Pakistan J. Zool., vol. 45(2), pp. 317-321, 2013. Humidity Dependent Population Growth of the Psocid, Liposcelis yunnaniensis (Psocoptera: Liposcelididae) Muhammad Waqar Hassan, 1, * Wei Dou 2 and Jin-Jun Wang 2 1 University College of Agriculture and Environmental Sciences, The Islamia University of Bahawalpur, Pakistan 2 Key Laboratory of Entomology and Pest Control Engineering, College of Plant Protection, Southwest University, Chongqing 400716, China Abstract.- We investigated the effect of four different humidities on population growth of the psocid Liposcelis yunnaniensis (Psocoptera: Liposcelididae). The four different relative humidities used were 43, 55, 63, and 75%, respectively. In a 30-d period the initial four female psocids increased to the mean populations of 24±5.72 on 75% humidity and 21±3.45 on 63% humidity. The psocids developing on the humidity of 43 and 55% showed no increase in their population and all the adult female psocids died. The results showed that population growth was highest on higher humidities and the lower humidities of 43 and 55% lead to the death of the insects. According to the analysis of variance there was no significant difference in the population growth between the higher humidities of 75% and 63% RH. An analysis was also done with respect to the psocids placement in 4 different compartments of the incubator from top to bottom. It was found that there was no statistical difference in population growth of the psocids in different chambers of the desiccators which could be due to any variation in temperature inside the incubator. Psocid population growth is explained graphically with respect to different humidities and its placement on different heights of incubator. Key words: Relative humidity, population growth, stored product Psocids, Liposcelis management. INTRODUCTION Unlike in the previous decades, stored product psocids have become prominent and have received much attention around the world in recent years. Psocids of family Liposcelididae have been reported worldwide: United Kingdom (Turner, 1994), Spain (Pascual-Villalobos et al., 2005), Australia (Rees, 2002), Mexico (Garcia Aldrete and Gutierrez Diaz, 1995), the United States (Mockford, 1991), Zimbabwe (Mashaya, 2001), and some Asian countries (Indonesia, Malaysia, Singapore, Philippines, Thailand, China, and India (Rajendran, 1994; Rees, 1994; Leong and Ho, 1995; Wang et al., 1999). Their rise into prominence could be due to the fact that these have shown resistance to residual insecticides and fumigant phosphine (Nayak et al., 1998, Nayak and Collins, 2008) and markets regard them increasingly as contaminants (Nayak, 2006). Stored-product protectants such as pyrethroids, carbamates as well as organophosphate insecticides __________________________ * Corresponding author: waqar_722@hotmail.com 0030-9923/2013/0002-0317 $ 8.00/0 Copyright 2013 Zoological Society of Pakistan have been shown to be ineffective against stored- product psocids (Nayak et al., 2003, Wang et al., 2004) and novel insecticides such as spinosad are only effective when mixed with other compounds, for example, to increase its efficacy to the desired levels (Nayak et al., 2005; Nayak and Daglish, 2007). Stored cereal grains remain heavily infested with psocids which are favored by the hot and humid conditions such as those existing in tropical areas of the world (Wang et al., 1998). Psocids have a relationship with the humid conditions and are typically seen in moist areas. The bodies of Liposcelis species contain water which is directly proportional to the humidity in the ambient environment. An environment containing less than 58% RH is regarded as dry atmosphere for psocids residing indoors and above this critical RH, psocids have to utilize food energy to transport water vapour into their bodies, enabling them to replace transpired water vapour and maintain body mass even in the absence of food that contains water (Knülle and Spadafora, 1969). In high humidity, their life spans range from six months to a year (Broadhead and Hobby, 1944). Their egg laying can be stopped by lowering the surrounding humidity (Knülle and