No-choice Feeding Assays Research Articles

Could bacteriophages be used as a novel pest management tool to control gut endosymbionts in Western Flower Thrips?

Several species of Thysanoptera are considered agricultural pests, especially Frankliniella occidentalis (Western Flower Thrips, WFT). The damage WFT causes to plants can either be direct by feeding and oviposition activity or indirect by WFT serving as vectors for several plant viruses, bacteria, and fungi. Properties of WFT like polyphagy, cryptic lifestyle, fast reproduction and the ability to quickly develop insecticide resistance make them difficult to control. Alternative pest management tactics are thus in high demand. Potential targets are the facultative or obligate endosymbionts that affect the life history parameters of WFT. The known endosymbionts of WFT: BFo1/BFo2 (B = bacteria, Fo = Frankliniella occidentalis, number indicate different types) positively influence their fertility and development. Elimination of these endosymbionts could result in a decreased individual reproduction level and decreased population growth. Bacteriophages specific against BFo1/BFo2 were isolated and characterized and were applied in a no-choice feeding assay to female WFT. Antibiotic and sugar solutions served as controls. Phage-treated thrips showed no significant difference in survival, fecundity, oviposition rate or developmental time of the progeny compared to the control, whereas antibiotic treatment caused a decline in survival, fecundity, and oviposition rate, but not in the developmental time of offspring. The results showed a rapid decline of the bacteriophage concentration in the feed solution, which the WFT salivary gland products might cause. The complex relationship between thrips, endosymbionts and bacteriophages, needs further attention before bacteriophages could be used as potential management tools.

Efficacy and residual toxicity of chitosan for Rhagoletis pomonella (Diptera: Tephritidae).

Chitosan is a naturally derived polymer that has significant potential for use as a bioinsecticide. Despite this, there is a lack of research as to the efficacy of chitosan for many insect pest species. The apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), is one such pest for which chitosan toxicity has not been explored. In this study, the toxicity of chitosan for R. pomonella adults was tested via no-choice feeding assays. An aging trial was further used to test the mortality of flies provided dried chitosan-sucrose treatments (CST), which were aged for 0 or 3 days in greenhouse conditions. This study found that the CST is toxic for R. pomonella adults when ingested, leading to a significant increase in the rate of mortality compared to control groups. The use of dried chitosan, however, did not change the mortality of flies, suggesting this will not be an effective delivery mechanism. Effective biopesticide delivery systems have not been defined for chitosan use outside of a laboratory, indicating the need for further research testing delivery mechanisms. It is suggested that an effective method of delivery can be as a food-based bait in attract-and-kill traps, as chitosan must be ingested to kill flies. Forming a viscous solution, chitosan may be best suited to these lure systems.

Choice and No-Choice Feeding Assays of Cotton Fleahoppers (Pseudatomoscelis seriatus) on Cotton Expressing the Mpp51Aa2 Protein

In Texas, the cotton fleahopper (Pseudatomoscelis seriatus (Reuter)) is considered a highly economically damaging pest of cotton (Gossypium hirsutum L.). Current control methods rely heavily on foliar chemical insecticides throughout the growing season. Considering the cost of insecticides and the critical timeliness of their application, chemical control methods are often not optimized to reduce potential yield losses. The Mpp51Aa2.834_16 gene in cotton (ThryvOn) has shown effectiveness against thrips and several piercing and sucking mirid insect pests, suggesting it has the potential to mitigate yield losses caused by the cotton fleahopper. Choice and no-choice caged feeding assays were conducted to assess the impact of cotton fleahoppers on ThryvOn cotton square retention under controlled laboratory conditions. In the choice assay, feeding by cotton fleahoppers significantly reduced square retention in the gene-lacking cotton to 46%, while the ThryvOn cotton retained 60% of the squares. In the no-choice assay, cotton fleahopper nymph feeding significantly reduced square retention in the cotton not expressing Mpp51Aa2 to 61%, whereas the ThryvOn cotton was unaffected. Based on the differences in square retention observed in both the choice and no-choice feeding assays, our findings indicate that the Mpp51Aa2 protein influences cotton fleahopper feeding preferences and the susceptibility of cotton plants to damage caused by cotton fleahoppers. Our study offers confirmation of the activity of ThryvOn on cotton fleahoppers observed in the field. The ThryvOn trait’s activity towards cotton fleahoppers is consistent with that found for other mirid pests in cotton.

