Showing papers in "Entomologia Experimentalis Et Applicata in 2008"
TL;DR: It is argued that herbivore‐induced plant responses, insect ecosystem engineers, and mutualisms involving ant–honeydew‐producing insects all generate interaction linkages among insect herbivores, thereby producing complex indirect interaction webs on terrestrial plants.
Abstract: One of the most important issues in ecology is understanding the causal mechanisms that shape the structure of ecological communities through trophic interactions. The focus on direct, trophic interactions in much of the research to date means that the potential significance of non-trophic, indirect, and facilitative interactions has been largely ignored in traditional food webs. There is a growing appreciation of the community consequences of such non-trophic effects, and the need to start including them in food web research. This review highlights how non-trophic, indirect, and facilitative interactions play an important role in organizing the structure of plant-centered arthropod communities. I argue that herbivore-induced plant responses, insect ecosystem engineers, and mutualisms involving ant-honeydew-producing insects all generate interaction linkages among insect herbivores, thereby producing complex indirect interaction webs on terrestrial plants. These interactions are all very common and widespread on terrestrial plants, in fact they are almost ubiquitous, but these interactions have rarely been included in traditional food webs. Finally, I will emphasize that because the important community consequences of these non-trophic and indirect interactions have been largely unexplored, it is critical that indirect interaction webs should be the focus of future research.
128 citations
TL;DR: The historical and cultural reasons for this impasse between plant volatiles and pollination ecology are examined, focusing on the ways that questions in each field are addressed, and the potential for productive cross‐talk.
Abstract: Although research on plant volatiles and pollination ecology has grown explosively over the past 15 years, there remains little dialogue between these fields. Here I examine the historical and cultural reasons for this impasse, focusing on the ways that questions in each field are addressed, and the potential for productive cross-talk. The specialization-generalization debate in pollination has cast doubt on the importance of sensory biology in mediating plant-pollinator interactions on the community scale. However, chemical 'filters' of volatile or nectar-borne repellents are likely to explain the absence of specific interactions in plant-pollinator webs. In addition, the omission of plant volatiles from path analyses measuring the relative impacts of herbivores and pollinators on plant fitness may be one reason for large unexplained variance terms in such models. Floral scent functions in concert with visual and gustatory cues by attracting pollinators from a distance, increasing approaches and landings, and mediating outcrossing rates through changes in visitation frequency and duration. All dimensions of floral chemistry, including ontogenetic and diel variation in scent emissions, have the potential to respond to balancing selection between herbivores and pollinators. The available data reveal that chemical aspects of floral phenotypes are important across the specialization-generalization spectrum, and thus are widely applicable to mainstream pollination ecology.
125 citations
TL;DR: Development and oviposition of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), were studied in relation to varying N fertilization levels to find out whether these effects can have important implications for population dynamics and pest status of beet armyworms in the field.
Abstract: Nitrogen (N) is one of the most critical chemical elements for plant and animal growth, exerting a variety of bottom-up effects. Development and oviposition of the beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae), were studied in relation to varying N fertilization levels (42, 112, 196, and 280 p.p.m.) in cotton [ Gossypium hirsutum L. (Malvaceae)]. Low N fertilization of cotton plants led to reduced plant biomass and a lower percentage of N in leaf blades and in leaf petioles. Development of S. exigua larvae fed with plants with reduced N applications (42 and 112 p.p.m.) was prolonged relative to treatments receiving higher N fertilization. Almost all larvae reared on artificial diets underwent only five instars before pupation. However, most larvae reared on cotton plants, irrespective of N levels, experienced a supernumerary sixth larval instar. Furthermore, significantly more larvae reared on lower N cotton plants underwent supernumerary development compared to larvae reared on higher N cotton plants. Life-time feeding damage per larva ranged from 55 to 65 cm 2 , depending on the nutritional quality of the food plant, although the differences were not statistically significant. Larvae distinguished between cotton plants with various nutritional qualities and fed preferentially on higher N plants. Female moth oviposition choice was also affected by host plant nutritional quality: cotton plants with higher N levels were preferentially chosen by S. exigua females for oviposition. The mechanisms of these effects are unclear, but they can have important implications for population dynamics and pest status of beet armyworms in the field.
121 citations
TL;DR: The interactions observed suggest that EPN and M. anisopliae work together synergistically in potted Euonymus fortunei Blondy (Celastraceae) under greenhouse conditions and may provide a powerful and economically feasible approach for black vine weevil larval control.
Abstract: Combined use of the entomopathogenic nematodes (EPNs), Heterorhabditis bacteriophora Poinar (Heterorhabditidae), Steinernema feltiae Bovien, and Steinernema kraussei Steiner (Steinernematidae) and the insect-pathogenic fungus, Metarhizium anisopliae (Metsch.) Sorokin (Clavicipitaceae) was evaluated for control of third-instar black vine weevil, Otiorhynchus sulcatus Fabricius (Coleoptera: Curculionidae). Black vine weevil larvae were exposed to various concentrations of M. anisopliae and EPNs and mortality was assessed weekly or at 3-day intervals under laboratory and greenhouse conditions. The EPNs were added simultaneously, or 1 or 2 weeks after application of M. anisopliae . Throughout the experiments, the combined application of EPNs with M. anisopliae resulted in increased efficacy against black vine weevil. When the EPNs were applied 1 or 2 weeks after application of the fungus, 100% larval mortality was obtained, even when the biocontrol agents were used at reduced rates. The interactions observed suggest that EPN and M. anisopliae work together synergistically in potted Euonymus fortunei Blondy (Celastraceae) under greenhouse conditions and may provide a powerful and economically feasible approach for black vine weevil larval control.
119 citations
TL;DR: It is suggested that secondary metabolites other than GSs or differences in nutrient levels affect performance of the species studied, and that generalist feeding has a stronger effect on GS levels.
