Host Plant Choice Research Articles

Evolutionary patterns and functional effects of 3D chromatin structures in butterflies with extensive genome rearrangements

Chromosome rearrangements may distort 3D chromatin architectures and thus change gene regulation, yet how 3D chromatin structures evolve in insects is largely unknown. Here, we obtain chromosome-level genomes for four butterfly species, Graphium cloanthus, Graphium sarpedon, Graphium eurypylus with 2n = 30, 40, and 60, respectively, and Papilio bianor with 2n = 60. Together with large-scale Hi-C data, we find that inter-chromosome rearrangements very rarely disrupted the pre-existing 3D chromatin structure of ancestral chromosomes. However, some intra-chromosome rearrangements changed 3D chromatin structures compared to the ancestral configuration. We find that new TADs and subTADs have emerged across the rearrangement sites where their adjacent compartments exhibit uniform types. Two intra-chromosome rearrangements altered Rel and lft regulation, potentially contributing to wing patterning differentiation and host plant choice. Notably, butterflies exhibited chromatin loops between Hox gene cluster ANT-C and BX-C, unlike Drosophila. Our CRISPR-Cas9 experiments in butterflies confirm that knocking out the CTCF binding site of the loops in BX-C affected the phenotypes regulated by Antp in ANT-C, resulting in legless larva. Our results reveal evolutionary patterns of insect 3D chromatin structures and provide evidence that 3D chromatin structure changes can play important roles in the evolution of traits.

A story of becoming a horticultural threat, cypress jewel beetle Lamprodila festiva (Coleoptera, Buprestidae): analytical approach of its European escalation based on bibliographical sources

The cypress jewel beetle, Lamprodila festiva, as one of the most destructive local invasive pests in Europe is currently an extreme threat to the coniferous Cupressaceae trees. The beetle spread at an unprecedented pace and intensity and poses a threat to many countries. Our study aimed to map the Palearctic distribution of L. festiva and measure the dispersal's pace and directions. Besides, one of our goals was visualising the adult’s seasonal activity and their host plant choice preference. A meta-analytical assessment was carried out to answer these questions based on the related bibliographical sources available in scientific databases. Our results confirmed that L. festiva has spread with extraordinary speed and success across the western Palaearctic areas, where the consequences of global warming have provided optimal conditions. The first population successful reproduction was started at five well-differentiated natural reserve areas across Europe in a latent manner. The flight season of L. festiva typically occurs from May to July, with the peaks varying depending on the area of distribution. Our studies have shown that L. festiva is a typical oligophagous pest, favouring certain species within its range of host plants. Thus, the genera Thuja, Platycladus and Juniperus species are most affected by its damage. Starting from its exceptional distribution characteristics, realising biological explanatory and applied protection research related to this species can become an urgent expectation in the future.

The Odorant Receptor Recognizing Camphor in a Camphor Tree Specialist Orthaga achatina (Lepidoptera: Pyralidae).

Camphor has been used as an effective repellent and pesticide to stored products for a long history, but Orthaga achatina (Lepidoptera: Pyralidae) has evolved to specifically feed on the camphor tree Cinnamomum camphora. However, the behavioral response of O. achatina to camphor and the molecular basis of camphor perception are totally unknown. Here, we demonstrated that both male and female adults were behaviorally attracted to camphor, suggesting the adaptation of O. achatina to and utilization of camphor as a signal of C. camphora. Second, in 40 O. achatina OR genes obtained by analyzing antenna transcriptomes, only OachOR16/Orco significantly responded to camphor in the Xenopus oocyte system. Finally, by molecular docking analysis and site-directed mutagenesis, the Ser209 residue is confirmed to be essential for binding of the oachOR16 with camphor. This study not only reveals the camphor-based host plant choice and olfactory mechanisms of O. achatina but also provides a molecular target for screening more potential insect repellents.

