Host plant scents attract rolled-leaf beetles to Neotropical gingers in a Central American tropical rain forest

Leaf volatile chemicals are known to reduce herbivory rates by repelling or intoxicating insect herbivores and by attracting the predators and parasitoids of herbivores. However, leaf volatiles may also be used by insect herbivores as cues to locate their host plants. Leaf volatiles are suggested to be important host search cues for herbivores in structurally complex and diverse habitats, such as tropical rain forests. A group of insect herbivores, the rolled-leaf beetles (Coleoptera: Chrysomelidae: Hispinae), have maintained a highly specialized interaction with Neotropical gingers (Zingiberales) for ca. 60 million years. In this study, we explored chemical attraction to host plants under controlled laboratory conditions, using four sympatric rolled-leaf beetle species, Cephaloleia dorsalis Baly, Cephaloleia erichsonii Baly, Cephaloleia fenestrata Weise, and Cephaloleia placida Baly. For each beetle species, we investigated (i) whether it was repelled or attracted by leaf scents produced by four host and four non-host plant species, including Neotropical gingers in the families Marantaceae, Costaceae, and Zingiberaceae; and (ii) its ability to use scents to detect its host plant. We found that rolled-leaf beetles can detect and are attracted by leaf volatiles from both host and non-host gingers. Additionally, when beetles were simultaneously exposed to leaf volatiles from host and non-host plants, three rolled-leaf beetle species were significantly more attracted by volatiles from their host plants than from non-hosts. Only one of the beetle species was not able to discriminate between host and non-host scents.     

The effects of non-host plant essential oil volatiles on the behaviour of the pollen beetle Meligethes aeneus

The use of semiochemicals for manipulation of the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae) is being investigated for potential incorporation into a push‐pull control strategy for this pest, which damages oilseed rape, Brassica napus L. (Brassicaceae), throughout Europe. The response of M. aeneus to non‐host plant volatiles was investigated in laboratory assays to establish whether they have any effect on host plant location behaviour. Two approaches were used. First a novel, moving‐air bioassay using air funnels was developed to compare the response of M. aeneus to several non‐host plant essential oils. The beetles avoided the host plant flowers in the presence of non‐host volatiles, suggesting that M. aeneus uses olfactory cues in host location and/or acceptance. The results were expressed as ‘repellency values’ in order to compare the effects of the different oils tested. Lavender (Lavendula angustifolia Miller) (Lamiaceae) essential oil gave the highest repellency value. In addition, a four‐arm olfactometer was used to investigate olfactory responses, as this technique eliminated the influence of host plant visual and contact cues. The attraction to host plant volatiles was reduced by the addition of non‐host plant volatiles, but in addition to masking the host plant volatiles, the non‐host volatiles were avoided when these were presented alone. This is encouraging for the potential use of non‐host plants within a push‐pull strategy to reduce the pest colonisation of crops. Further testing in more realistic semi‐field and field trials is underway.     

Host location in Oomyzus gallerucae (Hymenoptera: Eulophidae), an egg parasitoid of the elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Eggs of the elm leaf beetle Xanthogaleruca luteola are often heavily attacked by the chalcidoid wasp Oomyzus gallerucae. We studied the chemical signals mediating interactions between the egg parasitoid, its host, and the plant Ulmus campestris. Olfactometer bioassays with O. gallerucae showed that volatiles of the host-plant complex attract the parasitoid. In order to determine the source of attractive volatiles within this host-plant-complex, we tested separately the effect of odours of eggs, gravid elm leaf beetle females, faeces of the beetles and elm twigs (with undamaged leaves and leaves damaged either mechanically or by feeding of the beetles). Odours of faeces of the elm leaf beetle were attractive, whereas neither volatiles from eggs nor from gravid females acted as attractants. Volatiles from undamaged or damaged plants did not elicit a positive reaction in O. gallerucae, whereas volatiles from feeding-damaged plants onto which host eggs had been deposited were attractive. This latter result suggests that it is not feeding but deposition of host eggs onto elm leaves that induces the production of plant volatiles attractive to the egg parasitoid. Investigations of the search patterns of O. gallerucae within the habitat by laboratory bioassays revealed that the egg parasitoid encounters host eggs by chance. Contact kairomones from faeces were demonstrated to be important in microhabitat acceptance, while contact kairomones isolated from the host eggs are relevant for host recognition. Received: 12 February 1997 / Accepted: 29 April 1997     