Adenosine triphosphate overrides the aversive effect of antifeedants and toxicants: a model alternative phagostimulant for sugar-based vector control tools

BackgroundSugar, when used as the phagostimulant in attractive toxic bait control tools, limits the efficacy and selectivity of this technology. Thus, more potent and selective phagostimulants than sugar are required to improve this technology. The potency of adenosine triphosphate (ATP) as an alternative model phagostimulant was assessed to determine its capacity to override the aversive effects of select antifeedants and toxicants. How ATP and sucrose modulate the rate of toxicity in the yellow fever mosquito Aedes aegypti was also examined.MethodsA no-choice feeding assay was used to investigate the phagostimulatory ability of ATP to override the aversive effects of structurally divergent antifeedant and toxicant compounds, and to modulate the rate of toxicity over 24 h. Binary combinations of antifeedant and toxicant compounds, at various concentrations, were similarly assessed for enhanced lethal potency. In comparison, no-choice open access and cotton wick feeding assays were used to determine the phagostimulatory role of sucrose in the ingestion of boric acid-laced diets. Dissections of the guts were performed to determine the diet destination as dependant on the phagostimulant.ResultsATP is a potent phagostimulant that dose dependently overrides aversion to antifeedant and toxicant tastants. Feeding on antifeedant- or toxicant-laced diets that was induced by ATP selectively resulted in rapid knockdown (nicotine, lobeline and caffeine) or death (boric acid and propylene glycol), with a combination of the two lethal compounds inducing a synergistic effect at lower concentrations. ATP- and sucrose-induced feeding predominantly directed the antifeedant- or toxicant-laced meals to the midgut and the crop, respectively.ConclusionsATP is an efficacious alternative model phagostimulant to sucrose that overrides the aversive effects of antifeedants and toxicants, resulting in rapid toxic effects. Furthermore, this study demonstrates that variation in the rate of toxicity between ATP- and sugar-induced feeding is at least partly regulated by the differential feeding response, volume imbibed and the destination of the meals. Additional research is needed to identify structurally related, stable analogues of ATP due to the ephemeral nature of this molecule. For future applications, the workflow presented in this study may be used to evaluate such analogues for their suitability for use in attractive bait stations designed to target a broad range of haematophagous arthropods and prevent off-target species’ feeding.Graphical

Impacts of Bioassay Type on Insecticide Resistance Assessment in the German Cockroach (Blattodea: Ectobiidae).

The German cockroach, Blattella germanica (L.), is one of the most critical urban pests globally due to the health risks it imposes on people, such as asthma. Insecticides are known to manage large cockroach population sizes, but the rapid rate at which they develop resistance is a continuing problem. Dealing with insecticide resistance can be expensive and time-consuming for both the consumer and the pest management professional (PMP) applying the treatment. Each cockroach population is unique because different strains have different insecticide susceptibilities, so resistance profiles must be considered. This study addressed the above issue in a controlled laboratory setting. Cockroach strains from Indianapolis, Indiana, Danville, Illinois, and Baltimore, Maryland, USA were used. Four insecticide active ingredients (AIs) most used by consumers and PMPs were selected for testing in vial bioassays to establish resistance profiles. Next, no-choice and choice feeding assays with four currently registered bait products were performed to assess the impacts of competing food and circadian rhythms on bait resistance levels. The results indicate that emamectin benzoate (Optigard) was the most effective AI in causing the highest mortality in all strains in vial and no-choice bioassays; whereas, the other AIs and products were more impacted by resistance. The results acquired from these studies can help develop rapid tests for use by PMPs based on the no-choice feeding assay while also adding more information supporting current resistance and cross-resistance evolution theories.

