The effectiveness of natural enemies against arthropod herbivores can depend on the characteristics of the plant on which they are found. The influence of the plant on the egg-laying behaviour of the promising whitefly predator, Serangium parcesetosum Sicard (Col., Coccinellidae) was examined in order to be able to use it effectively in biological control programs. The present work investigated the possible influence of the portion of the leaf on the number of eggs laid as well as the effect of plant species on the way in which eggs are deposited by S. parcesetosum. The experiments were conducted on cucumber and cotton leaves with Bemisia tabaci (Germ.) (Hom., Aleyrodidae) as prey in the absence and presence of a natural enemy, the lacewing, Chrysoperla carnea (Stephens) (Neur., Chrysopidae) at two different temperatures. The results showed that at 18 degrees C, S. parcesetosum females significantly preferred to lay their eggs between the veins and close to the veins of cucumber leaves, mean of 10.1 and 7.5 eggs, in the absence of C. carnea, respectively, while in its presence significantly more eggs were deposited close to the veins and close to the petiole. On cotton leaves, close to the petiole, a mean of 8.4 eggs in the absence of the lacewing, as well as close to the veins, mean of 6.3 eggs in the presence of the lacewing, were found to be the most suitable leaf portions for egg-laying. At 30 degrees C, the females laid their eggs preferentially close to the veins of cucumber leaves in the absence and presence of C. carnea. On cotton leaves, S. parcesetosum females significantly preferred to lay their eggs close to the petiole, mean of 7.6 and 6.1 eggs, as well as close to the veins, mean of 6.2 and 8.7 eggs, in the absence and presence of the lacewing, respectively. At both temperatures, the ladybird females laid their eggs singly on cucumber leaves in the absence and presence of C. carnea. While on cotton leaves, the females had a tendency to deposit their eggs together in the absence and presence of the lacewing, except at 30 degrees C in its absence. Within the same plant species, significant differences were found in the total number of eggs laid by S. parcesetosum females on cotton leaves at 18 degrees C as well as on cucumber leaves at 30 degrees C in the absence and presence of the natural enemy. In addition to the effects of presence and absence of C. carnea, and where eggs were laid, some significant differences due to plant species was found at both temperatures.