Learning-based oviposition constancy in insects

The search for resources occupies a major part of the time and energy budget of many insects. In this context, many insects display constancy behavior, in which they learn to return to the same, predictably rewarding resource repeatedly. Flower constancy is one such behavior, where nectar-feeding insects restrict foraging visits to a few plant species, sometimes overlooking potentially better-rewarding plants. This phenomenon is well documented in multiple species and is believed to be an optimal strategy to maximize benefits, while minimizing energy and time expenditure. Oviposition constancy is a similar behavior, where insects, dependent on previous experience, restrict their visits to a few types of potential oviposition sites. In contrast to flower constancy, the prevalence of oviposition constancy and the rationale behind this behavior are relatively unknown. An improved understanding of oviposition constancy can act as a lens into the evolutionary history of local insect adaptations, it can help gauge the impact of climate change on insect plant interactions, and it can aid the design of crop-pest management strategies. In this review, we discuss the potential benefits of oviposition constancy in insects and the extent of plasticity occurring in host-plant choice for oviposition.

Electrophysiological and Behavioral Responses of Batocera horsfieldi Hope to Volatiles from Pistacia chinensis Bunge.

Following infestation by phytophagous insects, changes in the composition and relative proportion of volatile components emitted by plants may be observed. Some phytophagous insects can accurately identify these compounds to locate suitable host plants. We investigated whether herbivore-induced plant volatiles (HIPVs) generated by herbivory on Pistacia chinensis Bunge (Sapindales: Aceraceae) might be semiochemicals for the host location of Batocera horsfieldi Hope (Coleoptera: Cerambycidae). We performed two-choice bioassays (indoor darkroom, inside cages) on plants damaged by adult feeding and intact control plants. Volatiles from these plants were then collected and identified, and the response of adult antennae to these compounds was tested via electroantennography (EAG). The behavioral responses of B. horsfieldi to these compounds were finally assessed using a Y-tube olfactometer. Host plant choice tests show that B. horsfieldi prefers feeding-damaged P. chinensis over healthy trees. In total, 15 compounds were collected from healthy and feeding-damaged P. chinensis, 10 of which were shared in both healthy and feeding-damaged P. chinensis, among which there were significant differences in the quantities of five terpenes, including α-pinene, β-pinene, α-phellandrene, D-limonene, and β-ocimene. In EAG assays, the antennae of B. horsfieldi adults responded strongly to (Z)-3-hexen-1-ol, β-ocimene, 3-carene, γ-terpinene, D-limonene, myrcene, and α-phellandrene. The antennae of B. horsfieldi adults responded in a dose-response manner to these compounds. Y-tube behavioral experiments showed that four compounds attracted mated females ((Z)-3-hexen-1-ol, β-ocimene, 3-carene, and α-phellandrene), two compounds ((Z)-3-hexen-1-ol and α-phellandrene) attracted males, and adults of both sexes avoided D-limonene. Feeding bioassays showed that (Z)-3-hexen-1-ol and β-ocimene could promote the feeding of B. horsfieldi and that D-limonene inhibited this response. These results could provide a theoretical basis for developing attractants or repellents for B. horsfieldi.

Bacterial Pesticidal Protein Mpp51Aa1 Delivered via Transgenic Citrus Severely Impacts the Fecundity of Asian Citrus Psyllid, Diaphorina citri.