Glassy-Winged Sharpshooters Cease Feeding and Avoid Plants Treated With Sub-Lethal Doses of the Neonicotinoid Insecticide Imidacloprid.

Insecticides are a primary means for suppressing populations of insects that transmit plant pathogens. Application of insecticides for limiting the spread of insect-transmitted plant pathogens is often most effective when applied on an area-wide scale. The glassy-winged sharpshooter is a vector of the bacterial pathogen Xylella fastidiosa, which causes numerous plant diseases including Pierce's disease of grapevine. The glassy-winged sharpshooter has been the subject of an area-wide suppression program in California for nearly two decades. Overreliance on a limited number of active ingredients including the neonicotinoid imidacloprid has resulted in increased levels of resistance to commonly applied products. In California, glassy-winged sharpshooters move between citrus, an important overwintering host, and vineyards. Accordingly, imidacloprid is routinely applied via the irrigation system in vineyards and citrus orchards. For soil applied applications, it may take days to weeks for concentrations in plants to increase to lethal doses. Further, as the dose of imidacloprid required to kill sharpshooters increases due to resistance, so too does the period that sharpshooters are exposed to sub-lethal doses. Response of glassy-winged sharpshooter to cowpea plants treated with sub-lethal doses of imidacloprid was evaluated by conducting no-choice and choice tests. In no-choice feeding assays, glassy-winged sharpshooters caged on plants treated with sub-lethal doses of imidacloprid ceased feeding and produced little excreta. Further, sub-lethal exposure to a range of doses over a 4-d period did not affect viability over a 9-wk post-exposure holding period on untreated plants. In choice-tests, glassy-winged sharpshooters avoided treated plants and were observed predominately on untreated plants. Results suggest that application of imidacloprid to vineyards and citrus orchards may push glassy-winged sharpshooters out of treated habitats rather than kill them.

Chemical defense acquired via pharmacophagy can lead to protection from predation for conspecifics in a sawfly.

Chemical defense is a widespread anti-predator strategy exhibited by organisms, with individuals either synthesizing or extrinsically acquiring defensive chemicals. In some species, such defences can also be transferred among conspecifics. Here, we tested the effects of pharmacophagy on the defense capability of the turnip sawfly, Athalia rosae, which can acquire neo-clerodane diterpenoids (clerodanoids) via pharmacophagy when having access to the plant Ajuga reptans. We show that clerodanoid access mediates protection against predation by mantids for the sawflies, both in a no-choice feeding assay and a microcosm setup. Even indirect access to clerodanoids, via nibbling on conspecifics that had access to the plant, resulted in protection against predation albeit to a lower degree than direct access. Furthermore, sawflies that had no direct access to clerodanoids were consumed less frequently by mantids when they were grouped with conspecifics that had direct access. Most, but not all, of such initially undefended sawflies could acquire clerodanoids from conspecifics that had direct access to the plant, although in low quantities. Together our results demonstrate that clerodanoids serve as a chemical defense that can also be transferred by interactions among conspecifics. Moreover, the presence of chemically defended individuals in a group can confer protection onto conspecifics that had no direct access to clerodanoids.

Sequestration and Cyanobacterial Diet Preferences in the Opisthobranch Molluscs Dolabrifera nicaraguana and Stylocheilus rickettsi

