Evolution of sensitivity to warning cues from kin in plants with a structured population.

Plants exchange a variety of information intra- and interspecifically by using various mediating cues. For example, plant individuals that are injured by herbivores release volatile chemicals, which induce receiver plants to express anti-herbivore resistance. Remarkably, some plant species were known to represent kin specificity in the response, where cues from a damaged individual induce a higher level of resistance in a kin receiver than in a non-kin receiver. Such higher sensitivity to warning cues from kin could be advantageous via two mechanisms. If each herbivore tends to attack plants with a certain genotype, plants should be more sensitive to warning cues from kin that share genetic properties. In addition, if herbivores successively attack the neighboring plant with a high probability, and if related plants tend to grow in close proximity, plants may be more sensitive to warning cues from neighboring kin under the presence of a trade-off between sensitivity to kin and non-kin. In the present study, we constructed a mathematical model including those mechanisms to investigate the evolutionary process of the higher sensitivity to warning cues from kin than sensitivities to cues from non-kin. According to the analysis of evolutionary dynamics, we revealed that both mechanisms could contribute, although higher sensitivity to cues from kin is more likely to evolve when the spatial range of competition is greater than the range of effective alarm cues. This result highlights the importance of the competition regime in the evolution of signaling among kin.

Booklice Liposcelis bostrychophila are efficiently attracted by the combination of 2,3,5,6-tetramethylpyrazine and ultraviolet light.

BACKGROUND: Booklice Liposcelis bostrychophila are frequently found almost everywhere, including private houses and cleanrooms of factories and institutes. They often cause serious hygienic as well as agricultural problems, but a useful trap has not been developed so far. Therefore, an effective way to monitor and capture booklice is required. RESULTS: We here identified a new attractant, 2,3,5,6-tetramethylpyrazine (TMP), which efficiently captured booklice in combination with UV light. When booklice placed at both right and left edges of an assay tray were exposed to light stimulus from the center, test insects gathered at the center. The attraction was stronger with shorter wavelengths than longer ones: 365-nm ultraviolet (UV) light showed the strongest attraction of four tested light wavelengths. We found that cocoa powder attracted booklice weakly but significantly under total darkness. Furthermore, the cocoa smell was confirmed to enhance the attraction to light at all tested wavelengths irrespective of the difference between two brands of cocoa powders. Gas chromatography-mass spectrometry indicated that both cocoa products contain TMP as a major odor compound. Exposure of booklice to TMP significantly enhanced the attraction to UV light: the combined use with TMP almost doubled the attraction compared to the light only. By contrast, TMP homologs, pyrazine and dimethylpyrazines, showed strong repellent activities under UV light exposure. CONCLUSION: TMP enhanced the UV light attraction for booklice while pyrazine and dimethylpyrazines diminished it. Use of these attractant and repellent pyrazine derivatives together with UV light would enable us to develop a practical new way to monitor and capture booklice. © 2023 Society of Chemical Industry.

The exposure of field-grown maize seedlings to weed volatiles affects their growth and seed quality.

Plants exposed to volatiles emitted from artificially damaged conspecific or heterospecific plants exhibit increased resistance to herbivorous insects. Here, we examined whether volatiles from artificially damaged weeds affect maize growth and reproduction. Seven days after germination, maize seedlings were exposed to volatiles emitted by artificially damaged mugwort (Artemisia indica var. maximowiczii) or tall goldenrod (Solidago altissima) plants either separately, or as a mixture of the two, for seven days. Unexposed seedlings were used as controls. Treated and control seedlings were cultivated in an experimental field without any insecticides applied. Plants exposed to either of the three volatile treatments sustained significantly less damage than controls. Additionally, seedlings exposed to either goldenrod or mixed volatiles produced more leaves and tillers than control plants. Furthermore, a significant increase in the number of ears was observed in plants exposed to the volatile mixture. In all treated plants, ear sugar content was significantly higher than that in the controls. Further, we cultivated seedlings that were either exposed to the volatile mixture or unexposed, under the conventional farming method using pesticides. Similar significant differences were observed for sugar content, number of tillers, leaves, damaged leaves, and ears. Laboratory experiments were conducted to further evaluate the mechanisms involved in the improved performance of volatile-treated plants. A significant reduction in the growth of common armyworm (Mythimna separata) larvae was observed when maize plants were exposed to the volatile mixture. This treatment did not affect the amount of jasmonic acid in the seedlings, whereas salicylic acid content increased upon exposure. The characteristic differences in chemical composition of mugwort and goldenrod volatiles were confirmed and, in turn, the volatile mixture differed significantly from the volatiles of either species.

