Choice Feeding Assays Research Articles

Search for Snail Repellents: Antimollusc Activities from Stemona parviflora and Six Other Chinese Stemona Species.

Snails are important agricultural pests difficult to control, but data regarding molluscicidal assays are scant. Stemona alkaloids are typical secondary metabolites for the taxa and have been broadly investigated for their pharmacological and toxicological effects. This makes it possible for us to further develop the toxicities of these compounds to snails. In this work, we tested the antifeedant properties of leaves from seven Chinese Stemona species against the land snail species Bradybaena ravida in choice and non-choice feeding assays. The tested leaves Stemona parviflora exhibited the most deterrent effects, and a further phytochemical investigation of aerial parts led to the identification of 16 alkaloids. Among them, three novel alkaloids could be identified. The alkaloidal fraction and single alkaloids were further assayed against this snail species, and the results suggest a cocktail effect because the impact of the alkaloidal fraction was higher than the effects caused by single alkaloids. The study can promote the search process of natural antimollusc products from plants to control snails.

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.

Cotton plants as ideal models for teaching and research on inducible direct plant defenses

Cotton (Gossypium hirsutum) stores defensive compounds in glands covering its leaves and other tissues. The density and the chemical filling of these glands increase systematically in developing leaves in response to herbivory on older leaves. Cotton seedlings are known to respond more strongly to actual caterpillar herbivory than to mere physical damage. It is not clear whether this amplified response is linked to insect-derived elicitors or difference in damage properties. To investigate this, we assessed the effect of repeated artificial damage without and with application of regurgitant from Spodoptera exigua caterpillars. Repeated mechanical damage led to a systemic increase of gland density, gland size, and content of defensive terpenes, with no detectable additional elicitation upon regurgitant treatment. Dual choice feeding assays further showed that defense induction triggered by just physical damage made newly developing leaves far less palatable to S. exigua larvae as compared to leaves from undamaged seedlings, whereas they did not distinguish between leaves from damaged plants treated with or without regurgitant. Our study confirms that the systemic induction of cotton glands is an unspecific response to physical damage, although cotton is known to respond to caterpillar-associated elicitors for other defensive traits. Cotton glands induction can be readily visualized under modest magnification, making the experiments described in this study highly suited to teach chemical ecology and aspects of plant defense theory in practical classes.

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.

Evidence for Cardiac Glycosides in Foliage of Colorado Potato Beetle-Resistant Solanum okadae.

Leptinotarsa decemlineata, the Colorado potato beetle (CPB), is a herbivore that primarily feeds on Solanum foliage and is a global pest of the potato agricultural industry. Potato breeding through cross-hybridization with CPB-resistant wild relatives is used for genetic improvement. The wild species Solanum okadae was demonstrated to deter CPB feeding in choice and no choice feeding assays. Liquid chromatography-mass spectrometry (LC-MS) was used for comparative metabolite profiling between S. okadae and CPB-susceptible domesticated potato variety, Solanum tuberosum cv. Shepody. Major foliar metabolites detected were steroidal glycoalkaloids (SGAs) with tomatine and dehydrotomatine produced in S. okadae and solanine and chaconine in S. tuberosum cv. Shepody. Cardiac glycosides were also detected in the foliar metabolite profile of S. okadae but not S. tuberosum cv. Shepody. This class of plant compounds have known insecticidal activity through inhibition of animal Na+/K+ ATPase. Thin-layer chromatography (TLC) separation of foliar extracts also provided evidence for cardiac glycosides in S. okadae. Cardiac glycosides are known inhibitors of Na+/K+ ATPase, and foliar extracts from S. okadae (OKA15), but not S. tuberosum cv. Shepody, were able to inhibit the Na+/K+ ATPase of CPB. These findings suggest a novel mechanism of plant resistance against CPB involving production of cardiac glycosides in S. okadae.