Abstract: Plants display a wide range of chemical defences that may differ in effectiveness against generalist and specialist insect herbivores. Host plant-specific secondary chemicals such as glucosinolates (GS) in Brassicaceae typically reduce the performance of generalist herbivores, whereas specialists have adaptations to detoxify these compounds. The concentration of glucosinolates may also alter upon herbivory, allowing the plant to tailor its response to specifically affect the performance of the attacking herbivore. We studied the performance of three Lepidoptera species, two specialists [ Pieris rapae L. (Pieridae), Plutella xylostella L. (Yponomeutidae)] and one generalist [ Mamestra brassicae L. (Noctuidae)], when feeding on eight cultivars of Brassica oleracea L. and a native congener ( Brassica nigra L.) and related this to the GS content. We tested the hypotheses (i) that a generalist herbivore is more affected by high GS concentrations, and (ii) that generalist feeding has a stronger effect on GS levels. Although performance of the three herbivores was different on the B. oleracea cultivars, M. brassicae and P. xylostella had a similar ranking order of performance on the eight cultivars. In most of the cultivars, the concentration of indole GS was significantly higher after feeding by P. rapae or M. brassicae than after P. xylostella feeding. As a consequence, the total concentration of GS in the cultivars showed a different ranking order for each herbivore species. The generalist M. brassicae performed equally well as the specialist P. xylostella on cultivars with high concentrations of GS. Our findings suggest that secondary metabolites other than GSs or differences in nutrient levels affect performance of the species studied.
108 citations
TL;DR: Overall, this study shows that M. anisopliae V275 is robust and offers much promise for the control of soil‐dwelling stages of thrips as part of an integrated pest‐management programme.
Abstract: The potential of several entomopathogenic fungi to control soil-dwelling stages of western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), was evaluated in various growing media. Two Metarhizium anisopliae (Metsch) Sorokin strains, V275 and ERL700, were the most effective, causing 85-96% mortality of thrips larvae and pupae (as measured by relative adult emergence rates), 11 days after inoculation. Mortality in other M. anisopliae-treated media ranged from 51-84%; Beauveria bassiana (Balsamo) Vuillemin strains caused 54-84% mortality, and Paecilomyces fumosoroseus (Wize) 63-75% mortality. In contrast, mortality from the insecticide treatment (fipronil 1 g 1 -1 medium) was only 15-54%. Metarhizium anisopliae V275 was selected for more in-depth evaluation under greenhouse conditions. There was no significant difference in M. anisopliae efficacy in growing media whether it was applied as drench (84-93%) or premixed into the medium as dry conidia (85-92%). The use of M. anisopliae with reduced rates of either fipronil or imidacloprid did not significantly improve control. Overall, our study shows that M. anisopliae V275 is robust and offers much promise for the control of soil-dwelling stages of thrips as part of an integrated pest-management programme.
89 citations
TL;DR: Behavioral evidence for a female‐produced volatile sex attractant pheromone in D. citri is provided and will be an important contribution to current monitoring and management practices for the pest.
Abstract: Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is an important worldwide pest of citrus. It vectors three phloem-restricted bacteria in the genus Candidatus Liberibacter that cause huanglongbing (citrus greening disease). Studies were conducted to examine the behavioral responses of male and female D. citri to conspecifics of the same and opposite sex, with and without associated citrus host plants, in both open-air arena choice assays and Y-tube olfactometer assays. Virgin and mated male D. citri colonized citrus plants that were currently or had been previously colonized by virgin or mated female D. citri in greater numbers than control plants without females. However, males or females did not accumulate more on plants colonized by conspecifics of the same sex compared to uninfested plants, and females showed no preference for plants pre-infested with males compared with uninfested controls. In complementary Y-tube olfactometer assays, virgin and mated males chose arms with odor sources from mated females compared with blank controls in the absence of associated citrus host plant volatiles. In both behavioral assays, mated female D. citri appeared more attractive than virgin females. The vibrational calling behavior of male D. citri was reduced when males were challenged by the odors of conspecific mated females relative to when males were challenged by the odor of other males. Collectively, our results provide behavioral evidence for a female-produced volatile sex attractant pheromone in D. citri . Future identification and synthesis of a sex attractant pheromone will be an important contribution to current monitoring and management practices for D. citri .
88 citations
TL;DR: Findings provide essential information for the interpretation of prey detection data from field‐collected predators’ gut contents and uncovered potential sources of error caused by detection of prey DNA following secondary cannibalistic and intraguild predation.
Abstract: This study aimed to determine factors that influence the detection of DNA of Plutella xylostella L. (Lepidoptera: Plutellidae) in the gut contents of arthropod predators when the polymerase chain reaction is used to amplify a diagnostic fragment of the gene coding for cytochrome oxidase subunit I. The effects of temperature, time since feeding, subsequent food intake, sex, weight, and species of predator on prey detectability were studied in the laboratory. Three types of predator were studied: the spider Venator spenceri Hogg. (Araneae: Lycosidae), a bug with sucking mouthparts, Nabis kinbergii (Reuter) (Heteroptera: Nabidae), and a coccinellid with chewing mouthparts, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae). In all experiments, the detectability of prey DNA was negatively correlated with time post-feeding. The duration of detectability differed among the predator species. The time calculated for median detection success at 20 °C ranged from 49.6 h in V. spenceri to 36.1 h in N. kinbergii and 17.1 h in H. variegata. In H. variegata, but not in V. spenceri, the rate of detection decreased with increasing temperature. Subsequent food intake did not affect the detectability of DNA of P. xylostella in V. spenceri. In H. variegata, sex and weight of the predator did not influence detection of prey DNA. In addition, this study uncovered potential sources of error caused by detection of prey DNA following secondary cannibalistic and intraguild predation. The results provide essential information for the interpretation of prey detection data from field-collected predators' gut contents.
83 citations
TL;DR: Lack of cross‐resistance between Cry1F and Cry1Ab suggest that maize hybrids expressing these two toxins are likely to be compatible for resistance management of O. nubilalis.