The role of olfactory cues in the sequential radiation of a gall‐boring beetle,Mordellistena convicta

1. Herbivorous insects often have close associations with specific host plants, and their preferences for mating and ovipositing on a specific host‐plant species can reproductively isolate populations, facilitating ecological speciation. Volatile emissions from host plants can play a major role in assisting herbivores to locate their natal host plants and thus facilitate assortative mating and host‐specific oviposition. 2. The present study investigated the role of host‐plant volatiles in host fidelity and oviposition preference of the gall‐boring, inquiline beetle, Mordellistena convicta LeConte (Coleoptera: Mordellidae), using Y‐tube olfactometers. Previous studies suggest that the gall‐boring beetle is undergoing sequential host‐associated divergence by utilising the resources that are created by the diverging populations of the gall fly, Eurosta solidaginis Fitch (Diptera: Tephritidae), which induces galls on the stems of goldenrods including Solidago altissima L. (Asteraceae) and Solidago gigantea Ait. 3. Our results show that M. convicta adults are attracted to galls on their natal host plant, avoid the alternate host galls, and do not respond to volatile emissions from their host‐plant stems. 4. These findings suggest that the gall‐boring beetles can orient to the volatile chemicals from host galls, and that beetles can use them to identify suitable sites for mating and/or oviposition. Host‐associated mating and oviposition likely play a role in the sequential radiation of the gall‐boring beetle.     

Cockchafer Larvae Smell Host Root Scents in Soil

In many insect species olfaction is a key sensory modality. However, examination of the chemical ecology of insects has focussed up to now on insects living above ground. Evidence for behavioral responses to chemical cues in the soil other than CO₂ is scarce and the role played by olfaction in the process of finding host roots below ground is not yet understood. The question of whether soil-dwelling beetle larvae can smell their host plant roots has been under debate, but proof is as yet lacking that olfactory perception of volatile compounds released by damaged host plants, as is known for insects living above ground, occurs. Here we show that soil-dwelling larvae of Melolontha hippocastani are well equipped for olfactory perception and respond electrophysiologically and behaviorally to volatiles released by damaged host-plant roots. An olfactory apparatus consisting of pore plates at the antennae and about 70 glomeruli as primary olfactory processing units indicates a highly developed olfactory system. Damage induced host plant volatiles released by oak roots such as eucalyptol and anisol are detected by larval antennae down to 5 ppbv in soil air and elicit directed movement of the larvae in natural soil towards the odor source. Our results demonstrate that plant-root volatiles are likely to be perceived by the larval olfactory system and to guide soil-dwelling white grubs through the dark below ground to their host plants. Thus, to find below-ground host plants cockchafer larvae employ mechanisms that are similar to those employed by the adult beetles flying above ground, despite strikingly different physicochemical conditions in the soil.     

Relevance of visual and olfactory cues for host location in the mustard leaf beetle Phaedon cochleariae

The relevance of visual and olfactory cues for host‐plant location is investigated in males and females of the oligophagous mustard leaf beetle Phaedon cochleariae Fabricius (Coleoptera: Chrysomelidae). Different objects are offered in a walking arena and the behaviour of beetles is observed. Beetles orient toward vertically or horizontally striped black and white pattern independent of stripe orientation. The results suggest that contrast facilitates orientation in the field, whereas the pattern itself may be less important for host location in dense vegetation. The response to green and yellow objects is tested to investigate discrimination abilities between young (green) and mature (yellow) leaves. Beetles prefer green over yellow independent of material (cardboard or leaves of Nasturtium officinale R. Br., Brassicaceae). Preference behaviour tested in a dual‐choice contact assay coincides with visual preferences, where adults prefer young, more nutritious leaves for feeding and oviposition. Furthermore, females discriminate between visual cues of green leaves and green cardboard, whereas males do not, indicating that females are more sensitive in colour discrimination. Differences in colour wavelength influence the choice of beetle behaviour more strongly than differences in intensity. Both sexes of P. cochleariae prefer volatiles of the host plant N. officinale, whereas only females respond to the main volatile compound 2‐phenylethyl isothiocyanate. Given a choice between visual and olfactory cues, males orientate towards the colour cues, whereas females do not show any preferences. In males, visual cues may thus override olfactory cues, whereas, in females, both are equally important, which may reflect different ecological requirements and/or physiological abilities.     

