Determining Larval Host Plant Use by a Polyphagous Lepidopteran Through Analysis of Adult Moths for Plant Secondary Metabolites

Many polyphagous insect species are important economic pests on one or more of their crop hosts. For most important insect pests, the common crop hosts are well-known, but knowledge of weedy and unmanaged hosts is limited. Furthermore, the relative contribution of different hosts to local and regional populations has rarely been ascertained because this requires having some way to determine which plant hosts are the source of the adult moths observed ovipositing in a crop field at a given place and time. One way of determining the larval host of polyphagous pest species is to analyze for several plant-derived chemicals that are each specific to a different small set of related plant species and are preserved in detectable amounts in adult moths. In this paper, we describe novel methods for analyzing adults of the polyphagous lepidopteran, the tobacco budworm (TBW) Heliothis virescens (F.), for plant secondary metabolites, specifically cotinine and gossypol, which are diagnostic for larval feeding on tobacco and cotton, respectively. Cotinine was extracted from individual TBW moths with acetic acid and methanol, then concentrated and analyzed directly by gas chromatography/mass spectrometry (GC/MS). The same moths then were analyzed for bound gossypol by creating a Schiff’s base that used aniline, and the resulting dianilino–gossypol complex was quantified using high pressure chromatography coupled with a triple quadrupole mass spectrometer (MS) as the detector. Based on analysis of standards, the detection limit for the cotinine was less than 1.5 ppb by dry weight. Comparable standards were not available for the gossypol derivative so a quantitative limit of detection could not be calculated. When TBW moths reared on known hosts were analyzed for gossypol and/or cotinine, all of the moths reared on tobacco or cotton were correctly identified, although some false positives were recorded with the gossypol method. Analysis of TBW moths of various ages and at various lengths of time after death determined that a significant gossypol signal was detectable in all moths reared on cotton. TBW moths collected from the vicinity of cotton fields in July and August in North Carolina also were analyzed. A much larger portion of the moths were derived from tobacco (6.7–46.4%) than from cotton (0–3.6%) in both months. Thus, these methods can be reliably used to estimate the proportion of TBW derived from noncotton host plants in populations trapped around Bt cotton fields, thereby providing insight into the risk of TBW evolving resistance to Bt cotton.     

Host Plant Volatiles Synergize Response to Sex Pheromone in Codling Moth, Cydia pomonella

Plant volatile compounds synergize attraction of codling moth males Cydia pomonella to sex pheromone (E,E)-8,10-dodecadien-1-ol (codlemone). Several apple volatiles, known to elicit a strong antennal response, were tested in a wind tunnel. Two-component blends of 1 pg/min codlemone and 100 pg/min of either racemic linalool, (E)-beta-farnesene, or (Z)-3-hexen-1-ol attracted significantly more males to the source than codlemone alone (60, 58, 56, and 37%, respectively). In comparison, a blend of codlemone and a known pheromone synergist, dodecanol, attracted 56% of the males tested. Blends of pheromone and plant volatiles in a 1:100 ratio attracted more males than 1:1 or 1:10,000 blends. Adding two or four of the most active plant compounds to codlemone did not enhance attraction over blends of codlemone plus single-plant compounds. Of the test compounds, only farnesol was attractive by itself; at a release rate of 10,000 pg/min, 16% of the males arrived at the source. However, attraction to a 1:10,000 blend of codlemone and farnesol (42%) was not significantly different from attraction to codlemone alone (37%). In contrast, a codlemone mimic, (E)-10-dodecadien-1-ol, which attracted 2% males by itself, had a strong antagonistic effect when blended in a 1:10,000 ratio with codlemone.     