Eat, Drink, Live: Foraging behavior of a nectarivore when relative humidity varies but nectar resources do not

To meet energetic and osmotic demands, animals make dynamic foraging decisions about food quality and quantity. In the wild, foraging animals may be forced to consume a less preferred or sub-optimal food source for long periods of time. Few choice feeding assays in laboratory settings approximate such contingencies. In this study the foraging behaviors of the hawkmoth Manduca sexta were measured when adult moths were placed within different relative humidity (RH) environments (20%, 40%, 60% and 80% RH) and provided with only one of the following experimental nectars: 0% (water), 12% or 24 % w/V sucrose solutions. Overall, ambient humidity influenced survivorship and foraging behaviors. Moth survivorship increased at higher ambient humidity regardless of experimental nectar. Moths that had access to experimental nectar imbibed large volumes of fluid regardless of what nectar was offered when placed at the lowest humidity (20% RH). However, when placed at the highest humidity (80% RH), moths imbibed higher volumes of fluid when given access to experimental nectar with sucrose in comparison with water. RH also influenced daily foraging behaviors: peak nectar consumption occurred earlier at lower RH levels. Consistent with previous studies in which moths could choose among nectar solutions, total energy intake was not affected by ambient RH under no-choice conditions. However, the proportion of time spent foraging and total energy consumption were significantly reduced across all RH levels in no-choice assays, when compared with previous studies of choice assays under the same conditions. Our results show that even when M. sexta moths are presented with limited options, they can alter their foraging behavior in response to environmental changes, enabling them to meet osmotic and/or energetic demands.

Microbial metabolites elicit distinct olfactory and gustatory preferences in bumblebees.

Animals such as bumblebees use chemosensory cues to both locate and evaluate essential resources. Increasingly, it is recognized that microbes can alter the quality of foraged resources and produce metabolites that may act as foraging cues. The distinct nature of these chemosensory cues however and their use in animal foraging remain poorly understood. Here, we test the hypothesis that species of nectar-inhabiting microbes differentially influence pollinator attraction and feeding via microbial metabolites produced in nectar. We first examined the electrophysiological potential for bumblebee (Bombus impatiens) antennal olfactory neurons to respond to microbial volatile organic compounds (mVOCs), followed by an olfactory preference test. We also assessed gustatory preferences for microbial-altered nectar through both no-choice and choice feeding assays. Antennal olfactory neurons responded to some mVOCs, and bees preferred nectar solutions inoculated with the bacterium Asaia astilbes over the yeast Metschnikowia reukaufii based on volatiles alone. However, B. impatiens foragers consumed significantly more Metschnikowia-inoculated nectar, suggesting distinct roles for mVOCs and non-volatile metabolites in mediating both attraction and feeding decisions. Collectively, our results suggest that microbial metabolites have significant potential to shape interspecific, plant-pollinator signalling, with consequences for forager learning, economics and floral host reproduction.

Cover crop seed preference of four common weed seed predators

AbstractInvertebrate seed predators (ISPs) are an important component of agroecosystems that help regulate weed populations. Previous research has shown that ISPs' seed preference depends on the plant and ISP species. Although numerous studies have quantified weed seed losses from ISPs, limited research has been conducted on the potential for ISPs to consume cover crop seeds. Cover crops are sometimes broadcast seeded, and because seeds are left on the soil surface, they are susceptible to ISPs. We hypothesized that (1) ISPs will consume cover crop seeds to the same extent as weed seeds, (2) seed preference will vary by plant and ISP species, and (3) seed consumption will be influenced by seed morphology and nutritional characteristics. We conducted seed preference trials with four common ISPs [Pennsylvania dingy ground beetle (Harpalus pensylvanicus), common black ground beetle (Pterostichus melanarius), Allard's ground cricket (Allonemobius allardi) and fall field cricket (Gryllus pennsylvanicus)] in laboratory no choice and choice feeding assays. We compared seed predation of ten commonly used cover crop species [barley (Hordeum vulgare), annual ryegrass (Lolium multiflorum), pearl millet (Pennisetum glaucum), forage radish (Raphanus sativus), cereal rye (Secale cereale), white mustard (Sinapis alba), crimson clover (Trifolium incarnatum), red clover (Trifolium pratense), triticale (×Triticosecale) and hairy vetch (Vicia villosa)] and three weed species [velvetleaf (Abutilon theophrasti), common ragweed (Ambrosia artemisiifolia) and giant foxtail (Setaria faberi)]. All four ISPs readily consumed cover crop seeds (P < 0.05), but cover crops with hard seed coats and seed hulls such as hairy vetch and barley were less preferred. Our results suggest that farmers should select cover crop species that are avoided by ISPs if they plan on broadcasting the seed, such as with aerial interseeding.

