No description available.

No description available.

The maternal rearing environment (MRE) of an organism can be a key determinant of an organism's host choice decisions, its own fitness, or the fitness of its offspring. Here, it is investigated if the MRE of an organism can influence lower or higher trophic levels. A series of reciprocal cross-over experiments was conducted using pea aphids (Acyrthosiphon pisum), bean (Vicia faba) or pea (Pisum sativum) plants, and an aphid natural enemy, the parasitoid wasp Aphidius ervi, as model organisms. In each experiment, pea aphid offspring experienced either the same or an alternative plant host to that experienced by their mothers. This PhD showed that the MRE of pea aphids and parasitoid wasps was not a main contributory factor of host choice decisions or offspring fitness but influenced mother parasitoid wasp fecundity. Additionally, the MRE of pea aphids influenced the foliar nutrient concentration of pea plants when infested with the aphid's offspring. First, over shorter infestation periods, variation in foliar nitrogen and essential amino acid concentrations of pea leaves could be explained by pea aphid MRE. Over longer infestation periods, variation in foliar nitrogen and essential amino acid concentrations of pea leaves was explained by a combination of pea aphid MRE and aphid genotype. Second, the 13C concentration of pea leaf tissue, an indicator of stomatal aperture and leaf water stress, varied with pea aphid MREs over longer infestation periods. However, stomatal conductance and the expression of abscisic acid-responsive genes did not vary in a manner that was consistent with leaf water stress. Additional components of an organism's maternal rearing conditions are considered, including symbioses, as a more realistic MRE compared with that observed in nature. Taking account of MREs could provide a better understanding of the factors influencing the fitness of many organisms interacting in natural and managed ecosystems.

Los áfidos (Hemiptera: Aphididae) son insectos fitófagos, de tamaño pequeño, se pueden presentar en su forma alada o áptera, son considerados una plaga que afectan diversos cultivos agrícolas y ornamentales. Algunas especies pueden ser transmisores de virus que causan enfermedad en las plantas. Por lo general se encuentran en zonas tropicales. Este estudio nos ayudará a identificar las diversas especies de áfidos encontrados en cultivos del distrito de Asia, Cañete para poder ampliar el estudio de afidofauna peruana. Los áfidos de este trabajo se colectaron en plantas de interés económico y ornamental, tales como manzana, níspero, plátano, naranja, cucarda, hemerocallis, papiro, molle, tomate y granada. Se reportan nueve especies de àfidos en el distrito de Asia, Provincia de Cañete, Perú. Las especies fueron: Aphis craccivora,Aphis gossypii, Aphis nasturtii, Aphis spiraecola, Aphis punicae, Myzus hemerocallis, Pentalonia nigronervosa, Toxoptera aurantii y Schizaphis rotundiventris. Cuatro de ellas se registraron por primera vez para el distrito de Asia, Cañete, Aphis nasturtii, Aphis punicae, Pentalonia nigronervosa y Schizaphis rotundiventris.Aphids (Hemiptera: Aphididae) are phytophagous insects with small size, we can found them alate or apterous forms. The aphids are a pest that affect many crops. Some species could be virus transmitters that cause plants disease. This study could help us to identificate the diversity of aphid species founding in crops from Asia, Cañete so we can amplify the study of peruvian aphid fauna. Plants aphids of this study were collected in plants with economical and ornamental interest like apple, loquat, banana, orange, hibiscus, lily, papyro, molle, tomato and pomengranate. Nine species of aphids from Asia, Cañete in Peru are reported. The following species were: Aphis craccivora, Aphis gossypii, Aphis nasturtii, Aphis spiraecola, Aphis punicae, Myzus hemerocallis, Pentalonia nigronervosa, Toxoptera aurantii y Schizaphis rotundiventris. Four of them were registered for the first time in Asia, Cañete, Aphis nasturtii, Aphis punicae, Pentalonia nigronervosa y Schizaphis rotundiventris.

The use of stable nitrogen isotope data in ecological and physiological studies is based in the assumption that nitrogen fractionates predictably during metabolism, leading to a broadly conserved pattern whereby consumers are isotopically enriched with respect to their diets. The application of stable isotope data to such studies is limited is by our understanding of the factors in that cause variability in the Δ15N values of consumers. In particular, parasites and fluid-feeders have been shown to demonstrate isotopic depletion with respect to their food sources. One factor that has been suggested to influence the Δ15N values seen in fluid-feeding consumers is the presence of endosymbionts and their contribution to nitrogen metabolism. The experiments described in this thesis directly test the hypothesis that the endosymbiotic bacteria Buchnera aphidicola is influencing the Δ15N value of the pea aphid on host alfalfa plants. Here I find that although aphids cured of their bacterial symbionts are less isotopically depleted than untreated aphids, they are still not enriched with respect to their phloem sap diet, indicating that endosymbiont metabolism alone is not responsible for the isotopic depletion observed in pea aphids. Metabolism of nitrogen in the pea aphid-Buchnera symbiosis has been well described with decades of physiological studies and with the publication of the pea aphid and Buchnera genomes. The two key features of metabolism in the pea aphid-Buchnera symbiosis are the recycling of waste ammonia by the aphid and the upgrading of the nonessential amino acids found in phloem sap to essential amino acids through collaborative metabolism between the pea aphid and Buchnera. Consistent with the described role of Buchnera in nitrogen metabolism, amino acid analyses of symbiotic and aposymbiotic aphids demonstrates an accumulation of the nonessential amino acids glutamine and glutamate and lower amounts of essential amino acids in the aposymbiotic aphids. I tested the influence of dietary amino acid profile on the Δ15N value of pea aphids and found that aphids are only isotopically depleted when they feed on diets with unbalanced amino acid compositions and are isotopically enriched when fed on a diet with a balanced profile of amino acids. I used isotopically labeled fructose to determine whether the difference in Δ15N value of pea aphids on diets of varying amino acid profiles is correlated to the amount of de novo amino acid synthesis occurring in the aphid. I found that there was a significantly higher incorporation of the labeled carbon backbone in the protein of pea aphids feeding on the unbalanced diets, supporting the idea that increased de novo amino acid synthesis are responsible for the differences in Δ15N values among aphids feeding on the two diets. The findings of this study highlight the influence of endosymbionts on the Δ15N values for pea aphids, demonstrate that dietary amino acid composition can influence the Δ15N value of pea aphids through the demand for metabolic upgrading of amino acids, and provide a model for the study of Δ15N values in systems where metabolism has been well characterized by experimental and genomic data.

