Population growth of the psocid, Liposcelis rufa Broadhead (Psocoptera: Liposcelididae), at constant temperatures and relative humidities

Psocids (Psocoptera) have risen to prominence worldwide as serious pests in stored grain, grain processing facilities, and food-product warehouses in the last 15 years. However, little information is available on the biology and ecology of these pests. Therefore, we investigated the effects of eight temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35, 37.5, and 40.0°C) and four relative humidities (43, 55, 63, and 75%) on population growth of the psocid Liposcelis rufa Broadhead. L. rufa did not survive at 43% RH, at all temperatures tested; at 55% RH, at the highest four temperatures; and at 63% RH, at 40°C. Relative humidities of 63 and 75% influenced population growth similarly at the lower temperatures of 22.5, 25, and 27.5°C. L. rufa populations grew at the lowest four temperatures at 55% RH. L. rufa population increase was greater at temperatures of 32.5, 35, and 37.5°C and 75% RH. However, the highest population increase occurred at 35°C, where populations grew 73-fold; growth at 32.5 and 37.5°C were 64 and 60-fold respectively. At 40°C, L. rufa populations declined or barely grew indicating that this temperature is detrimental for this species. The ability of L. rufa to multiply at 55% RH, at temperatures of 22.5, 25, 27.5, and 30.0°C may allow it to thrive under conditions of low relative humidity where other Liposcelis species may not. In addition, its ability to multiply rapidly at high temperatures of 35 and 37.5°C and 75% RH may allow it to thrive at temperatures too high for most Liposcelis species.