Population fluctuations of the common green lacewing, Chrysoperla carnea Stephens, and those of the sweetpotato whitefly, Bemisia tabaci (Gennadius), were followed for 4 yr in cotton, Gossypium hirsutum L., fields in Israel. Samples were taken and insecticidal controls were applied to determine the importance of C. carnea as a controlling factor of Bemisia in cotton. The results showed that although the lacewings occurred in the field together with Bemisia and their larvae fed on Bemisia nymphs, C. carnea was not an efficient controlling agent of whiteflies. This lack of efficiency probably was related to behavioral preferences of the predator as well as to its nutritional demands that were met only marginally by feeding on whiteflies. Application of the insecticide monocrotophos often resulted in an increase in lacewing egg populations. Influence of other insecticides on the eggs and larvae was often detrimental.