No description available.

No description available.

Bacterial endosymbionts can have profound impacts on their host’s ecology. Notably, endosymbionts can protect their hosts against natural enemies and influence host plant interactions. The endosymbiont Candidatus Arsenophonus infects a wide taxonomic range of arthropod hosts, and is suspected of an uncharacterized mutualistic role in hemipterous insects. In the soybean aphid, Aphis glycines, an introduced pest of soybeans in the United States, Arsenophonus is the sole facultative endosymbiont. The focus of this dissertation is to characterize the role of Arsenophonus in the aphid, with an overall emphasis on its impact on aphid management strategies. I first used diagnostic PCR to determine Arsenophonus infection frequency and strain diversity for native and introduced soybean aphids. I found that Arsenophonus infection is a uniform strain that is highly prevalent in soybean aphid. I then determined if Arsenophonus was a defense symbiont by curing two genotypes of soybean aphid of their natural Arsenophonus infection, resulting in infected and uninfected isolines within the same genetic background. I subjected these isolines to assays with three parasitoid species and a common aphid fungal pathogen, Pandora neoaphidis. I did not find differences in parasitism or fungal infections within the treatments. These results indicate that, although Arsenophonus is widespread, the symbiont should not interfere with biological control efforts. I next examined the influence of Arsenophonus on the ability of soybean aphid “biotypes” to colonize resistant Rag plants. I cured three additional soybean aphid biotypes. All isolines were subjected to growth rate assays on resistant Rag versus susceptible soybean. My results indicate that Arsenophonus infected soybean aphids have an increased population growth compared to uninfected aphids regardless of soybean plant type Finally, I induced soybean plants with jasmonic acid (JA) or salicylic acid (SA) to determine the effective plant defense against soybean aphid feeding. I also used Arsenophonus infected and uninfected aphids to determine any interaction between Arsenophonus and plant defense. I found SA treatment decreased soybean aphid population growth for one experiment, but had no effect when replicated. JA treatment had no effect, and there were no interactions between Arsenophonus infection and plant treatments.

Erynia neoaphidis Remaudiere and Hennebert (Zygomycetes: Entomophthorales) is an obligate pathogen of invertebrates, especially aphids, and has therefore been studied as a possible biological control agent for a number of years. However, a number of important physiological and ecological questions regarding optimal conditions for conidial production and transmission 0 f the fungus through an aphid population had to be answered. This thesis investigated some of these aspects. Solid and liquid media were used to culture the fungus, and E. neoaphidis was cultured on a fully defined medium for the first time. A sporulation monitor and digital image analysis was used to quantify conidial production from E. neoaphidis biomass produced in vivo and in vitro. This was a completely novel method and is useful for gathering data on large numbers of conidia, 50 that size distributions can be constructed and the physiological status of the conidia inferred from this. E. neoaphidis infected aphid cadavers produced more, smaller conidia when grown in vitro. Biomass harvested from exponential growth phase in fed batch culture produced significantly more conidia than biomass harvested from any other growth phase although further work on the nutritional requirements of E. neoaphidis in vitro is required. The duration of the conidial discharge was also greatest from biomass harvested at the exponential phase and therefore. biomass harvested from the exponential phase should be used if the fungus is to be applied as a control agent. E. neoaphidis biomass kept at low humidity during simulated winter conditions produced infective conidia after 24 weeks, indicating that mycosed cadavers may act as a reservoir to infect the next season's hosts. Pesticides adversely affected the growth and production of conidia by E. neoaphidis, with herbicides having the least deleterious effects, and therefore being most compatible in an integrated pest management program. Laboratory and field studies were used to assess the transmission of E. neoaphidis through aphid populations. Position of the inoculum on the host plant affected the primary transmission of the fungus through aphid populations in the laboratory and in the field, and secondary transmission of the fungus in the laboratory. It is therefore important to apply the fungus to where it will maximally spread. There was some evidence for effects of host and inoculum density on the transmission of the fungus, especially in the laboratory, indicating that, in practice, the fungus is unlikely to spread rapidly through low densities of aphids and therefore to achieve control of such populations, a high inoculum density may be required. There was also very Iittle transmission of the fungus via aphid vectors to susceptible aphid populations on different host, although as a general observation, vectoring of conidia by the wind may be very important. The smaller conidia produced by in vivo biomass may be vectored more easily by wind than the large conidia produced in vitro.

Thesis (Ph. D.) -- University of Western Sydney, Hawkesbury, 2000. / Includes bibliographical references (leaves 160-187).