Gary W Felton

Pennsylvania State University | Penn State · Department of Entomology

Water is essential to plant growth and drives plant evolution and interactions with other organisms, such as herbivores. However, water availability fluctuates, and these fluctuations are intensified by climate change. How plant water availability influences plant-herbivore interactions in the future is an important question in basic and applied ec...

1. Interactions between plants and natural enemies of insect herbivores influence plant productivity and survival by reducing herbivory. Plants attract natural enemies via herbivore‐induced plant volatiles (HIPVs), but how water availability (WA) influences HIPV‐mediated defenses is unclear. 2. We use tomato (Solanum lycopersicum), tomato fruitworm...

Insect guts often harbor an abundance of bacteria. Many of these members are commensal, but some may emerge as opportunistic pathogens when the host is under stress. In this study, we evaluated how dietary nutritional concentration mediates a shift from commensal to pathogenic, and if host species influences those interactions. We used the lepidopt...

Fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) is becoming an invasive pest globally, and it causes significant yield losses in sorghum (Sorghum bicolor (L.) Moench) and maize (Zea mays L.). In this study, we demonstrated that sorghum and maize flavonoids affect survival of FAW larvae. Larvae reared on an artificial diet supplemented with s...

Key Message This review provides an overview, analysis, and reflection on insect elicitors and effectors (particularly from oral secretions) in the context of the ‘arms race’ with host plants. Abstract Following injury by an insect herbivore, plants rapidly activate induced defenses that may directly or indirectly affect the insect. Such defense p...

Insects have intimate relationships with gut microbiota, where bacteria can contribute important functions to their invertebrate hosts. Lepidopterans are important insect pests, but how they engage with their gut bacteria and how that translates to impacts on the host are lacking.

Local adaptations of host plants to climatic conditions along an elevation gradient can affect insect-plant interactions. Using local accessions sampled from different elevations within South America, plant defense responses and herbivore growth were evaluated on two host plants: a) cherry tomato, Solanum lycopersicum var. cerasiforme, and b) wild...

Bacterial gut symbionts of insect herbivores can impact their host through different mechanisms. However, in most lepidopteran systems we lack experimental examples to explain how specific members of the gut bacterial community influence their host. We used fall armyworm (Spodoptera frugiperda) as a model system to address this core question. We im...

Insects frequently confront different microbial assemblages. Bacteria inhabiting an insect gut are often commensal, but some can become pathogenic when the insect is compromised from different stressors. Herbivores are often confronted by various forms of plant resistance, but how defenses generate opportunistic microbial infections from residents...

Elevation gradients are used as a proxy to simulate climate change effects. A field study was conducted along an elevational gradient in Nepal to understand the effects of abiotic conditions on agriculturally important insect herbivore populations (tobacco caterpillar: Spodoptera litura, tomato fruit worm: Helicoverpa armigera, and South American l...

Koinobiont endoparasitoid wasps whose larvae develop inside a host insect alter several important facets of host physiology, potentially causing cascading effects across multiple trophic levels. For instance, the hijacking of the host immune responses may have effects on how insects interact with host plants and microbial associates. However, the p...

Stomata play a central role in plant responses to abiotic and biotic stresses. Existing knowledge regarding the roles of stomata in plant stress is centered on abiotic stresses and plant-pathogen interactions, but how stomata influence plant-herbivore interactions remains largely unclear. Here, we summarize the functions of stomata in plant-insect...

Natural enemies play an important role in managing insect pests. Orius sauteri (Poppius) (Hemiptera: Anthocoridae), a predator of many soft-body insects, is an important biological control agent in Asia. Understanding this predator’s egg-laying preferences and a habitat needs is important for its success in pest control. We investigated the plant a...

Plants can have fundamental roles in shaping bacterial communities associated with insect herbivores. For larval lepidopterans (caterpillars), diet has been shown to be a driving force shaping gut microbial communities, where the gut microbiome of insects feeding on different plant species and genotypes can vary in composition and diversity. In thi...

Plants growing under reduced water availability can affect insect herbivores differently, in some instances benefitting them. However, the forces mediating these positive impacts remain mostly unclear. To identify how water availability impacts plant quality and multi-trophic interactions, we conducted manipulative field studies with two population...

Silicon (Si) is a beneficial mineral that enhances plant protection against abiotic and biotic stresses, including insect herbivores. Si increases mechanical and biochemical defenses in a variety of plant species. However, the use of Si in agriculture remains poorly adopted despite its widely documented benefits in plant health. In this study, we t...

Herbivore‐induced plant volatiles (HIPVs) are widely recognized as an ecologically important defensive response of plants against herbivory. Although the induction of this “cry for help” has been well‐documented, only a few studies has investigated the inhibition of HIPVs by herbivores, and little is known about whether herbivores have evolved mech...

