Reliable survey of arthropods is a crucial for their conservation, community ecology, and pest control on terrestrial plants. However, efficient and comprehensive surveys are hindered by challenges in collecting arthropods and identifying especially small species. To address this issue, we developed a non-destructive environmental DNA (eDNA) collection method termed "plant flow collection" to apply eDNA metabarcoding to terrestrial arthropods. This involves spraying distilled or tap water, or using rainfall, which eventually flows over the surface of the plant, and is collected in a container that is set at the plant base. DNA is extracted from collected water and a DNA barcode region of cytochrome c oxidase subunit I (COI) gene is amplified and sequenced using a high-throughput Illumina Miseq platform. We identified more than 64 taxonomic groups of arthropods at the family level, of which 7 were visually observed or artificially introduced species, whereas the other 57 groups of arthropods, including 22 species, were not observed in the visual survey. These results show that the developed method is possible to detect the arthropod eDNA remained on plants although our sample size was small and the sequence size was unevenly distributed among the three water types tested.

Plant ecological traits affect the species identity of plant-colonizing arthropods, which in turn induces species-specific trait changes in plants, forming feedback between plants and arthropods. Such feedback can amplify initial differences in species composition, leading to large variations (i.e., high β diversity). We hypothesized that the differences in plant initial conditions have sustained effects on arthropod community composition and species richness. To test this hypothesis, we monitored arthropod community assembly on a willow tree species, Salix eriocarpa, which was experimentally manipulated into three initial treatments: undamaged (in chamber 1); damaged by the specialist leaf beetle, Plagiodera versicolora (chamber 2); and “exposed” plants that were undamaged but were exposed to volatiles from damaged plants (in chamber 2). The arrival and population dynamics of the leaf beetle were affected by the plant’s initial condition (chamber 1 vs. 2), which could result from the microscale environmental heterogeneity between chambers (chamber effect) and/or from the herbivory-related impacts (direct herbivory and exposure to induced volatiles in chamber 2). The community composition on damaged and exposed plants became significantly different on day 32. In addition, the divergence in composition between plant individuals was significantly smaller in undamaged plants (chamber 1) than in damaged and exposed plants (chamber 2) on day 60. The compositional variations (β diversity) between chambers, between treatments, and between days, comprised a large proportion (two third) of the total species richness (γ diversity) in the whole community of arthropods. These results suggest that plant initial condition is a key driver of community assembly and the maintenance of species diversity.

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.

We evaluated the effectiveness of using a blend of volatiles that attract Cotesia vestalis, a specialist parasitoid wasp of diamondback moth (DBM) larvae, to control DBM larvae on cabbage plants under open field conditions. We set three dispensers of the synthetic C. vestalis attractant together with one sugary-food feeder in a cabbage plot (10 m × 1 m; the treated plot) on one side of a pesticide-free open agricultural field (approximately 20 m × 20 m) from June to September in 2010 and July to August in 2011. On the other side of the field, we created a control cabbage plot of the same size in which neither dispensers nor a feeder was set. The incidences of DBM larvae and C. vestalis cocoons in the control and treated plots were compared. In 2010, the incidence of DBM larvae in the treated plot was significantly lower than that in the control plot. Poisson regression analyses in 2010 showed that the rate of increase in the number of C. vestalis cocoons along with an increase in the number of DBM larvae in the treated plot was significantly higher than that in the control plot. In 2011, the incidence in both the treated and control plots remained low (five larvae per plant or less) with no significant difference between the plots. Poisson regression analyses in 2011 showed that the number of C. vestalis cocoons in the treated plot was significantly higher than that in the control plot, irrespective of the number of DBM larvae. This 2-year field study suggested that the dispensers recruited native C. vestalis from the surrounding environment to the treated plot, and the dispensers controlled the number of DBM larvae in 2010 when the density of DBM larvae exceeded the economic injury levels for the cabbage crop. We also compared the incidences of other arthropods in the control and treated plots. The incidences of Pieris rapae larvae and Plusiinae spp. were not affected by the treatments. The number of aphids in the treated and control plots was inconsistent between the 2 years. Based on these 2-year results, the possible use of C. vestalis attractants in open agricultural fields is discussed.