The Role of Plant Hormones in the Interaction of Colletotrichum Species with Their Host Plants

Colletotrichum is a plant pathogenic fungus which is able to infect virtually every economically important plant species. Up to now no common infection mechanism has been identified comparing different plant and Colletotrichum species. Plant hormones play a crucial role in plant-pathogen interactions regardless whether they are symbiotic or pathogenic. In this review we analyze the role of ethylene, abscisic acid, jasmonic acid, auxin and salicylic acid during Colletotrichum infections. Different Colletotrichum strains are capable of auxin production and this might contribute to virulence. In this review the role of different plant hormones in plant—Colletotrichum interactions will be discussed and thereby auxin biosynthetic pathways in Colletotrichum spp. will be proposed.     

Experience-Induced Habituation and Preference Towards Non-Host Plant Odors in Ovipositing Females of a Moth

In phytophagous insects, experience can increase positive responses towards non-host plant extracts or induce oviposition on non-host plants, but the underlying chemical and behavioral mechanisms are poorly understood. By using the diamondback moth, Plutella xylostella, its host plant Chinese cabbage, and a non-host plant Chrysanthemum morifolium, as a model system, we observed the experience-altered olfactory responses of ovipositing females towards volatiles of the non-host plant, volatiles of pure chemicals (p-cymene and α-terpinene) found in the non-host plant, and volatiles of host plants treated with these chemicals. We assessed the experience-altered oviposition preference towards host plants treated with p-cymene. Naive females showed aversion to the odors of the non-host plant, the pure chemicals, and the pure chemical-treated host plants. In contrast, experienced females either became attracted by these non-host odors or were no longer repelled by these odors. Similarly, naive females laid a significantly lower proportion of eggs on pure chemical-treated host plants than on untreated host plants, but experienced females laid a similar or higher proportion of eggs on pure chemical-treated host plants compared to untreated host plants. Chemical analysis indicated that application of the non-host pure chemicals on Chinese cabbage induced emissions of volatiles by this host plant. We conclude that induced preference for previously repellent compounds is a major mechanism that leads to behavioral changes of this moth towards non-host plants or their extracts.     

Host Plant Constancy in Ovipositing Manduca sexta

Journal of Chemical Ecology - Many pollinating insects exhibit flower constancy, i.e. they target flower species they have already experienced and fed from. While the insects might profit from...     

Semiochemical-Mediated Location of Host Habitat by Apanteles carpatus (Say) (Hymenoptera: Braconidae), a Parasitoid of Clothes Moth Larvae

In Y-tube olfactometer bioassays, adult Apanteles carpatus (Say), were attracted to beaver or rabbit pelts infested with larvae of the casemaking clothes moth (CCM)Tinea pellionella L. Porapak Q-captured volatiles from a CCM-infested beaver pelt were also very attractive, whereas isolated CCM larvae or larval feces were not. Coupled gas chromatographic–electroantennographic detection (GC-EAD) analysis of the Porapak Q volatile extract revealed two compounds that elicited responses by A. carpatus antennae. Coupled GC–mass spectrometry (MS) in electron impact and chemical ionization modes of these compounds indicated, and GC-MS and GC-EAD of authentic standards confirmed, that they were nonanal and geranylacetone. While each compound singly did not attract A. carpatusa 1:1 blend of both compounds was as attractive as the volatile extract. Because these compounds are host habitat-derivedA. carpatus must be a habitat rather than host specialist, responding to kairomonal indicators of localized and specific habitats such as animal hair or feather. The tritrophic interaction between A. carpatusits clothes moth hosts and their animal-derived habitats is similar to the well-studied relationship between parasitoids of insect herbivores and their host plant habitats.     

Phenol and Polyaromatic Hydrocarbons Are Stronger Drivers Than Host Plant Species in Shaping the Arbuscular Mycorrhizal Fungal Component of the Mycorrhizosphere