Behaviours of phoretic mites (Acari) associated with Ips pini and Ips grandicollis (Coleoptera: Curculionidae) during host‐tree colonization

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Visual cues override olfactory cues in the host-finding process of the monophagous leaf beetle Altica engstroemi

It is generally assumed that specialist insect herbivores utilize plant odours to find their particular host plants and that visual cues are of minor importance in the host‐finding process. We performed Y‐tube olfactometer bioassays and small‐scale field experiments to determine whether, under laboratory and field conditions, the monophagous herbivore Altica engstroemi J. Sahlberg (Coleoptera: Chrysomelidae: Alticinae) is guided to its host plant Filipendula ulmaria (L.) Maxim. (Rosaceae) by visual or olfactory cues. The olfactometer tests showed that A. engstroemi was never attracted to odours, either from undamaged or from damaged plants. Even starvation for 24 h did not change this behaviour. However, the field experiment showed that visual cues alone were sufficient to attract a significant number of starved beetles when offered a choice between bagged host plants and bagged green plastic control ‘plants’. Our findings contrast with the general view that plant odours constitute the major cue in the host‐finding process among specialized phytophagous insects. A review of the literature for the period 1986–2006 inclusive, relating to host‐plant finding in Chrysomelidae, identified studies of 19 chrysomelid species, all of which were guided by olfactory cues. No species were guided to their host by visual cues. Although some studies demonstrated that chrysomelids may exhibit orientation responses to colour or contrast, our study on A. engstroemi is the only one demonstrating that visual cues affect host‐plant selection in a chrysomelid species. We suggest that the use of visual cues in host‐finding may evolve among chrysomelids with limited dispersal ability in persistent habitats and may be found among species monophagous on abundant host plants that dominate the structure of the plant community, that is, where the host plant's presence is predictable in time and space.     

Plant volatiles mediate attraction to host and non-host plant in apple fruit moth, Argyresthia conjugella

Plant volatiles mediate host finding in insect herbivores and lead to host fidelity and habitat‐specific mating, generating premating reproductive isolation and facilitating sympatric divergence. The apple fruit moth, Argyresthia conjugella Zeller (Lepidoptera: Argyresthiidae), is a particularly suitable species to study the cues and behavioural mechanisms leading to colonization of a new host: it recurrently oviposits on the non‐host plant, apple Malus domestica Borkh. (Rosaceae), where the larvae cannot complete their development. The larval host of the apple fruit moth (Lepidoptera, Argyresthiidae), is rowan Sorbus aucuparia L. (Rosaceae). Fruit setting in rowan, however, fluctuates strongly over large areas in Scandinavia. Every 2–4 years, when too few rowanberries are available for egg laying in forests, apple fruit moth females oviposit instead on apple in nearby orchards, but not on other fruits, such as pear or plum. This poses the question of which cues mediate attraction to rowan and apple, and how apple fruit moth discriminates rowan from apple. Chemical analysis and antennal recordings showed that 11 out of 15 rowan volatiles eliciting an antennal response in A. conjugella females co‐occur in rowan and apple headspace, in a different proportion. In the field, A. conjugella was attracted to several of these plant volatiles, especially to 2‐phenyl ethanol, methyl salicylate, and decanal. Addition of anethole to 2‐phenyl ethanol had a strong synergistic effect, the 1 : 1 blend is a powerful attractant for A. conjugella males and females. These results confirm that volatiles common to both plants may account for a host switch in A. conjugella from rowan to apple. Some of the most attractive compounds, including 2‐phenyl ethanol, anethole, and decanal, which have been found in several apple cultivars, were not present in the headspace of the apple cultivar, Aroma, which is also susceptible to attack by A. conjugella. This supports the idea that the odour signal from apple is suboptimal for attraction of A. conjugella, but is nonetheless sufficient for attraction, during times when rowan is not available for egg laying.     