The Buckwheat Effect: A Biopesticide for Wireworm?

Growing buckwheat (Fagopyrum esculentum Moench. Caryophyllales: Polygonaceae) in rotation with potato and other vegetable crops has been reported to decrease the density of an invasive wireworm species (Agriotes sputator Linnaeus. Coleoptera: Elateridae) in Nova Scotia, Canada. It was predicted that the negative effects on wireworm populations result from phytochemicals by buckwheat that act as deterrents, anti-feedants, or toxins in the roots or when released into the soil. Choice assays were conducted to test the attractiveness of germinating, branching, and flowering buckwheat, red spring wheat (Triticum aestivum Linnaeus. Poales: Poaceae) and island barley (Hordeum vulgare Linnaeus. Poales: Poaceae) to the larvae. Twenty-one day, no choice feeding assays were conducted to determine change in mass and mortality of A. sputator larvae when fed buckwheat or barley. There was no evidence that the wireworms were deterred by buckwheat and the germinating stage of all three crops was the most attractive based on the 24-h choice assays. After the 21-d no choice feeding assays, no differences between hosts were observed; however, wireworm herbivory significantly reduced the growth of barley but not buckwheat. The findings from the no choice feeding assays suggest that buckwheat may produce anti-feedants, but longer term feeding assays and field trials are required to confirm this possibility.

Impaired Taste Associative Memory and Memory Enhancement by Feeding Omija in Parkinson's Disease Fly Model.

Neurodegeneration can result in memory loss in the central nervous system (CNS) and impairment of taste and smell in the peripheral nervous system (PNS). The neurodegeneration seen in Parkinson’s disease (PD) is characterized by functional loss of dopaminergic neurons. Recent studies have also found a role for dopaminergic neurons in regulating taste memory rewards in insects. To investigate how taste memories and sugar sensitivity can be affected in PD, we utilized the DJ-1β mutant fruit fly, DJ-1βex54, as a PD model. We performed binary choice feeding assays, electrophysiology and taste-mediated memory tests to explore the function of the DJ-1β gene in terms of sugar sensitivity as well as associative taste memory. We found that PD flies exhibited an impaired ability to discriminate sucrose across a range of sugar concentrations, with normal responses at only very high concentrations of sugar. They also showed an impairment in associative taste memory. We highlight that the taste impairment and memory defect in DJ-1βex54 can be recovered by the expression of wild-type DJ-1β gene in the dopaminergic neurons. We also emphasized the role of dopaminergic neurons in restoring taste memory function. This impaired memory property of DJ-1βex54 flies also allows them to be used as a model system for finding supplementary dietary foods that can improve memory function. Here we provide evidence that the associative taste memory of both control and DJ-1βex54 flies can be enhanced with dietary supplementation of the medicinal plant, omija.

Influence of fall armyworm previous experience with soybean genotypes on larval feeding behavior

Previous experience on host plants can modify insect feeding behavior. Because insect habituation and induction of preference to host plants are variable across species of plants and insects, it is necessary to investigate each insect-plant interaction to determine whether this phenomenon occurs or not in the system. In this study we investigated the potential occurrence of habituation and induction of preference in fall armyworm (FAW) Spodoptera frugiperda to soybean genotypes. Neonate FAW larvae reared on artificial diet were divided into four treatment groups and fed for one generation with either the resistant soybeans PI 227687 or IAC 100 or the susceptible soybeans BRS Valiosa RR or IGRA RA 626 RR. Biological parameters of FAW were recorded. Eggs obtained from FAW of each genotype group were separated, and the newly hatched larvae were fed on the same genotypes experienced by their parents for additional 8 days. FAW larval preference and leaf area consumed were evaluated in choice feeding assays with the four soybean genotypes within a 24-h period. Genotypes PI 227687 and IAC 100 negatively affected FAW development, demonstrating they are FAW-resistant. FAW larvae exposed to both resistant genotypes consumed more foliage of genotype IGRA RA 626 RR in the choice assays, whereas larvae reared on both susceptible genotypes did not show any preference. From our preliminary study, FAW does not show habituation and induction of preference toward the experienced soybean genotypes. The importance of our findings to host plant resistance and insect-plant biology fields is discussed.