Changes in soil microbial communities in response to hydrocarbon pollution are critical indicators of disturbed ecosystem conditions. A core component of these communities that is functionally adjusted to the life-history traits of the host and environmental factors consists of arbuscular mycorrhizal fungi (AMF). AMF communities associated with Poa trivialis and Phragmites australis growing at a phenol and polynuclear aromatic hydrocarbon (PAH)-contaminated site and at an uncontaminated site were compared based on LSU rDNA sequencing. Dissimilarities in species composition and community structures indicated soil pollution as the main factor negatively affecting the AMF diversity. The AMF communities at the contaminated site were dominated by fungal generalists (Rhizophagus, Funneliformis, Claroideoglomus, Paraglomus) with wide ecological tolerance. At the control site, the AMF communities were characterized by higher taxonomic and functional diversity than those exposed to the contamination. The host plant identity was the main driver distinguishing the two AMF metacommunities. The AMF communities at the uncontaminated site were represented by Polonospora, Paraglomus, Oehlia, Nanoglomus, Rhizoglomus, Dominikia, and Microdominikia. Polonosporaceae and Paraglomeraceae were particularly dominant in the Ph. australis mycorrhizosphere. The high abundance of early diverging AMF could be due to the use of primers able to detect lineages such as Paraglomeracae that have not been recognized by previously used 18S rDNA primers.     

Involvement of a Specific Chemosensory Protein from Bactrocera dorsalis in Perceiving Host Plant Volatiles

Insects have evolved many physiological and behavioral adaptations to recognize external complex chemicals. Olfaction plays an important role in perceiving volatile chemicals, utilizing them to locate host sites, conspecifics, and enemies. Chemosensory proteins (CSPs) are present in high concentrations within the sensory sensilla of insects and are endowed with a heterogeneous range of functions. However, direct evidence for the involvement of CSPs in olfactory function is still lacking. In this study, a fluorescence-based ligand binding assay using Bdor-CSP2 illustrated its ability to bind the majority of the selected ligands of different shapes and chemical structures that are ecologically significant, host plant volatiles of Bactrocera dorsalis. RNAi-mediated silencing coupled with electrophysiological tests showed lower electrophysiological responses to (3Z)-hex-3-en-1-ol, trans-2-hexenal, 6-methylhept-5-en-2-one, and 3-methylbutyl acetate in dsBdor CSP2 treated flies compared with the untreated controls. The reduced expression of Bdor-CSP2 by RNA interference was confirmed by semi-quantitative PCR, real-time quantitative PCR and Western blot, which suggested the RNAi-treatment was responsible for the observed reduction of antennal responses in EAG recordings. These data suggest that the expression of Bdor-CSP2 is necessary for the recognition of antennal responses to some plant host volatiles by B. dorsalis.     

化工装置内高压蒸汽主管道设计

结合某化工项目主装置内高压蒸汽系统管道设计经验,讨论高压蒸汽管道设计中的管道材质选择及管道壁厚的计算、管道应力计算及分析、结合管架形式合理选择隔热管托、确定保温层结构及保温层厚度等高压蒸汽管道设计中所涉及的问题。     

Prey and Non-prey Arthropods Sharing a Host Plant: Effects on Induced Volatile Emission and Predator Attraction

It is well established that plants infested with a single herbivore species can attract specific natural enemies through the emission of herbivore-induced volatiles. However, it is less clear what happens when plants are simultaneously attacked by more than one species. We analyzed volatile emissions of lima bean and cucumber plants upon multi-species herbivory by spider mites (Tetranychus urticae) and caterpillars (Spodoptera exigua) in comparison to single-species herbivory. Upon herbivory by single or multiple species, lima bean and cucumber plants emitted volatile blends that comprised mostly the same compounds. To detect additive, synergistic, or antagonistic effects, we compared the multi-species herbivory volatile blend with the sum of the volatile blends induced by each of the herbivore species feeding alone. In lima bean, the majority of compounds were more strongly induced by multi-species herbivory than expected based on the sum of volatile emissions by each of the herbivores separately, potentially caused by synergistic effects. In contrast, in cucumber, two compounds were suppressed by multi-species herbivory, suggesting the potential for antagonistic effects. We also studied the behavioral responses of the predatory mite Phytoseiulus persimilis, a specialized natural enemy of spider mites. Olfactometer experiments showed that P. persimilis preferred volatiles induced by multi-species herbivory to volatiles induced by S. exigua alone or by prey mites alone. We conclude that both lima bean and cucumber plants effectively attract predatory mites upon multi-species herbivory, but the underlying mechanisms appear different between these species.     