Host-parasite interactions between phytoplankton and fungi (chytrids) are key processes in aquatic ecosystems. However, individual-level heterogeneity in these interactions remains unexplored, although its importance in predicting the spread of diseases has been demonstrated in epidemiology. In this study, we experimentally tested whether individual-level heterogeneity could be a good indicator of phytoplankton-chytrid interactions, using a freshwater green alga Staurastrum sp., the diatoms Ulnaria sp. and Fragilaria crotonensis, and chytrid fungi. The number of attached fungi per host cell showed a non-random clumped parasite distribution on Ulnaria sp. and F. crotonensis, but a random Poisson distribution on Staurastrum sp. To explore the potential mechanisms of these patterns, we developed a mathematical model describing sequential encounters between chytrid zoospores and host cells. The statistical fits of the model explained the parasite distributions for Ulnaria sp. and F. crotonensis well, indicating that the clumped parasite distributions may result from an infection rate, increasing with the number of infections that already occurred on each host cell. Simultaneous analysis of volatile organic compounds (VOCs) from uninfected and infected host populations revealed that, among 13 VOCs detected, 6 components characterized the differences in VOC compositions between species and infection status. In particular, the level of beta-ionone, potentially acting against fungal activities, was significantly reduced in the presence of chytrid infection of Staurastrum sp. These VOCs are targets for future studies, which potentially act as chemical signals influencing chytrid zoospores’ behaviors. The combination of mathematical and chemical analyses represents a promising approach to better understand the individual-level processes of phytoplankton-chytrid interactions.

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.

Abstract EcoPlate quantifies the ability of a microbial community to utilize 31 distinct carbon substrates, by monitoring color development of microplate wells during incubation. Well color patterns represent metabolic profiles. Previous studies typically used color patterns representing average values of three technical replicates on the final day of the incubation and did not consider substrate chemical diversity. However, color fluctuates during incubation and color varies between replicates, undermining statistical power to distinguish differences among samples in microbial functional composition and diversity. Therefore, we developed a protocol to improve statistical power with two approaches. First, we optimized data treatment for color development during incubation and technical replicates. Second, we incorporated chemical structural information for the 31 carbon substrates into the computation. Our framework implemented as the protocol in the R environment is able to compare the statistical power among different calculation methods. When we applied it to data from aquatic microcosm and forest soil systems, we observed substantial improvement in statistical power when we incorporated temporal patterns during incubation instead of using only endpoint data. Using maximum or minimum values of technical replicates also sometimes gave better results than averages. Incorporating chemical structural information based on fuzzy set theory could improve statistical power but only when relative color density information was considered; it was not seen when the pattern was first binarized into the presence or absence of metabolic activity. Finally, we discuss research directions to improve these approaches and offer some practical considerations for applying our methods to other datasets.

Summary Herbivorous arthropods often induce phenotypic changes in plants of terrestrial systems, which include increased direct resistance to herbivores. In addition, infested plants release quantitatively and qualitatively different volatiles from those of uninfested plants, which are so‐called herbivore‐induced plant volatiles (HIPVs). Due to HIPVs, plants are more conspicuous to herbivorous arthropods and their natural enemies (carnivorous arthropods) than uninfested plants, thus acting as foraging cues in tri‐trophic systems. Intriguingly, herbivore and natural enemy responses to HIPVs are highly diverse. Whether they are attracted or repelled by HIPVs depend on the plant–herbivore–natural enemy species combination, suggesting a HIPV multifunctionality. We hypothesized that co‐evolutionary diversification of foraging strategies in herbivores and natural enemies, where arthropods adapted to diverse plant ecological traits, served to explain HIPV multifunctionality. We developed a food chain model of plant–herbivore–natural enemy to test our hypothesis, where plants exhibited three different states and different apparency (uninfested < lightly infested < highly infested) and quality (lightly infested > highly infested). The shifts between plant states were mediated by herbivore life cycle, interactions among herbivores, natural enemies and plant reproduction. The natural enemy evolutionary stable strategy (ESS) was predicted to choose the lightly and heavily infested plants in broad ranges of induced direct resistance and plant apparency (HIPV levels), implying that HIPVs acted as the induced indirect resistance. The corresponding herbivore ESS was to choose (or avoid) HIPVs when HIPV levels were low (or high). When the induced direct resistance was very high and thus herbivore quality was low, natural enemies tended to avoid increased HIPVs with increasing herbivory levels. This was associated with herbivore ESS choice for HIPVs, leading to intraspecific enemy‐free space. These predicted ESS diversities explained observed herbivore and natural enemy responses to HIPVs in several contrasting plant systems, including willow trees, lima bean and wild tobacco. Our findings suggest that non‐lethal herbivory and variations in induced plant responses are key mechanisms for evolutionary diversification of animal foraging behaviour and thus structure of ecological networks.

