A Preliminary Study of Pest Insect Detection during Paddy Storage in Small-Scale Grain Silos

Abstract. Fumigation has been commonly used for control of stored product insect pests. However, fumigation is not necessary if the level of insect infestation is not above the allowed tolerance. Such tolerance is expressed in terms of the number of insects per unit weight of grain. The objective of this research was to evaluate the feasibility of 1) detecting Sitophilus zeamais (maize weevil) presence in a silo and 2) evaluating the number of insects based on carbon dioxide (CO₂) concentration monitoring. Three simulated storage trials were conducted in two 3.956 metric ton galvanized steel silos located in Nakhon Pathom province, Thailand from August to September 2016. In the first silo, nine plastic containers filled with a known number of adult S. zeamais (2 insects per kilogram of paddy (IPK)) and brown rice were inserted into the grain mass at the height of 0.3 meter below the grain surface. In the second silo (control), no insect containers were placed. For each trial, CO₂ concentrations in both silos were monitored using non-dispersive infrared CO2 loggers for four days. The insect population in the first silo was calculated from the difference in CO₂ production rates between two silos. For all trials, CO₂ concentrations increased linearly. However, insect population was always overestimated. Estimating insect populations of the three trials were 4.35, 10.58, and 17.83 IPK. It was anticipated that the overestimation was caused by naturally infesting insects and mold development on the paddy. Based on the results of this study, monitoring of CO₂ concentrations could potentially be an effective decision support tool for control of stored grain insects and management of stored paddy quality. However, additional research is needed to correlate measured CO₂ concentration to amount of insects present.