Host Plant Invests in Growth Rather than Chemical Defense When Attacked by a Specialist Herbivore

Plant defensive compounds may be a cost rather than a benefit when plants are attacked by specialist insects that may overcome chemical barriers by strategies such as sequestering plant compounds. Plants may respond to specialist herbivores by compensatory growth rather than chemical defense. To explore the use of defensive chemistry vs. compensatory growth we studied Brugmansia suaveolens (Solanaceae) and the specialist larvae of the ithomiine butterfly Placidina euryanassa, which sequester defensive tropane alkaloids (TAs) from this host plant. We investigated whether the concentration of TAs in B. suaveolens was changed by P. euryanassa damage, and whether plants invest in growth, when damaged by the specialist. Larvae feeding during 24 hr significantly decreased TAs in damaged plants, but they returned to control levels after 15 days without damage. Damaged and undamaged plants did not differ significantly in leaf area after 15 days, indicating compensatory growth. Our results suggest that B. suaveolens responds to herbivory by the specialist P. euryanassa by investing in growth rather than chemical defense.     

Simulation Modeling to Interpret the Captures of Moths in Pheromone-Baited Traps Used for Surveillance of Invasive Species: the Gypsy Moth as a Model Case

When pheromone traps are used for detection of an invasive pest and then delimitation of its distribution, an unresolved issue is the interpretation of failure to capture any target insects. Is a population present but not detected, a so-called false negative? Using the gypsy moth (Lymantria dispar) as an exemplar, we modeled the probability of males being captured in traps deployed at densities typical for surveillance (1 per 2.6 km² or 1 per mi²) and delimitation (up to 49 per 2.6 km²). The simulations used a dynamic wind model generating a turbulent plume structure and varying wind direction, and a behavior model based on the documented maneuvers of gypsy moths during plume acquisition and along-plume navigation. Several strategies of plume acquisition using Correlated Random Walks were compared to ensure that the generated dispersions over three days were not either overly clumped or ranged many km. Virtual moths were released into virtual space with patterns mimicking prior releases of gypsy moth males in Massachusetts at varying distance from a baited trap. In general, capture rates of virtual and real moths at varying trap densities were similar. One application of this approach was to estimate through bootstrapping the probabilities of not detecting populations having densities ranging from 1 to 100 moths per 2.6 km² and using traps that varied from 25 to 100 % in their efficiencies of capture. Low-level populations (e.g., 20–30 per 2.6 km²) often were not detected with one trap per 2.6 km², especially when traps had low efficiencies.     

Perception of Host Plant Volatiles in Hyalesthes obsoletus: Behavior, Morphology, and Electrophysiology

The Palearctic planthopper Hyalesthes obsoletus is the natural vector of the grapevine yellow disease Bois noir. Grapevine is an occasional host plant of this polyphagous planthopper. To deepen our knowledge of the role of plant volatile organic compounds for H. obsoletus host plant searching, we carried out behavioral, morphological, and electrophysiological studies. We tested the attraction of H. obsoletus to nettle, field bindweed, hedge bindweed, chaste tree, and grapevine by using a Y-shaped olfactometer. The results showed a significant attraction of male H. obsoletus to chaste tree, and of the females to nettle. Male H. obsoletus were repelled by odor from hedge bindweed. Ultrastructural studies of the antennae showed at least two types of olfactory sensilla at the antennal pedicel: plaque organs and trichoid sensilla. Volatile organic compounds from nettle and chaste tree were collected, and the extracts were analyzed by coupling gas-chromatography to both mass-spectrometry and electroantennography. The volatile organic compounds that elicited electrophysiological responses in male and female antennae were identified. These findings are discussed with respect to behavior of H. obsoletus males and females in the field.     