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.

Experimental Evaluation of Seaweeds as a Vector for Microplastics into Marine Food Webs.

The ingestion of microplastics has been shown for a great variety of marine organisms. However, benthic marine mesoherbivores such as the common periwinkle Littorina littorea have been largely disregarded in studies about the effects of microplastics on the marine biota, probably because the pathway for microplastics to this functional group of organisms was not obvious. In laboratory experiments we showed that the seaweed Fucus vesiculosus retains suspended microplastics on its surface. The numbers of microplastics that adhered to the algae correlated with the concentrations of suspended particles in the water. In choice feeding assays L. littorea did not distinguish between algae with adherent microplastics and clean algae without microplastics, indicating that the snails do not recognize solid nonfood particles in the submillimeter size range as deleterious. In periwinkles that were feeding on contaminated algae, microplastics were found in the stomach and in the gut. However, no microplastics were found in the midgut gland, which is the principle digestive organ of gastropods. Microplastics in the fecal pellets of the periwinkles indicate that the particles do not accumulate rapidly inside the animals but are mostly released with the feces. Our results provide the first evidence that seaweeds may represent an efficient pathway for microplastics from the water to marine benthic herbivores.

Impact of the dual defence system of Plantago lanceolata (Plantaginaceae) on performance, nutrient utilisation and feeding choice behaviour of Amata mogadorensis larvae (Lepidoptera, Erebidae)

Iridoid glycosides are plant defence compounds with potentially detrimental effects on non-adapted herbivores. Some plant species possess β-glucosidases that hydrolyse iridoid glycosides and thereby release protein-denaturing aglycones. To test the hypothesis that iridoid glycosides and plant β-glucosidases form a dual defence system, we used Plantago lanceolata and a polyphagous caterpillar species. To analyse the impact of leaf-age dependent differences in iridoid glycoside concentrations and β-glucosidase activities on insect performance, old or young leaves were freeze-dried and incorporated into artificial diets or were provided freshly to the larvae. We determined larval consumption rates and the amounts of assimilated nitrogen. Furthermore, we quantified β-glucosidase activities in artificial diets and fresh leaves and the amount of iridoid glycosides that larvae feeding on fresh leaves ingested and excreted. Compared to fresh leaves, caterpillars grew faster on artificial diets, on which larval weight gain correlated positively to the absorbed amount of nitrogen. When feeding fresh young leaves, larvae even lost weight and excreted only minute proportions of the ingested iridoid glycosides intact with the faeces, indicating that the hydrolysis of these compounds might have interfered with nitrogen assimilation and impaired larval growth. To disentangle physiological effects from deterrent effects of iridoid glycosides, we performed dual choice feeding assays. Young leaves, their methanolic extracts and pure catalpol reduced larval feeding in comparison to the respective controls, while aucubin had no effect on larval consumption. We conclude that the dual defence system of P. lanceolata consisting of iridoid glycosides and β-glucosidases interferes with the nutrient utilisation via the hydrolysis of iridoid glycosides and also mediates larval feeding behaviour in a concentration- and substance-specific manner.

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.