When exposed to herbivore-infested plant volatiles or volatiles from artificially damaged plants, intact plants enhance their defense against herbivores. This phenomenon is called plant-plant communication. Here, we outline studies on plant-plant communication from both ecological and plant physiological perspectives. Regarding the ecological perspective, we give an overview of studies showing that plant-plant communication affect direct and indirect defense levels of exposed plants, and herbivore performance on exposed plants. Cases of kin selection in plant-plant communications and intra-plant communication via airborne signals are also summarized. Regarding the plant physiological perspective, we give an overview of studies that showed specific responses of receiver plants to a volatile molecular species, to different configurations of a volatile molecular species and to blends of volatiles. Furthermore, we review the signaling pathways involved, priming, sensitivity, and how plants receive volatile compounds in plant-plant communications.

When damaged by herbivorous arthropods, plants are known to emit a blend of volatiles that have several ecological functions in nature. One of the well known functions is to attract carnivorous natural enemies of inflicting herbivores. Volatiles from infested plants are specific in terms of herbivore species and plant species. The carnivores are known to cope with such specificity by learning. The first part of this paper will show the learning behavior of parasitic wasps that attack aphids on bean plants. In the second part of this paper, we will focus on the multifunctional aspects of volatiles from plants that are either infested or intact. Our recent results on the tritrophic interaction of willow plants, willow leaf beetles and ladybirds showed that the volatiles from willow plants infested by leaf beetles mediated interactions between plants and leaf beetles, plants and ladybirds. Further, these interactions were affected by their physiological conditions, gender and developmental stages. Based on these data, we will discuss the interaction and information networks mediated by ecological volatiles.

Plant anti-herbivore defence is inducible by both insect feeding and egg deposition. However, little is known about the ability of insect eggs to induce defences directed not against the eggs themselves, but against larvae that subsequently hatch from the eggs. We studied how oviposition (OP) by the sawflyDiprion pinionPinus sylvestrisfoliage affects the plant's defensive potential against sawfly larvae. Larvae that initiated their development onP. sylvestristwigs on which they hatched from eggs gained less weight and suffered higher mortality than those fed on egg-free twigs. The poor performance of these larvae also affected the next herbivore generation since fecundity of resulting females was lower than that of females which spent their larval development on egg-free pine. Transcript levels ofP. sylvestrissesquiterpene synthases (PsTPS1,PsTPS2) were increased byD. piniOP, reached their highest levels just before larval hatching, and decreased when larvae started to feed. However, concentrations of terpenoid and phenolic metabolites presumed to act as feeding deterrents or toxins for herbivores did not change significantly after OP and feeding. Nevertheless, our performance data suggest that insect egg deposition may act to ‘warn’ a plant of upcoming feeding damage by larvae.

Abstract. The leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae) is a specialist herbivore, all of whose mobile stages feed on the leaves of salicaceous plants. Both the larval and adult stages of the ladybird Aiolocaria hexaspilota (Coleoptera: Coccinellidae) are dominant natural enemies of the larvae of the leaf beetle. To clarify the role of plant volatiles in prey‐finding behaviour of A. hexaspilota, the olfactory responses of the ladybird in a Y‐tube olfactometer are studied. The ladybird adults show no preference for willow plants Salix eriocarpa that are infested by leaf beetle adults (nonprey) over that for intact plants but move more to the willow plants infested by leaf beetle larvae (prey) than to intact plants. Moreover, ladybird larvae show no preference for willow plants infested by leaf beetle larvae or adults over intact plants. Using gas chromatography‐mass spectrometry, six volatile compounds are released in larger amounts in the headspace of willow plants infested by leaf beetle larvae than in the headspace of willow plants infested by leaf beetle adults. In addition, the total amount of volatiles emitted from willow plants that are either intact or infested by leaf beetle adults is much smaller than that from willow plants infested by leaf beetle larvae. These results indicate that volatiles from S. eriocarpa infested by P. versicolora inform A. hexaspilota adults about the presence of the most suitable stage of their prey, whereas A. hexaspilota larvae do not use such information.