Identification of a tomato UDP-arabinosyltransferase for airborne volatile reception.

Volatiles from herbivore-infested plants function as a chemical warning of future herbivory for neighboring plants. (Z)-3-Hexenol emitted from tomato plants infested by common cutworms is taken up by uninfested plants and converted to (Z)-3-hexenyl ß-vicianoside (HexVic). Here we show that a wild tomato species (Solanum pennellii) shows limited HexVic accumulation compared to a domesticated tomato species (Solanum lycopersicum) after (Z)-3-hexenol exposure. Common cutworms grow better on an introgression line containing an S. pennellii chromosome 11 segment that impairs HexVic accumulation, suggesting that (Z)-3-hexenol diglycosylation is involved in the defense of tomato against herbivory. We finally reveal that HexVic accumulation is genetically associated with a uridine diphosphate-glycosyltransferase (UGT) gene cluster that harbors UGT91R1 on chromosome 11. Biochemical and transgenic analyses of UGT91R1 show that it preferentially catalyzes (Z)-3-hexenyl ß-D-glucopyranoside arabinosylation to produce HexVic in planta.

Herbivory-Induced Plant Volatiles Mediate Multitrophic Relationships in Ecosystems.

Herbivory-induced plant volatiles (HIPVs) are involved in biotic interactions among plants as well as herbivorous and carnivorous arthropods. This review looks at the specificity in plant-carnivore communication mediated by specific blends of HIPVs as well as describes plant-herbivore and plant-plant communication mediated by specific HIPVs. Factors affecting the net benefits of HIPV production have also been examined. These specific means of communication results in high complexity in the 'interaction-information network', which should be explored further to elucidate the mechanism underlying the numerous species coexisting in ecosystems.

Aerial (+)-borneol modulates root morphology, auxin signalling and meristematic activity in Arabidopsis roots.

One of the characteristic aspects of odour sensing in humans is the activation of olfactory receptors in a slightly different manner in response to different enantiomers. Here, we focused on whether plants showed enantiomer-specific response similar to that in humans. We exposed Arabidopsis seedlings to methanol (control) and (+)- or (-)-borneol, and found that only (+)-borneol reduced the root length. Furthermore, the root-tip width was more increased upon (+)-borneol exposure than upon (-)-borneol exposure. In addition, root-hair formation was observed near the root tip in response to (+)-borneol. Auxin signalling was strongly reduced in the root tip following exposure to (+)-borneol, but was detected following exposure to (-)-borneol and methanol. Similarly, in the root tip, the activity of cyclin B1:1 was detected on exposure to (-)-borneol and methanol, but not on exposure to (+)-borneol, indicating that (+)-borneol inhibits the meristematic activity in the root. These results partially explain the (+)-borneol-specific reduction in the root length of Arabidopsis. Our results indicate the presence of a sensing system specific for (+)-borneol in Arabidopsis.

The rice wound-inducible transcription factor RERJ1 sharing same signal transduction pathway with OsMYC2 is necessary for defense response to herbivory and bacterial blight.

