Effect of Hypoxia on the Lethal Mortality Time of Adult Sitophilus oryzae L.

SIMPLE SUMMARY: The rice weevil is a major pest of stored grains that leads to losses resulting in food and income insecurity among farmers. Pesticides, often used by farmers to control insect pests of stored products, are becoming unattractive due to health risks to applicators, consumers, and the environment. Hermetic (airtight) storage methods have been used as alternatives to pesticides. Understanding when insects die during hermetic storage is vital, in order to improve pest management. We conducted experiments to assess the time required to attain mortality of adult rice weevils when the oxygen levels reached below 5% in airtight containers. Results revealed that it required 69.7, 187.8, and 386.6 h to kill 50% of adult rice weevils exposed to 1%, 3%, and 5% oxygen levels, respectively. No adult emerged from infested grains following exposure to 1 and 3% oxygen levels, but some did at 5% oxygen level. Based on these results, we recommend that grain be kept in hermetic airtight conditions for at least 39 days to achieve adult rice weevil mortality and minimize grain reinfestation. ABSTRACT: Sitophilus oryzae is one of the most destructive pests of stored grains. It leads to significant quantitative and qualitative losses, resulting in food and income insecurity among farmers. Chemical pesticides are the most common methods used by farmers and other grain value chain actors to manage this pest. However, pesticides are increasingly becoming unattractive for pest control due to health hazards posed to applicators, consumers, the environment, and insect resistance. Modified atmospheres have the potential to manage stored insect pests as an alternative to pesticides. There is limited understanding of when insect pests die when grain is stored in airtight containers. This experiment was conducted to assess the time required to reach mortality of adult S. oryzae when exposed to 1, 3, and 5% oxygen levels. Results revealed that the LT50 for 1, 3, and 5% of oxygen were reached after 69.7 h, 187.8 h, and 386.6 h of exposure, respectively. No adult emergence was observed on infested grains following exposure to 1 and 3% oxygen levels. This result provides vital rationale for storing grain in hermetic storage conditions for at least 39 days to achieve adult S. oryzae mortality and minimize grain reinfestation.