Generalist Insect Research Articles

Mathematical modeling predicts that endemics by generalist insects are eradicated if nearly all plants produce constitutive defense

Plants with constitutive defense chemicals exist widely in nature. The phenomenon is backed by abundant data from plant chemical ecology. Sufficient data are also available to conclude that plant defenses act as deterrent and repellent to attacking herbivores, particularly deleterious generalist insects. In the wild, generalist species are usually not endemic, meaning they are not restricted to certain plant species in a region. Therefore, our objective is to inspect theoretically whether evolution of chemical defenses in all plant species eradicate an endemic by any generalist species. The objective is addressed by developing deterministic ordinary differential equations under the following conditions: Plants without constitutive defenses are susceptible to oviposition by generalist insects, while they become defended against generalists by storing chemical defenses. From the models, we explicitly obtain that a generalist-free stable state is only possible if the vast majority of all plant individuals have chemical defenses. The model also allows one to predict the highest possible percentage of undefended plant individuals, which may be considered as free-riders.

Effects of temperature and storage duration on quality of an insect artificial diet.

Artificial diets are widely used to produce insects for research and education programs. Completed diets, in which the diets are fully made from individual ingredients and ready to use, often have high water activity, making them vulnerable to degradation. Proper storage is critical to maintaining diet quality, yet the storage conditions are not well investigated. In this study, we characterized the effects of storage conditions (temperatures and storage duration) on the quality of a diet capable of rearing both specialist and generalist insect species. The completed diet, produced by both private industry and a USDA-Agricultural Research Service laboratory, was exposed to varying temperatures during a 24-hour transit over 1600km. After transit, it was stored at 4°C for a total storage period of 28 days. In a separate experiment, the completed diet was stored immediately after diet production at five fixed temperatures (-20, 4, 22, 25, and 33°C) for up to 28 days. For both experiments, at 5 intervals after storage (1, 7, 14, 21, and 28 days), diet quality was accessed by life history parameters (survival, molting, and weight) of western corn rootworm (Diabrotica virgifera virgifera LeConte) larvae, the most serious maize pest in the United States. Our results showed that exposure to varying temperatures between -2°C and 27°C for 24 hours had no significant impact on diet quality. However, extended storage (beyond 24 hours) at any of the fixed temperatures negatively affected diet quality. Insects reared on diets stored for over 24 hours at fixed temperatures ranging from -20°C to 33°C had significant declines in performance. Among the tested temperatures, -20°C and 4°C were found to be the most effective for preserving diet quality. At these low temperatures, there were no significant changes in insect weight and survival for diets stored within 21 and 28 days, respectively, though molting was significantly reduced within 7 days of storage. These findings provide the base of information on the storage conditions for completed diets, supporting the production of healthy insects.

Arthropod activity density and predation are supported by mixed cropping of maize with common sainfoin (Onobrychis viciifolia) and reduced tillage

AbstractMixed cropping with legumes may mitigate negative impacts of maize, Zea mays L. (Poaceae), production on arthropods by providing additional habitat structures and food resources. Still, knowledge about effects of less common legume partner crops for mixed cropping of maize is scarce. Activity density of epigeic predatory arthropods and proxies for ecosystem functions related to biological pest control were assessed on an experimental field. Plots of mixed cropping of maize and sainfoin, Onobrychis viciifolia Scop. (Fabaceae), and respective single plant species (plot size: 6 × 5 m; n = 48) differed in combination of the seed rate of each partner crop and tillage treatment. Using the “rapid ecosystem function assessment” approach in each plot on three occasions, we tested whether the activity density of generalist arthropod predators and their associated ecosystem functions can be promoted by mixed cropping of maize with sainfoin. Our data show that, compared with tilled maize as a pure culture, mixed cropping can increase activity density of generalist arthropod predators and insect predation potential but effects were limited to strip‐tilled cropping systems and partly depended on sampling date. Thus, from an ecological viewpoint, mixed cropping of sainfoin and maize in strip‐till systems offers the possibility to promote predatory insects and their potential for pest regulation. However, this system is inherently more prone to weed occurrence. Competition effects between cropping partners and weeds may reduce yields and hence lead to trade‐offs between enhancement of arthropods and economic viability.