Differing acceptance of familiar and unfamiliar plant species by an oligophagous beetle

The mustard leaf beetle, Phaedon cochleariae (F.) (Coleoptera: Chrysomelidae), is specialized to feed and develop on various species within the Brassicaceae. In this study, we investigated the acceptance of several host plant species (Brassica rapa L. and Sinapis alba L.), commonly used by the beetle (familiar plants), and of various unfamiliar plants, including systematically and chemically related [Bunias orientalis L. (Brassicaceae) and Tropaeolum majus L. (Tropaeolaceae), both Brassicales], as well as unrelated non‐host plant species [Plantago lanceolata L. (Plantaginaceae); Lamiales]. Emphasis was laid on the acceptance of the neophyte B. orientalis, and on underlying cues responsible for the acceptance of the various species. Behavioural responses to plant volatiles were studied using a static four‐chamber olfactometer. Stimulants and deterrents were investigated by bioassay‐guided solid phase extraction and semi‐preparative high performance liquid chromatography. A difference in acceptance of plant species was found: odours and polar compounds of all Brassicales evoked attraction and feeding stimulation, respectively, in Ph. cochleariae. Glucosinolates and their volatile hydrolysis products could be the main compounds that are involved in attraction of the beetles. In contrast, Ph. cochleariae did not respond to odours of the non‐host P. lanceolata, and some fractions of this plant had feeding‐deterrent effects, due to the presence of iridoid glycosides, among others. Although adult females accepted the neophyte B. orientalis for oviposition, neonate larvae did not survive on it. The flavonoid‐containing fraction of this plant was deterrent, whereas a similar fraction had been shown to cause some feeding stimulation when derived from S. alba. Differences in qualitative and quantitative composition of related metabolites lead to differentiated plant acceptance, proving the complexity of plant cues and of insect responses that determine host acceptance behaviour. The possibility of a diet breadth enlargement to B. orientalis and the role of Ph. cochleariae as a putative native biocontrol agent of this invasive plant are discussed.     

Additive and synergistic integration of multimodal cues of both hosts and non-hosts during host selection by woodboring insects

Host selection by herbivorous insects is primarily thought to depend on attraction to olfactory cues emitted from the host species. However, the discrimination of these hosts from non-host species may also arise from the adaptive detection and avoidance of non-host cues, including visual characteristics. Many generalist, conifer-colonising beetles, for example, use characteristic volatiles to identify and discriminate against non-host angiosperm trees such as aspens and birches while flying. These trees also differ in bark reflectance characteristics, which could also mediate host/non-host discrimination by interacting with semiochemicals. We tested this hypothesis by evaluating the responses of eight species of polyphagous woodboring beetles to traps which simulated the visual appearance of coniferous hosts (black) and angiosperm non-hosts (white), and which were baited with host or non-host volatiles. As predicted, three species of large woodboring beetle and a woodboring wasp all avoided white, non-host-simulating traps that were baited with attractive kairomones, and preferred black, host-simulating traps. Conversely, three ambrosia beetle species demonstrated weaker visual preferences, possibly because they preferentially colonise fallen hosts that would transmit less accurate visual information. However, the ambrosia beetle Trypodendron lineatum did show a greater preference for host-coloured traps when these released host-associated kairomones in addition to their pheromone, and also avoided white non-host traps, but only when these released non-host volatiles. To our knowledge, this is the first evidence that multiple non-host cues could synergistically mediate the adaptive discrimination of hosts and non-hosts. Our results suggest that successful host location by generalists arises from the complex integration of cues in multiple sensory modes, and that foraging herbivores evaluate both hosts and non-hosts during their search.     

