Stem cells are undifferentiated cells that remarkable ability to self-renew and produce differentiated cells that support normal development and tissue homeostasis. The authors isolated spherical stem cells from the midgut epithelium of the late third larval instars of Culex pipiens mosquitoes. In vitro, cultivated epithelial stem cells were able to proliferate
and differentiate in fresh culture for 48 hr in absence of 20- hydroxyecdysone (20-E). The stem cells were the most common cells in the initial culture. One hundred of epithelial stem cells had been cultured. After 24 hr became 132 cells, 78% was undifferentiated stem cells and 8.3% &13.7% was enterocytes and goblet cells respectively. This ratio slightly
decreased after de 48 hr to be 74% undifferentiated stem cells, 4.5 % enterocytes and 5.6 % goblet cells. After 72 hr the undifferentiated stem cells were not able to proliferate .The most differentiated goblet and enterocytes survived few days then died.