Variation in immune response in the generalist herbivore fall webworm across four common host plants

AbstractDietary generalist herbivorous insects are widespread and often occur in a variety of environments. Across their geographic range, herbivorous insects may encounter variable plant traits as they feed on high‐quality or low‐quality plants. Herbivorous insect larvae experience both bottom‐up (host plant) and top‐down (parasitoid) factors that affect survival. Host plant quality may affect larval growth and survival in that larvae feeding on low‐quality plants often suffer reduced fitness. However, herbivores on different host plants are also subject to different levels of parasitism. High‐quality plants confer stronger larval performance (higher survival, more offspring), but larvae may also face higher parasitism. In some herbivore species, diet mediates larval immune response. The generalist insect herbivore fall webworm (FW), Hyphantria cunea Drury (Lepidoptera: Erebidae), is a moth native to North America, and its larvae have considerable variance in their performance when reared on different host plants. We investigated whether diet affects the immune response in FW larvae when they are reared on different host plant species known to vary in food quality. We measured immune response by melanization of a nylon filament. We found significant differences in immune response across host plants, indicating that diet mediates immune response in FW larvae. Our study helps elucidate the factors that cause variation in immune response in a generalist herbivore.

Safety of the Entomopathogenic Fungus Beauveria bassiana for Wild and Laboratory-Reared Chrysoperla lucasina Strains.

The need to reduce the impact of plant protection products on agroecosystems fosters the use of augmentative biological control involving the release of beneficial species into the field, the employment of entomopathogenic microbials, and the protection of naturally occurring biocontrol agents. This study aimed to investigate the compatibility of the entomopathogenic fungus Beauveria bassiana with the generalist insect predator Chrysoperla lucasina, in comparative experiments involving a laboratory-reared and a wild chrysopid strain. The larvae of the predators were exposed to different concentrations of fungal conidia up to a concentration of 107 conidia/mL by contact and ingestion. The treated insects showed only slight differences in terms of survival and immature development time compared to the untreated control insects. A significant decrease in the proportion of the male adults of C. lucasina that emerged from the laboratory-reared larvae that were exposed to higher concentrations of the fungus suggested a potentially different susceptibility between the sexes. A slightly lower adult emergence rate was observed in the wild strain, while no significant differences were recorded in the adult reproductive performance. These findings indicate that the B. bassiana strain ATCC 74040, at concentrations commonly used in the field, did not pose a significant risk to C. lucasina and can be safely used in combination with this predator for sustainable pest management.

Developing Oak Buds Produce Volatile Emissions in Response to Herbivory by Freshly Hatched Caterpillars.

Plant responses to damage by insectivorous herbivores are well-documented in mature leaves. The resulting herbivore-induced plant volatiles (HIPVs) protect the plant by attracting carnivorous arthropods and even some insectivorous vertebrates, to parasitize or consume the plant invaders. However, very little is known about plant production of HIPVs in developing buds, particularly when herbivorous insects are too small to be considered a prey item. It is additionally unclear whether plants respond differently to generalist and specialist chewing insects that overlap in distribution. Therefore, we compared HIPV production of Downy oak (Quercus pubescens Willd.) buds infested with freshly hatched caterpillars of Tortrix viridana (specialist) and Operophtera brumata (generalist), against uninfested buds. Of the compounds identified in both years of the experiment, we found that (Z)-hex-3-enyl acetate, (E)-β-ocimene, acetophenone, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate, α-copaene, α-humulene, (E)-caryophyllene, and (E,E)-α-farnesene appeared to be higher in infested buds compared to controls. We found no difference in HIPV production between the specialist and the generalist herbivores. Production of HIPVs was also associated with leaf damage, with higher HIPV production in more severely attacked buds. Thus, our study shows that oak trees already start responding to insect herbivory before leaves are developed, by producing compounds similar to those found in damaged mature leaves. Future work should focus on how Downy oak may benefit from initiating alarm cues at a time when carnivorous arthropods and insectivorous vertebrates are unable to use herbivorous insects as host or food.