The Asian citrus psyllid (ACP) Diaphorina citri vectors the causative agent of citrus greening disease that has the capacity to decimate citrus production. As an alternative and more sustainable approach to manage D. citri than repeated application of chemical insecticides, we investigated the potential use of the bacteria-derived pesticidal protein, Mpp51Aa1, when delivered by transgenic Citrus sinensis cv. Valencia sweet orange or Citrus paradisi cv. Duncan grapefruit. Following confirmation of transcription and translation of mpp51aa1 by transgenic plants, no impact of Mpp51Aa1 expression was seen on D. citri host plant choice between transgenic and control Duncan grapefruit plants. A slight but significant drop in survival of adult psyllids fed on these transgenic plants was noted relative to those fed on control plants. In line with this result, damage to the gut epithelium consistent with that caused by pore-forming proteins was only observed in a minority of adult D. citri fed on the transgenic Duncan grapefruit. However, greater impacts were observed on nymphs than on adults, with a 40% drop in the survival of nymphs fed on transgenic Duncan grapefruit relative to those fed on control plants. For Valencia sweet orange, a 70% decrease in the number of eggs laid by adult D. citri on transgenic plants was noted relative to those on control plants, with a 90% drop in emergence of progeny. These impacts that contrast with those associated with other bacterial pesticidal proteins and the potential for use of Mpp51Aa1-expressing transgenic plants for suppression of D. citri populations are discussed. IMPORTANCE Pesticidal proteins derived from bacteria such as Bacillus thuringiensis are valuable tools for management of agricultural insect pests and provide a sustainable alternative to the application of chemical insecticides. However, relatively few bacterial pesticidal proteins have been used for suppression of hemipteran or sap-sucking insects such as the Asian citrus psyllid, Diaphorina citri. This insect is particularly important as the vector of the causative agent of citrus greening, or huanglongbing disease, which severely impacts global citrus production. In this study, we investigated the potential of transgenic citrus plants that produce the pesticidal protein Mpp51Aa1. While adult psyllid mortality on transgenic plants was modest, the reduced number of eggs laid by exposed adults and the decreased survival of progeny was such that psyllid populations dropped by more than 90%. These results provide valuable insight for potential deployment of Mpp51Aa1 in combination with other control agents for the management of D. citri.

Nutrient supply and accessibility in plants: effect of protein and carbohydrates on Australian plague locust (Chortoicetes terminifera) preference and performance.

In contrast to predictions from nitrogen limitation theory, recent studies have shown that herbivorous migratory insects tend to be carbohydrate (not protein) limited, likely due to increased energy demands, leading them to preferentially feed on high carbohydrate plants. However, additional factors such as mechanical and chemical defenses can also influence host plant choice and nutrient accessibility. In this study, we investigated the effects of plant protein and carbohydrate availability on plant selection and performance for a migratory generalist herbivore, the Australian plague locust, Chortoicetes terminifera. We manipulated the protein and carbohydrate content of seedling wheat (Triticum aestivum L.) by increasing the protein:carbohydrate ratio using nitrogen (N) fertilizer, and manipulated the physical structure of the plants by grinding and breaking down cell walls after drying the plants. Using a full factorial design, we ran both choice and no-choice experiments to measure preference and performance. We confirmed locust preference for plants with a lower protein-carbohydrate ratio (unfertilized plants). Unlike previous studies with mature wild grass species, we found that intact plants supported better performance than dried and ground plants, suggesting that cell wall removal may only improve performance for tougher or more carbohydrate-rich plants. These results add to the growing body of evidence suggesting that several migratory herbivorous species perform better on plants with a lower protein:carbohydrate ratio.

Sympatric Pieris butterfly species exhibit a high conservation of chemoreceptors.

Sensory processes have often been argued to play a central role in the selection of ecological niches and in the formation of new species. Butterflies are among the best studied animal groups with regards to their evolutionary and behavioral ecology and thereby offer an attractive system to investigate the role of chemosensory genes in sympatric speciation. We focus on two Pieris butterflies with overlapping host-plant ranges: P. brassicae and P. rapae. Host-plant choice in lepidopterans is largely based on their olfactory and gustatory senses. Although the chemosensory responses of the two species have been well characterized at the behavioral and physiological levels, little is known about their chemoreceptor genes. Here, we compared the chemosensory genes of P. brassicae and P. rapae to investigate whether differences in these genes might have contributed to their evolutionary separation. We identified a total of 130 and 122 chemoreceptor genes in the P. brassicae genome and antennal transcriptome, respectively. Similarly, 133 and 124 chemoreceptors were identified in the P. rapae genome and antennal transcriptome. We found some chemoreceptors being differentially expressed in the antennal transcriptomes of the two species. The motifs and gene structures of chemoreceptors were compared between the two species. We show that paralogs share conserved motifs and orthologs have similar gene structures. Our study therefore found surprisingly few differences in the numbers, sequence identities and gene structures between the two species, indicating that the ecological differences between these two butterflies might be more related to a quantitative shift in the expression of orthologous genes than to the evolution of novel receptors as has been found in other insects. Our molecular data supplement the wealth of behavioral and ecological studies on these two species and will thereby help to better understand the role of chemoreceptor genes in the evolution of lepidopterans.

