Abstract
Cannibalistic behaviour of males and females of Gerris thoracicus, G. swakopensis, and Limnoporus refoscutellatus was studied in the laboratory. Single adults were placed together with 15 first instar larvae in plastic basins, and the number of dead larvae were counted after ten hours. Larvae were either progeny of the test adult or of alien parents. Females were more cannibalistic than males in all species. The average number of dead larvae within ten hours varied from 0.5 (L. rufoscutellatus males, own progeny) to 4.5 (G. thoracicus females, alien larvae). Females of the two Gerris species and males of L. rufoscutellatus killed significantly less often their own descendants than unrelated progeny.