Abstract: Evolution of resistance by insect pests is the greatest threat to the continued success of Bacillus thuringiensis (Bt) toxins used in insecticide formulations or expressed by transgenic crop plants such as CrylF-expressing maize [(Zea mays L.) (Poaceae)]. A strain of European corn borer, Ostrinia nubilalis (Hiibner) (Lepidoptera: Crambidae), obtained from field collections throughout the central US Corn Belt in 1996 was selected in the laboratory for resistance to Cry1F by exposure to the toxin incorporated into artificial diet. The selected strain developed more than 3000-fold resistance to Cry1F after 35 generations of selection and readily consumed Cry1F expressing maize tissue; yet, it was as susceptible to CrylAb and Cry9C as the unselected control strain. Only a low level of cross-resistance (seven-fold) to CrylAc was observed. These lacks of cross-resistance between Cry1F and CrylAb suggest that maize hybrids expressing these two toxins are likely to be compatible for resistance management of O. nubilalis.
83 citations
TL;DR: Endophytic B. bassiana as an endophyte in banana tissues greatly reduced banana weevil populations and their damage to plants, and can thus be an alternative method for effective delivery of this fungus to banana plants for the management of C. sordidus.
Abstract: The entomopathogen Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) survives as an endophyte in a wide range of plants, offering substantial protection against tunneling insect pests. Although current research indicates that the fungus can live as an endophyte in tissue-cultured banana plants, there is no information on the efficacy of endophytic B. bassiana against the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae). Our study aimed at determining the effects of endophytic B. bassiana on oviposition rate and populations of the banana weevil, and their plant damage. Screenhouse studies were undertaken in which 8-week-old B. bassiana-inoculated tissue-cultured banana plants [cultivar Kibuzi, Musa spec. (Musaceae), genome group AAA-EA] were infested with female banana weevils. Five days after plant infestation with the banana weevil, there was no effect of B. bassiana on oviposition rate and egg hatchability. However, after 15 weeks, the presence of B. bassiana as an endophyte in banana tissues greatly reduced banana weevil populations and their damage to plants. Between 53.4 and 57.7% of the banana weevil adults died because of B. bassiana infection, resulting in a reduction of plant damage by 29.1-62.7% depending on plant part. Beauveria bassiana was re-isolated from different plant parts, but to a greater extent from the roots and rhizomes than from pseudostem bases. Artificial inoculation of B. bassiana in banana plants caused no negative impact on banana growth. Our study demonstrated for the first time that endophytic B. bassiana reduced populations of C. sordidus and the plant damage they cause, and can thus be an alternative method for effective delivery of this fungus to banana plants for the management of C. sordidus.
78 citations
TL;DR: An overview of oviposition behaviour in the Asphondyliini is provided, as well as descriptions of the ovipositor and the female post‐abdominal segments.
Abstract: Larvae of gall midges (Diptera: Cecidomyiidae) induce the activation of plant cells, partial cell lysis, and differentiation of nutritive tissue. Specialized nutritive tissue is essential for larval development and plays a key role in gall organization. Midges of the tribes Lasiopterini and Asphondyliini, however, do not induce nutritive tissues as part of the formation of their galls. Instead, these ‘ambrosia galls’ contain fungal mycelia that line the interior surface of the chambers. The fungi not only provide Lasiopterini with nutrition, they also penetrate the stems, induce the lysis of the middle lamella of host cells, and open a channel to the vascular bundles. Larvae of Lasioptera arundinis (Schiner) (Lasiopterini) follow the fungus and feed on its mycelium along with adjoining stem cells of Phragmites australis (Cav.) Trin. (Poaceae). Eggs together with fungal conidia are deposited by the imago on the host. Asphondyliini use a needle-like ovipositor to introduce fungal conidia and eggs into the organs they attack. Larvae of Schizomyia galiorum Kieffer (Asphondyliini) are unable to initiate the gall or to develop in the flowers of Galium mollugo L. (Rubiaceae) without their fungal associate. In this article, I provide an overview of oviposition behaviour in the Asphondyliini, as well as descriptions of the ovipositor and the female post-abdominal segments. Gall formation by Lasiopterini and Asphondyliini and the role of associated fungi are discussed, as is the role of the fungus as an inquiline or an organizer of gall tissues and a nutritive device.
TL;DR: The results raise the possibility of a coordinated whole plant response to herbivory, even when the herbivore specializes on only one plant tissue type, and a whole plant approach may be key to understanding how plants respond to Herbivory.
Abstract: We tested for rapid changes in photosynthate transport and partitioning in response to Lymantria dispar (L.) (Lepidoptera: Lymantriidae) (gypsy moth) herbivory in Populus nigra L. (Salicaceae). Transport and partitioning of [ 11 C]-photosynthate from young mature leaves were measured in vivo before and 18 h after leaf chewing by gypsy moth larvae, which were caged on three older leaves. Following herbivory, there was an increase in export speed of recently fixed carbon from younger mature leaves. The increased export speed was due to a quicker transit time of 11 C through the leaf, rather than a change in transport speed through the phloem. Additionally, basipetal partitioning of [ 11 C]photosynthate was increased following herbivory. Neither of these changes was observed in control plants. This enhancement of export occurs even though herbivores are well known to induce increases in carbon allocation to secondary metabolites within leaves. Our results demonstrate that the use of non-destructive imaging of 11 C tracer is a powerful tool for examining plant responses to herbivory. Although the mechanisms underlying the rapid increase in carbon flux to stems and roots remain to be elucidated, our results raise the possibility of a coordinated whole plant response to herbivory. Thus, even when the herbivore specializes on only one plant tissue type, a whole plant approach may be key to understanding how plants respond to herbivory.
TL;DR: Testing whether host‐plant utilization in Germany, hence the increase in BN, is related to genetic host races of the vector and, if so, whether these have evolved locally or have immigrated from southern populations that traditionally use the new host plant is tested.