Identification of chemical cues of Camellia sinensis (Ericales: Theaceae) and alternate host plants for preference by tea mosquito bug Helopeltis theivora (Hemiptera: Miridae)

The tea mosquito bug (TMB), Helopeltis theivora (Hemiptera: Miridae) is a polyphagous pest causing serious economic loss in tea plantations of north east India. The push-pull companion cropping system can be used as a component of integrated pest management system to control the pest. We examined the host plant choice of H. theivora for Duranta erecta (Lamiales: Verbenaceae), Senna tora (Fabale: Fabaceae), Lawsonia inermis (Myrtales: Lythraceae), Psidium guajava (Myrtales: Myrtaceae) and Melastoma malabathricum (Myrtales: Melastomataceae) including the primary host, Camellia sinensis (Ericales: Theaceae) using two-choice olfactometric bioassay. The growth index and relative growth index of H. theivora were calculated for different host plants. H. theivora preferred the odor released from the mechanically damaged leaves of C. sinensis and P. guajava. The further study on biochemical constituents of all the host plants reflected the role of soluble sugar, total flavonoids and terpenoids as cues for host preference by H. theivora which indicate a scope for electroantennographic assessment in future. The information generated for P. guajava preference can be utilized in trap cropping or trap formulating approaches for management of H. theivora.

Genome-wide association study reveals WRKY42 as a novel plant transcription factor that influences oviposition preference of Pieris butterflies.

Insect herbivores are amongst the most destructive plant pests, damaging both naturally occurring and domesticated plants. As sessile organisms, plants make use of structural and chemical barriers to counteract herbivores. However, over 75% of herbivorous insect species are well adapted to their host's defenses and these specialists are generally difficult to ward off. By actively antagonizing the number of insect eggs deposited on plants, future damage by the herbivore's offspring can be limited. Therefore, it is important to understand which plant traits influence attractiveness for oviposition, especially for specialist insects that are well adapted to their host plants. In this study, we investigated the oviposition preference of Pieris butterflies (Lepidoptera: Pieridae) by offering them the choice between 350 different naturally occurring Arabidopsis accessions. Using a genome-wide association study of the oviposition data and subsequent fine mapping with full genome sequences of 164 accessions, we identified WRKY42 and AOC1 as candidate genes that are associated with the oviposition preference observed for Pieris butterflies. Host plant choice assays with Arabidopsis genotypes impaired in WRKY42 or AOC1 function confirmed a clear role for WRKY42 in oviposition preference of female Pieris butterflies, while for AOC1 the effect was mild. In contrast, WRKY42-impaired plants, which were preferred for oviposition by butterflies, negatively impacted offspring performance. These findings exemplify that plant genotype can have opposite effects on oviposition preference and caterpillar performance. This knowledge can be used for breeding trap crops or crops that are unattractive for oviposition by pest insects.

Biology and Rearing of an Emerging Sugar Beet Pest: The Planthopper Pentastiridius leporinus.

