Divergence in selection of host species and plant parts among populations of a phytophagous insect

The diversification of phytophagous insects is often attributed to diverging processes of host plant specialization onto different, often closely related, host plants. Some insect clades have diversified by specializing not only on different plant species but also on different plant parts of the same hosts. This is the case in Greya moths (Prodoxidae) where both Greya obscura and G. politella are tightly linked to host plants of the genus Lithophragma (Saxifragaceae). We assess how these species differ in their choice of plants and use of plant parts. Previous work showed that strong local host specialization in G. politella is mediated by floral scent variation among Lithophragma species. Here, we identify geographic variation in host plant use in the close relative G. obscura, relate the emerging patterns to previous studies of geographic variation in host use in G. politella and evaluate potential processes underlying the variation among and within species. First, we show that G. obscura also uses floral chemistry to locate hosts but that additional plant cues must be involved in deciding whether to oviposit on a plant, because females did not discriminate against chemically different host species in no-choice trials. We also found that, although all known populations of G. politella oviposit only in flowers, all G. obscura populations examined here distributed their eggs among both floral and scape tissues both in the field and in laboratory experiments. The distribution of eggs among plant parts, however, varied among moth populations, and also depended on the Lithophragma species they attacked. Together, these results show the potential for phytophagous insect species and populations to diverge in use of plant parts as part of the process of speciation and adaptation. These two layers of specialization enhance the potential for subsequent diversification in phytophagous insect lineages.     

Transcriptional profile and differential fitness in a specialist milkweed insect across host plants varying in toxicity

Interactions between plants and herbivorous insects have been models for theories of specialization and co‐evolution for over a century. Phytochemicals govern many aspects of these interactions and have fostered the evolution of adaptations by insects to tolerate or even specialize on plant defensive chemistry. While genomic approaches are providing new insights into the genes and mechanisms insect specialists employ to tolerate plant secondary metabolites, open questions remain about the evolution and conservation of insect counterdefences, how insects respond to the diversity defences mounted by their host plants, and the costs and benefits of resistance and tolerance to plant defences in natural ecological communities. Using a milkweed‐specialist aphid (Aphis nerii) model, we test the effects of host plant species with increased toxicity, likely driven primarily by increased secondary metabolites, on aphid life history traits and whole‐body gene expression. We show that more toxic plant species have a negative effect on aphid development and lifetime fecundity. When feeding on more toxic host plants with higher levels of secondary metabolites, aphids regulate a narrow, targeted set of genes, including those involved in canonical detoxification processes (e.g., cytochrome P450s, hydrolases, UDP‐glucuronosyltransferases and ABC transporters). These results indicate that A. nerii marshal a variety of metabolic detoxification mechanisms to circumvent milkweed toxicity and facilitate host plant specialization, yet, despite these detoxification mechanisms, aphids experience reduced fitness when feeding on more toxic host plants. Disentangling how specialist insects respond to challenging host plants is a pivotal step in understanding the evolution of specialized diet breadths.     

Multiple plant traits influence community composition of insect herbivores: a comparison of two understorey shrubs

Structural and nutritional plant traits influence the ability of insect herbivores to locate, consume and persist on their hosts yet it is uncommon for ecologists to consider how multiple plant traits influence insect community composition. We sampled herbivorous insects on two understorey shrub species common to eucalypt forests of south-eastern Australia, namely Cassinia arcuata (Asteraceae) and Daviesia ulicifolia (Fabaceae). Regression analyses were used to assess the relative influence of plant structure (canopy volume), nutritional quality (macronutrients and total phenolics) and plant productivity (leaf litter) on insect abundance and species richness. Total N content of D. ulicifolia was significantly higher than C. arcuata, while the concentrations of P, K, Ca and Mg were higher in C. arcuata. Total phenolics and leaf litter were significantly lower in D. ulicifolia compared to C. arcuata. Insect composition was similar between the two shrubs but C. arcuata supported greater abundances. Canopy volume and the macronutrients P and Ca were important predictors of insect abundance on C. arcuata, whereas canopy volume alone, but neither plant productivity nor macronutrients, influenced the abundance of insects on D. ulicifolia. Ca was an important predictor of insect species richness on C. arcuata and P was an important predictor on D. ulicifolia. By quantifying a range of plant traits, we have provided an understanding of factors likely to influence the composition of herbivorous insects inhabiting these two shrubs. Traits including leaf architecture, foliar morphology and volatile terpenoids may yet explain the greater number of insects on C. arcuata since they influence the availability of microhabitats and apparency of host plants.     

