No description available.

No description available.

Sitka spruce (Picea sitchensisi is one of the most widely planted forest trees in the UK and and its high timber yields make it a commercially important species. The green spruce aphid Elatobium abietinum is a serious defoliating pest of Sitka spruce, and has been shown to have a significant impact on productivity. Little is known about how future changes in forest management will affect the abundnace, and hence impact, of this pest. This study set out to compare aphid performance and populations on trees of different ages, in stands under varying forms of forest management, and to try to identify the most important factors responsible for variation in aphid abundance. The results of this research highlighted key differences in aphid abundance with respect to variations in tree age and forest stand structure. These patters appeared to be linked with a number of biotic and abiotic factors, including foliage suitability, the level of shade within forest plots, canopy temperature and the abundance of certain natural enemies. Population densities of E. abietinum in the field were significantly higher on young regenerating trees growing in shaded environments compared with light environments. In addition, aphids reared on potted plants achieved a significantly higher growth rate when reared on trees grown under high levels of shade compared with lower levels of shade, a trend which was not explained by differences in the percentage dry weight of nitrogen in needles. Exposure to high temperatures (above 25°C) was detrimental to the individual performance (in terms of growth rate and survival) of E. abietinum. A significant negative relationship was detected between populations of aphidophagous syrphids and peak populations of E. abietinum implying that these predators may play an important role in suppressing aphid densities. Alternatives to the traditional "clearfell and replant" approach to forest management can influence the abundance, and hence impact, of E. abietinum. Forests managed under the uniform shelterwood system supported large aphid populations, whereas the group selection system of forest management, which gives rise to a highly structurally diverse forest, with a high frequency of canopy gaps (increasing light penetration), and high level of ground flora (enhancing certain natural enemy groups including hoverflies), my offer benefits in terms of reduced aphid populations. The findings of this study will have important applications in the future management of commercial Sitka spruce forests in the UK, and will enable more accurate predications to be made of the threat posed by this damaging pest in the future.

No description available.

No description available.

No description available.

Errata pasted onto front end paper. / Includes bibliographical references (50 leaves). / vii, 77, [50] leaves, [26] leaves of plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Entomology, 1981

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.