High-Temperature And Controlled Atmospheres Treatments For Sitophilus Zeamais

Heated controlled atmosphere(CA) treatments are environmentally friendly and have potential as alternatives to chemical fumigation for disinfesting postharvest fresh, dry fruits and stored products. To accurately determine the minimal thermal requirements to kill target insects over a wide range of temperatures and CA conditions, it is desirable to develop a model system to quickly assess the target insect thermotolerance. This paper developed a controlled atmosphere/heating block systems(CA-HBS) and evaluated the performance of the CA-HBS, including the gas tightness of the systems and the stability of gas concentrations and temperature variations. The CA-HBS was used to rapidly assess tolerances of adult maize weevil, Sitophilus zeamais, both under regular air(RA) and CA(1% O2 and 15% CO2)conditions. The major contents and conclusions of studies are follows:(1) This study detected the gas tightness of the systems.It was available to determine gas tightness of the CA-HBS by comparing the readings of flow meters in the systems. The results showed that the new CA-HBS had a relatively constant leakage rate and the relative leakage decreased with increasing flow rate.(2) This study determined the stability of gas concentrations.The variety of gas concentrations coming into and going out the insect treatment chamber was analysed and compared at three different set point levels. The results showed that the CA-HBS could keep O2 and CO2 concentration variations to within ±0.067% and±0.167% at three set points, resulting in relatively stable gas compositions. The average difference in O2 concentrations entering and exiting the system was small(0.021%). CO2 concentrations entering the system were higher than concentrations exiting the system,resulting in an average difference of 0.233%.(3) This study analysed the stability of temperature.In the directly and indirectly entering method, the influence of ambient gas on the temperature variations of two positions(P1 and P2) on the bottom block surface in the treatment chamber was explored at three heating rates(1, 5 and 10°C/min), respectively. Theresults showed that in the indirectly entering method, when the temperature of the heating block reached the set-point temperature, the temperatures in the inlet(P1) and centre(P2)reached the set-point at the same time. Furthermore, there were no clear differences between the programmed heating rates and those calculated from the measured temperatures at either the inlet(P1) or the centre(P2) of the block. This shows that passing the channels through the top and bottom blocks sufficiently preheated the gas.(4) This study discussed the thermal death kinetics of adult maize weevil, Sitophilus zeamais, under RA conditions.The influence of different temperature、time and heating rates on the mortality of adult maize weevil, Sitophilus zeamais, were determined in the RA treatment. The results showed that thermal death curves of S. zeamais followed a 0-order kinetic reaction model. Insect mortality at high heating rates(≥0.5°C /min) was significantly higher than that at the low heating rate(0.1°C /min), indicating that the high temperatures and rapid heating treatments should provide control of these stages, and avoid acclimation often found in conventional heat treatments.(5) This study researched thermal death characteristics of S. zeamais in the high temperature and controlled atmospheres treatments.CA gas concentrations of 1% O2 and 15% CO2 was chosen to compare insect mortality response under heated CA and heated RA. To test the effect of heated CA treatments on adult S. zeamais, insects were exposed to 44- 48°C. Heating rates of 0.1, 0.5, 1, 5 and 10°C / min were compared under both RA and CA environment(1% O2 ? 15% CO2). The results showed that the mortality of S. zeamais adults was higher under CA treatment than in the heat treatment alone. In CA treatments, however, there was no significant difference(P > 0.05) in average insect mortality when heating rate was ≥0.5°C / min. Mortality at the slowest heating rate(0.1°C / min) was significantly higher(P < 0.05) than at the faster heating rates(≥0.5°C /min), indicating that the CA treatments could avoid the thermal adaptation in the heat treatments.