Target for lipid-to-carbohydrate intake minimizes cost of growth.

Many theoretical treatments of foraging use energy as currency, with carbohydrates and lipids considered interchangeable as energy sources. However, herbivores must often synthesize lipids from carbohydrates since they are in short supply in plants, theoretically increasing the cost of growth. We tested whether a generalist insect herbivore (Locusta migratoria) can improve its growth efficiency by consuming lipids, and whether these locusts have a preferred caloric intake ratio of carbohydrate to lipid (C : L). Locusts fed pairs of isocaloric, isoprotein diets differing in C and L consistently selected a 2C : 1L target. Locusts reared on isocaloric, isoprotein 3C : 0L diets attained similar final body masses and lipid contents to locusts fed the 2C : 1L diet, but they ate more and had a ~12% higher metabolic rate, indicating an energetic cost for lipogenesis. These results demonstrate that some animals can selectively regulate carbohydrate-to-lipid intake and that consumption of dietary lipids can improve growth efficiency.

UDP-glycosyltransferases act as key determinants of host plant range in generalist and specialist Spodoptera species

Phytophagous insects have evolved sophisticated detoxification systems to overcome the antiherbivore chemical defenses produced by many plants. However, how these biotransformation systems differ in generalist and specialist insect species and their role in determining insect host plant range remains an open question. Here, we show that UDP-glucosyltransferases (UGTs) play a key role in determining the host range of insect species within the Spodoptera genus. Comparative genomic analyses of Spodoptera species that differ in host plant breadth identified a relatively conserved number of UGT genes in generalist species but high levels of UGT gene pseudogenization in the specialist Spodoptera picta. CRISPR-Cas9 knockouts of the three main UGT gene clusters of Spodoptera frugiperda revealed that UGT33 genes play an important role in allowing this species to utilize the poaceous plants maize, wheat, and rice, while UGT40 genes facilitate utilization of cotton. Further functional analyses in vivo and in vitro identified the UGT SfUGT33F32 as the key mechanism that allows generalist S. frugiperda to detoxify the benzoxazinoid DIMBOA (2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one), a potent insecticidal phytotoxin produced by poaceous plants. However, while this detoxification capacity is conserved in several generalist Spodoptera species, Spodoptera picta, which specializes on Crinum plants, is unable to detoxify DIMBOA due to a nonfunctionalizing mutation in SpUGT33F34. Collectively, these findings provide insight into the role of insect UGTs in host plant adaptation, the mechanistic basis of evolutionary transitions between generalism and specialism and offer molecular targets for controlling a group of notorious insect pests.

Salicylic acid positively regulates maize defenses against lepidopteran insects

In response to insect attack, plants use intricate signaling pathways, including phytohormones, such as jasmonate (JA), ethylene (ET), and salicylic acid (SA), to activate defenses. Maize (Zea mays) is one of the most important staple food crops around the world. Previous studies have shown that the JA and ET signaling play important roles in maize defense against insects, but little is known about whether and how SA regulates maize resistance to insect herbivores. In this study, we ectopically expressed the NahG (salicylate hydroxylase) gene in maize plants (NahG maize) to block the accumulation of SA. It was found that compared with the wild-type (WT) maize, the NahG maize exhibited decreased resistance to the generalist insects Spodopteralitura and Spodoptera frugiperda and the specialist Mythimna separata, and the compromised resistance in the NahG maize was associated with decreased levels of defensive metabolites benzoxazinoids (Bxs) and chlorogenic acid (CA). Quantification of simulated S. litura feeding-induced JA, JA-isoleucine conjugate (JA-Ile), and ET in the WT and NahG maize indicated that SA does not regulate JA or JA-Ile, but positively controls ET. We provide evidence suggesting that the SA pathway does not crosstalk with the JA or the ET signaling in regulating the accumulation of Bxs and CA. Transcriptome analysis revealed that the bHLH, ERF, and WRKY transcription factors might be involved in SA-regulated defenses. This study uncovers a novel and important phytohormone pathway in maize defense against lepidopterous larvae.