A multidisciplinary approach was used to assess chemical ecological dietary interactions between marine organisms as a tool to isolate novel ecologically relevant compounds with biotechnological potential. First, laboratory-based feeding preference assays of the sea hareDolabrifera nicaraguana(previously known asD. dolabrifera), an anaspidean mollusc, were conducted by simultaneously offering six food options collected from nearby tidal pools in the Coiba National Park in the Tropical Eastern Pacific of Panama. An evaluation of preferred dietary repertoire revealedD. nicaraguanasignificantly preferred cf.Lyngbyasp. over the cyanobacteriumSymplocasp., green algaChaetomorphasp., and red algaSpyridiasp. A no-choice feeding assay using cf.Lyngbyasp. or green algaCladophorasp. supported this finding. Secondly, we conducted bioactivity-guided fractionation using the preferred food source ofD. nicaraguana, the ‘hair-like” cf.Lyngbyasp. from which we also isolated and elucidated two new depsipeptide compounds, veraguamide M (1) and veraguamide N (2). Veraguamides M (1) and N (2) showedin vitroactivity toward the malaria-causing parasitePlasmodium falciparumwith GI50values of 4.2 and 4.3 μM, respectively, and therapeutic windows of 7.0–8.0 (based on moderate cytotoxicities to mammalian Vero cells with GI50values of 29.3 and 34.1 μM, respectively). Veraguamide N (2) was also active againstLeishmania donovani, the causative agent of visceral leishmaniasis, with a GI50value of 6.9 μM. We then evaluated sequestration of these new compounds byD. nicaraguanaused in the feeding assays and found trace amounts of the dietary sequestered compounds. Finally, we evaluated sequestration of these new compounds by the sea hareStylocheilus rickettsi(previously known asS. striatus) that were grazing on the cf.Lyngbyasp. used in the feeding assays and found both to be sequestered. This study is the first example whereby compounds with significant activity against tropical parasites have been found in both the sea hareS. rickettsiand its cyanobacterial food source. These results suggest that chemical ecological studies involving sea hares and cyanobacteria continue to provide a diverse source of bioactive compounds with biotechnological potential.

Effect of extract of Amazon Moss on Spodoptera Frugiperda (JE Smith) (Lepidoptera: noctuidae) in maize

Bryophytes are a potential group for the discovery of biologically active substances to pest control. The objective of this study was to evaluate the antifeedant and insecticidal effect of the ethanolic extract of Sematophyllum subsimplex (Hedw). Mitt. on second-instar larvae of Spodoptera frugiperda (JE Smith, 1797) on corn (Zea mays L.) leaves. The bioassay involved placing individual larvae in petri dishes and fed circular corn leaf sections with 50 µl of the extract at concentrations of 2.0%, 1.0%, 0.5% and 0.25% µg/µl, and DMSO (control), with five replicates, in no-choice feeding assays. Herbivory and mortality rates were assessed 24, 48 and 72 hours after application of the extract. The concentration of 0.25 μg/μl had a positive antifeedant effect shortly after 24 hours. All tested concentrations caused high mortality rates, suggesting insecticidal activity. This is the first scientific work to report the antifeedant and/or insecticidal activity of S. subsimplex and can be the basis for botanical insecticide formulation.

Quantification of Macronutrients Intake in a Thermogenetic Neuronal Screen using Drosophila Larvae.

Foraging and feeding behaviors allow animals to access sources of energy and nutrients essential for their development, health, and fitness. Investigating the neuronal regulation of these behaviors is essential for the understanding of the physiological and molecular mechanisms underlying nutritional homeostasis. The use of genetically tractable animal models such as worms, flies, and fish greatly facilitates these types of studies. In the last decade, the fruit fly Drosophila melanogaster has been used as a powerful animal model by neurobiologists investigating the neuronal control of feeding and foraging behaviors. While undoubtedly valuable, most studies examine adult flies. Here, we describe a protocol that takes advantage of the simpler larval nervous system to investigate neuronal substrates controlling feeding behaviors when larvae are exposed to diets differing in their protein and carbohydrates content. Our methods are based on a quantitative colorimetric no-choice feeding assay, performed in the context of a neuronal thermogenetic-activation screen. As a read-out, the amount of food eaten by larvae over a 1 h interval was used when exposed to one of the three dye-labeled diets that differ in their protein to carbohydrates (P:C) ratios. The efficacy of this protocol is demonstrated in the context of a neurogenetic screen in larval Drosophila, by identifying candidate neuronal populations regulating the amount of food eaten in diets of different macronutrient quality. We were also able to classify and group the genotypes tested into phenotypic classes. Besides a brief review of the currently available methods in the literature, the advantages and limitations of these methods are discussed and, also, some suggestions are provided about how this protocol might be adapted to other specific experiments.