Simple SummarySyndrome des Basses Richesses (SBR) is a bacterial yellowing disease of sugar beet (Beta vulgaris) that reduces the sugar content of the root tissue significantly. There is currently neither a cure for the disease nor effective control measures for the main insect vector, the Cixiid planthopper Pentastiridius leporinus. SBR is therefore spreading in Germany and has caused substantial yield losses in recent years. The development of effective control measures requires a better understanding of P. leporinus biology, including its life cycle and feeding behavior. We therefore established methods for the continuous mass rearing of P. leporinus. In host plant choice experiments, we found that the nymphs are polyphagous when offered sugar beet, winter wheat or maize. Life cycle data indicated that adult planthoppers emerge 170 days after hatching, having passed through five larval instar stages. We developed a state-of-the-art qRT-PCR protocol using TaqMan probes to study the prevalence of two bona fide SBR pathogens: Candidatus Arsenophonus phytopathogenicus (Gammaproteobacteria) and Candidatus Phytoplasma solani (stolbur phytoplasma). These were identified during field studies in newly-infected regions of Rhineland-Palatinate and south Hesse, Germany, where we also observed insect mobility patterns in two consecutive years, including the abundance of adults at four locations and soil-depth monitoring of nymphs. We documented the spread of P. leporinus northward and eastward in Germany, accompanied by an increase in the number of SBR-carrying planthoppers. Interestingly, P. leporinus does not appear to hibernate during winter. Stolbur phytoplasma has a significant impact on SBR pathology in sugar beet.The rapid spread of the bacterial yellowing disease Syndrome des Basses Richesses (SBR) has a major impact on sugar beet (Beta vulgaris) cultivation in Germany, resulting in significant yield losses. SBR-causing bacteria are transmitted by insects, mainly the Cixiid planthopper Pentastiridius leporinus. However, little is known about the biology of this emerging vector, including its life cycle, oviposition, developmental stages, diapauses, and feeding behavior. Continuous mass rearing is required for the comprehensive analysis of this insect. Here we describe the development of mass rearing techniques for P. leporinus, allowing us to investigate life cycle and ecological traits, such as host plant choice, in order to design agronomic measures that can interrupt the life cycle of nymphs in the soil. We also conducted field studies in recently-infected regions of Rhineland-Palatinate and south Hesse, Germany, to study insect mobility patterns and abundance at four locations during two consecutive years. The soil-depth monitoring of nymphs revealed the movement of the instars through different soil layers. Finally, we determined the prevalence of SBR-causing bacteria by designing TaqMan probes specific for two bona fide SBR pathogens: Candidatus Arsenophonus phytopathogenicus (Gammaproteobacteria) and Candidatus Phytoplasma solani (stolbur phytoplasma). Our data suggest that P. leporinus is spreading northward and eastward in Germany, additionally, the abundance of SBR-carrying planthoppers is increasing. Interestingly, P. leporinus does not appear to hibernate during winter, and is polyphagous as a nymph. Stolbur phytoplasma has a significant impact on SBR pathology in sugar beet.

Plant defences and spider-mite web affect host plant choice and performance of the whitefly Bemisia tabaci

Herbivores select host plants depending on plant quality and the presence of predators and competitors. Competing herbivores change host plant quantity through consumption, but they can also change plant quality through induction of plant defences, and this affects the performance of herbivores that arrive later on the plant. Some herbivores, such as the spider mite Tetranychus evansi, do not induce, but suppress plant defences, and later-arriving herbivores can profit from this suppression. It has been suggested that the dense web produced by this spider mite serves to prevent other herbivores to settle on the plant and benefit from the suppressed defences. Here, we confirmed this by studying the preference and performance of the whitefly Bemisia tabaci, a generalist herbivorous pest. To disentangle the effects through changes in plant defences from the effects of spider-mite web, we included treatments with a strain of the closely-related web-producing spider mite T. urticae, which induces plant defences. Whiteflies did perform worse on plants with defences induced by T. urticae, but, in contrast to other herbivores, did not perform better on plants with defences suppressed by T. evansi. Moreover, the web of both spider mites reduced the juvenile survival of whiteflies, and whiteflies avoided plants that were covered with web. Hence, whitefly performance was not only affected by plant quality and induced plant defences, but also through the web produced by spider mites, which thus serves to protect against potential competitors, especially when these could profit from the suppression of plant defences by the mites.