Food and time: dietary plasticity of different sources of a generalist insect herbivore.

Painted lady butterflies (Vanessa cardui L.,Nymphalidae) are generalist herbivores and serve as a model system across several fields of biology. While it has been demonstrated that V. cardui caterpillars can develop on different host plants, much of this work has been done on commercially sourced caterpillars, which could limit our understanding of wild V. cardui populations. In this study, we sought to explore possible differences in how commercial and wild V. cardui caterpillars may respond to feeding on different host plants, and subsequently, how their diet impacts immune response and survival. Here, we analyzed performance, survival, and immune response of wild and commercially sourced V. cardui caterpillars over several generations on diets that consisted of either 1 of 4 different host plant species or a mixed diet including all 4 species. Qualitatively, we observed that wild larvae had a better larval performance and hemocyte counts compared to the commercial larvae. The results demonstrate that both wild and commercially sourced caterpillars grew and survived best on the same diet treatments (mallow, narrowleaf plantain, and a mixed diet) during development across generations. Immune responses showed similar patterns across host plants between wild and commercial populations, with individuals showing lowered immune responses on dandelion and lupine and higher ones on mallow, plantain and the mixed diet; although the relative rankings on those 3 diets varied. Survival also demonstrated similar patterns, in that individuals reared on dandelion and lupine had the lowest survival.

Viral Infection Induces Changes to the Metabolome, Immune Response and Development of a Generalist Insect Herbivore.

Host plant consumption and pathogen infection commonly influence insect traits related to development and immunity, which are ultimately reflected in the behavior and physiology of the insect. Herein, we explored changes in the metabolome of a generalist insect herbivore, Vanessa cardui (Lepidoptera: Nymphalidae), in response to both dietary variation and pathogen infection in order to gain insight into tritrophic interactions for insect metabolism and immunity. Caterpillars were reared on two different host plants, Plantago lanceolata (Plantaginaceae) and Taraxacum officinale (Asteraceae) and subjected to a viral infection by Junonia coenia densovirus (JcDV), along with assays to determine the insect immune response and development. Richness and diversity of plant and caterpillar metabolites were evaluated using a liquid chromatography-mass spectrometry approach and showed that viral infection induced changes to the chemical content of V. cardui hemolymph and frass dependent upon host plant consumption. Overall, the immune response as measured by phenoloxidase (PO) enzymatic activity was higher in individuals feeding on P. lanceolata compared with those feeding on T. officinale. Additionally, infection with JcDV caused suppression of PO activity, which was not host plant dependent. We conclude that viral infection combined with host plant consumption creates a unique chemical environment, particularly within the insect hemolymph. Whether and how these metabolites contribute to defense against viral infection is an open question in chemical ecology.

High intraspecific variability and previous experience affect polyphenol metabolism in polyphagous Lymantria mathura caterpillars.

Polyphagous insect herbivores feed on multiple host-plant species and face a highly variable chemical landscape. Comparative studies of polyphagous herbivore metabolism across a range of plants is an ideal approach for exploring how intra- and interspecific chemical variation shapes species interactions. We used polyphagous caterpillars of Lymantria mathura (Erebidae, Lepidoptera) to explore mechanisms that may contribute to its ability to feed on various hosts. We focused on intraspecific variation in polyphenol metabolism, the fates of individual polyphenols, and the role of previous feeding experience on polyphenol metabolism and leaf consumption. We collected the caterpillars from Acer amoenum (Sapindaceae), Carpinus cordata (Betulaceae), and Quercus crispula (Fagaceae). We first fed the larvae with the leaves of their original host and characterized the polyphenol profiles in leaves and frass. We then transferred a subset of larvae to a different host species and quantified how host shifting affected their leaf consumption and polyphenol metabolism. There was high intraspecific variation in frass composition, even among caterpillars fed with one host. While polyphenols had various fates when ingested by the caterpillars, most of them were passively excreted. When we transferred the caterpillars to a new host, their previous experience influenced how they metabolized polyphenols. The one-host larvae metabolized a larger quantity of ingested polyphenols than two-host caterpillars. Some of these metabolites could have been sequestered, others were probably activated in the gut. One-host caterpillars retained more of the ingested leaf biomass than transferred caterpillars. The pronounced intraspecific variation in polyphenol metabolism, an ability to excrete ingested metabolites and potential dietary habituation are factors that may contribute to the ability of L. mathura to feed across multiple hosts. Further comparative studies can help identify if these mechanisms are related to differential host-choice and response to host-plant traits in specialist and generalist insect herbivores.