Impacts of acute elevated seawater temperature on the feeding preferences of an Antarctic amphipod toward chemically deterrent macroalgae

As mean global temperatures continue to rise, regional seawater temperature measurements have revealed that some geographic areas are warming faster than others. One region that is experiencing particularly rapid warming is the western Antarctic Peninsula. Previous studies investigating direct effects of warming on Antarctic marine invertebrates have established that small increases in temperature can have significant impacts on aspects of behavior, physiology, and growth rates in these largely stenothermal organisms. To investigate how warming may impact feeding preferences of an ecologically important mesograzer on macroalgae of the Antarctic Peninsula, we examined the impacts of exposure to acute elevated temperature on the ecologically important omnivorous amphipod Gondogeneiea antarctica (Chevreux) at Palmer Station, Antarctica (64°46′S, 64°03′W) in April–May 2011. Amphipods were exposed to 1.5 °C (mean monthly upper summer temperature) or 3.5 °C (representative of current transient summer temperature peaks and projected mean for 2100) for a 24 h period. These amphipods were then used in choice-feeding assays with artificial food containing chemical extracts from six species of sympatric macroalgae known to produce feeding deterrents. We found that during acute exposure to elevated temperature (+2.0 °C), amphipods lost their feeding preferences in assays with artificial foods containing lipophilic (one macroalga), hydrophilic (three macroalgae), or combined lipophilic/hydrophilic (one macroalga) extracts. Our findings suggest that increased frequency in transient peaks and longer-term upward trends in ambient summer seawater temperature have the potential to alter feeding preferences in a common mesograzer that could influence macroalgal communities that dominate benthic communities along the western Antarctic Peninsula.

Preference and Performance of Black Cutworm (Lepidoptera: Noctuidae) on Poa Species

Abstract Black cutworm (Agrotis ipsilon Hufnagel) is a destructive pest of golf course turf. Previous work suggests that Poa pratensis ‘Midnight’ is resistant to black cutworm, but it is not known if resistance also exists among other Poa species and cultivars. This study compared preference and performance of black cutworm on Poa species and cultivars to a susceptible host plant, creeping bentgrass (Agrostis stolonifera L. ‘Penncross’) in laboratory choice feeding assays and rearing experiments. Seven-and 14-day-old larvae were used in performance feeding tests. Larvae reared on all Poa spp. exhibited significantly lower developmental and survival rates than larvae fed creeping bentgrass. Young (7 days old) larvae did not survive to pupation. Although older (14 days old) larvae pupated and eclosed on Poa, larval weight gain was significantly lower than those reared on creeping bentgrass. In choice feeding bioassays, regardless of larval stage, black cutworm preferred creeping bentgrass over all Poa species and cultivars. The results of this research suggest that although Poa species are generally resistant to black cutworm, the resistance varies among cultivars and insect growth stage.

Evaluating the fungal endophyte Neotyphodium occultans for resistance to the rice leaf bug, Trigonotylus caelestialium, in Italian ryegrass, Lolium multiflorum

Fungal endophytes of the genus Neotyphodium (Ascomycota: Clavicipitaceae) form symbiotic associations with many grass species of the subfamily Pooideae, including some important forage and turf grasses from the genus Lolium. Some Neotyphodium-infected grasses have enhanced resistance to the rice leaf bug, Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae), one of the major pests in rice production in Japan. The insects can grow on Lolium grasses and thus cause a conflict of interest between production of forage and rice. Endophyte-mediated resistance to T. caelestialium is likely to be conferred by N-formylloline, one of the major loline alkaloids (saturated 1-aminopyrrolizidines) observed in some grass–Neotyphodium associations. We checked the feasibility of using Neotyphodium occultans, the native endophyte of Italian ryegrass (Lolium multiflorum Lam.), to reduce T. caelestialium, as this endophyte produces N-formylloline, but no known mammalian toxins. To this end, we conducted choice and no-choice feeding assays using T. caelestialium first instars and 35 N. occultans-infected Italian ryegrass plants with different in planta N-formylloline concentration. Some N. occultans-infected ryegrass showed significant resistance to T. caelestialium. The preference and the survival of this insect were considerably lower on infected plants, and the higher the in planta N-formylloline concentration, the greater the adverse effects on the insect. The incremental risk of death of the insect was assumed to be due to intake of the chemical, and in addition, to the decreased amount of feeding caused by its insect-deterrent effect. These results indicated that the use of the N. occultans–grass associations has potential to reduce T. caelestialium propagation in ryegrass crops. The breeding of N. occultans-infected Italian ryegrass cultivars with high N-formylloline concentrations should be an effective way to develop pasture grasses with a greater protective effect against T. caelestialium.