KEY MESSAGE: This study describes biological functions of the bHLH transcription factor RERJ1 involved in the jasmonate response and the related defense-associated metabolic pathways in rice, with particular focus on deciphering the regulatory mechanisms underlying stress-induced volatile emission and herbivory resistance. RERJ1 is rapidly and drastically induced by wounding and jasmonate treatment but its biological function remains unknown as yet. Here we provide evidence of the biological function of RERJ1 in plant defense, specifically in response to herbivory and pathogen attack, and offer insights into the RERJ1-mediated regulation of metabolic pathways of specialized defense compounds, such as monoterpene linalool, in possible collaboration with OsMYC2-a well-known master regulator in jasmonate signaling. In rice (Oryza sativa L.), the basic helix-loop-helix (bHLH) family transcription factor RERJ1 is induced under environmental stresses, such as wounding and drought, which are closely linked to jasmonate (JA) accumulation. Here, we investigated the biological function of RERJ1 in response to biotic stresses, such as herbivory and pathogen infection, using an RERJ1-defective mutant. Transcriptome analysis of the rerj1-Tos17 mutant revealed that RERJ1 regulated the expression of a typical family of conserved JA-responsive genes (e.g., terpene synthases, proteinase inhibitors, and jasmonate ZIM domain proteins). Upon exposure to armyworm attack, the rerj1-Tos17 mutant exhibited more severe damage than the wildtype, and significant weight gain of the larvae fed on the mutant was observed. Upon Xanthomonas oryzae infection, the rerj1-Tos17 mutant developed more severe symptoms than the wildtype. Among RERJ1-regulated terpene synthases, linalool synthase expression was markedly disrupted and linalool emission after wounding was significantly decreased in the rerj1-Tos17 mutant. RERJ1 appears to interact with OsMYC2-a master regulator of JA signaling-and many OsJAZ proteins, although no obvious epistatic interaction was detected between them at the transcriptional level. These results indicate that RERJ1 is involved in the transcriptional induction of JA-mediated stress-responsive genes via physical association with OsMYC2 and mediates defense against herbivory and bacterial infection through JA signaling.

Processing of Airborne Green Leaf Volatiles for Their Glycosylation in the Exposed Plants.

Green leaf volatiles (GLVs), the common constituents of herbivore-infested plant volatiles (HIPVs), play an important role in plant defense and function as chemical cues to communicate with other individuals in nature. Reportedly, in addition to endogenous GLVs, the absorbance of airborne GLVs emitted by infested neighboring plants also play a major role in plant defense. For example, the exclusive accumulation of (Z)-3-hexenyl vicianoside in the HIPV-exposed tomato plants occurs by the glycosylation of airborne (Z)-3-hexenol (Z3HOL); however, it is unclear how plants process the other absorbed GLVs. This study demonstrates that tomato plants dominantly accumulated GLV-glycosides after exposure to green leaf alcohols [Z3HOL, (E)-2-hexenol, and n-hexanol] using non-targeted LC-MS analysis. Three types of green leaf alcohols were independently glycosylated without isomerization or saturation/desaturation. Airborne green leaf aldehydes and esters were also glycosylated, probably through converting aldehydes and esters into alcohols. Further, we validated these findings in Arabidopsis mutants- (Z)-3-hexenal (Z3HAL) reductase (chr) mutant that inhibits the conversion of Z3HAL to Z3HOL and the acetyl-CoA:(Z)-3-hexen-1-ol acetyltransferase (chat) mutant that impairs the conversion of Z3HOL to (Z)-3-hexenyl acetate. Exposure of the chr and chat mutants to Z3HAL accumulated lower and higher amounts of glycosides than their corresponding wild types (Col-0 and Ler), respectively. These findings suggest that plants process the exogenous GLVs by the reductase(s) and the esterase(s), and a part of the processed GLVs contribute to glycoside accumulation. Overall, the study provides insights into the understanding of the communication of the plants within their ecosystem, which could help develop strategies to protect the crops and maintain a balanced ecosystem.

Effective distance of volatile cues for plant-plant communication in beech.