Geographical matching of volatile signals and pollinator olfactory responses in a cycad brood-site mutualism

Brood-site mutualisms represent extreme levels of reciprocal specialization between plants and insect pollinators, raising questions about whether these mutualisms are mediated by volatile signals and whether these signals and insect responses to them covary geographically in a manner expected from coevolution. Cycads are an ancient plant lineage in which almost all extant species are pollinated through brood-site mutualisms with insects. We investigated whether volatile emissions and insect olfactory responses are matched across the distribution range of the African cycad Encephalartos villosus. This cycad species is pollinated by the same beetle species across its distribution, but cone volatile emissions are dominated by alkenes in northern populations, and by monoterpenes and a pyrazine compound in southern populations. In reciprocal choice experiments, insects chose the scent of cones from the local region over that of cones from the other region. Antennae of beetles from northern populations responded mainly to alkenes, while those of beetles from southern populations responded mainly to pyrazine. In bioassay experiments, beetles were most strongly attracted to alkenes in northern populations and to the pyrazine compound in southern populations. Geographical matching of cone volatiles and pollinator olfactory preference is consistent with coevolution in this specialized mutualism.     

A subset of chemosensory genes differs between two populations of a specialized leaf beetle after host plant shift

Due to its fundamental role in shaping host selection behavior, we have analyzed the chemosensory repertoire of Chrysomela lapponica. This specialized leaf beetle evolved distinct populations which shifted from the ancestral host plant, willow (Salix sp., Salicaceae), to birch (Betula rotundifolia, Betulaceae). We identified 114 chemosensory candidate genes in adult C. lapponica: 41 olfactory receptors (ORs), eight gustatory receptors, 17 ionotropic receptors, four sensory neuron membrane proteins, 32 odorant binding proteins (OBPs), and 12 chemosensory proteins (CSP) by RNA‐seq. Differential expression analyses in the antennae revealed significant upregulation of one minus‐C OBP (ClapOBP27) and one CSP (ClapCSP12) in the willow feeders. In contrast, one OR (ClapOR17), four minus‐C OBPs (ClapOBP02, 07, 13, 20), and one plus‐C OBP (ClapOBP32) were significantly upregulated in birch feeders. The differential expression pattern in the legs was more complex. To narrow down putative ligands acting as cues for host discrimination, the relative abundance and diversity of volatiles of the two host plant species were analyzed. In addition to salicylaldehyde (willow‐specific), both plant species differed mainly in their emission rate of terpenoids such as (E,E)‐α‐farnesene (high in willow) or 4,8‐dimethylnona‐1,3,7‐triene (high in birch). Qualitatively, the volatiles were similar between willow and birch leaves constituting an “olfactory bridge” for the beetles. Subsequent structural modeling of the three most differentially expressed OBPs and docking studies using 22 host volatiles indicated that ligands bind with varying affinity. We suggest that the evolution of particularly minus‐C OBPs and ORs in C. lapponica facilitated its host plant shift via chemosensation of the phytochemicals from birch as novel host plant.     

TWO HERBIVORES AND CONSTRAINTS ON SELECTION FOR RESISTANCE IN BRASSICA RAPA

Although most plants experience herbivory by several insect species, there has been little empirical work directed toward understanding plant responses to these simultaneous selection pressures. In an experiment in which herbivory by flea beetles (Phyllotreta cruciferae) and diamondback moths (Plutella xylostella) was manipulated in a factorial design, I found that selection for resistance to these herbivores is not independent in Brassica rapa. Specifically, the effect of flea beetle damage on B. rapa fitness depends on the amount of diamondback moth damage a plant experiences: damage by these herbivores has a nonadditive effect on plant fitness. When diamondbacks are abundant, plants that sustain high levels of damage by flea beetles are favored by natural selection, but when diamondbacks are rare, a low level of damage by flea beetles is favored. However, resistance to the later-feeding diamondback moth is not affected by the presence or absence of damage by early-feeding flea beetles. Thus, there are no plant-mediated ecological interactions between these herbivores that affect the outcome of selection for resistance. Because these herbivores do not independently affect plant fitness, neither is likely to develop a pairwise coevolutionary relationship with its host. Instead, coevolution is diffuse.     

