Helopeltis theivora Waterhouse, is an important pest of tea (Camellia L.) in South India. Pachypeltis maesarum Kirkaldy has also been recently recorded infesting tea. Field observations revealed that Ludwigia peruviana (L.) Hara, a swamp weed, served as an alternate host for these pests. Biology of H. theivora and P. maesarum was studied on this weed. The incubation period of H. theivora was longer than P. maesarum. The total nymphal period was shorter for P. maesarum when compared with that of H. theivora. Finite rate of increase in numbers (λ) of H. theivora and P. maesarum females was 1.1086 and 1.0691, respectively. A parasitoid on nymphs and adults of H. theivora, Leiophron sp. (Hymenoptera: Braconidae) was recorded on L. peruviana for the first time. Knowledge on the phenology of these mirids may help to take better management decisions, so that proper assessments can be made before applying pesticides.