Predators of monarch butterfly eggs and neonate larvae are more diverse than previously recognised

Conserving threatened organisms requires knowledge of the factors impacting their populations. The Eastern monarch butterfly (Danaus plexippus L.) has declined by as much as 80% in the past two decades and conservation biologists are actively seeking to understand and reverse this decline. While it is well known that most monarchs die as eggs and young larvae, few studies have focused on identifying what arthropod taxa contribute to these losses. The aim of our study was to identify previously undocumented predators of immature monarchs in their summer breeding range in the United States. Using no-choice feeding assays augmented with field observations, we evaluated 75 arthropod taxa commonly found on the primary host plant for their propensity to consume immature monarchs. Here we report 36 previously unreported monarch predators, including representatives from 4 new orders (Orthoptera, Dermaptera, Lepidoptera and Opiliones) and 11 taxa (Acrididae, Gryllidae, Tettigoniidae, Forficulidae, Anthocoridae, Geocoridae, Lygaeidae, Miridae, Nabidae, Erebidae and Opilliones). Surprisingly, several putative herbivores were found to readily consume immature monarchs, both in a targeted fashion or incidentally as a result of herbivory. This work expands our understanding of the monarch predator community and highlights the importance of unrecognized predation on insects of conservation concern.

Plant Resistance to Colorado Potato Beetle (Coleoptera: Chrysomelidae) in Diploid F2 Families Derived From Crosses Between Cultivated and Wild Potato.

Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), is a serious global pest of potato, Solanum tuberosum L. Management of L. decemlineata has relied heavily on insecticides, but repeated evolution of insecticide resistance has motivated the exploration and development of alternative strategies, such as plant resistance. The recent development of two diploid potato families derived from crosses between cultivated and wild potato species (S. chacoense and S. berthaultii) has provided a unique opportunity to reexamine plant traits for resistance breeding. In this 2-yr study, we surveyed select F2 clones for the induction of L. decemlineata mortality and a reduction in defoliation in no-choice feeding assays when challenged with adults and larvae from three sites in Wisconsin. We tested for an association with glandular trichome density and foliar levels of the glycoalkaloids chaconine and solanine. Several potato clones demonstrated resistance in specific feeding assays, but none excelled consistently across experiments. Mortality and defoliation generally differed significantly among L. decemlineata populations, which could be indicative of heritable variation in beetle responses to plant defenses or variation in the physiological status of the beetle populations tested. Contrary to expectations, higher trichome density increased mortality or decreased defoliation in only a few cases, and levels of mortality and defoliation were unrelated to foliar glycoalkaloid content, warranting further investigation of the defense mechanisms of resistant clones. In addition to identifying several potential L. decemlineata resistance sources, this study underscores the need to include multiple insect populations in surveys of plant resistance to this diverse pest.

A non-native macroalga is less attractive for herbivores but more susceptible to light limitation and grazing stress than a comparable native species