“This is not an Apple”–Yeast Mutualism in Codling Moth

The larva of codling moth Cydia pomonella (Tortricidae, Lepidoptera) is known as the worm in the apple, mining the fruit for food. We here show that codling moth larvae are closely associated with yeasts of the genus Metschnikowia. Yeast is an essential part of the larval diet and further promotes larval survival by reducing the incidence of fungal infestations in the apple. Larval feeding, on the other hand, enables yeast proliferation on unripe fruit. Chemical, physiological and behavioral analyses demonstrate that codling moth senses and responds to yeast aroma. Female moths are attracted to fermenting yeast and lay more eggs on yeast-inoculated than on yeast-free apples. An olfactory response to yeast volatiles strongly suggests a contributing role of yeast in host finding, in addition to plant volatiles. Codling moth is a widely studied insect of worldwide economic importance, and it is noteworthy that its association with yeasts has gone unnoticed. Tripartite relationships between moths, plants, and microorganisms may, accordingly, be more widespread than previously thought. It, therefore, is important to study the impact of microorganisms on host plant ecology and their contribution to the signals that mediate host plant finding and recognition. A better comprehension of host volatile signatures also will facilitate further development of semiochemicals for sustainable insect control.     

杀虫剂对不同寄主植物上的小菜蛾幼虫羧酸酯酶的体内抑制

敌敌畏对取分西洋菜，菜心和萝卜的小菜蛾４龄幼虫β－ＮＡ羧酸酯酶的体内抑制动态规律有显著的差异。取食不同寄主植物的小菜蛾β－ＮＡ羧酸酯酶活性在受到敌敌畏的的抑制之后，其恢复速度不同，取食西洋菜的小菜蛾幼虫β－ＮＡ羧酸酯酶活性的恢复速度明显高于取食菜心和萝卜的小菜蛾。     

Herbivore-Induced Plant Volatiles Can Serve as Host Location Cues for a Generalist and a Specialist Egg Parasitoid

Herbivore-induced plant volatiles are important host finding cues for larval parasitoids, and similarly, insect oviposition might elicit the release of plant volatiles functioning as host finding cues for egg parasitoids. We hypothesized that egg parasitoids also might utilize HIPVs of emerging larvae to locate plants with host eggs. We, therefore, assessed the olfactory response of two egg parasitoids, a generalist, Trichogramma pretiosum (Tricogrammatidae), and a specialist, Telenomus remus (Scelionidae) to HIPVs. We used a Y-tube olfactometer to tests the wasps’ responses to volatiles released by young maize plants that were treated with regurgitant from caterpillars of the moth Spodoptera frugiperda (Noctuidae) or were directly attacked by the caterpillars. The results show that the generalist egg parasitoid Tr. pretiosum is innately attracted by volatiles from freshly-damaged plants 0–1 and 2–3 h after regurgitant treatment. During this interval, the volatile blend consisted of green leaf volatiles (GLVs) and a blend of aromatic compounds, mono- and homoterpenes, respectively. Behavioral assays with synthetic GLVs confirmed their attractiveness to Tr. pretiosum. The generalist learned the more complex volatile blends released 6–7 h after induction, which consisted mainly of sesquiterpenes. The specialist T. remus on the other hand was attracted only to volatiles emitted from fresh and old damage after associating these volatiles with oviposition. Taken together, these results strengthen the emerging pattern that egg and larval parasitoids behave in a similar way in that generalists can respond innately to HIPVs, while specialists seems to rely more on associative learning.     

Identification of Sex Pheromone Components of a New Zealand Geometrid Moth, the Common Forest Looper Pseudocoremia suavis, Reveals a Possible Species Complex