In response to volatiles emitted from a plant infested by herbivorous arthropods, neighboring undamaged conspecific plants become better defended against herbivores; this is referred to as plant‒plant communication. Although plant‒plant communication occurs in a wide range of plant species, most studies have focused on herbaceous plants. Here, we investigated plant‒plant communication in beech trees in two experimental plantations in 2018 and one plantation in 2019. Approximately 20% of the leaves of a beech tree were clipped in half in the spring seasons of 2018 and 2019 (clipped tree). The damage levels to leaves in the surrounding undamaged beech trees were evaluated 90 days after the clipping (assay trees). In both years, the damage levels decreased with a reduction in the distance from the clipped tree. In 2019, we also recorded the damage levels of trees that were not exposed to volatiles (nonexposed trees) as control trees and found that those that were located <5 m away from clipped trees had significantly less leaf damage than nonexposed trees. By using a gas chromatograph-mass spectrometer, ten and eight volatile compounds were detected in the headspaces of clipped and unclipped leaves, respectively. Among them, the amount of (Z)-3-hexenyl acetate in clipped leaves was significantly higher than that in nonclipped leaves. Our result suggests that green leaf volatiles such as (Z)-3-hexenol and (Z)-3-hexenyl acetate and other volatile organic compounds emitted from clipped trees induced defenses in the neighboring trees within the 5 m radius. The effective distances of plant‒plant communication in trees were discussed from the viewpoint of the arthropod community structure in forest ecosystems.

Effects of Prohydrojasmon on the Number of Infesting Herbivores and Biomass of Field-Grown Japanese Radish Plants.

Prohydrojasmon (PDJ), an analog of jasmonic acid (JA), was found to induce direct and indirect defenses against herbivores in non-infested plants. To test whether PDJ can be used for pest control in crop production, we conducted experiments in pesticide-free Japanese radish fields from October 4 to December 12 in 2015. Twenty-four Japanese radish plants in three plots were treated with a 100 times-diluted commercial formulation (5%) of PDJ (treated plants), and 24 plants in three different plots were treated with water (control plants) until November 29 every week. Throughout the observation period, the number of aphids, leaf-mining fly larvae, vegetable weevils, and thrips was significantly lower on the treated plants than on the control plants. In contrast, the number of lepidopteran larvae was not significantly different between the treated and control plants throughout the study period. Parasitized aphids (mummies) were also observed in both plots. Poisson regression analyses showed that a significantly higher number of mummies was recorded on the treated plants as compared to that on the control plants when the number of aphids increased. This suggested that PDJ application to Japanese radish plants attracted more parasitoid wasps on the treated plants than on the control plants. We also identified eight terpenoids and methyl salicylate as the PDJ-induced plant volatiles in the headspace of the treated plants. Some of these volatiles might be responsible for attracting aphid-parasitoid wasps in the field. However, for other insect pests, we did not find any natural enemies. Interestingly, the genes of the JA and salicylic acid signaling pathways were differentially upregulated in the treated plants. We also observed that the PDJ treatments induced the expression of the genes related to glucosinolate biosynthesis and the subsequent isothiocyanate formation. Additionally, the weights of both the aboveground and belowground parts of the treated plants were significantly lower than those of the respective parts of the control plants. These results indicated that the treatment of Japanese radish plants with a 100 times-diluted commercial formulation of PDJ induced their direct and indirect defenses against several insect pest species to reduce their numbers, and negatively affected their biomass.

Field-Grown Rice Plants Become More Productive When Exposed to Artificially Damaged Weed Volatiles at the Seedling Stage.

It is known that undamaged plants that have been exposed to volatiles from damaged con- or heterospecific plants become more resistant against herbivores. This is one of the plants' induced resistant responses against herbivores. To test whether this response can be used for rice production, we conducted the following experiments over 2 years (2012 and 2013). Rice seedlings were first planted in the rice seedling bed for 2 weeks in early May. There, half of the rice seedlings were exposed to artificially damaged weed volatiles three times for 12 days (treated plants). Weeds were randomly collected from the areas that were >100 m away from the seedling bed and the rice paddy fields. The remaining seedlings were not exposed (control plants). In the middle of May, bunches (ca. three seedlings per bunch) were transplanted to the rice paddy field. In July, leaf damage was observed. The total number of leaves in the treated and control plants was not significantly different. In contrast, the total number of damaged leaves in the treated plants was significantly lower than that in the control plants. In September, rice grains were harvested. The average weight of a rice grain from the treated and control plants was not significantly different. However, the weight of grains per bunch of treated plants was significantly higher than that of control plants; this indicated a significant increase of the number of grains by 23% in 2012 and by 18% in 2013 in the treated plants compared to that in the control plants. The volatiles emitted from the weeds included monoterpenoids (40.4% in total), green leaf volatiles (46.5%), short-chain alcohols (5.3%), short-chain ketone (5.4%), short-chain acetate (0.5%), short-chain aldehyde (1.1%), and hydrocarbon (0.7%). These results suggest that exposure of volatiles from artificially damaged weeds to rice seedlings has the potential to increase rice production.