Abstract: Within the past 10 years, the yellows disease ‘bois noir’ (BN) has become one of the commercially most important diseases of grapevine [ Vitis vinifera L. (Vitaceae)] in Europe. Infection pressure is caused by phytoplasmas of the stolbur 16SrXII-A group that are transmitted by a planthopper vector, Hyalesthes obsoletus Signoret (Homoptera: Auchenorrhyncha). Infestation happens as an accidental side-effect of the feeding behaviour of the vector, as vector and pathogen proliferation is dependent on other plants. In Germany, the increase of BN is correlated with the use of a new host plant by the vector, increase in abundance of the vector on the new host plant, and dissemination of host plant-specific pathogen strains. In this article, we investigate geographic and host-associated range expansion of the vector. We test whether host-plant utilization in Germany, hence the increase in BN, is related to genetic host races of the vector and, if so, whether these have evolved locally or have immigrated from southern populations that traditionally use the new host plant. The genetic population analysis demonstrates a recent expansion and circum-alpine invasion of H. obsoletus into German and northern French wine-growing regions, which coincides with the emergence of BN. No H. obsoletus mitochondrial DNA haplotype host-plant affiliation was found, implying that the ability to use alternative host plants is genetically intrinsic to H. obsoletus . However, subtle yet significant random amplified polymorphic DNA (RAPD) genetic differentiation was found among host plant populations. When combined, these results suggest that a geographic range expansion of H. obsoletus only partly explains the increase of BN, and that interactions with host plants also occur. Further possible beneficial factors to H. obsoletus , such as temperature increase and phytoplasma interactions, are discussed.
TL;DR: It is suggested that ergot alkaloids can be eliminated from an endophyte of perennial ryegrass while retaining significant insect resistance, and similarity of larval response to the two mutants suggested that ergovaline and/or ergine account for the somewhat greater potency of wild‐type Lp1 compared to the knockouts, whereas simpler ergot aloids contribute little to that added resistance.
Abstract: Neotyphodium and Epichloe species (Ascomycota: Clavicipitaceae) are fungal symbionts (endophytes) of grasses. Many of these endophytes produce alkaloids that enhance their hosts' resistance to insects or are toxic to grazing mammals. The goals of eliminating from forage grasses factors such as ergot alkaloids that are responsible for livestock disorders, while retaining pasture sustainability, and of developing resistant turf grasses, require better understanding of how particular alkaloids affect insect herbivores. We used perennial ryegrass Lolium perenne L. (Poaceae) symbiotic with Neotyphodium lolii x Epichloe typhina isolate Lp1 (a natural interspecific hybrid), as well as with genetically modified strains of Lp1 with altered ergot alkaloid profiles, to test effects of ergot alkaloids on feeding, growth, and survival of the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), a generalist grass-feeding caterpillar. Neonates or late instars were provided clippings from glasshouse-grown plants in choice and rearing trials. Wild-type endophytic grass showed strong antixenosis and antibiosis, especially to neonates. Plant-endophyte symbiota from which complex ergot alkaloids (ergovaline and lysergic acid amides such as ergine) or all ergot alkaloids were eliminated by endophyte gene knockout retained significant resistance against neonates. However, this activity was reduced compared to that of wild-type Lp1, providing the first direct genetic evidence that ergot alkaloids contribute to insect resistance of endophytic grasses. Similarity of larval response to the two mutants suggested that ergovaline and/or ergine account for the somewhat greater potency of wild-type Lp1 compared to the knockouts, whereas simpler ergot alkaloids contribute little to that added resistance. All of the endophyte strains also produced peramine, which was probably their primary resistance component. This study suggests that ergot alkaloids can be eliminated from an endophyte of perennial ryegrass while retaining significant insect resistance.
TL;DR: The evidence of milkweed latex itself is summarized as a multivariate defense including the amount exuded and toxin concentrations within, assessing the coordinated evolution of latex traits and how this fits with the previous notion of ‘plant defense syndromes’, and proposing a novel hypothesis that includes an ‘evolving community of herbivores’ that may promote the escalation of particular defensive strategies as plant lineages diversify.
Abstract: A tremendous diversity of plants exude sticky and toxic latex upon tissue damage, and its production has been widely studied as a defensive adaptation against insect herbivores. Here, we address variation in latex production and its constituent chemical properties (cardenolides and cysteine proteases) in 53 milkweeds [ Asclepias spp. (Apocynaceae)], employing a phylogenetic approach to test macroevolutionary hypotheses of defense evolution. Species were highly variable for all three traits, and they showed little evidence for strong phylogenetic conservatism. Latex production and the constituent chemical defenses are thus evolutionarily labile and may evolve rapidly. Nonetheless, in phylogenetically independent analyses, we show that the three traits show some correlations (and thus share a correlated evolutionary history), including a positive correlation between latex exudation and cysteine protease activity. Conversely, latex exudation and cysteine protease activity both showed a trade-off with cardenolide concentrations in latex. We also tested whether these traits have increased in their phenotypic values as the milkweeds diversified, as predicted by plant defense escalation theory. Alternative methods of testing this prediction gave conflicting results ‐ there was an overall negative correlation between amount of evolutionary change and amount of latex exudation; however, ancestral state reconstructions indicated that most speciation events were associated with increases in latex. We conclude by (i) summarizing the evidence of milkweed latex itself as a multivariate defense including the amount exuded and toxin concentrations within, (ii) assessing the coordinated evolution of latex traits and how this fits with our previous notion of ‘plant defense syndromes’, and finally, (iii) proposing a novel hypothesis that includes an ‘evolving community of herbivores’ that may promote the escalation or decline of particular defensive strategies as plant lineages diversify.
TL;DR: It is demonstrated that substantial natural refuge is present for Bt‐resistance management of H. zea throughout the mid‐South and Southeast portions of the US cotton belt and that adults move extensively from their natal host origins.
