L. japonica females when tested as a mixture with other unidentified components.