It has been suggested that non-native species are more tolerant towards abiotic stress than ecologically comparable native species. Furthermore, non-native marine macroalgae should be under lower grazing pressure than native seaweeds, because they left their co-evolved enemies behind. As a consequence, they generally need to allocate less energy to defences and can invest more into compensating the negative effects of abiotic stress or, assuming that grazing pressure is low but not zero, to defensive reactions following grazer attack. This, in turn, should make them more stress tolerant and less susceptible to herbivory. However, empirical evidence for both concepts is still scarce and very little is known about whether enemy release is commonly associated with an enhanced tolerance towards abiotic or biotic stress. We therefore ran an experimental study that (a) assessed attractiveness for grazers, (b) verified whether short-term low-light stress impairs growth and (c) investigated whether light limitation and previous grazing interactively affect the consumption of two macroalgae from Madeira Island, the native brown alga Stypopodium zonale and the non-native red alga Grateloupia imbricata by the sea urchin Paracentrotus lividus. To come to ecologically meaningful low-light stress levels, pilot studies were performed in order to determine the light compensation point of photosynthesis for each algal species and then we established six light regimes around this point by reducing the amount of incoming light. Simultaneously, we let one sea urchin graze on each algal individual to stimulate a chemical defence in the seaweeds if present. In parallel to this, we kept the same number of algal replicates in the absence of sea urchins. After 21 days, we compared algal growth in the absence of grazers as well as the attractiveness of previously grazed and non-grazed algal material for P. lividus across all light regimes. Algal attractiveness was assessed in no-choice feeding assays. The observation that the non-native alga was less consumed by the grazer than the native species generally confirms the concept of enemy release. However, light limitation reduced growth in the non-native but not in the native seaweed, while previous grazing reduced consumption of the native but enhanced it in case of the non-native alga. These findings do not corroborate the assumption that enemy release can, through the re-allocation of energy, enhance tolerance to abiotic (light limitation) or biotic (grazing) stressors in non-native marine macroalgae.

Nipped in the bud: mesograzer feeding preference contributes to kelp decline.

Small invertebrate grazers can disproportionately reduce plant fitness by discriminately consuming valuable tissues, but the context and attendant consequences of this activity at higher levels of ecological organization rarely are considered. To assess the impact of a gastropod mesograzer Lacuna vincta on fecundity and potential reproductive output of the habitat-forming kelp Saccharina latissima, we measured the intensity and distribution of grazing damage on kelp blades at five sites of varying kelp density, during the annual reproductive peak (October-November) in Nova Scotia. We found most grazing damage on reproductive individuals consisted of superficial excavations, and was concentrated on the central sorus (region where sporangia develop) compared to the vegetative blade margins. Grazing intensity on sori (percent grazed) averaged 29.6% across sites and sampling periods. The distribution of grazing on non-reproductive individuals was opposite to that of reproductive ones, indicating that snails shift feeding from blade margins to the center as sori develop. Choice and no-choice feeding assays in the laboratory revealed that focused grazing on sori is likely due to an active feeding preference for sporogenous over vegetative tissue. This preference was correlated with the distribution of chemical defense between tissues (phlorotannin content was ~2.5 times higher in vegetative tissue than sori), but not nutritional quality (no difference in C/N ratio). We deduce, with support from histological observations, that consumption of sorus tissue by L. vincta reduces fecundity of S. latissima. Extrapolating our results to estimate potential reproductive output within kelp beds suggests that spore supply and recruitment limitation may be predominantly imposed by the scarcity of reproductive individuals in the most degraded kelp beds. However, loss of reproductive output to grazing could extend recruitment limitations that impede recovery of waning kelp populations in Nova Scotia.

Suitability of Creeping Bentgrass and Bermudagrass Cultivars for Black Cutworms and Fall Armyworms (Lepidoptera: Noctuidae).

The black cutworm, Agrotis ipsilon Hufnagel, and fall armyworm, Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), are common turfgrass pests of golf courses in the southeastern United States. Heat-tolerant bentgrass (Agrostis stolonifera L.) cultivars are expanding the range of bentgrass further south, but these cultivars have not been studied for their potential host plant resistance to black cutworm or fall armyworm. The goals of the study were to investigate feeding response of black cutworm and fall armyworm to these newer heat-tolerant creeping bentgrass cultivars, as well as commonly used cultivars of bermudagrass [Cynodon dactylon (Loppers.)]. Choice and no-choice feeding assays and fecundity tests were conducted in the laboratory and greenhouse to evaluate performance and preference of the two insects. When given a choice, neither black cutworm nor fall armyworm showed a preference for the majority of new cultivars tested. There were no differences in leaf area consumption or insect development for either pest in no-choice feeding assays. Black cutworm females preferred laying eggs in bentgrass compared with bermudagrass, but will oviposit onto bermudagrass, suggesting that both turf species are suitable hosts of this pest. The broad host ranges of generalist caterpillar pests of turfgrass hinder the application of host plant resistance in integrated pest management on golf courses.