Abstract: Selection pressure on bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by cotton, Gossypium hirsutum (L.) (Malvaceae), that produces one or more Bacillus thuringiensis Berliner (Bt) proteins is reduced by plantings of non-Bt refuge cotton that produce non-selected individuals. However, the contributions of non-Bt, non-cotton crop hosts to the overall effective refuge for H. zea on Bt cotton have not been estimated. A 2-year, season-long study was conducted in five US cotton-producing states to assess the spatial and temporal population dynamics and host use of H. zea. Helicoverpa zea larval estimates in commercial crop fields demonstrated that non-cotton crop hosts, such as maize, Zea mays L. (Poaceae), grain sorghum, Sorghum bicolor (L.) Moench (Poaceae), peanut, Arachis hypogaea L. (Fabaceae), and soybean, Glycine max (L.) Merrill (Fabaceae), collectively support much larger larval populations than cotton throughout the season. Larval populations were almost entirely restricted to maize in the middle part of the season (June and portions of July), and were observed in non-cotton crop hosts more frequently and typically in larger numbers than in cotton during the period when production would be expected in cotton (July and August). Numbers of H. zea larvae produced in replicated strip trials containing various crop hosts paralleled production estimates from commercial fields. In contrast, the number of H. zea adults captured in pheromone traps at interfaces of fields of Bt cotton and various crop hosts rarely varied among interfaces, except in instances where maize was highly attractive. With the exception of this early season influence of maize, moth numbers were not related to local larval production. These data demonstrate that H. zea adults move extensively from their natal host origins. Therefore, non-cotton crop hosts, and even relatively distant hosts, contribute significantly to effective refuge for H. zea on Bt cotton. The results presented here demonstrate that substantial natural refuge is present for Bt-resistance management of H. zea throughout the mid-South and Southeast portions of the US cotton belt.
TL;DR: The non‐consumptive component of the predator is important for all of the herbivore stages vulnerable to predation in this study, and possible implications of considering non‐Consumptive effects of predators in biological control of agricultural pests are discussed.
Abstract: The non-consumptive (or trait-mediated) effects of predators on prey are known to contribute substantially to the negative impact of insect predators on herbivorous insects Our goal now is to understand what factors alter the relative importance of the consumptive (or density-mediated) and non-consumptive components of the total predator impact This is important both for understanding the effects of predators in natural systems as well as for successfully manipulating predators for biological control in agriculture In this study, we tested whether herbivore ontogeny influenced the contribution of consumptive and non-consumptive effects of a predator on herbivore survivorship and plant damage by the herbivores We addressed these questions using the native plant Solanum ptychanthum Dunal (Solanaceae), the predator Podisus maculiventris Say (Heteroptera: Pentatomidae), and first-, third-, and fourth-instar Manduca sexta L (Lepidoptera: Sphingidae) In field cage experiments, we found that first- and third-instar M sexta were more vulnerable to predators compared to fourth instars In the presence of predators, M sexta caterpillars spent less time on feeding compared to caterpillars in the absence of predators The amount of damage the plants received was reduced in the presence of the predator and the consumptive and non-consumptive components contributed approximately equally to this reduction Thus, the non-consumptive component of the predator is important for all of the herbivore stages vulnerable to predation in our study We conclude with a discussion of possible implications of considering non-consumptive effects of predators in biological control of agricultural pests
TL;DR: The results indicated that BPH has complicated feeding behaviors, which warrants further investigation.
Abstract: The fine structure of the salivary sheaths in plant tissues can provide important information on homopteran probing and ingestion behaviors. Salivary sheaths secreted by the brown planthopper (BPH), Nilaparvata lugens (Stal) (Homoptera: Delphacidae), and their tissue pathway were investigated using light, scanning electron, and transmission electron microscopy. About half of the salivary flanges on the surface of the food substrate were connected with internal salivary sheaths. Only 43% of the salivary sheaths showed side branches. Many sculpture-like protuberances and small cavities had been formed on the outer surface of the salivary sheath, but the sheath lumen circumferences were sealed. Brown planthoppers showed a preference for probing and leaving salivary sheaths in the susceptible rice variety TN1 rather than in the resistant variety B5 during the first 2 days of the experiments. The salivary sheaths in rice tissues reached the inner tissue layer of the leaf sheaths and stems, but were mostly observed to end in the first and second layer of the leaf sheaths. Brown planthoppers also preferred to probe into the thick segment of the outer leaf sheath. After ingestion by the insect, the cytoplasm in both phloem and companion cells degraded and the main organelles were lost. Numerous small vesicles were found in most of the phloem cells, but cell walls remained intact. Large numbers of symbiont-like structures were observed inside the salivary sheath lumen. These results indicated that BPH has complicated feeding behaviors, which warrants further investigation.
TL;DR: The results suggest the potential of controlled crossing methods to obtain Eucalyptus trees with chemical profiles having enhanced activity against this mosquito and reveal a significant relationship between total essential oil yields and 1,8‐cineole concentration.
Abstract: The insecticidal activity of essential oils from 12 species of Eucalyptus (Myrtaceae) was evaluated on larvae of Aedes aegypti (L.) (Diptera: Culicidae), the most important vector of dengue and yellow fever in the Americas. Oils were obtained by hydrodistillation and their chemical composition was determined by gas chromatography coupled to mass spectrometry; yields ranged from 0.2 to 2.5%. Essential oils were mainly composed of 1,8-cineole, α-pinene, α-phellandrene, β-phellandrene, γ-terpinene, 4-terpineol, α-terpineol, p-cymene, and spathulenol. Larvicidal effects were tested on susceptible third or fourth stage Ae. aegypti larvae, determining median lethal concentration (LC 50 ) and median effective concentration (EC 50 )). Essential oils from Eucalyptus dunnii (Maiden), Eucalyptus gunnii (Hook), Eucalyptus tereticornis (Smith), Eucalyptus camaldulensis (Dehn), and Eucalyptus saligna (Smith) showed the best larvicidal activities with LC 50 values of 25.2,21.1,22.1,26.8, and 22.2, respectively. No significant differences were observed between LC 50 and EC 50 values of the same oil. Regression analysis revealed a significant relationship between total essential oil yields and 1,8-cineole concentration. Significant relationships were also revealed between larval mortality and the concentration of 1,8-cineole and p-cymene. This indicated that Eucalyptus species with high oil yields have higher 1,8-cineole concentrations and lowerp-cymene concentrations and have less effect onAe. aegypti. Our results suggest the potential of controlled crossing methods to obtain Eucalyptus trees with chemical profiles having enhanced activity against this mosquito.