Water availability is an important factor that influences plant-insect interactions. While the influence of water limitation on plant resistance traits has received much attention, how water availability affects plant tolerance to herbivory is rarely tested. Here we show that lower water availability reduced tolerance capacity of tomato plants as m...

The effect of temperature on insect-plant interactions in the face of changing climate is complex as the plant, its herbivores and their interactions are usually affected differentially leading to an asymmetry in response. Using experimental warming and a combination of biochemical and herbivory bioassays, the effects of elevated temperatures and h...

It is well known that the interactions of insect herbivores and their host plant can be mediated by microbes. Our central hypothesis is that herbivore-associated fungi might directly or indirectly affect plant–insect interactions. In this study, we identified five orally secreted fungi from field-collected black cutworm, Agrotis ipsilon, including...

Insects manifest phenotypic plasticity in their development and behavior in response to plant defenses, via molecular mechanisms that produce tissue-specific changes. Phenotypic changes might vary between species that differ in their preferred hosts and these effects could extend beyond larval stages. To test this, we manipulated the diet of southe...

Plants face many environmental stresses that can impact their survival, development, and fitness. Insects are the most diverse, abundant and threatening herbivores in nature. As a consequence, plants produce direct chemical and physical defenses to reduce herbivory. They also release volatiles to recruit natural enemies that indirectly protect them...

Salivary glucose oxidase (GOX) is one of the most abundant salivary proteins in generalist caterpillar Helicoverpa zea. GOX has been hypothesized to benefit H. zea by modulating direct defense responses of plants. Although the function of this protein has been studied, its role remains unclear. The study aims to test the hypothesis that GOX induces...

Drought is known to benefit insect herbivores indirectly through plants in some instances; however, the mechanisms that lead to these benefits remain debated and limited. To understand the impact of drought on the quality of host plants and the interactions of insect herbivores with the arthropod community associated with host plants, we conducted...

Main conclusion: The study challenges the general belief that plants are highly sensitive to oral cues of herbivores and reveals the role of the damage level on the magnitude of defense induction. Many leaf-feeding caterpillars share similar feeding behaviors involving repeated removal of previously wounded leaf tissue (semicircle feeding pattern)...

Animals have ubiquitous associations with microorganisms, but microbial community composition and population dynamics can vary depending upon many environmental factors, including diet. The bacterial communities present in caterpillar (Lepidoptera) guts are highly variable, even among individuals of a species. Across lepidopteran species, it is unc...

Insects possess specific immune responses to protect themselves from different types of pathogens. Activation of immune cascades can inflict significant developmental costs to the surviving host. To characterize infection kinetics in a surviving host that experiences baculovirus inoculation, it is crucial to determine the timing of immune responses...

Colorado potato beetle (CPB; Leptinotarsa decemlineata) has been detected in Xinjiang, China, since 1993 and has caused serious damage to potato production during its eastward expansion to new geographic ranges. Symbiotic bacteria often play an essential role for insects to exploit novel food sources and expand into otherwise inaccessible ecologica...

Neonicotinoid seed treatments are frequently used in cotton (Gossypium hirsutum L. [Malvales: Malvaceae]) production to provide protection against early-season herbivory. However, there is little known about how these applications affect extrafloral nectar (EFN), an important food resource for arthropod natural enemies. Using enzyme-linked immunoso...

Microplitis croceipes is a solitary parasitoid that specializes on noctuid larvae of Helicoverpa zea and Heliothis virescens. Both the parasitoid and its hosts are naturally distributed across a large part of North America. When parasitoids deposit their eggs into hosts, venom and polydnaviruses (PDVs) are also injected into the caterpillars, which...

Crop domestication and selective breeding have altered plant defense mechanisms, influencing insect-plant interactions. A reduction in plant resistance/tolerance against herbivory is generally expected in domesticated species, however, limited efforts have been made to compare inducibility of plant defenses between wild and domesticated genotypes....

Plants produce suites of defenses that can collectively deter and reduce herbivory. Many defenses target the insect digestive system, with some altering the protective peritrophic matrix (PM) and causing increased permeability. The PM is responsible for multiple digestive functions, including reducing infections from potential pathogenic microbes....

Insect herbivory induces plant defense responses that are often modulated by components in insect saliva, oral secretions or regurgitant, frass, or oviposition fluids. These secretions contain proteins and small molecules that act as elicitors or effectors of plant defenses. Several non-protein elicitors have been identified from insect oral secret...

The Lyonet's gland is a widespread accessory labial gland in Lepidoptera. Although its function is ambiguous, the Lyonet's gland arguably plays an important role in silk production. Our knowledge of the Lyonet's gland in heliothine species is extremely limited; it is reportedly missing from Helicoverpa armigera and Heliothis virescens, whereas it i...

Although the tritrophic interactions of plants, insect herbivores and their natural enemies have been intensely studied for several decades, the roles of entomopathogens in their indirect modulation of plant-insect relationships is still unclear. Here, we employed a sublethal dose of a baculovirus with a relatively broad host range (AcMNPV) to expl...