Transcriptome Analysis for Identification of Genes Related to Growth and Development, Digestion and Detoxification, Olfaction in the Litchi Stink Bug Tessaratoma papillosa.

Tessaratoma papillosa is a major pest of Litchi chinensis and Dimocarpus longan. Adult and nymph secretions are not only harmful to plants but also to humans. At present, there are not a lot of research on T. papillosa, especially omics research. We used high-throughput sequencing technology to sequence the T. papillosa transcriptome and obtained 67,597 unigenes homologous to Halyomorpha halys (88.03%). Subsequently, RNA-SEQ and comparative analyses were performed on the 14 different developmental stages and tissues. A total of 462 unigenes related to growth and development, 1,851 unigenes related to digestion and detoxification, and 70 unigenes related to olfaction were obtained. Moreover, expression analysis showed that the T. papillosa major life activities genes are uniformly expressed across all developmental states. However, the adult midgut gene expression patterns were utterly different from that of the nymphs. Similarly, female fat body genes exhibited distinct expression patterns compared to that of males and nymphs. Thus, different developmental stages and physiological functions affect gene expression patterns. We also found that most of the differential genes were associated with cellular maintenance. This study will help understand the growth and development of litchi stink bugs, their choice of host plants, food digestion and detoxification, and their reproductive behavior. In addition, this result can provide reference information for some target genes in the process of control of T. papillosa.

The omnivorous predator Macrolophus pygmaeus induces production of plant volatiles that attract a specialist predator

It has become clear that omnivorous predators can induce plant defences that affect the performance and host plant choice of herbivores. They are also known to induce the production of plant volatiles that can affect the behaviour of herbivores searching for plants. These volatiles may also affect the searching behaviour of other predators, which was investigated here. The predatory mite Phytoseiulus persimilis preferred plants previously exposed to the omnivorous mirid Macrolophus pygmaeus over clean plants. The mites were equally attracted to plants previously exposed to the omnivore and subsequently infested by spider mites (Tetranychus urticae, prey of the predatory mite and the omnivore) and plants infested with spider mites alone. Moreover, the mites were more attracted to plants infested with prey and subsequently exposed to the omnivore than plants infested with prey but not exposed to the omnivore. The predatory mites were also significantly more attracted to plants on which the omnivores were still present. Experience of the predatory mites with volatiles from plants previously exposed to the omnivore and without prey resulted in a loss of the preference for volatiles emitted by plants exposed to the omnivore. Analysis of the volatiles showed that plant exposure to omnivores induced qualitative and quantitative changes in the volatile blend. Together, these results suggest that omnivorous predators induce the production of plant volatiles that can interfere with the searching behaviour of other predators. The consequences of such interference for biological pest control remain to be investigated.

Effect of gypsum dust on lepidopterous larvae

Airborne particulate matter is a significant concern to human health, but the effects of the deposition of dust on other species in the wild has not been well investigated. The vulnerability of insects to mineral dusts has been well known from agricultural management and the current co-occurrence of endangered species with dust-producing industry makes this knowledge more relevant and in need of expansion. To investigate the effects of fugitive gypsum dust on an endangered butterfly species, we exposed a surrogate lepidopterous species (Gloveria medusa; Lasiocampidae) to realistic quantities of gypsum dust either on its hostplant or externally applied to larvae. We then used surviving larvae in a choice experiment to ascertain if previous exposure to gypsum contaminated hostplant affected larval preferences. Consumption of gypsum-dusted foodplant increased risk of death for larvae significantly compared with both controls (hazard ratio = 4.80; 95% CI = 2.08–11.03; p = 0.0002) and the external treatment (HR = 2.85; 95% CI 1.41–5.76; p = 0.003). External treatment elevated death rate, but not significantly (HR = 1.68; 95% CI =0.65–4.33; p = 0.28). Elevated risk of death was greater for smaller larvae. Hostplant choice after previous exposure was not significant, but suggestive that larvae consume more of the hostplant in the condition that they previously experienced (either with or without gypsum). Based on these results and previous studies, we conclude that fugitive gypsum dust may affect populations through direct mortality, reduced developmental rates, lower weights, and extended development periods that disrupt natural phenology. Use of dust to reduce insect infestations is an ancient practice, and knowledge of these effects should be revived to address chronic harms of fugitive dust on insects as they face worldwide declines.

