Fruit-tree borer, Maroga melanostigma (Wallengren), is a native Australian pest in many species of trees. It is of particular economic importance in prune (Prunus domestica) trees because the presence of this wood boring insect can reduce productivity by an average of 5% per tree. Large areas of orchards can be affected. There are currently no chemicals registered for control of this pest. Young, New South Wales is the second largest prune-growing district in Australia and the area most seriously affected by M. melanostigma. Prune growers in the district utilise integrated pest management and were supportive of a project to investigate biological control options for this economically damaging pest. The two main objectives of the project were 1) to understand the life cycle of M. melanostigma, so biological controls could be timed appropriately; and 2) to investigate biological control options for this pest. Life cycle studies were commenced in the first season (2003/04) using field cages and light trapping. These investigations continued throughout the project. In Young, moths were found to emerge from wood over a two month period (December and January). Oviposition was assumed to be during this period however, even after extensive searches of trees, no eggs were observed. Historical data were collated to determine locations and timings of moth emergence elsewhere in Australia. The data showed that M. melanostigma has been found in every state and territory Australia, with moths observed from October through to March. The biological control options reviewed were egg parasitoids (Trichogramma species only), entomopathogenic nematodes and entomopathogenic fungi. Trichogramma were favoured because of previous research undertaken against the same pest in pecans in Moree, NSW. Entomopathogenic nematodes were also investigated due to research indicating their effectiveness in cryptic situations, such as borer tunnels in trees. Fungi were considered but dismissed due to lack of literature supporting their effectiveness in reducing lepidopteran pest damage in trees. A major field trial was designed with the assistance of a biometrician and the trial blocks laid out based on this advice. There were three trial sites, each containing four blocks of approximately 200 trees (~800 trees/site). Two blocks were designated as release blocks and two as non-release blocks to correspond with the trial’s two treatments. In the first season (2003/04) an initial visual assessment of borer damage was undertaken after leaf fall on each of the trees in the trial. This information was used as baseline data, to compare against damage levels following biological control releases in the second and third years of the project. Natural parasitism in the field was assessed using cultured eggs of Helicoverpa armigera (Hübner) before and between Trichogramma carverae (Oatman and Pinto) releases. Temperature and relative humidity were recorded in each of the trial sites, for the duration of the trial, using commercially available data loggers. In the second season (2004/05), Trichogramma releases were made during the period of moth activity and H. armigera eggs were used to monitor parasitism in the trial orchards. Parasitised eggs were reared through and all parasitoids were identified as T. carverae. Damage assessments were again carried out after leaf fall to compare release versus non-release blocks, as well as to determine if there was any change in borer activity. Early instar larvae were collected from non-trial blocks and exposed to the entomopathogenic nematode Steinernema carpocapsae in a laboratory investigation. Results from this limited bioassay were inconclusive. In the third season (2005/06), Trichogramma releases were again made during the period of moth activity and H. armigera eggs were used to monitor parasitism in the trial orchards. Parasitised eggs were reared through to emergence. The emerged parasites were identified as T. carverae, T. pretiosum and T. nr brassicae. Damage assessments were again made of all the trees in the trial. Results were statistically analysed to detect any differences between treatments. There was no statistically significant evidence that the releases of T. carverae reduced damage from M. melanostigma over the duration of the trial. Although damage increased across both release and non-release treatments in most blocks during the trial investigations, the increase was slightly lower in trees in which Trichogramma had been released. It should be noted that the experiments were affected by serious drought conditions which prevailed during the three seasons of the trial. / Master of Science (Hons)
| Identifer | oai:union.ndltd.org:ADTP/204281 |
| Date | January 2007 |
| Creators | Marte, Susan Plantier, University of Western Sydney, College of Health and Science, Centre for Plant and Food Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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