Insect herbivores possess a diverse and abundant gut microbiota that may influence plant growth in nature. The application of plant beneficial bacteria to improve agricultural production and soil quality has long been of interest. Thus, these insect-associated microbiota have the potential to be developed into effective bio-fertilizers. The bacteri...

Symbioses between insects and microbes are ubiquitous, but vary greatly in terms of function, transmission mechanism, and location in the insect. Lepidoptera (butterflies and moths) are one of the largest and most economically important insect orders; yet, in many cases, the ecology and functions of their gut microbiomes are unresolved. We used hig...

Plants can influence the effectiveness of microbial insecticides through numerous mechanisms. One of these mechanisms is the oxidation of plant phenolics by plant enzymes, such as polyphenol oxidases (PPO) and peroxidases (POD). These reactions generate a variety of products and intermediates that play important roles in resistance against herbivor...

Plants possess a suite of traits that make them challenging to consume by insect herbivores. Plant tissues are recalcitrant, have low levels of protein, and may be well defended by chemicals. Insects use diverse strategies for overcoming these barriers, including co-opting metabolic activities from microbial associates. In this review, we discuss t...

Insect-associated microbes can contribute to the physiological and ecological functions of insects. Despite a few examples in beetles and piercing-sucking insects, the varied mechanisms of how insect-associated bacteria mediate plant-insect interactions are still not fully understood. The polyphagous herbivore Helicoverpa zea is a major agricultura...

The original version of this article unfortunately contained a mistake. Fig. 3 and Fig. 4a were identical and the original version of Fig. 4a had been accidentally replaced. © 2018 Springer Science+Business Media, LLC, part of Springer Nature

Significance The role of herbivore-associated microbes in mediating plant–herbivore interactions has gained recent attention. We show that a parasitoid associated with its caterpillar host not only suppresses the immune system of the caterpillar but also suppresses the induced defenses of the caterpillar’s host plant. Parasitoids inject eggs into t...

Insect saliva is one of the first secretions to come in contact with plants during feeding. The composition and role of caterpillar saliva has not been as thoroughly studied as that of sucking insects. This study focuses on characterizing the proteome of the cabbage looper (Trichoplusia ni) saliva using iTRAQ labeling and LC-MS/MS. We also measured...

The Lyonet’s gland is a widespread accessory labial gland in Lepidoptera. Albeit its function is ambiguous, the Lyonet’s gland arguably plays an important role in silk production. Our knowledge on the Lyonet’s gland in heliothine species is limited; it is apparently missing from H. armigera and Heliothis virescence, whereas reduced in size in H. ze...

The underlying adaptive mechanisms by which insect strains are associated with specific plants are largely unknown. In this study, we investigated the role of herbivore-induced defenses in the host plant association of fall armyworm (Spodoptera frugiperda) strains. We tested the expression of herbivore-induced defense-related genes and the activity...

Generalist herbivores feed on a wide array of plants and need to adapt to varying host qualities and defenses. One of the first insect derived secretions to come in contact with the plant is the saliva. Insect saliva is potentially involved in both the pre-digestion of the host plant as well as induction/suppression of plant defenses, yet how the s...

Transcriptome IDs. (XLSX)

Differentially expressed genes. (XLSX)

Validations of RNASeq results using real time qPCR. (TIF)

Real time quantitative PCR primers. (DOCX)

Cluster dendogram of biological samples. (TIF)

Trinity assembly statistics. (DOCX)

It is becoming abundantly clear that the microbes associated with plants and insects can profoundly influence plant-insect interactions. Here, we focus on recent findings and propose directions for future research that involve microbe-induced changes to plant defenses and nutritive quality as well as the consequences of these changes for the behavi...

Lepidopteran larvae secrete saliva on plant tissues during feeding. Components in the saliva may aid in food digestion, whereas other components are recognized by plants as cues to elicit defense responses. Despite the ecological and economical importance of these plant-feeding insects, knowledge of their saliva composition is limited to a few spec...

Insect gut-associated microbes modulating plant defenses have been observed in beetles and piercing-sucking insects, but the role of caterpillar-associated bacteria in regulating plant induced defenses has not been adequately examined. We identified bacteria from the regurgitant of field-collected Helicoverpa zea larvae using 16S ribosomal RNA (rRN...

Baculoviruses are food-borne microbial pathogens that are ingested by insects on contaminated foliage. Oxidation of plant-derived phenolics, activated by insect feeding, can directly interfere with infections in the gut. Since phenolic oxidation is an important component of plant resistance against insects, baculoviruses are suggested to be incompa...

Lepidoptera herbivores deposit copious amounts of saliva when feeding. Their saliva is produced by the paired mandibular and labial glands and evidence indicates that it may play an important role in allowing an herbivore to establish on its host plant. Genomic studies of Lepidoptera saliva are beginning to reveal the role of saliva in herbivory. M...