TL;DR: It is shown that different trophic levels are differentially affected by jasmonic acid‐induced changes, which resulted in a lower nectar production than actual feeding damage by P. rapae caterpillars.
Abstract: Herbivore-induced plant defences influence the behaviour of herbivores as well as that of their natural enemies. Jasmonic acid is one of the key hormones involved in both these direct and indirect induced defences. Jasmonic acid treatment of plants changes the composition of defence chemicals in the plants, induces volatile emission, and increases the production of extrafloral nectar. However, few studies have addressed the potential influence of induced defences on flower nectar chemistry and pollinator behaviour. These have shown that herbivore damage can affect pollination rates and plant fitness. Here, we have investigated the effect of jasmonic acid treatment on floral nectar production and the attraction of pollinators, as well as the effect on the behaviour of an herbivore and its natural enemy. The study system consisted of black mustard plants, Brassica nigra L. (Brassicaceae), pollinators of Brassica nigra (i.e., honeybees and syrphid flies), a specialist herbivore, Pieris rapae L. (Lepidoptera: Pieridae), and a parasitoid wasp that uses Pieris larvae as hosts, Cotesia glomerata L. (Hymenoptera: Braconidae). We show that different trophic levels are differentially affected by jasmonic acid-induced changes. While the herbivore prefers control leaves over jasmonic acid-treated leaves for oviposition, the parasitoid C. glomerata is more attracted to jasmonic acid-treated plants than to control plants. We did not observe differences in pollinator preference, the rates of flower visitation by honeybees and syrphid flies were similar for control and jasmonic acid-treated plants. Plants treated with jasmonic acid secreted less nectar than control plants and the concentrations of glucose and fructose tended to be lower than in nectar from control plants. Jasmonic acid treatment resulted in a lower nectar production than actual feeding damage by P. rapae caterpillars.
TL;DR: It is suggested that cue‐lure or similar natural chemicals play a role in the Q‐fly mating system and γ‐Irradiation used to induce sterility had no significant effect on attraction to cue‐ lure by Q‐flies.
Abstract: Feeding on yeast hydrolysate (a source of nitrogen) has a strong influence on the physiology and behaviour of the Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), affecting longevity, sexual maturation, oogenesis, and mating performance. In this study, we demonstrate that access to yeast hydrolysate also influences the development of attraction to cue-lure in Q-flies. We provided virgin Q-flies various periods of access to yeast hydrolysate (continuous, 48 h, 24 h, or deprived). Attraction of males to cue-lure was increased and occurred at an earlier age when they were fed yeast hydrolysate. Males given continuous access were strongly attracted to cue-lure at a younger age (8 days after emergence), but by 12 days after emergence attraction of males given access to yeast hydrolysate for 48 h did not differ from males given continuous access. Attraction by males deprived or given just 24 h access to yeast hydrolysate was always significantly lower than those of males with continuous access. Male attraction to cue-lure was highest in the early morning. While cue-lure is most often thought of as a male attractant, virgin female Q-flies were caught in cue-lure traps at dusk at ages when they are known to be sexually mature. We suggest that cue-lure or similar natural chemicals play a role in the Q-fly mating system. γ-Irradiation used to induce sterility had no significant effect on attraction to cue-lure by Q-flies.
TL;DR: It is suggested that the high rates of dropping induced by H. axyridis and the subsequent decrease in H.Axyridis foraging efficiency may partially explain why H. Axyridis is less effective at controlling pea aphids than it is at controlling other aphid species that do not drop.
Abstract: Antipredator defensive behaviors are a well-studied and often crucial part of prey life histories, but little has been done to quantify how such behaviors affect natural enemies, their foraging, and their effectiveness as biological control agents. We explored how the generalist predatory coccinellid Harmonia axyridis Pallas (Coleoptera: Coccinellidae) affects the dropping behavior of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), and in turn, how that defensive behavior affects the foraging efficiency of the predator. Experimental arenas that allowed or prevented pea aphid dropping were compared to determine how dropping influences the foraging of multiple life stages of H. axyridis: second instars, fourth instars, and adults. Dropping reduced predation on aphids by all ladybeetle life stages. Despite older predators inducing more dropping, aphid dropping reduced predation by approximately 40% across all ladybeetle life stages. Aphid dropping and predator consumption of aphids were both correlated with how much the predator moved, which also increased with predator life stage. We suggest that the high rates of dropping induced by H. axyridis and the subsequent decrease in H. axyridis foraging efficiency may partially explain why H. axyridis is less effective at controlling pea aphids than it is at controlling other aphid species that do not drop.
TL;DR: In honeybees, γ‐aminobutyric acid (GABA)‐ergic and histaminergic neurons both contribute inhibitory networks to the antennal lobe, Interestingly, temporal properties differ markedly in different brain areas, while in the antenNal lobe odor‐evoked activity develops over slow time courses, while responses in Kenyon cells are phasic and transient.
Abstract: olfactory receptor neurons, different populations of local neurons in the antennal lobes, projection neurons linking antennal lobes to the mushroom bodies, and the intrinsic cells of the mushroom bodies themselves, the Kenyon cells. These studies confirm the combinatorial nature of coding at all of these stages. However, the transmission of odor-evoked activity patterns from projection neuron dendrites via their axon terminals onto Kenyon cells is accompanied by a progressive spar sening of the population code. Activity patterns also show characteristic temporal properties. While a part of the temporal response properties reflect the physical sequence of odor filaments, another part is generated by local neuron networks. In honeybees, y-aminobutyric acid (GABA)-ergic and histaminergic neurons both contribute inhibitory networks to the antenna I lobe. Interestingly, temporal properties differ markedly in different brain areas. In particular, in the antennal lobe odor-evoked activity develops over slow time courses, while responses in Kenyon cells are phasic and transient. The termination of an odor stimulus is reflected by a decrease in activity within most glomeruli of the antennal lobe and an off-response in some glomeruli, while in the mushroom bodies about half of the odor-activated Kenyon cells also exhibit off-responses.