Gas chromatography–electroantennographic detection analysis of sex pheromone gland extracts of the common forest looper Pseudocoremia suavis (Lepidoptera: Geometridae), a polyphagous defoliator of introduced Pinaceae and many New Zealand trees, revealed four compounds that elicited antennal responses. The two major active compounds (6Z)-cis-9,10-epoxynonadec-6-ene and (3Z,6Z)-cis-9,10-epoxynonadeca-3,6-diene were identified by comparison with known standards. Of the two minor active compounds, one was tentatively identified as (3Z,6Z)-cis-9,10-epoxyhenicosa-3,6-diene, whereas the other could not be identified because of insufficient amounts in extracts. (6Z)-cis-9,10-Epoxynonadec-6-ene, (3Z,6Z)-cis-9,10-epoxynonadeca-3,6-diene, and (3Z,6Z)-cis-9,10-epoxyhenicosa-3,6-diene were present in P. suavis gland extracts from Eyrewell Forest, a Pinus radiata plantation in the South Island of New Zealand, in a ratio of 35:65:5, respectively. Trapping trials in Eyrewell Forest established that (6Z)-cis-9,10-epoxynonadec-6-ene attracted male P. suavis. However, addition of (3Z,6Z)-cis-9,10-epoxyhenicosa-3,6-diene to the lure at <10% of (6Z)-cis-9,10-epoxynonadec-6-ene reduced capture of male moths, suggesting that one of its enantiomers was acting as a behavioral antagonist. During January–March of 2005, a blend trial involving single, binary, and ternary mixtures of the three components at Eyrewell Forest and at three other sites (two in the South Island and one in the North Island) revealed the existence of a second taxon of P. suavis at the three additional sites that was attracted to lures containing (3Z,6Z)-cis-9,10-epoxynonadeca-3,6-diene, either singly or in binary and ternary mixtures with (6Z)-cis-9,10-epoxynonadec-6-ene and (3Z,6Z)-cis-9,10-epoxyhenicosa-3,6-diene. This second taxon was not attracted to lures loaded solely with (6Z)-cis-9,10-epoxynonadec-6-ene.     

Colorado Potato Beetle Toxins Revisited: Evidence the Beetle Does Not Sequester Host Plant Glycoalkaloids

The Colorado potato beetle feeds only on glycoalkaloid-laden solanaceous plants, appears to be toxic to predators, and has aposematic coloration, suggesting the beetle may sequester alkaloids from its host plants. This study tested 4th instars and adults, as well as isolated hemolymph and excrement, to determine if the beetles sequester, metabolize, or excrete alkaloids ingested from their host plants. HPLC analysis showed: that neither the larvae nor the adults sequestered either solanine or chaconine from potato foliage; that any alkaloids in the beetles were at concentrations well below 1 ppm; and that alkaloids were found in the excrement of larvae at approximately the same concentrations as in foliage. Analysis of alkaloids in the remains of fed-upon leaflet halves plus excreta during 24 hr feeding by 4th instars, as compared to alkaloids in the uneaten halves of the leaflets, showed that equal amounts of alkaloids were excreted as were ingested. The aposematic coloration probably warns of a previously-identified toxic dipeptide instead of a plant-derived alkaloid, as the Colorado potato beetle appears to excrete, rather than sequester or metabolize, the alkaloids from its host plants.     

Crosstalk between Melatonin and Reactive Oxygen Species in Plant Abiotic Stress Responses: An Update

Melatonin acts as a multifunctional molecule that takes part in various physiological processes, especially in the protection against abiotic stresses, such as salinity, drought, heat, cold, heavy metals, etc. These stresses typically elicit reactive oxygen species (ROS) accumulation. Excessive ROS induce oxidative stress and decrease crop growth and productivity. Significant advances in melatonin initiate a complex antioxidant system that modulates ROS homeostasis in plants. Numerous evidences further reveal that melatonin often cooperates with other signaling molecules, such as ROS, nitric oxide (NO), and hydrogen sulfide (H₂S). The interaction among melatonin, NO, H₂S, and ROS orchestrates the responses to abiotic stresses via signaling networks, thus conferring the plant tolerance. In this review, we summarize the roles of melatonin in establishing redox homeostasis through the antioxidant system and the current progress of complex interactions among melatonin, NO, H₂S, and ROS in higher plant responses to abiotic stresses. We further highlight the vital role of respiratory burst oxidase homologs (RBOHs) during these processes. The complicated integration that occurs between ROS and melatonin in plants is also discussed.