Host plant choice and effect of temperature on feeding behaviour of Perzelia arda (Lepidoptera: Depressariidae), a leaf‐tying larva, on Nothofagaceae from the Andean Patagonian forest

AbstractEnvironmental temperature may cause changes in the physiology and feeding behaviour of herbivorous insects and, consequently, in the damage they can cause. In the Andean Patagonian forest, an eco‐region dominated by trees of the Nothofagaceae family, it is common to find the leaf‐tying larvae Perzelia arda consuming seeds and leaves of several species of Nothofagus genus. The pattern of damage caused by P. arda in these forests varies from year to year and even within seasons. We hypothesise that this phenomenon may be related to an increase in the ambient temperature of this region. The purpose of this work was to determine the host plant preferences of P. arda among four species of Nothofagus genus and to evaluate whether temperature influences the feeding behaviour of the larvae. We first evaluated the food preferences of P. arda by means of two‐choice tests, using leaves of N. alpina, N. obliqua, N. antarctica and N. pumilio as stimuli. Secondly, we evaluated the effect of three levels of temperature on herbivory. Our results demonstrated that P. arda feed on and equally choose the four species of host plants studied. Temperature influenced the feeding behaviour of the larvae; high levels of consumption of N. obliqua occurred at 6°C and differed for the other host plant suggesting that consumption also depends on the type of food resource. In conclusion, the feeding behaviour of P. arda depends on a complex interaction between host plant and abiotic conditions. Further studies are required for a better understanding about the use of resources by this native insect, as well as the ecological consequences.

Herbivore-induced plant volatiles mediate behavioral interactions between a leaf-chewing and a phloem-feeding herbivore

Plants respond adaptively to herbivore stress in order to maintain fitness. Upon herbivore attack, plants emit blends of volatile organic compounds (VOCs) that differ from those that are constitutively emitted. These defense responses are typically specific to the identity of the attacking herbivore and often linked to the herbivore's feeding guild (e.g. chewing, phloem-feeding). Herbivores use plant volatiles to locate suitable host plants and changes in volatile emissions can affect host-plant location. Therefore, herbivores from separate feeding guilds can interact indirectly through the modulation of plant responses. In this study we tested how damage by an herbivore from one feeding guild affected the host-plant choice of an herbivore from a separate feeding guild, and vice versa. A chewing herbivore, the Colorado potato beetle (Leptinotarsa decemlineata), and a phloem feeding herbivore, the green peach aphid (Myzus persicae), were assayed in olfactometers to assess behavioral responses to odors emitted by potato plants (Solanum tuberosum) that were damaged by herbivores from the other feeding guild. Leptinotarsa decemlineata oriented more frequently towards undamaged plants compared to M. persicae damaged plants. Surprisingly, M. persicae preferred plants that were damaged by L. decemlineata, although previous studies had shown that they perform worse on these plants. Distinct differences were detected in the volatile profiles of herbivore-damaged and undamaged plants. Leptinotarsa decemlineata induced stronger volatile emissions compared to undamaged control plants, while M. persicae tended to suppress volatile emissions. These herbivores demonstrate contrasting induction of plant volatiles and behavioral responses. Exploring the nature of co-occurring herbivores and how they perceive potential hosts can play a significant role in understanding the ecological functions and community dynamics of plant plasticity and interactions with a variety of herbivores.