TL;DR: The feeding capacities of female parasitoids of three species with different reproductive strategies on their host, sweetpotato whitefly, and the significance of host‐feeding of E. sophia for biological control of B. tabaci is discussed.
Abstract: Parasitoids in the genera Encarsia and Eretmocerus (Hymenoptera: Aphelinidae) are important biological control agents of whiteflies through their reproductive as well as host-feeding activities. The feeding capacities of female parasitoids of three species with different reproductive strategies [Encarsia sophia (Girault & Dodd), Encarsia formosa Gahan, and Eretmocerus melanoscutus Zolnerowich & Rose] on their host, sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype B (Homoptera: Aleyrodidae), were evaluated on cabbage in a single-instar no-choice experiment in the laboratory and a mixed-instar choice experiment in the greenhouse. In both single- and mixed-instar experiments, significant differences in host-feeding capacities were found among the three parasitoid species. Encarsia sophia exhibited superior capacity of host-feeding compared to E. formosa and E. melanoscutus. In the single-instar experiment, parasitoids fed more on younger (smaller) hosts than older (larger) hosts. In the mixed-instar experiments, all three parasitoid species exhibited a clear preference for feeding on older hosts compared to younger hosts. Total number of whitefly nymphs fed on by E. sophia was approximately three times that of the other two parasitoid species. Whitefly mortality accounted for by host-feeding by E. sophia was up to 59.7%, and, thus, equivalent to parasitization. The significance of host-feeding of E. sophia for biological control of B. tabaci is discussed.
TL;DR: Investigation of plant defenses in two closely related wild brassicaceous plant species and the feeding strategy of the parasitoid larvae shows that there is no conflict between direct and indirect plant defenses for this plant–host–parasitoid complex.
Abstract: Most studies on plant defenses against insect herbivores investigate direct and indirect plant defenses independently. However, these defenses are not necessarily mutually exclusive. Plant metabolites can be transmitted through the food chain and can also affect the herbivore’s natural enemies. A conflict may arise when a natural enemy is attracted to a plant that is suboptimal in terms of its own fitness. In addition, plant defenses are often studied in cultivated plant species in which artificial selection may have resulted in reduced resistance against insect herbivores. In this study, we investigated both direct and indirect plant defenses in two closely related wild brassicaceous plant species, Brassica nigra L. and Sinapis arvensis L. The herbivore Pieris brassicae L. (Lepidoptera: Pieridae), which is specialized on brassicaceous plant species, developed faster and attained higher pupal mass when reared on B. nigra than on S. arvensis . In contrast, Cotesia glomerata L. (Hymenoptera: Braconidae), which is a gregarious endoparasitoid of P. brassicae caterpillars, developed equally well on P. brassicae irrespective of the food plant on which its host had been reared. The feeding strategy of the parasitoid larvae, that is, selectively feeding on hemolymph and fat body, is likely to allow for a much wider host-size range without affecting the size or development time of the emerging parasitoids. In flight chamber experiments, C. glomerata , which had an oviposition experience in a host that fed on Brussels sprout, exhibited significant preference for host-damaged B. nigra over host-damaged S. arvensis plants. Headspace analysis revealed quantitative and qualitative differences in volatile emissions between the two plant species. This parasitoid species may use a range of cues associated with the host and the host’s food plant in order to recognize the different plant species on which the host can feed. These results show that there is no conflict between direct and indirect plant defenses for this plant‐host‐ parasitoid complex.
TL;DR: Field trapping experiments showed that grape mealybugs can be dispersed by wind, but that there is a marked decline in numbers with increasing distance from the source plant, and the implications for the field spread and management of grapevine leafroll disease are discussed.
Abstract: The importance of the grape mealybug, Pseudococcus maritimus (Ehrhorn) (Homoptera: Pseudo-coccidae), as a pest of wine grapes, Vitis vinifera L. (Vitaceae), has increased as a result of recent reports that it is capable of transmitting at least one of the viruses associated with grapevine leafroll disease. However, its natural rate of movement between host plants - and hence its role in the epidemiology of this disease - is poorly understood. In order to better assess the risk of field spread of leafroll disease by this insect, several experiments were conducted to determine the extent to which P. maritimus can move between grape plants, both by walking and by airborne dispersal. In experiments with first instars, both field and shade-house studies indicated that the mealybugs do not walk far and only very rarely reach adjacent plants by this means. Field trapping experiments showed that grape mealybugs can be dispersed by wind, but that there is a marked decline in numbers with increasing distance from the source plant. The implications of these observations for the field spread and management of grapevine leafroll disease are discussed.
TL;DR: Treatment with a methyl ester of a JA precursor, methyl linolenate (MeLin), also causes maize plants to attract this wasp, yet does not cause elevated levels of endogenous JA, and has the potential to increase the host‐finding ability of C. kariyai.
Abstract: Treatment of both uninfested and armyworm-infested maize plants with jasmonic acid (JA) is known to attract the parasitic wasp, Cotesia kariyai Watanabe (Hymenoptera: Braconidae). Here, we show that treatment with a methyl ester of a JA precursor, methyl linolenate (MeLin), also causes maize plants to attract this wasp, yet does not cause elevated levels of endogenous JA. The volatile chemicals emitted from either infested or uninfested maize plants treated with MeLin were qualitatively and quantitatively different from those emitted from JA-treated plants. Among compounds emitted from MeLin-treated plants, α-pinene and menthol attracted wasps in pure form in a two-choice test using a choice chamber. A mixture of methyl salicylate, α-copaene, and β-myrcene also attracted wasps. In contrast, (Z)-3-hexenyl acetate was among the main attractants for C. kariyai in JA-treated plants. These data show that in addition to JA, MeLin also has the potential to increase the host-finding ability of C. kariyai, but that the composition of attractants they induce differs.