Primary attraction and kairomonal host discrimination in three species of Dendroctonus (Coleoptera: Scolytidae)

Abstract 1 Synthetic blends of bole and foliage volatiles of four sympatric species of conifers were released from pheromone‐baited multiple‐funnel traps to determine if three species of tree‐killing bark beetles (Coleoptera: Scolytidae): (i) exhibited primary attraction to volatiles of their hosts and (ii) discriminated among volatiles of four sympatric species of host and nonhost conifers. 2 Bole and foliage volatiles from Douglas‐fir, Pseudotsuga menziesii (Mirb.) Franco, increased the attraction of coastal and interior Douglas‐fir beetles, Dendroctonus pseudotsugae Hopkins, to pheromone‐baited traps. Primary attraction to bole volatiles was observed in interior D. pseudotsugae. Beetles were significantly less attracted to the pheromone bait when it was combined with volatiles of lodgepole pine, Pinus contorta var. latifolia Engelm. or interior fir, Abies lasiocarpa × bifolia. 3 The monoterpene myrcene synergized attraction of mountain pine beetles, Dendroctonus ponderosae Hopkins, to their aggregation pheromones, but there was no evidence of primary attraction to host volatiles or discrimination among volatiles from the four conifers. 4 There was significant primary attraction of the spruce beetle, Dendroctonus rufipennis Kirby, to bole and foliage volatiles of interior spruce, Picea engelmannii × glauca, but beetles did not discriminate among volatiles of four sympatric conifers when they were combined with pheromone baits. 5 Our results indicate that host volatiles act as kairomones to aid pioneer Douglas‐fir beetles and spruce beetles in host location by primary attraction, and that their role as synergists to aggregation pheromones is significant. For the mountain pine beetle, we conclude that random landing and close range acceptance or rejection of potential hosts would occur in the absence of aggregation pheromones emanating from a tree under attack.     

The bacterial community of entomophilic nematodes and host beetles

Insects form the most species‐rich lineage of Eukaryotes and each is a potential host for organisms from multiple phyla, including fungi, protozoa, mites, bacteria and nematodes. In particular, beetles are known to be associated with distinct bacterial communities and entomophilic nematodes. While entomopathogenic nematodes require symbiotic bacteria to kill and reproduce inside their insect hosts, the microbial ecology that facilitates other types of nematode–insect associations is largely unknown. To illuminate detailed patterns of the tritrophic beetle–nematode–bacteria relationship, we surveyed the nematode infestation profiles of scarab beetles in the greater Los Angeles area over a five‐year period and found distinct nematode infestation patterns for certain beetle hosts. Over a single season, we characterized the bacterial communities of beetles and their associated nematodes using high‐throughput sequencing of the 16S rRNA gene. We found significant differences in bacterial community composition among the five prevalent beetle host species, independent of geographical origin. Anaerobes Synergistaceae and sulphate‐reducing Desulfovibrionaceae were most abundant in Amblonoxia beetles, while Enterobacteriaceae and Lachnospiraceae were common in Cyclocephala beetles. Unlike entomopathogenic nematodes that carry bacterial symbionts, insect‐associated nematodes do not alter the beetles' native bacterial communities, nor do their microbiomes differ according to nematode or beetle host species. The conservation of Diplogastrid nematodes associations with Melolonthinae beetles and sulphate‐reducing bacteria suggests a possible link between beetle–bacterial communities and their associated nematodes. Our results establish a starting point towards understanding the dynamic interactions between soil macroinvertebrates and their microbiota in a highly accessible urban environment.     

Foraging behavior of Brachygastra lecheguana (Hymenoptera: Vespidae) on Banisteriopsis malifolia (Malpighiaceae): Extrafloral nectar consumption and herbivore predation in a tending ant system