We investigated how adults of willow leaf beetle Plagiodera versicolora find shoots with new leaves that were suitable food resources for them by focusing on shoot odor. Female and male beetles (starved and satiated) preferred the odor from intact shoots of Salix eriocarpa to clean air. Starved females preferred odor from shoots with leaves infested by conspecifics to odor from intact shoots. However, satiated females as well as starved and satiated males showed no significant discrimination between the two odors. Pooling of the preference data revealed that starved individuals of females and males preferred odor from infested shoots to an extent that was significantly different from satiated individuals, while the distribution of starved and satiated females was not significantly different from that of males. These olfactory responses would provide an explanation for the host plant finding behavior of this specialist herbivore in the field.

植物の香りは節足動物の行動を制御するはたらきがある。そこで、植物の香りが節足動物の初期移入と定着に影響を与えているかを調べた。京都大学生態学研究センターのヤナギ林に生育するヤナギ属植物6種それぞれから2個体選び、枝を2本ずつ取り挿し木のポット植えを作成した。1か月育てた後、植食者が移入する前の状況として、非食害時の（健全な）植物の香りを捕集し、ガスクロマトグラフ質量分析計で分析・同定を行った。捕集した翌日に、ヤナギ林に隣接した圃場にポット植えの健全植物を置き、節足動物の初期侵入過程を1週間記録した。1つの植物個体が放出する香りは複数の揮発性物質が混ざり合ってできている。本研究では、1つの個体が放出する香りの複数成分の量を多変量と考えて、各個体間の香りブレンドの類似度をBray-Curtis距離を用いて計算し植物種間に違いがあるかどうか比較すると同意に、違いを生み出す主要成分の特定を目指した。また、香りブレンドの類似度と節足動物群集組成の類似度の間に相関があるかどうかも解析した。今回は、これらの解析結果を発表する。

植物が花や果実、葉から放出する揮発性物質(香り)は、複数の成分の混合である（松井ほか2016）。香り成分の組成や各成分の放出量、総放出量は植物の種類や生育する環境、食害などによって差が生じる。これまでの室内での香り成分の研究では、気温などが一定で変動がなく、自然環境とはかけ離れている。しかし、自然状態に近づけるために野外で実験を行うのは、雨風や実験中に侵入する昆虫の影響といった問題などのため、困難である。また、時間や手間が掛かることもあり、野外において長期に渡って得られたデータは少ない。本研究は枝間・個体間で香り成分の動態にどのような違いが見られるのかを明らかにすることを目的とし、2か月間、イヌコリヤナギ(Salix integra)に注目し、野外で香りの調査を行った。香り成分の捕集は、京都大学生態学研究センター(滋賀県大津市)の圃場に生育するイヌコリヤナギ(Salix integra)を対象として行った。期間は、2016年9月11日～10月27日（全25回）で、捕集の頻度は2日に1回とした。調査対象は6個体選び、各個体から葉の量や大きさが似通った枝（1年枝～2年枝）を2本ずつ選定した。選定した枝は、同じ枝から枝分かれしている2本を選んだ。枝ごとに袋を被せ、そこに吸着管（吸着剤：tenax）１本を繋げた。吸着管の先からポンプで袋の中の空気を吸う（100ml/min、30分間）ことで、吸着管に袋の中の香り成分を吸着させた。吸着管に集めた香りはガスクロマトグラフ質量分析計(GC-MS)を用いて分析・同定を行った。解析は主座標分析(Principal Coordinate Analysis;PCoA)を利用した。野外では長期的に見ると香りが大きく変動することが明らかとなった。また、個体間で比較を行うと香り成分の変動に違いが見られた。成分ごとに見るとtrans-.beta.-Ocimeneなどの食害された時に放出される香り成分に特に大きな変動が見られた。これは調査期間が、植食性昆虫が葉の上に存在し、活発に行動する期間と被った為などの理由が考えられる。

