Technical Abstract: The insidious flower bug, Orius insidiosus, can be maintained on a minimal artificial diet (control diet) composed of brewers yeast, soy protein hydrolysate and chicken yolk but the fecundity is poor even though level of protein in the diet exceeds the amount consumed by adults fed eggs of the Indian meal moth, Plodia interpunctella. To determine what components of prey eggs were responsible for the higher level of egg production egg homogenates were applied to desalting columns. The desalted proteins were collected, freeze-dried, and fractionated by isoelectric focusing (pH 3-10 gradient). Resultant fractions were bioassayed in test diets. Ovipositional rates were evaluated using a short 1-week bioassay. Adult predators were placed on the diets the third day after eclosion and allowed to feed for six days and provided with an oviposition substrate for 24 hrs on day seven. Egg production was significantly increased only in a fraction with an isoelectric point of pH 5. SDS-PAGE revealed the presence of several Commassie blue-stained bands. These results point to a specific chemical factor required by females of Orius insidiosus for egg laying.