Time of the season: the effect of host photoperiodism on diapause induction in an insect herbivore,Leptinotarsa decemlineata

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Determining host plant preferences for the critically endangered Lord Howe Island stick insect (<Emphasis Type="Italic">Dryococelus australis</Emphasis>) to assist reintroduction

The Lord Howe Island stick insect (Dryococelus australis) is one of the world’s rarest insects. However, the opportunity to reintroduce the species to Lord Howe Island, and commence the path to recovery, may occur within the next 5 years. Understanding the insect’s host plant and habitat preferences on Lord Howe Island is critical to maximising the likelihood of reintroduction success. However, very little ecological information was documented before the species became extinct on the island in the 1930s. Here we examine the Lord Howe Island stick insect’s preference for potential host plants, a key aspect of habitat suitability. We conducted preference trials using 15 common plant species found on Lord Howe Island. Both nymphs and adults consumed some but not all of these plant species. Nymphs were able to survive on 7 of these 15 plants for the duration of the 26-day trials although failed to survive on some of the plants most preferred by adults. Overall, these data reveal that there are numerous plants on Lord Howe Island that the stick insect can consume, though their suitability varies with different developmental stages of the insect. These data are encouraging for any future reintroduction attempts and would greatly aid the selection and monitoring of release sites.     

Intraspecific variability in host plant quality and ovipositionaI preferences in Eucheira socialis (Lepidoptera: Pieridae)

Abstract.

• 1 This study investigates interactions between Eucheira socialis (Pieridae: Lepidoptera), a strict monophagous herbivore, on Arbutus xalapensis (Ericaceae), a host plant with few herbivores. This tight association of insect on plant has many attributes conducive to reciprocal rather than diffuse evolution.
• 2 An indirect way of testing plant–insect coevolutionary theories is to test for the necessary conditions for reciprocal evolution in ecological time. Two conditions for coevolution were studied: (1) host plants vary in their suitability for larval growth and development, and (2) ovipositing insects discriminate among these plants based on their relative suitability.
• 3 Large differences in host plant suitability were found and relative differences were consistent from year to year.
• 4 There was no evidence that female insects based their ovipositional decisions on relative tree quality, which implies that factors other than host plant quality are involved in the maintenance and evolution of oviposition behaviour in Eucheira.
• 5 Of seven factors known to influence ovipositional preferences of insects among plants independent of potential larval success, the most likely causal factor in this system is the ability of females to balance a time/energy budget for finding potential oviposition sites, discriminating among them, and actually ovipositing.

     

Mechanisms of species‐sorting: effect of habitat occupancy on aphids' host plant selection

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Phenological phases of the host plant shape plant–treehopper interaction networks

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To Smell you Better: Prior Food Deprivation Increases Herbivore Insect Responsiveness to Host Plant Odor Cues

Hunger plays a crucial role in insect feeding behavior, however food deprivation is rarely considered when insect responses to plant host and related chemical stimuli are investigated. Here we assessed, by means of experiments with Y-tube olfactometer, the effect of food deprivation time on the response of a specialist (Xanthogaleruca luteola) and a generalist (Diabrotica speciosa) herbivore beetle species (Coleoptera: Chrysomelidae) to odor cues of their respective host plants. Increasing food deprivation periods enhanced responses to host plant odor in both species, with insects remaining for longer in the olfactometer arm carrying plant odor than in the control, moving less frequently between olfactometer arms, and being more efficient in moving towards the plant odor as their first choice. These trends were less significant in the generalist species, which also required a longer fasting threshold (48 h) in comparison with the specialist (8 h). Our results, showing that prior food deprivation time can influence insect herbivore responsiveness to plant stimuli and that those effects may vary between species, highlight the risk of neglecting this factor in studies involving insect responses to host or chemical stimuli.     