TL;DR: The use of microcolonies appears to be well‐suited to measure lethal and sublethal effects of insecticidal proteins expressed in transgenic plants on bumblebees.
Abstract: In order to assess the risk that insecticidal transgenic plants may pose for bumblebees, we tested whether Bombus terrestris (L.) (Hymenoptera: Apidae) workers are able to detect insecticidal proteins dissolved in sucrose solution and whether consumption of these proteins will affect survival and offspring production. Feeders containing either Bacillus thuringiensis toxin (Cry1Ab), Kunitz soybean trypsin inhibitor (SBTI), or Galanthus nivalis agglutinin (GNA) were offered to bumblebee colonies at low (0.01% wt/vol for SBTI and GNA, 0.001% for Cry1Ab) and high concentrations (0.1% for SBTI and GNA, 0.01% for Cry1Ab) together with a control (pure sucrose solution) in a glasshouse chamber. No difference was found in the number of visits and the duration of visits among the different concentrations for each of the insecticidal proteins, indicating that bumblebees do not discriminate the compounds. To investigate the impact of the different insecticidal proteins on B. terrestris , microcolonies were established by placing three newly emerged bumblebee workers in wooden boxes. Within a few days, a hierarchy in each microcolony was established and the dominant worker developed its ovaries and laid haploid eggs. Bumblebees were fed with Cry1Ab (0.01%), SBTI, or GNA (both at 0.01 and 0.1%) dissolved in sucrose solution and also fed mixed floral pollen for a maximum period of 80 days. Additionally, microcolonies with three drones each were established to measure individual bee longevity. While the Cry1Ab did not affect microcolony performance, the consumption of SBTI and especially GNA affected survival of B. terrestris workers and drones and caused a significant reduction in the number of offspring. The use of microcolonies appears to be well-suited to measure lethal and sublethal effects of insecticidal proteins expressed in transgenic plants on bumblebees.
TL;DR: The results suggested that alfalfa cv.
Abstract: We studied the development and feeding behaviour of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), on the Radius and Sapko alfalfa ( Medicago sativa L.) (Fabaceae) cultivars. Three saponins and flavones were identified in the alfalfa cultivars after thin layer chromatography separation. Cultivar Radius differed from Sapko in that it had a higher level of saponins, including zanhic acid tridesmoside and 3-GlcA,28-AraRhaXyl medicagenic acid glycoside. The flavones identified, including 7- O - β -D-glucuronopyranosyl-4 ′ - O- [2 ′ - O- E-feruloyl- O - β -D-glucuronopyranosyl(1 → 2)O - β -D-glucuronopyranoside] apigenin, 7- O -{2- O- E-feruloyl-[ β -D-glucuronopyranosyl(1 → 3)]O - β -D-glucuronopyranosyl(1 → 2)- O - β -D-glucuronopyranoside} apigenin, and 4 ′ - O- [2 ′ - O -Eferuloyl- O - β -D-glucuronopyranosyl(1 → 2)- O - β -D-glucuronopyranoside] apigenin, occurred in tissues of both alfalfa cultivars. However, cv. Radius had very low mean flavonoid concentrations in comparison to cv. Sapko. Pea aphids that fed on cv. Radius plants showed a reduction in reproduction and survival. The aphid pre-reproductive period on cv. Radius was prolonged and the reproductive and post-reproductive periods on cv. Radius were reduced, compared to those on cv. Sapko. Cultivar Radius also negatively influenced aphid probing behaviour. This was especially the case during the initial period of the pathway phase. The results suggested that alfalfa cv. Radius, which had a higher level of saponins and a lower level of flavonoids, was less accepted by the pea aphid.
TL;DR: It is found that H. futilis could be conditioned to associate the presence of nectar with a novel aroma, in this case vanilla, and remember this aroma over the course of several hours, which could enhance the spiders’ ability to find nectar, either when moving between different parts of the same plant or among different plant species.
Abstract: Carnivorous arthropods are known to rely on non-prey foods, such as honeydew, pollen, and nectar. Consumption of plant-based nutrients by spiders also appears to be widespread, especially in cursorial species. This is not surprising, as studies have shown that these spiders’ activity levels, survivorship, and reproduction are increased when their diet includes plant-based nutrients, especially under conditions of prey scarcity. However, the sensory and behavioral means by which they recognize and locate non-prey food is unknown. Here we show that immatures of a nectarivorous spider [ Hibana futilis Banks (Araneae: Anyphaenidae)] can recognize and remember particular chemical stimuli associated with nectar. Following ingestion of minute amounts of sugar, these spiders exhibited counterturning and other local searching behaviors that increased their chances of finding more nectar. When placed on test arenas, spiders that were naive with respect to nectar aroma located artificial nectaries composed of diluted honey significantly faster than unscented nectaries composed of 1 sucrose solution. These results indicate that H. futilis is neurophysiologically and behaviorally adapted for recognizing olfactory stimuli. Interestingly, only spiders that ingested sugar and were engaged in local search responded to nectar aroma, suggesting that stimulation into local search is necessary to prime olfactory responses. We found that H. futilis could be conditioned to associate the presence of nectar with a novel aroma, in this case vanilla, and remember this aroma over the course of several hours. In arenas with vanilla-scented nectaries, spiders that had previous experience feeding on vanillascented sucrose droplets located the nectaries significantly faster than did vanilla-naive spiders. The capacity to remember specific aromas could enhance the spiders’ ability to find nectar, either when moving between different parts of the same plant or among different plant species. The results here indicate that nectarivorous spiders possess the sensory capabilities and programed behaviors necessary for efficient detection, recognition, and location of nectar sources.