Factors Influencing Expression of Antixenosis in Soybean to Anticarsia gemmatalis and Spodoptera frugiperda (Lepidoptera: Noctuidae).

This study aimed to evaluate some factors that influence the expression of antixenosis in soybean genotypes against Anticarsia gemmatalis Hübner and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Free-choice and no-choice feeding assays were performed with the resistant soybean genotype IAC 100 and the susceptible genotype BRSGO 8360 using A. gemmatalis and S. frugiperda larvae. The following factors that may affect expression of resistance were evaluated: one larva versus two larvae per leaf disc; use of larvae without prior feeding suspension versus larvae starved for 3 h prior to the assay; leaf discs versus entire leaflets; upper part versus lower part of the plant; and, vegetative versus reproductive growth stages. The level of resistance exhibited by the genotype IAC 100 was high enough to not be obscured by the effects of all factors assayed in the present study upon the feeding preference of A. gemmatalis and S. frugiperda larvae. However, our results demonstrate the importance of knowing the optimal conditions for conducting an assay for evaluating resistance of genotypes for specialist and generalist insect species. Utilization of two larvae of A. gemmatalis per leaf disc, not starved before the assays, with leaf discs from the upper part of plants at the reproductive growth stage provided better discrimination of differences in antixenosis expression in soybean genotypes. For S. frugiperda, use of one larva per leaf disc, not starved before the assays, with leaf discs from the lower part of plants at the reproductive growth stage gave more satisfactory results for feeding preference tests.

Induced defense mechanisms in an aquatic angiosperm to insect herbivory

In terrestrial angiosperms, defense and resistance mechanisms against herbivores have been studied extensively; yet this topic is poorly understood in aquatic angiosperms. We investigated induced response mechanisms in Myriophyllum spicatum to the generalist insect herbivore Acentria ephemerella in three independent experiments. Various morphological and chemical response variables were examined in grazed apical shoots and compared to undamaged controls. We further estimated plant palatability of induced and non-induced apices in choice assays, and assessed the growth response of Acentria larvae in no-choice feeding assays. Leaves of induced apices were splayed out horizontally and changed in color from green to red. The dry matter content and thus plant toughness increased by up to 19%, but silica levels stayed constant. Induced apices exhibited a decline in chlorophyll content of up to 34%, reflected also by a 10% decrease in nitrogen levels, while nitrogen increased by 14% in lower parts of grazed shoots. Also, herbivore-deterring total phenolic compounds increased by up to 20% in apices. In choice trials, Acentria larvae strongly avoided grazed tips, and growth was reduced by 25% on induced apices. In total, we observed five different induced resistance and defensive traits in grazed apices: changes in appearance, increased plant toughness, delocalization of N-containing metabolites, increased polyphenols, and reduced nutritional value. The observed changes prevent herbivore damage and loss of apical tissue, which are most valuable for plant fitness. Our study presents the first evidence of multiple, parallel defense strategies including constitutive and induced defense mechanisms in a freshwater angiosperm.

Do mothers always know best? Oviposition mistakes and resulting larval failure of Pieris virginiensis on Alliaria petiolata, a novel, toxic host

Alliaria petiolata is a European biennial herb that invades North American forests and has direct negative effects on associated flora and fauna. In some places, A. petiolata has invaded the habitat of Pieris virginiensis, a rare, univoltine butterfly that normally uses native spring ephemeral crucifer hosts. There are occasional observations of P. virginiensis laying eggs on A. petiolata, but the frequency and effects of these “mistake oviposition events” are not yet known. We investigated P. virginiensis oviposition preference through field observations in three locations (NY, OH, PA), and also through laboratory experiments measuring egg deposition of adult females on either a native or invasive crucifer. In addition, we examined neonate larval performance through no-choice feeding assays on both A. petiolata leaves and cabbage leaves painted with A. petiolata leaf extracts. We found that P. virginiensis lays significantly more eggs on the exotic A. petiolata than on its native host Cardamine diphylla in both field and laboratory experiments. Caterpillars fed either A. petiolata leaf tissue or its ethanol extract did not survive to pupation, and most died after only a few days. Continual invasion and persistence of A. petiolata in P. virginiensis habitats may lead to genetic bottlenecking and possibly local extinctions without human intervention.