Evolutionary patterns in biogeography and host plant association: 'taxonomic conservatism' in Lophopidae (Hemiptera, Fulgoromorpha)

Abstract.  The association between the Lophopidae (Hemiptera, Fulgoromorpha) and their host plants was studied within a phylogenetic framework. Host plant use was optimized on Lophopidae phylogeny and the most parsimonious hypothesis is presented. This hypothesis describes the evolution of host plant use by the Lophopidae, and postulates the ancestral plant family used. This scenario is discussed within the biogeographical evolutionary context of the fulgoromorphan families, and is corroborated by information from both insect and host plant fossils. The association of the Lophopidae and their host plants is made by comparing the angiosperms and Lophopidae phylogenies, demonstrating at this level of comparison that the insects show 'taxonomic conservatism' for their host plants.     

Three-way interaction among plants,bacteria, and coleopteran insects

Main conclusion

Coleoptera, the largest and the most diverse Insecta order, is characterized by multiple adaptations to plant feeding. Insect-associated microorganisms can be important mediators and modulators of interactions between insects and plants. Interactions between plants and insects are highly complex and involve multiple factors. There are various defense mechanisms initiated by plants upon attack by herbivorous insects, including the development of morphological structures and the synthesis of toxic secondary metabolites and volatiles. In turn, herbivores have adapted to feeding on plants and further sophisticated adaptations to overcome plant responses may continue to evolve. Herbivorous insects may detoxify toxic phytocompounds, sequester poisonous plant factors, and alter their own overall gene expression pattern. Moreover, insects are associated with microbes, which not only considerably affect insects, but can also modify plant defense responses to the benefit of their host. Plants are also frequently associated with endophytes, which may act as bioinsecticides. Therefore, it is very important to consider the factors influencing the interaction between plants and insects. Herbivorous insects cause considerable damage to global crop production. Coleoptera is the largest and the most diverse order in the class Insecta. In this review, various aspects of the interactions among insects, microbes, and plants are described with a focus on coleopteran species, their bacterial symbionts, and their plant hosts to demonstrate that many factors contribute to the success of coleopteran herbivory.

     

跳甲的食性及食性分化

跳甲隶属于鞘翅目叶甲科跳甲亚科,是一类具有重要经济意义的植食性昆虫。本文对跳甲食性及食性分化的研究进展进行了综述,诠释了寄主植物的概念,分析了昆虫食性专化发生的原因。跳甲亚科的寄主植物的范围虽广,但有85%的属为专食性属。一般认为,专食性的跳甲亚科和萤叶甲亚科是由食性较广的叶甲亚科进化而来的,食性分化在其中可能起了重要作用。广食性代价推动了食性分化的发生,广食性代价假说受到越来越多的实验支持。有关食性分化方向的观点倾向于寄主植物转向化学物质相似的植物,表现为寄主转移、寄主扩张和形成寄主型等;食性分化推动了同域物种形成。跳甲食性分化的研究对于丰富研究昆虫与植物相互关系的协同进化理论也有重要作用。     

An Experimental Test of Trade-Offs Associated with the Adaptation to Alternate Host Plants in the Introduced Herbivorous Beetle, <Emphasis Type="Italic">Ophraella communa</Emphasis>

The adaptation to alternate host plants of introduced herbivorous insects can be vital to agriculture due to the emergence of crop pests. Historically, it is assumed that there are trade-offs associated with the adaptation to new host plants; a generalist genotype that adapts to an alternate host is expected to have a relatively lower fitness on the ancestral host than a specialist genotype (physiological cost) or a relatively lower host-searching ability for the ancestral host plant (behavioral cost). In this study, we tested the costs of adaptation to a new host plant in the introduced herbivorous insect, Ophraella communa LeSage (Coleoptera: Chrysomelidae). In its native range (United States), O. communa feeds mostly on Ambrosia artemisiifolia L. (Asterales: Asteraceae) and cannot utilize the related species, Ambrosia trifida L. (Asterales: Asteraceae), as a host plant. On the other hand, the introduced O. communa population in Japan utilizes A. trifida extensively, and is adapting to it, both physiologically and behaviorally. We compared larval performance on the ancestral and alternate plants and adult host-searching ability between the native and introduced beetle populations. The introduced O. communa showed higher larval survival and adult feeding preference for the alternate host plant A. trifida than did the native O. communa, indicating that the introduced O. communa has rapidly adapted to the alternate host plant. However, there are no differences in either larval performance on the ancestral host A. artemisiifolia or host-searching accuracy between the native and introduced O. communa.     

