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Molecular and physiological insights into the potential efficacy of CO2-augmented postharvest cold treatments for false codling moth

Boardman, L., Sørensen, J.G., Grout, T.G., Terblanche, J.S.
Postharvest biology and technology 2017 v.132 pp. 109-118
Thaumatotibia leucotreta, carbon dioxide, carbon dioxide enrichment, cold stress, cold tolerance, cold treatment, cross resistance, cryoprotectants, disinfestation, heat-shock protein 70, hemocytes, hypercapnia, hypoxia, insect physiology, insects, larvae, lipids, long term experiments, mechanism of action, mortality, plant pests, stress response, sugars, Southern Africa
Cold sterilisation may be supplemented with elevated CO2 (hypercapnia) to increase pest mortality however, in some cases, such treatment combinations have generated unexpected high levels of pest survival. Consequently, determining the mechanistic basis of potential interactions or any cross resistance between CO2 and low temperature stress is critical for effective pest disinfestation through cold sterilization. Here, using larvae of false codling moth Thaumatotibia leucotreta, a crop pest in southern Africa, we explored the effects of various hypercapnic pre-treatments on larval survival to standard cold exposures, and a diverse array of biochemical traits that may be indicative of key cellular stress responses or damage and repair processes. Short (<4h) pre-treatments with a single stressor (cold or hypercapnia), multiple stress combinations (hypercapnia with hypoxia, and cold hypercapnia), followed by 10h cold exposure had little effect on larval survival (>96%). Longer 24h pre-treatments (hypercapnia+cold) followed by 5 d cold exposure led to significant differences in larval survival (0–80%), with the recovery conditions between exposures greatly affecting larval survival. In contrast with the short-term cold exposures, larvae from the long-term experiments had increased haemocyte mortality, protein concentration and heat shock protein 70 levels, while the concentrations of key cryoprotective sugars were decreased. No changes in membrane lipids could be attributed to the presence of CO2. These molecular correlates can be used as testable hypotheses for future work to further identify the mode of action of CO2 reducing (or enhancing) cold tolerance in these insects. From an insect physiology standpoint, chronic hypercapnic cold sterilization protocols appear to be a viable post-harvest option for control of T. leucotreta.