α-Linolenic acid in Papilio machaon larvae regurgitant induces a defensive response in Apiaceae.

Papilio machaon hippocrates C. Felder et R. Felder, 1864 (Papilionidae) larvae are pests of plants of the family Apiaceae. It is unclear whether Apiaceae plants show induced defensive responses against P. machaon hippocrates larvae, and if so, how these responses are induced. Comparison of the fatty acid (FA) composition of the leaves of host plants and the regurgitant of P. machaon hippocrates larvae by LC-MS revealed a great increase in α-linolenic acid (α-LA) in the regurgitant compared with the FAs contained in the leaves. However, specific FA amino acid conjugates, known as elicitor compounds, such as volicitin, were not detected. Sterile host plants (Saposhnikovia divaricata (Turcz.) Schischk., Apiaceae) were treated with α-LA to mimic the damage made by P. machaon hippocrates larvae. After α-LA treatment to leaves, induced defensive reactions, i.e., release of volatile compounds such as α- and ß-pinene and camphene (possible induced indirect defense) and the accumulation of specialized metabolites such as (R)-falcarinol and bergapten (possible induced direct defense) were observed. These findings highlight the role of α-LA in the interaction between P. machaon hippocrates larvae and Apiaceae host plants.

Targeting diamondback moths in greenhouses by attracting specific native parasitoids with herbivory-induced plant volatiles.

We investigated the recruitment of specific parasitoids using a specific blend of synthetic herbivory-induced plant volatiles (HIPVs) as a novel method of pest control in greenhouses. In the Miyama rural area in Kyoto, Japan, diamondback moth (DBM) (Plutella xylostella, Lepidoptera: Plutellidae) larvae are an important pest of cruciferous crops in greenhouses, and Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of DBM, is found in the surrounding areas. Dispensers of HIPVs that attracted C. vestalis and honey feeders were set inside greenhouses (treated greenhouses). The monthly incidence of DBMs in the treated greenhouses was significantly lower than that in the untreated greenhouses over a 2-year period. The monthly incidences of C. vestalis and DBMs were not significantly different in the untreated greenhouses, whereas monthly C. vestalis incidence was significantly higher than monthly DBM incidence in the treated greenhouses. Poisson regression analyses showed that, in both years, a significantly higher number of C. vestalis was recorded in the treated greenhouses than in the untreated greenhouses when the number of DBM adults increased. We concluded that DBMs were suppressed more effectively by C. vestalis in the treated greenhouses than in the untreated greenhouses.

Synchronous Occurrences of the Diamondback Moth (Lepidoptera: Plutellidae) and its Parasitoid Wasp Cotesia vestalis (Hymenoptera: Braconidae) in Greenhouses in a Satoyama Area.

We characterized the correlation between the occurrences of diamondback moth, Plutella xylostella (L.), larvae and their dominant native parasitoid wasp, Cotesia vestalis (Haliday), in commercial greenhouses in a satoyama area, called Miyama, in Kyoto, Japan. In the three greenhouses used in this study, cruciferous 'mizuna' (Brassica rapa var. laciniifolia [Brassicales: Brassicaceae]) crops were grown. Pesticides against diamondback moth were not routinely applied in the greenhouses. We confirmed that populations of diamondback moth and C. vestalis were maintained on the wild crucifer plant Rorippa indica in the surrounding area from March to December. In the greenhouses, we observed several occurrences of diamondback moth larvae that were, in most cases, followed by occurrences of C. vestalis. We found that C. vestalis females were attracted by volatiles emitted from mizuna plants that were lightly infested with second-stadium diamondback moth larvae under laboratory conditions. The synchronous appearance of diamondback moth larvae and C. vestalis could be explained by the latter being attracted by the volatiles emitted from mizuna plants infested by diamondback moth larvae in the greenhouses.