In the Brazilian savanna many plant species bear regular associations with patrolling ants that are aggressive towards insect herbivores. However, not only ants but also several species of predatory wasps are attracted to plants due to the extrafloral nectaries (EFNs). Such wasps feed on both herbivores and plant exudates. In this study we describe the foraging behavior of the social Polistinae wasp Brachygastra lecheguana in the extrafloral nectaried shrub Banisteriopsis malifolia, and investigated the influence of patrolling ants Camponotus blandus on the activity of the wasp. Brachygastra lecheguana fed on the endophytic larvae of Anthonomus (Curculionidae) beetles that developed inside flower buds. The wasp lacerated the bud layers to reach the beetle larvae located at the bud core. The wasp visits to Ba. malifolia were statistically related to the abundance of flower buds and beetles. Ant exclusion experiments revealed that the hunting behavior of B. lecheguana on beetles was not related to the absence of C. blandus. However we found that wasps spent more time consuming extrafloral nectar on branches where ants were excluded. This is the first study reporting extrafloral nectar consumption by B. lecheguana, as well as the predation on herbivores in natural areas. In cerrado vegetation, ants benefit the plant by reducing insect herbivores, and our study provides evidence that the B. lecheguana – Ba. malifolia system represents a potential interaction where the wasp may also benefit the host plant. The value of this wasp species as a plant‐guard is discussed.     

叶甲科昆虫的定殖机制

在复杂的生态环境中,叶甲科昆虫利用寄主植物的挥发物作为嗅觉信号,并协同视觉信号共同作用以提高其远距离搜寻和定位寄主的效率。叶甲科昆虫也释放信息素来调节同种或者异种个体的行为反应;找到寄主植物后,叶子的形态学特性和化学组分的浓度等接触性因素就会影响叶甲科昆虫对寄主植物的最终选择。叶甲对上述这些信号物质的反应也受叶甲本身状态的影响,如生殖、滞育、饥饿、交配以及取食等。叶甲科昆虫对寄主植物的搜寻、辨识和接受、取食以及繁殖的过程受一种或多种因素协同影响。从嗅觉、视觉和触觉等方面对叶甲科昆虫的定殖机制做一综述。     

Specialization of the olfactory receptor cells in the bark beetleIps typographus and its predatorThanasimus formicarius to bark beetle pheromones and host tree volatiles

Summary Olfactory receptor cells of the spruce bark beetle,Ips typographus, and its predator, the clerid beetleThanasimus formicarius, were studied using electrophysiological techniques. Recordings were made of nerve impulses from single cells and of the summated receptor potential (electroantennogram).Information from bark beetle pheromones and host volatiles is detected by separate olfactory receptor cells inI. typographus. Those which detected bark beetle pheromones responded to only one key substance. Some receptor cells which responded to spruce bark volatiles were strongly activated by one of the synthetic host compounds tested. However, too few host compounds were tested to reach definite conclusions about the specialization of host odour cells. T. formicarius has evolved olfactory receptor cells for bark beetle pheromones. These have similar specificities (specialist types) to those of the bark beetles. Furthermore, the predator has olfactory receptor cells for many bark beetle pheromones. This indicates thatT. formicarius is able to detect and discriminate between many bark beetle species. No significant differences were found between prey and predator cells which responded to host volatiles.     

Plant–herbivorous beetle networks: molecular characterization of trophic ecology within a threatened steppic environment

DNA barcoding facilitates many evolutionary and ecological studies, including the examination of the dietary diversity of herbivores. In this study, we present a survey of ecological associations between herbivorous beetles and host plants from seriously threatened European steppic grasslands. We determined host plants for the majority (65%) of steppic leaf beetles (55 species) and weevils (59) known from central Europe using two barcodes (trnL and rbcL) and two sequencing strategies (Sanger for mono/oligophagous species and Illumina for polyphagous taxa). To better understand the ecological associations between steppic beetles and their host plants, we tested the hypothesis that leaf beetles and weevils differ in food selection as a result of their phylogenetic relations (within genera and between families) and interactions with host plants. We found 224 links between the beetles and the plants. Beetles belonging to seven genera feed on the same or related plants. Their preferences were probably inherited from common ancestors and/or resulted from the host plant's chemistry. Beetles from four genera feed on different plants, possibly reducing intrageneric competition and possibly due to an adaptation to different plant chemical defences. We found significant correlations between the numbers of leaf beetle and weevil species feeding on particular plants for polyphagous taxa, but not for nonpolyphagous beetles. Finally, we found that the previous identifications of host plants based on direct observations are generally concordant with host plant barcoding from insect gut. Our results expand basic knowledge about the trophic relations of steppic beetles and plants and are immediately useful for conservation purposes.