Limited influence of gain and loss of symbionts on host plant selection in specialized pea aphid genotypes

Recent advances in insect-microbe interactions show that microbial associates can modulate the behaviors of their hosts, such as defensive or food choice behaviors. For phytophagous insects, host plant choice is of utmost importance, because most of them are specialized on a few plant species, which represent not only their food source but often their habitat and reproduction site. Therefore, identifying how microbial symbionts could influence host plant selection provides valuable information on their potential role in the evolution of the diet breath of phytophagous insects. In this study, we investigated whether bacterial symbiont loss or acquisition modulate host plant selection in the pea aphid Acyrthosiphon pisum Harris (Hemiptera: Aphididae). Several aphid lineages were considered, originating from three plant-specialized populations, each adapted to a different plant species. The symbiotic status of aphid lineages was experimentally manipulated to mimic natural events of symbiont loss and acquisition through horizontal transfer. Host plant selection was then tested by releasing aphids in a cage containing three plant species (1 host and 2 non-hosts) and determining the proportion of aphids on each plant. Our results show minor effects of the symbiotic status on aphid host plant choice, indicating that this trait is determined primarily by the aphid genome.

A sensitive period for the induction of host plant preference in a generalist herbivorous insect

Many species use early life sensory experiences to guide phenotypic plasticity and facilitate decision making during later adult settlement in new habitats or location of suitable resources. However, only some of the available sensory information in the environment is relevant for future decision making and, in addition, it may only be informative during certain times during development. This means that sampling of environmental information that should be retained to adulthood could be limited to certain sensitive periods. In the polyphagous moth Spodoptera littoralis , recent studies have demonstrated that adult females exhibit an innate preference hierarchy for certain plants that can be modulated by olfactory experience during the larval stage. This olfactory-driven phenotypic plasticity requires that information about plant quality is transferred over the full metamorphosis. However, the timing of information acquisition that affects adult behaviour and whether there is a sensitive period for the sensory experience inducing host plant preferences are not known. In this study, we tested whether experience used by adult females during host plant choice was acquired during early or later larval stages and whether adult females can retain larval experience from only one or from sequential feeding events on different plants. We found that only plant feeding experience during the later larval stages induced a host plant preference shift in adult females. Furthermore, our experiments demonstrated that when given an artificial diet in the later larval stage, adult females relied on their innate plant preference hierarchy even if they had feeding experience from a host plant in the early stages. The existence of a sensitive period during late larval stages may be constrained not only by neural development or limitations, but also by ecological factors affecting when the larval experience is most reliable for adult decisions. • Larval experience affects adult moth host plant decisions. • There is a sensitive period for host plant cue transfer over the full metamorphosis. • Only experience at late larval instars affects adult host plant choice decisions. • Adults use innate preference when exposed to early instar plant experience.

Host Plant Choice Determined by Reproductive Interference between Closely Related Butterflies

AbstractA number of empirical studies have concluded that reproductive interference (RI) contributes to parapatric species distributions or sexual exclusion. However, the possibility that divergent host plant use in phytophagous insects is due to sexual exclusion has seldom been considered. Here, we present evidence that RI is responsible for different host plant use by two Pierid butterfly species, Pieris napi and Pieris melete. When a novel host species was introduced about 50 years ago, two Pierid butterfly species at first used both the ancestral host species and the novel one. Subsequently, P. napi shifted to use only the novel host, while P. melete shifted to specialize on the ancestral host. To explain these patterns, we investigated whether the two host species differ in suitability for larval growth and survival. Additionally, we tested whether RI occurred between the two butterfly species using large outdoor field cages. Courtship of females by conspecific and heterospecific males reduces the number of eggs laid by approximately half. However, RI is asymmetric and would generate selection on P. melete females to evolve to avoid the more suitable host species preferred by P. napi. Thus, our study suggests that sexual exclusion can explain the shift in host plant use by these two butterfly species.