Multifunctionality of herbivory-induced plant volatiles in chemical communication in tritrophic interactions.

Uninfested plants emit only trace quantities of volatiles (constitutively emitted plant volatiles). In contrast, some plants emit relatively large quantities of volatiles in response to herbivory (herbivory-Induced plant volatiles: HIPVs). Organisms belonging to different trophic levels use plant volatiles in context-dependent manners; consequently, volatiles can be adaptive, non-adaptive, or maladaptive to the emitter plants. In this review, we focus on the multifunctional aspects of HIPVs, which vary qualitatively and quantitatively in emitting plant species and infesting herbivore species, in plant-carnivore interactions, plant-herbivore interactions, and plant-omnivore interactions. Additionally, we review the evidence of plant-plant communication and its effects on tritrophic interactions involving plants, herbivores, and carnivores. Prospects on interactions mediated by plant volatiles induced by herbivorous arthropods are discussed.

Oviposition Experience of Parasitoid Wasps with Nonhost Larvae Affects their Olfactory and Contact-Behavioral Responses toward Host- and Nonhost-Infested Plants.

In nature, parasitoid wasps encounter and sometimes show oviposition behavior to nonhost species. However, little is known about the effect of such negative incidences on their subsequent host-searching behavior. We tested this effect in a tritrophic system of maize plants (Zea mays), common armyworms (hosts), tobacco cutworms (nonhosts), and parasitoid wasps, Cotesia kariyai. We used oviposition inexperienced C. kariyai and negative-experienced individuals that had expressed oviposition behavior toward nonhosts on nonhost-infested maize leaves. We first observed the olfactory behavior of C. kariyai to volatiles from host-infested plants or nonhost-infested plants in a wind tunnel. Negative-experienced wasps showed significantly lower rates of taking-off behavior (Step-1), significantly longer duration until landing (Step-2), and lower rates of landing behavior (Step-3) toward nonhost-infested plants than inexperienced wasps. However, the negative-experience did not affect these three steps toward host-infested plants. A negative experience appears to have negatively affected the olfactory responses to nonhost-infested plants. The chemical analyses suggested that the wasps associated (Z)-3-hexenyl acetate, a compound that was emitted more in nonhost-infested plants, with the negative experience, and reduced their response to nonhost-infested plants. Furthermore, we observed that the searching duration of wasps on either nonhost- or host-infested plants (Step-4) was reduced on both plant types after the negative experiences. Therefore, the negative experience in Step-4 would be nonadaptive for wasps on host-infested plants. Our study indicated that the density (i.e., possible encounters) of nonhost species as well as that of host species in the field should be considered when assessing the host-searching behavior of parasitoid wasps.

Silkworms suppress the release of green leaf volatiles by mulberry leaves with an enzyme from their spinnerets.

In response to herbivory, plants emit a blend of volatile organic compounds that includes green leaf volatiles (GLVs) and terpenoids. These volatiles are known to attract natural enemies of herbivores and are therefore considered to function as an indirect defense. Selection should favor herbivores that are able to suppress these volatile emissions, and thereby make themselves less conspicuous to natural enemies. We tested this possibility for silkworms, which were observed to leave secretions from their spinnerets while feeding on mulberry leaves. When we ablated the spinnerets of silkworms, no secretions were observed. Leaves infested by intact silkworms released smaller amounts of GLVs than leaves infested by ablated silkworms, indicating that the spinneret secretion suppressed GLV production. This difference in GLV emissions was also reflected in the behavioral response of Zenillia dolosa (Tachinidae), a parasitoid fly of silkworms. The flies laid fewer eggs when exposed to the volatiles from intact silkworm-infested leaves than when exposed to the volatiles from ablated silkworm-infested leaves. We identified a novel enzyme in the secretion from the spinneret that is responsible for the GLV suppression. The enzyme converted 13(S)-hydroperoxy-(9Z,11E,15Z)-octadecatrienoic acid, an intermediate in the biosynthetic pathway of GLVs, into its keto-derivative in a stereospecific manner. Taken together, this study shows that silkworms are able to feed on mulberry in a stealthy manner by suppressing GLV production with an enzyme in secretions of their spinnerets, which might be a countermeasure against induced indirect defense by mulberry plants.