自然生態系において、生物は捕食や寄生、相利などの種間相互作用を通じて互いに影響を及ぼしあっている。従来、生物種間の相互作用を調べるには、操作実験を行う必要があった。しかし、操作実験では、操作の対象となった特定の種間相互作用しか調べることが出きない。本研究では、多種個体群密度の時系列データに対してCCM(Convergent Cross Mapping)を用いて種間相互作用を検出することを試みた。時系列データは、滋賀県大津市において、2016年9月7日より同年10月27日まで、2日に1回の計25回おこなった野外調査によって得た。圃場に植えられたイヌコリヤナギ（Salix integra）6個体から3枝を選び出し、枝上で確認できたすべての節足動物の種類と個体数を記録し、節足動物群集の時系列データに対してCCMを適用し、種間相互作用を推定した。 調査をおこなった25日間で74種、2455個体の節足動物を観察できた。まず、一日で観察された捕食者、植食者数の合計の個体数の時系列データに対してCCMを行ったが、すべての生物群の間において因果関係が認められなかった。次に、調査日全体で個体数が多かった6種について総当たりで解析を行ったが、やはり因果関係は検出されなかった。CCMによって種間相互作用が検出されなかった理由として考えられることの一つに、調査の結果発見された虫の個体数が少なすぎた可能性がある。本研究では、25日で約2500個体のデータを得たものの、調査開始日より調査終了日に向かって、一日に観察される個体数は減少していた。調査木や生物種によっては発見されないケースも多く、これがCCMによる因果関係の推定を困難にした主要因である可能性がある。

本研究では、生物群集の形成過程において「偶然性」と生物の定着順序が群衆構造に与える影響（＝「先住効果」）の強度を決定する機構は何か、というう問いに答えることを目的とする。特に植物上に形成される昆虫群集に注目して、以下の2つの仮説を提案する。[仮説1]植物上に最初に定着する植食者（＝「先駆者」）の種類の、植物個体間におけるばらつき（＝偶然性の高さ）は、植物の香りシグナルの質と量で決まる。[仮説2]先住効果は，先駆者が引き起こす植物の誘導応答（＝直接・間接防御）の種特異性が顕著なほど大きくなる。これらの仮説の検証のため、3種のアブラナ科アブラナ属植物（各種2品種の計6品種）を用いた実験を行い、植物上の節足動物の移入・定着・個体数、香りシグナルを含む二次代謝産物の時系列データを収集し統計解析を進める。これにより偶然性が強くかつ先住効果の大きな植物種が持つ香りシグナルと誘導応答の特性を解明し、群物形成過程が植物間で多様化する機構の理解をめざす。[仮説１]の検証のため、植物の品種間で見られる先駆昆虫群集の違いや同品種内での群集構造のばらつきと初期移入に関わる可能性の高い香りシグナル（揮発性物質）の組成を比較することが必要である。そこで、2020年度は、野外にポット植えの健全植物（3種6品種）を配置して先駆昆虫の移入過程を1ヶ月間記録した。また、健全な各植物の揮発性物質を吸着材（Tenax TA）に捕集し、ガスクロマトグラフ質量分析計（GC-MS)で種類(質)と量を特定した。2021年度は、[仮説２]の検証のために、2020年度の結果を考慮して選んだ、アブラナとセイヨウアブラナの2種とアブラナ2品種、セイヨウアブラナ1品種を用いて、先駆昆虫による種特異的環境改変作用の強度指標とする食害を受ける前と後の植物の二次代謝産物の生産量の変化を定量した。

We developed a new environmental DNA(eDNA) collecting method for the arthropods on crops. DNA barcode region, Cytochrome c oxidase subunit I (COI) gene, of the collected eDNA was comprehensively sequenced by a high-throughput sequencer after being extracted, purified, and amplified. As the result, we successfully collected and detected eDNA of pest species and their natural enemies collected from potted eggplant and cabbage and cabbage and rice plant planted directly in the ground. We also investigated the condition of pests when we could collect and detect the eDNA. As the result, it depended on the period of infestation by pest insects, the period after removing pest insects from a plant, and the number of insects feeding on a plant whether the eDNA was detected or not. For example, in some cases, eDNA was detected in an hour after feeding started by pest insects and, in other cases, eDNA was remained on a plant more than 7 days, after the pest insects were removed from the plant.