The digestive system of a cricket pulverizes polyethylene microplastics down to the nanoplastic scale

Microplastics (MPs; <5 mm) are a growing concern and a poorly understood threat to biota. We used a generalist insect (a cricket; Gryllodes sigillatus) to examine whether individuals would ingest and physically degrade MPs in their food. We fed crickets a range of concentrations (0, 2.5, 5, and 10% w/w) of fluorescent polyethylene MPs mixed into a standard diet and dissected the gut regions to isolate the MPs within. Comparing plastic content and fragment size within gut regions, we sought to identify whether and where crickets can fragment ingested MP particles. Given the digestive tract morphology of this species, we expected that the crickets would both ingest and egest the MPs. We also predicted that the MPs would be fragmented into smaller pieces during this digestive process. We found that G. sigillatus egested much smaller pieces than they ingested, and this fragmentation occurs early in the digestive process of this insect. We found this for both sexes as well as across the range of concentrations of MPs. The degree of plastic breakdown relative to plastic feeding time suggests that the ability to fragment MPs is intrinsic and not altered by how much time crickets have spent eating the plastics. The amount of plastics found in each region of the gut in relation to feeding time also suggests that this size and shape of PE microplastic does not cause any physical blockage in the gut. This lack of evidence for blockage is likely due to plastic breakdown. We found a ∼1000-fold reduction in plastic size occurs during passage through the digestive system, yielding particles very near nanoplastics (NPs; <1 μm), and likely smaller, that are then excreted back into the environment. These findings suggest that generalist insects can act as agents of plastic transformation in their environment if/when encountering MPs.

Reproductive biology and pollination ecology of Ipomoea triloba L. (Convolvulaceae): An alien invasive species of the Indo‐Burma biodiversity hotspot

AbstractIpomoea triloba L., an annual twining herb, is considered an alien invasive species and is distributed all around the globe including tropical Asia. It affects the yield of various economically important crops. Studies on floral phenology and reproductive biology are fundamental for the development of management strategies and the conservation of plants. Hence, we investigated the phenology, floral biology, pollen viability, stigma receptivity, pollination mechanism, and reproductive success of I. triloba at two different locations in one of the global biodiversity hotspots. Floral anthesis was diurnal, starting at 6:30 a.m. and lasting until 7:00 a.m. Pollen viability and stigma receptivity were found to coincide, thus suggesting the species was homogamous. The flowers were mostly visited and pollinated by sweat bees (Halictidae), blue‐banded bees (Amegilla sp.), flies (Mesembrius sp.), and butterflies (Appias olferna, Pelopidas agna, and Zizina otis). Further, the pollinator visitation frequency showed a moderately positive correlation with the number of open flowers in both study populations. The plant produced fruits in the absence of pollinators in self‐pollination treatments, indicating a self‐compatible breeding system and dependency on insect pollination for reproductive success. Further, pollen supplementation significantly enhanced the fruit setting and mean seed per fruit at both study sites, suggesting pollen limitation. Additionally, pollen production and pollen/ovule ratio also indicated the facultative autogamous breeding system in I. triloba. Overall, these reproductive characteristics such as mixed mating systems and generalist insect visitation may allow the invasive I. triloba to establish new populations from low numbers of propagules.