Invasion success of the seaweed Gracilaria vermiculophylla correlates with low palatibility

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 486:93-103 (2013) - DOI: https://doi.org/10.3354/meps10361 Invasion success of the seaweed Gracilaria vermiculophylla correlates with low palatibility Mareike Hammann1,*, Gaoge Wang2, Esther Rickert1, Sung Min Boo3, Florian Weinberger1 1Helmholtz Centre for Ocean Research (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany 2College of Marine Life Sciences, Ocean University of China, 5 Yushan Road, 266003 Qingdao, China 3Department of Biology, Chungnam National University, Daejeon 305-764, Korea *Email: mhammann@geomar.de ABSTRACT: Differences with respect to anti-herbivore defense were investigated in invasive and native populations of the seaweed Gracilaria vermiculophylla. S pecimens from 6 native populations in East Asia and from 8 populations invasive in Europe and the Mexican Pacific coast were maintained under identical conditions and offered to herbivorous snails from both the native range (Littorina brevicula) and Europe (L. littorea) in no-choice feeding assays. L. brevicula consumed in total significantly larger amounts of G. vermiculophylla tissue than did L. littorea. Further, both snail species least consumed the seaweed specimens originating from either non-native populations or from populations native to the Korean East Sea/Sea of Japan. The Korean East Sea/Sea of Japan had previously been identified as putative donor region of all the invasive populations of G. vermiculophylla. Thus, populations in the donor region as well as non-native populations in different invaded realms feature an increased capacity to resist feeding pressure. Differences in nutrient content did not account for the observed patterns of consumption, as palatability and carbon to nitrogen (C:N) ratio were not significantly correlated. Thus, mechanical or chemical defenses or the content of feeding cues influenced the behavior of the snails. We suggest that low palatability contributed to the invasion success of the species. KEY WORDS: Biological invasion · Invasive seaweeds · Enemy release hypothesis · Novel weapons hypothesis · Herbivory · Gracilaria vermiculophylla Full text in pdf format PreviousNextCite this article as: Hammann M, Wang G, Rickert E, Boo SM, Weinberger F (2013) Invasion success of the seaweed Gracilaria vermiculophylla correlates with low palatibility. Mar Ecol Prog Ser 486:93-103. https://doi.org/10.3354/meps10361 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 486. Online publication date: July 12, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Sorghum Seed Maturity Affects the Weight and Feeding Duration of Immature Corn Earworm,Helicoverpa zea, and Fall Armyworm,Spodoptera frugiperda, in the Laboratory

Corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae), and fall armyworm, Spodoptera frugiperda J.E. Smith, are occasional pests in sorghum, Sorghum bicolor L. Moench (Poales: Poaceae), and can be economically damaging when conditions are favorable. Despite the frequent occurrence of mixed-species infestations, the quantitative data necessary for developing yield loss relationships for S. frugiperda are not available. Although these species share similar biological characteristics, it is unknown whether their damage potentials in developing grain sorghum panicles are the same. Using no-choice feeding assays in the laboratory, this study examined larval growth and feeding duration for H. zea and S. frugiperda in the absence of competition. Each species responded positively when exposed to sorghum seed in the soft-dough stage, supporting evidence for the interactions between host-quality and larval growth and development. The results of this study also confirmed the suitability of using laboratory-reared H. zea to develop sorghum yield loss estimates in the field, and provided insights into the biological responses of S. frugiperda feeding on developing sorghum seed.