Oviposition inhibitor in umbelliferous medicinal plants for the common yellow swallowtail (Papilio machaon).

Umbelliferous medicinal plants, such as Angelica acutiloba Kitagawa and Angelica dahurica Bentham et Hooker filius ex Franchet et Savatier, account for a large percentage of crude drug consumption in Japan. The most serious problem in the cultivation of umbelliferous medicinal plants is the feeding damage caused by the common yellow swallowtail (Papilio machaon hippocrates C. & R. Felder, 1864). When we compared the numbers of eggs laid by P. machaon on six umbelliferous medicinal plants, the eggs on A. acutiloba, A. dahurica, and Glehnia littoralis Fr. Schmidt ex Miquel were the most numerous, those on Saposhnikovia divaricata Schischkin and Cnidium officinale Makino were rare, and Bupleurum falcatum Linné was not oviposited at all. To identify oviposition inhibitors for P. machaon in B. falcatum, S. divaricata, and C. officinale, the volatile chemical constituents of these umbelliferous medicinal plants were compared with GC-MS. We carried out multivariate analysis of gas chromatographic data and concluded that germacrene D, α-humulene, and trans-caryophyllene play important roles in protecting plants from oviposition by P. machaon. Their oviposition repellent activity was confirmed by the fact that the number of eggs laid on the leaves around a repellent device containing a mixture of germacrene D, α-humulene, and trans-caryophyllene was reduced by 40% compared to a control.

Parasitoid wasps' exposure to host-infested plant volatiles affects their olfactory cognition of host-infested plants.

Using Cotesia vestalis, a parasitoid wasp of diamondback moth larvae and three crucifer plant species (cabbage, komatsuna, and Japanese radish), we examined the effects of exposure to host-infested plant volatiles from one plant species on a newly emerged wasp's subsequent olfactory cognition of host-infested plant volatiles from the same or different plant species. The preference of C. vestalis between infested and uninfested plant volatiles was tested in a choice chamber. Volatile-inexperienced wasps significantly preferred infested cabbage and infested radish volatiles, but not infested komatsuna volatiles. After exposure to infested cabbage volatiles, wasps showed a significant preference for infested cabbage volatiles, while the significant preference for infested radish volatiles that had been observed in inexperienced wasps was no longer observed. After exposure to infested komatsuna volatiles, wasps significantly preferred infested komatsuna volatiles, and the pre-exposure significant preferences for infested cabbage volatiles and infested radish volatiles remained. After exposure to infested radish volatiles, the significant preferences for infested cabbage and infested radish volatiles did not change. Furthermore, wasps showed a significant preference for infested komatsuna volatiles. The compound compositions of the volatile blends from the three infested plant species were grouped separately in a principal coordinates analysis. The experience-based cognition of C. vestalis for host-infested plant volatiles of three plant species is discussed.

Intraspecific variation among Tetranychid mites for ability to detoxify and to induce plant defenses.

Two genotypes coexist among Kanzawa spider mites, one of which causes red scars and the other of which causes white scars on leaves, and they elicit different defense responses in host plants. Based on RNA-Seq analysis, we revealed here that the expression levels of genes involved in the detoxification system were higher in Red strains than White strains. The corresponding enzyme activities as well as performances for acaricide resistance and host adaptation toward Laminaceae were also higher in Red strains than White strains, indicating that Red strains were superior in trait(s) of the detox system. In subsequent generations of strains that had survived exposure to fenpyroximate, both strains showed similar resistance to this acaricide, as well as similar detoxification activities. The endogenous levels of salicylic acid and jasmonic acid were increased similarly in bean leaves damaged by original Red strains and their subsequent generations that inherited high detox activity. Jasmonic acid levels were increased in leaves damaged by original White strains, but not by their subsequent generations that inherited high detox activity. Together, these data suggest the existence of intraspecific variation - at least within White strains - with respect to their capacity to withstand acaricides and host plant defenses.