Submitted to: Journal of Thermal Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/21/2013
Publication Date: 3/20/2014
Citation: Neven, L.G., Lehrman, N., Hansen, L.D. 2014. Effects of temperature and modified atmospheres on diapausing 5th instar codling moth metabolism. Journal of Thermal Biology. 42:9-14. Interpretive Summary: Larvae of the codling moth, Cydia pomonella, are serious quarantine pests of in-shell walnuts, often as overwintering (diapausing) fully grown larvae. Previous research indicates that heat treatments in combination with high concentrations of carbon dioxide and low concentrations of oxygen may be effective for controlling this pest in walnuts, but the killing mechanism is unknown. Scientists at the USDA-ARS laboratory in Wapato, WA in collaboration with scientists at Central Washington University and Brigham Young University measured the metabolic and oxygen consumption rates of diapausing codling moth larvae in relation to temperature and modified atmospheres. They found that diapausing codling moths do not require oxygen to support metabolism at temperatures below 40°C. Heat treatments under high levels of carbon dioxide in combination with oxygen levels greater than 5% had little effect on mortality. Metabolism increased during heating scans when the atmosphere contained more than 5% oxygen and that this rate of increase was most likely due to membrane damage and loss of control of metabolism at higher temperatures. They determined that heat treatments under atmospheres containing less than 1% oxygen and 80% carbon dioxide were the most effective in inhibiting metabolism and resulting in death of the larvae. These results provide important information for the future development of non-chemical postharvest control of diapausing codling moth in walnuts.
Technical Abstract: Diapausing 5th instars of codling moth, Cydia pomonella, are serious quarantine pests of in-shell walnuts. Previous research indicates that heat treatments in combination with high concentrations of carbon dioxide and low concentrations of oxygen may be effective for controlling this pest in walnuts, but the killing mechanism is unknown. Therefore the effects of heat treatments with various modified atmospheres on the metabolic heat rate and oxygen consumption rate of diapausing codling moth were investigated with multi-channel differential scanning calorimeters, one equipped with a microrespirometer. Microrespirometric O2 and metabolic heat rates in air were measured simultaneously at isothermal temperatures from 5 to 50°C at 5ºC intervals. Both rates increased with increasing temperatures from 5 to 40°C. At 45 and 50°C, O2 consumption rate was zero. Metabolic heat rate was near zero at 45°C and zero at 50°C. The ratio of metabolic heat rate to O2 consumption rate at temperatures =40ºC shows that a major portion of the metabolic heat is from anaerobic metabolism. Metabolic heat rates were measured during continuous heating scans from 10 to 50°C at a rate of 0.4°C/min with air and modified atmospheres with lowered oxygen and high carbon dioxide. Metabolic heat rates in scans with modified atmospheres were all lower than those recorded under normal air. With O2 >2%, heat rates increased approximately linearly with increasing temperature from 10 to about 40ºC. Heat rates in scans with O2 > 5% all increased exponentially above 40ºC, indicative of rapidly increasing membrane damage and loss of control of oxidative metabolism at higher temperatures. With O2 = 2% and very high CO2 (e.g. 80%), heat rates decreased with increasing temperature above 35ºC. The results indicate that treatment of walnuts in air at >50ºC for a short period of time (minutes) will be effective in killing diapausing 5th instar codling moth larvae. High CO2 appears to have little or no effect on the lethal temperature if O2 is greater than 10%. As an alternative, atmospheres with O2 < 1% and CO2 > 80% at temperatures =45ºC are effective at completely stopping both aerobic and anaerobic metabolism in diapausing 5th instar codling moth larvae, but disinfestation is likely to require hours.