Doctoral Degrees (Conservation Ecology and Entomology)

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Browsing Doctoral Degrees (Conservation Ecology and Entomology) by Author "Boardman, Leigh"

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    Low temperature tolerance in insects : interactions with ambient gases
    (Stellenbosch : Stellenbosch University, 2013-12) Boardman, Leigh; Terblanche, J. S.; Sorensen, Jesper G.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Understanding the mechanisms of low temperature tolerance, and determining the conditions from which cellular damage may be repaired or is irreversible, is critical to insect pest control. Insect low temperature tolerance depends on the insects’ basal ability to withstand or repair the stress associated with low temperature exposure, or the ability to develop biochemical protection. Changes may be induced at the whole-animal level (e.g. respiration rate, water balance), or at the molecular level (e.g. induction of cryoprotective metabolites and proteins). Post-harvest low temperature disinfestation treatments can be augmented with controlled atmospheres treatments (CAT, e.g. low oxygen and/or high carbon dioxide) to improve their efficacy at ridding commodities of pests. Theoretically, the potential overlaps in the mechanisms which insects can use to counteract low temperature and CAT may result in cross tolerance. Research presented in this dissertation aimed to i) determine important baseline knowledge related to low temperature and gas stress, ii) identify potential mechanisms underlying low temperature and gas tolerance, iii) identify potential commonalities in cellular and molecular stress responses between gas and temperature stress, and iv) investigate whether fluctuating stressors resulted in protection or accumulated damage in an economic pest insect of southern Africa, false codling moth Thaumatotibia leucotreta. Results for low temperature tolerance showed that larvae were chill-susceptible and die upon freezing. In response to hypoxia (low oxygen, whole-animal oxygen limitation), behaviour and metabolic rate were affected, while low temperature tolerance remained unchanged. While the results were equivocal regarding the identification of mechanisms underlying insect low temperature tolerance and cross tolerance with CAT, multiple non-lethal stress exposures (e.g. pretreatments with low temperatures and hypoxia) gave larvae a higher tolerance to low temperatures mediated by overlaps between the underlying cellular and molecular responses. Lastly, fluctuating stressors were protective when compared to constant stress conditions, likely through regulation of whole-animal metabolic rate and heat shock protein 70. In conclusion, a fundamental understanding of T. leucotreta low temperature tolerance and the interactions with other environmental stressors has been obtained, and the efficacy of combining organism ecology, physiology and molecular biology research with applied aspects to make informed decisions regarding pest management strategies has been demonstrated.