Thesis
The pest status and management of Creiis lituratus (Hemiptera: Psyllidae)
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2006
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Abstract
The psyllid Creiis lituratus Froggatt has emerged as a significant pest in Eucalyptus dunnii Maiden plantations in northern NSW. Previously unknown as a pest species, this study was initiated to determine the relative hazard the psyllid represents to the viability of the commercial growth of E. dunnii in the region.
An examination of the lifecycle revealed five juvenile stages. The feeding by juveniles from theplant’s vascular system results in necrosis of the foliage. Young trees are colonised from the top but eventually the whole crown is affected. The adult psyllids emerge from the final instar and deposit eggs on the green stem material toward the end of shoots and on the leaf blade. The influence of temperature on the life cycle was studied. Up to seven generations per year can be completed in the region.
Population dynamics of C. lituratus were studied at two E. dunnii plantations in northern NSW. Over the summer period the populations crashed from peak densities reached in the previous year. Populations then build exponentially over a number of generations over the cooler months until the following summer when another decline occurs. Although the psyllid appears endemic throughout the E. dunnni estate, the incidence of high density populations, deemed outbreaks, was localised within a plantation. The sites that experienced high densities were associated with low rates of tree growth in the period February-May, ie. immediately prior to the population increase over winter. In the year the study was conducted (2002), this poor growth was attributed to drought stresses within the plantation. In other years when outbreaks have occurred ephemeral waterlogging was considered to be the stress factor.
The decline of host trees in outbreak areas can result in density dependent dispersal of adults to surrounding areas. This was detected at one plantation where high densities were reached and anomalous population increases occurred at sites adjacent to the outbreak. Chemical control should therefore be instigated prior to high levels of foliage damage (ie. ~ 70% necrosis). However, given the fact that poor growth facilitates outbreaks multiple benefits may be obtained through silvicultural practices maintaining optimal growing conditions.
The growth impacts due to C. lituratus were comparable to that resulting from apical herbivory by Christmas beetles, Anoplognathus chloropyrus. The impact of psyllid damage to the growth of the trees is closely associated with the refoliation of the crown. The impact to growth was generally negligible below ~35% necrosis and a linear negative relationship with growth was evident when that threshold was exceeded. Damage above this threshold resulted in the initiation of epicormic flushing and a decline in apical/lateral flushing due to shoot dieback. Complex interactions were observed involving herbivory, site quality and apical dominance. These interactions again support silvicultural responses to C. lituratus management such site selection, weed control, and fertilisation.
Trials of chemical treatments using the systemic insecticide dimethoate were successful in achieving >98% mortality of juveniles. In larger scale campaigns the same level of foliage coverage could not be achieved and the psyllid mortality was comparatively lower. In other field trials another systemic insecticide, imidacloprid, was applied as a soil drench within the first year of establishment. Treated trees exhibited resistance to psyllid infestation as well as general herbivory. Resistance persisted for >18 months and the protection afforded to the treated trees resulted in higher growth rates compared to control trees subsequent to psyllid infestation. Post-infestation applications of soluble nitrogenous fertiliser was also beneficial, its effect was additive to the beneficent effect of the insecticide on growth.
Naturally resistant phenotypes were identified in the field, propagated and subsequently evaluated in screen enclosures. The resistant material was significantly less preferred by ovipositing females in choice experiments. Also, the juveniles that subsequently developed on these resistant clones experienced higher levels of mortality in a predator-free environment. The use of either persistent systemic insecticides or resistant clones offers opportunities to reduce the risk and severity of population outbreaks.
A temperature-dependent population model was constructed in the Simile visual modeling environment (Simulistics Ltd. Edinburgh, Scotland). The model simulated population fluctuations over a 12-month period. Additional sub-models incorporated the interaction of soil moisture, tree foliage development and necrosis and growth increment. It is hoped that the model will facilitate future scenario testing of management and control responses.
Details
- Title
- The pest status and management of Creiis lituratus (Hemiptera: Psyllidae)
- Creators
- Paul J. Angel
- Contributors
- Christine Stone (Supervisor) - Forests NSWDoland Nichols (Supervisor) - Southern Cross UniversityJerry Vanclay (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- xx, 330
- Identifiers
- 991013299428702368
- Copyright
- © Paul J. Angel 2006
- Academic Unit
- Faculty of Science and Engineering; School of Environment, Science and Engineering
- Resource Type
- Thesis