Palatability of the Antarctic rhodophyte Palmaria decipiens (Reinsch) RW Ricker and its endo/epiphyte Elachista antarctica Skottsberg to sympatric amphipods

Although many macroalgae that occur throughout Western Antarctic Peninsular waters are known to produce defensive secondary metabolites that deter grazing, the rhodophyte, Palmaria decipiens is palatable to several sympatric meso- and macro-grazers. It has been hypothesized that high levels of mesoherbivory by amphipods may account for the conspicuous lack of filamentous epiphytes emerging from the thalli of marcophytes in this region. Nonetheless, Elachista antarctica is a filamentous phaeophyte found growing within, and emerging from the thallus of the rhodophyte P. decipiens. It is surprising that E. antarctica occurs exclusively in association with a palatable species of macroalgae considering the standing biomass of other chemically defended unpalatable species is very high. We tested the hypothesis that E. antarctica grows on P. decipiens due to the host's overwhelming palatability compared to that of the epiphyte. That is, the hypothesis that mesograzers prefer the host over the epiphyte, grazing around emerging filaments. Choice and no choice feeding assays with live tissues of E. antarctica and P. decipiens were conducted in three different trials with four sympatric amphipod species (Prostebbingia gracilis, Gondogeneia antarctica, Oradarea bidentata, and Paraphimedia integricauda) commonly found in association with P. decipiens. G. antarctica consumed both species but ate P. decipiens at a faster rate than the epiphyte in two of three trials. P. gracilis, O. bidentata, and P. integricauda fed on the epiphyte, E. antarctica at faster rates than upon P. decipiens. Aggressive grazing of the epiphyte by this suite of amphipods indicates that differences in palatability and differences in grazing pressure on host and epiphyte do not explain the exclusive epiphytism of E. antarctica on P. decipiens.

Grazer interactions with four species of Lyngbya in southeast Florida

Blooms of the toxic cyanobacteria Lyngbya spp. have been increasing in frequency and severity in southeast Florida in recent years. Lyngbya produces many active secondary metabolites which often act as feeding deterrents to generalist herbivores, possibly increasing the longevity of these nuisance blooms. Whilst diverse arrays of small invertebrate consumers are often found in association with Lyngbya, little is known of their grazing selectivity among species of Lyngbya. This study examines the feeding preference of grazers for four local Lyngbya species ( Lyngbya majuscula, Lyngbya confervoides, Lyngbya polychroa and Lyngbya spp.). Stylocheilus striatus and Haminoea antillarum showed no dietary selectivity between L. polychroa, L. majuscula and Lyngbya spp. in multiple choice feeding assays, whereas Bulla striata showed a distinct preference for L. polychroa ( P < 0.001). To determine whether preference might be related to species-specific secondary metabolites, L. majuscula, L. confervoides and L. polychroa non-polar and polar extracts were incorporated into artificial diets and offered to a range of mesograzers. No significant difference was noted in feeding stimulation or deterrence amongst extracts and the controls for any of the grazers. When fed a monospecific diet of L. polychroa, S. striatus consumed more ( P < 0.001) and attained a higher daily biomass ( P = 0.004) than S. striatus fed L. confervoides. As L. polychroa and L. confervoides often co-exist on local coral reefs and yield dense numbers of S. striatus, host switching to a more palatable species of Lyngbya may have important implications regarding top-down control of local blooms leading to proliferation of one species and decimation of another. S. striatus fed a diet of L. polychroa consumed more ( P = 0.003), had a greater increase in body mass ( P = 0.020) and higher conversion efficiency ( P = 0.005) than those fed L. confervoides regardless of host origin. Possible explanations for host switching between species of Lyngbya related to morphology, toxicity and nutrient requirements for growth are discussed.