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Considering the insecticidal effect of modified Atmospheres as an alternative technique to synthetic chemicals, a compact and lowcost laboratory controlled atmosphere device was developed and tested. Device consisted of gas cylinders and regulators, a gas mixer, rotameters, gas sampling ports, relative humidity unit, a temperature controlled environment and a gas chamber. Tests were carried out to determine the efficacy of the device by exposing adults of Tribolium confusum J. du Val and Callosobruchus maculatus (F.) to ternary mixtures of (60% CO2: 8% O2: 32% N2, 70% CO2: 4% O2: 26% N2, and 80% CO2: 1% O2: 19% N2) at seven exposure times (12, 24, 36, 48, 72, 96 and 120 h), relative humidity (r.h.) of (65, 75and 85%), constant temperature of 30C, flow of rate 50 ml/min, and operating pressure of 40 kPa. Results showed that device can maintain CO2, O2 and r.h. levels used in the investigation within 2, 1.5 and 3 % of the set points respectively and can generate mixtures of gases CO2, O2 and N2 ranging from 0 100%. Atmosphere containing 80% CO2, 1% O2 and 29% N2 was more lethal than atmospheres containing 70% CO2, 4% O2 and 26% N2 or 60% CO2, 8% O2 and 32% N2. Also atmospheres humidified to 65% r.h. were generally more lethal than those humidified to 75 and 85%. Atmosphere with 80% CO2, 1% O2 and 19% N2 caused highest mortality when 100% mortality of T. cofusum was achieved in 72 h compared to 24 h which was needed to obtain 100% mortality of C. maculatus adults.