A meta-analysis of the effects of galling insects on host plant secondary metabolites

The idea that galling insects actively manipulate host plant chemistry has been previously documented but has not been quantified across a range of galler and host plant taxa. We present the first quantitative review of the relationship between insect galling and levels of secondary metabolites in host plants. Using meta-analytic techniques, we examined this relationship across 40 galler and host plant species combinations. We found that galling insects are associated with significantly higher levels of tannins and phenolics; however, no difference was found for volatiles. Hymenoptera, Diptera and Hemiptera were associated with higher levels of secondary metabolites; however, only Hymenoptera was significant. The climatic zone of the study area did not explain significant differences in gall-induced secondary metabolites. Overall the results show that the ability of galling insects to manipulate host plant secondary chemistry is widespread across insect and plant taxa. The evolutionary success of galling insects may be in part due to this unique ability.     

Phytophagous insect fauna tracks host plant responses to exotic grass invasion

The high dependence of herbivorous insects on their host plants implies that plant invaders can affect these insects directly, by not providing a suitable habitat, or indirectly, by altering host plant availability. In this study, we sampled Asteraceae flower heads in cerrado remnants with varying levels of exotic grass invasion to evaluate whether invasive grasses have a direct effect on herbivore richness independent of the current disturbance level and host plant richness. By classifying herbivores according to the degree of host plant specialization, we also investigated whether invasive grasses reduce the uniqueness of the herbivorous assemblages. Herbivorous insect richness showed a unimodal relationship with invasive grass cover that was significantly explained only by way of the variation in host plant richness. The same result was found for polyphagous and oligophagous insects, but monophages showed a significant negative response to the intensity of the grass invasion that was independent of host plant richness. Our findings lend support to the hypothesis that the aggregate effect of invasive plants on herbivores tends to mirror the effects of invasive plants on host plants. In addition, exotic plants affect specialist insects differently from generalist insects; thus exotic plants affect not only the size but also the structural profile of herbivorous insect assemblages.     

Dramatic transcriptional changes in an intracellular parasite enable host switching between plant and insect

Phytoplasmas are bacterial plant pathogens that have devastating effects on the yields of crops and plants worldwide. They are intracellular parasites of both plants and insects, and are spread among plants by insects. How phytoplasmas can adapt to two diverse environments is of considerable interest; however, the mechanisms enabling the "host switching" between plant and insect hosts are poorly understood. Here, we report that phytoplasmas dramatically alter their gene expression in response to "host switching" between plant and insect. We performed a detailed characterization of the dramatic change that occurs in the gene expression profile of Candidatus Phytoplasma asteris OY-M strain (approximately 33% of the genes change) upon host switching between plant and insect. The phytoplasma may use transporters, secreted proteins, and metabolic enzymes in a host-specific manner. As phytoplasmas reside within the host cell, the proteins secreted from phytoplasmas are thought to play crucial roles in the interplay between phytoplasmas and host cells. Our microarray analysis revealed that the expression of the gene encoding the secreted protein PAM486 was highly upregulated in the plant host, which is also observed by immunohistochemical analysis, suggesting that this protein functions mainly when the phytoplasma grows in the plant host. Additionally, phytoplasma growth in planta was partially suppressed by an inhibitor of the MscL osmotic channel that is highly expressed in the plant host, suggesting that the osmotic channel might play an important role in survival in the plant host. These results also suggest that the elucidation of "host switching" mechanism may contribute to the development of novel pest controls.     