Mutually exclusive feeding yields Holling type III functional response

Abstract Many generalist predators, including fish, insects and mammals, temporarily focus on their search behaviour and can switch between prey species. Flexible and rapid behavioural plasticity enables a predator to forage optimally, as guided by search image formation and prey switching in response to changing prey abundances. More than half a century of studies have used Holling type III functional response to model the impact of this feeding behaviour on population dynamics, yet a mechanistic understanding for the pathway between individual behaviour and feeding rates remains poorly understood. To understand this common feeding behaviour, we developed three mechanistic models using first‐principles to provide direct derivations for the relationship between observed individual behaviour and feeding rates. The derived models yield three novel, generalised functional responses for predators characterised by prey switching and mutually exclusive feeding (i.e. feeding is limited to one prey species at a time). We show how these functional responses act as Holling type III response, and how they can be used to predict predators' diet compositions. Our results demonstrate that several behavioural forms of prey switching, as displayed in a wide range of predator species, consistently produce type III conforming functional responses. Read the free Plain Language Summary for this article on the Journal blog.

Selection pressure by specialist and generalist insect herbivores leads to optimal constitutive plant defense. A mathematical model.

Brassicaceae plants have the glucosinolate-myrosinase defense system, jointly active against herbivory. However, constitutive glucosinolate (GLS) defense is observed to occur at levels that do not deter all insects from feeding. That prompts the question of why Brassicaceae plants have not evolved a higher constitutive defense. The answer may lie in the contrasting relationship between plant defense and host plant preference of specialist and generalist herbivores. GLS content increases a plant's susceptibility to specialist insects. In contrast, generalists are deterred by the plant GLSs. Although GLSs can attract the natural enemies (predators and parasitoids) of these herbivores, enemies can reduce herbivore pressure to some extent only. So, plants can be overrun by specialists if GLS content is too high, whereas generalists can invade the plants if it is too low. Therefore, an optimal constitutive plant defense can minimize the overall herbivore pressure. To explain the optimal defense theoretically, we model the contrasting host selection behavior of insect herbivores and the emergence of their natural enemies by non-autonomous ordinary differential equations, where the independent variable is the plant GLS concentration. From the model, we quantify the optimal amount of GLSs, which minimizes total herbivore (specialists and generalists) pressure. That quite successfully explains the evolution of constitutive defense in plants from the perspective of optimality theory.

Experimental evidence reveals that vector host preference and performance across host plants is not altered by vector-borne plant viruses

Many plant pathogens are transmitted by generalist insects that move between host species, and vector preference and performance on different hosts affects pathogen transmission. Most studies of host–vector–pathogen interactions focus on a single host, however, and it is relatively unknown if viruses affect the host breadth of vectors. For example, although pea aphids (Acyrthosiphon pisum) often form tight associations with specific hosts, viruses transmitted by aphids can break down host defenses, potentially weakening these associations and increasing the host breadth of their vectors. Here, we assessed vector host preference and performance in an experiment with five pea aphid colonies with distinct host associations, five host species, and two viruses (Pea enation mosaic virus [PEMV] and Bean leafroll virus [BLRV]). Our prediction was that pea aphids would have higher performance on their inferior hosts and be less discriminating among hosts when those are infected, compared with noninfected hosts. Our results show that aphid performance, measured as the rate of increase on hosts, differed among hosts based on their host association, and relative performance among hosts was indeed altered by virus infection. Aphid preferences, measured using a choice bioassay in which aphids could settle on any of the five host species, also differed among aphid colonies but was not affected by virus infection status. We also did not find that infection status of hosts altered the performance of aphids on their preferred host. Furthermore, virus infection did not disrupt preference performance relationships for the aphids. Overall, our study suggests that host preference and performance are deeply ingrained in pea aphids, and that host associations may be robust to the presence of host-manipulating plant pathogens.

Endophytic insect pathogenic fungi-host plant-herbivore mutualism: elucidating the mechanisms involved in the tripartite interactions.

