The effects of controlled atmosphere (CA) and DDVP on population growth and resistance development by the psocid, Liposcelis bostrychophila Badonnel, were studied in the laboratory. Results indicated that the population of L. bostrychophila increased rapidly under natural conditions; after 11 weeks, this population had increased 48.1-fold at 288C, 80% relative humidity (r. h.). Exposure to CA (35% CO2, 1% O2) or DDVP (Dichlorvos, 0.3 mg/ml) alone failed to control the population growth. After 11 weeks, populations increased 4.3-and 9.1-fold, respectively. However, alternating exposure to CA and DDVP provided a significant increase in mortality as compared to those exposed to CA or DDVP alone. The results of bioassay showed that both populations exposed to CA and DDVP developed a low but significant resistance to CA and DDVP, respectively. After six exposures, the level of resistance to CA and DDVP increased 1.8-and 2.0-fold, respectively. Probit analysis did not show an appreciable increase in slope value of either population in spite of continuous exposures, indicating considerable heterogeneity of these psocids in response to CA or DDVP and suggesting a greater potential for the development of higher levels of resistance. It is suggested that alternating CA with insecticides could be an important management measure for psocids in storage. #2002 Elsevier Science Ltd. All rights reserved.