Effect of Temperature and Insect Infestation Levels on Oxygen Depletion in Hermetic Storage

SIMPLE SUMMARY: We examined the effect of temperature and initial pest infestation levels on oxygen depletion during hermetic storage. Jars were filled with cowpea grains and infested with 25 or 50 cowpea weevils. The jars were then hermetically sealed and stored at 20, 30, or 40 °C for 30 days. The results showed that oxygen depletion during hermetic storage varied depending on the temperature and the level of insect infestation. This study revealed that the optimum temperature for effectively depleting oxygen to 5% or below, regardless of the infestation level, was 30 °C. Grain quality was maintained with minimal damage and losses. Only at 20 °C did a few adult insects survive hypoxia for 30 days, and some emerged 45 days later when the jars were exposed to normal oxygen conditions. Therefore, hermetic storage containers should remain closed for more than 30 days to minimize re-infestation risks in areas where the average ambient temperature rarely exceeds 23 °C. ABSTRACT: Hermetic storage methods are effective at protecting grain against insect pests. Biotic and abiotic factors influence oxygen depletion during hermetic storage. We investigated the dual effects of temperature and initial pest infestation level on oxygen depletion during airtight storage. Glass jars filled with cowpea grain were infested (25 or 50 adult cowpea bruchids), then hermetically sealed and stored at 20, 30, or 40 °C for 30 days. Oxygen depletion, relative humidity, and temperature were monitored. Germination, grain moisture content, grain damage and weight loss, and adult emergence were assessed. Oxygen depletion varied by temperature and insect infestation level. However, 30 °C was the optimum temperature for oxygen depletion (reaching 5% or less in 10 days) regardless of insect infestation level. No changes were observed in germination and grain moisture content, minimal grain damage, or weight loss (<1%). Only at 20 °C were adult insects able to survive after 30 days and emerged 45 days post-treatment under normoxia. Therefore, hermetic storage containers should remain closed for more than 30 days to minimize re-infestation of grain in areas where average ambient temperatures rarely exceed 23 °C. Further research is needed to assess the effect of low temperatures on oxygen depletion and insect survival in hermetic storage beyond 30 days.