Abstract
Analysis of catches of Chrysoperla carnea (Steph.) in a light-trap and a suction trap at Rothamsted, southern England, showed that the light-trap catch varied as predicted from a model proposed to describe the functioning of a light-trap: catch = constant × , where W = trap illumination and I = background illumination. After adjustment to allow for changes in illumination during the flight period of C. carnea, the light-trap catch was very similar to the suction-trap catch. For C. carnea, a light-trap provides as unbiased a sample as a suction trap, but because of variation in trap effectiveness with variation in illumination, light-trap catches obscure changes in activity and abundance. Although similar studies are desirable to confirm this for other species, it is suggested that in light-trap studies catches should be adjusted to allow for changes in illumination during flight or trapping periods.