群集形成において初期移入者、移入者による環境改変作用の程度や質が重要な要素となる。本研究では、植物を環境とした植物と節足動物群集の相互作用系を新たなモデル系とすることで、植物の揮発性物質（香り）の情報性、食害誘導応答、履歴効果の視点から共存する近縁な植物上に、異なる節足動物群集が形成される過程と機構を明らかにすることを目的としている。 ヤナギ属植物6種のポット植えを用意し、植食者が移入する前の状況として、未食害植物の香りを捕集して分析・同定を行った。捕集した翌日に、ヤナギ林に隣接した圃場にポット植えの健全植物を置き、節足動物の初期侵入過程を1週間記録した。また、イヌコリヤナギ6個体を対象に、節足動物の種と個体数の記録を行うと同時に香りの組成についても2日に1度、25回という高頻度の時系列観測を行った。植物個体が放出する香りの複数成分の量を多変量と考えて、各個体間の香りブレンドの類似度をBray-Curtis距離を用いて計算し植物種間に違いがあるかどうか比較した。また、香りブレンドの類似度と節足動物群集組成の類似度の間に相関があるかどうかも解析した。その結果、植物の香り物質の組成・定着節足動物群集組成ともに、ヤナギ種間で差がみられた。しかし、両者の組成の間には有意な相関は見られなかった。また、最初に植物に移入してくる種（第一移入種）と香り物質の組成の間に関連がみられないことから、第一移入種の移入機構は植物の香り物質の組成ではない可能性が示された。その一方で、第一移入種の違いは定着群種組成の差には貢献していることから何らかの履歴効果の存在が示唆された。この履歴効果を生み出す機構の一つとして、第一移入種に食害を受けた誘導反応が、節足動物の移入及び群集形成に影響を及ぼしている可能性があることを考慮し、昆虫群集と香りの時系列データを組み合わせた時系列解析を行う予定である。

In many cases, parasitic wasps are attracted to host herbivore-infested plant odors. We focused on Cotesia vestalis, a parasitic wasp of diamondback moth larvae, and three crucifer plant species (cabbage, komatsuna and Japanese radish). We examined how the wasp responded to host-infested plant volatiles (HIPVs) of either the same or different plant species when the wasp has experienced HIPVs from one plant species. HIPVs from each plant species differently affected the wasp’s subsequent responses to HIPVs. We also investigated genetic variation among local populations of C. glomerata, a parasitic wasp of cabbage white butterfly larvae throughout Japan. Bayesian cluster analysis revealed two or three genetic clusters across the locations sampled. The pattern of genetic differentiation, estimated from the microsatellite data, indicated a significant level of difference in genetic structure between Hokkaido populations and other populations.

植物の間接防御には、植食者からの食害後に特異的な揮発性物質を放出し、捕食者を誘引する戦略がある。従来、このような間接防御に関する研究は農生態系での研究が主に行われており、1種類の植物とその上の植食者と捕食者の相互作用に注目が集まっていた。しかし、野外の植物群集においては、1種の植食者が同所的に生育する複数の近縁植物種を利用する系が多く存在する。したがって、植食者の天敵も複数種の植物の揮発性物質のブレンドを利用することになる。このような状況では、揮発性物質を介した植物-植食者-捕食者間相互作用は、非常に複雑である可能性が高く、植物の間接防御の働きを理解するためには新しいアプローチが必要である。そこで、同所的に生育するヤナギ7種とそれらを食害するヤナギルリハムシPlagiodera versicoloraおよびその主な天敵であるカメノコテントウAiolocaria hexaspilotを用いて以下の実験を行った。その結果、天敵の誘引性に植物間で有意な違いが見られ、主に4つの誘引性の違うグループに分けられた。また、植食者の産卵選好性が高い種ほど天敵の誘引性が高く、食べられにくい植物ほど天敵の誘引性が低いという関係も明らかになった。さらに、化学分析及びデータ解析を行った結果、植物を天敵の誘引性によって分けた4つのグループ間で、植物の揮発性物質の組成が有意に異なることを明らかとした。昨年度に続き,野外調査を行い、野外においても、室内実験と同じ傾向が見られることを示した。

Media report ヤナギルリハムシという植食者に食べられたヤナギ植物が特別な匂いを放出して、ヤナギルリハムシの捕食者であるカメノコテントウを呼ぶという、カメノコテントウとヤナギの関係

Media report ヤナギルリハムシという植食者に食べられたヤナギ植物が特別な匂いを放出して、ヤナギルリハムシの捕食者であるカメノコテントウを呼ぶ