A modified CDC miniature light trap capable of segregating the mosquito collection according to interval is described. This trap has been used with a controlled CO2 release system to measure the crepuscular and nocturnal activity of pest mosquitoes during the period May through September, 1980, in Lucas County, Ohio. Five Aedes species were found to be abundant and active during either the early evening hours or at sunset in a rural wooded habitat. Collections made at a stratification tower located in an urban wooded area indicated that Aedes vexans were more readily captured at ground level than at a high elevation; the converse was noted for Culex pipiens. The flight activity of Cx. pipiens was found to be greatest after midnight at both trap elevations.