Various techniques used by crop plants to evade insect pests and pathogen attacks have been documented. Among these, plant defense strategies induced by endophytic insect pathogenic fungi are arguably one of the most discussed. Endophytic fungi frequently colonize plants and inhabit their internal tissues for a portion of their lifespan without producing visible symptoms of the disease. This phenomenon is widespread and diverse in both natural and agricultural ecosystems, and is present in almost all plant organs. Many fungi can obtain nutrients by infecting and killing insects, and this ability has been developed numerous times in different fungal lineages. These species mainly consist of those in the order Hypocreales (Ascomycota), where the generalist insect pathogens, Beauveria sp. (Cordycipitaceae) and Metarhizium sp. (Clavicipitaceae) are two of the most studied endophytic entomopathogenic fungal genera. However, most fungi that kill insects do not survive in the tissues of living plants. The data published thus far show a high degree of variability and do not provide consistent explanations for the underlying mechanisms that may be responsible for these effects. This implies that available knowledge regarding the colonization of plant tissues by endophytic insect pathogenic fungi, the effects of colonization on plant metabolism, and how this contributes to a decrease in herbivore and pathogens damage is limited. To adequately utilize fungal-based products as biological control agents, these products must be effective and the reduction of pests and infection must be consistent and similar to that of chemical insecticides after application. This article discusses this possibility and highlights the benefits and the specific techniques utilized by endophytically challenged plants in invading insect pests and disease pathogens.

Co-Occurrence of Wing Deformity and Impaired Mobility of Alates with Deformed Wing Virus in Solenopsis invicta Buren (Hymenoptera: Formicidae).

Deformed wing virus (DWV), a major honey bee pathogen, is a generalist insect virus detected in diverse insect phyla, including numerous ant genera. Its clinical symptoms have only been reported in honey bees, bumble bees, and wasps. DWV is a quasispecies virus with three main variants, which, in association with the ectoparasitic mite, Varroa destructor, causes wing deformity, shortened abdomens, neurological impairments, and colony mortality in honey bees. The red imported fire ant, Solenopsis invicta Buren, is one of the most-invasive and detrimental pests in the world. In this study, we report the co-occurrence of DWV-like symptoms in S. invicta and DWV for the first time and provide molecular evidence of viral replication in S. invicta. Some alates in 17 of 23 (74%) lab colonies and 9 of 14 (64%) field colonies displayed deformed wings (DWs), ranging from a single crumpled wing tip to twisted, shriveled wings. Numerous symptomatic alates also exhibited altered locomotion ranging from an altered gait to the inability to walk. Deformed wings may prevent S. invicta alates from reproducing since mating only occurs during a nuptial flight. The results from conventional RT-PCR and Sanger sequencing confirmed the presence of DWV-A, and viral replication of DWV was confirmed using a modified strand-specific RT-PCR. Our results suggest that S. invicta can potentially be an alternative and reservoir host for DWV. However, further research is needed to determine whether DWV is the infectious agent that causes the DW syndrome in S. invicta.

Defensive furofuran lignans localized to the oil cells of Neocinnamomum delavayi and their metabolism by a specialist insect

Neocinnamomum delavayi (Lauraceae) leaves with abundant oil cells are seldom attacked by insects, but their chemical constituent and biological function remain obscure. Three furofuran lignans, including (+)-eudesmin (3), (+)-magnolin (4), and demethoxyaschantin (5), were identified to be the major specialized metabolites in the oil cells of N. delavayi leaves through laser microdissection coupled with NMR analysis. Compounds 3 and 4 exhibited obvious antifeedant activity against a generalist insect Spodoptera exigua, and their natural contents in the leaves could effectively defend against generalist insects. Intriguingly, three specific metabolites 9–11, the O-demethylation derivates of compounds 3–5, were identified from a native specialist insect Dindica polyphaenaria feeding with N. delavayi leaves, implying an adaptation mechanism of specialist insects to plant defensive compounds. The results revealed a chemical connection between plants and insects, which would contribute to our understanding of plant-insect interaction and insect management.