Water stress and kaolin spray affect herbivorous insects’ success on cotton

Ecological hypotheses of plant–insect herbivore interactions suggest that insects perform better on weakened plants and plants grown under optimal conditions are less damaged. This study tested the hypothesis that the colonization and oviposition rates by pests with different feeding strategies and levels of specialization are affected in different ways by two conditions commonly faced by commercially grown plants–water deficit and application of kaolin sprays, a reducer of abiotic plant stressors. We used four major pests of cotton as insect herbivore models. Three were chewing Lepidoptera: Alabama argillacea (Hüb.), a monophagous pest on cotton; Heliothis virescens (Fabr.), which is polyphagous, but with cotton as a primary host; and Chrysodeixis includens (Walk.), which is polyphagous, with cotton as secondary host. The fourth pest was a sap-sucking species, the polyphagous whitefly Bemisia tabaci (Gen.). In both choice and no-choice trials, the three chewing pests oviposited significantly less upon water-stressed plants; the greatest effect was observed for C. includens (>90 % reduction in oviposition under choice and >58 % under no-choice conditions). In contrast, the sap-sucking B. tabaci exhibited statistically more colonization and oviposition on water-stressed plants. Application of kaolin sprays reduced colonization and oviposition by all herbivore species tested, irrespective of irrigation regime and feeding strategies.     

Discrimination within and between host species by a butterfly: implications for design of preference experiments

Experiments designed to reveal variation among individual parasites in preference for different host species may generate misleading results. Apparent variation in the order of preference among host species can be generated solely from variation in the strength of discriminations made within host species. We illustrate this with a study of oviposition preference in the butterfly Melitaea cinxia. All butterflies were tested on the same six individual plants, three Plantago lanceolata (P) and three Veronica spicata (V). Some insects repeatedly preferred all individual P over all individual V or vice versa. We designated these as "pure" species ranks. Other insects repeatedly produced "mixed" ranks, preferring some individual V over some P, and some individual P over some V. We show how a "mixed" rank butterfly could differ from a "pure" rank insect by discriminating either more within plant species and/or less between them. Therefore, discrimination within host species can mask or confound discrimination among species. We discuss implications for the design of preference experiments.     

Effects of nonhost and host plants on insect herbivory covarying with plant size in the cruciferous plant <Emphasis Type="Italic">Turritis glabra</Emphasis>

Correlation between plant size and reproductive output may be modified by herbivory in accordance with host plant density and the presence of nonhost plants. To elucidate the effects of nonhost plant density and host plant density on the intensity of herbivory and reproductive output of the host plant in relation to plant size under natural conditions, we investigated the abundance of three lepidopteran insects, Plutella maculipennis, Anthocharis scolymus, and Pieris rapae the intensity of herbivory, and fruit set of their host plant, Turritis glabra (Cruciferae). To elucidate the effects of nonhost and host plant density, we selected four categories of plots under natural conditions: low density of nonhost and high density of host plants; low density of both nonhost and host plants; high density of both nonhost and host plants; and high density of nonhost and low density of host plants. The plant size indicated by stem diameter was a good predictor of the abundance of all herbivorous species. The effects of density of nonhost and host plants on the abundance of insects varied among species and stages of insects. As the abundance of insects affected the intensity of herbivory, herbivory was more apparent on larger host plants in plots with low density of both nonhost and host plants. Consequently, the correlation between plant size and the number of fruits disappeared in low plots with density of both nonhost and host plants. In this T. glabra– herbivorous insect system, the density of nonhost plants and host plants plays an important role in modifying the relationship between plants and herbivores under natural conditions. Received: July 19, 1999 / Accepted: June 15, 2000     

How do two specialist butterflies determine growth and biomass of a shared host plant?

Although insect herbivory can modify subsequent quantity and quality of their host plants, change in plant quantity following herbivory has received less attention than plant quality. In particular, little is known about how previous herbivore damage determines plant growth and biomass in an insect species-specific manner. We explored whether herbivore species-specific food demand influences plant growth and biomass. To do this, we conducted a series of experiments and field survey using two specialist butterflies, Sericinus montela and Atrophaneura alcinous, and their host plant, Aristolochia debilis. It is known that A. alcinous larva requires four times more food resources to fulfill its development than S. montela larva. Despite that A. alcinous larvae imposed greater damage on plants than S. montela larvae, plant growth did not differ due to herbivory by these species both in single and multiple herbivory events. On the other hand, total aboveground biomass of the plants was reduced more by A. alcinous than S. montela feeding regardless of the number of herbivory events. Feeding on plants with a history of previous herbivory neither decreased nor increased larval growth. Our results suggest that food demand of the two butterfly species determined subsequent plant biomass, although the plant response may depend on tolerance of the host plant (i.e., ability to compensate for herbivore damage). Such difference in the effects of different herbivore species on host plant biomass is more likely to occur than previously thought, because food demand differs in most herbivore species sharing a host plant.