Population dynamics, reproductive fecundity and predatory performance of Diplonychus indicus

Diplonychus indicus, a tropical, skilled predatory water bug with a global distribution, has been studied for its predatory performance. In this study, a detailed account and a thorough assessment on the population dynamics, reproductive fecundity, and the various factors, viz., effect of space size, temperature, food deprivation, aquatic vegetation, competition, and prey density influencing the predatory performance of D. indicus have been portrayed. Over the course of a year, the population dynamics of D. indicus was observed in a permanent pond located in the Kanyakumari region of Tamil Nadu, Southern India. Except for temperature, D. indicus nymphs and adults, had a positive correlation with abiotic (temperature, pH, dissolved oxygen, and rainfall) and biotic (Culex larvae) parameters. With regard to reproductive fecundity, on an average, 20 female individuals of D. indicus produced 1062 eggs, with a maximum hatching percentage of 88.3 at water temperatures of 25–26 °C, and an incubation period of 9.0 ± 0.35 days. The stadial duration of nymphs was 77.68 days, with the Ist stage being the shortest (5.2 ± 0.32 days) and the Vth stage the longest (34.22 ± 4.12). The IVth stage followed by the Vth stage had the highest rates of survival from egg to adult. The predatory performance of D. indicus nymphs evaluated based on the following factors, viz., space size, temperature, starvation, vegetation, competition, and prey density, are as follows. Maximum number of prey (Culex larvae) predated (411.20 ± 8.76) was in circular experimental glass container of 1 L volume space size; at a temperature of 25 °C (11.20 ± 0.30); after 24 h of starvation (558.26 ± 2.56); in 2.0 g density of aquatic vegetation (388.16 ± 2.32); with six competitors (2484.60 ± 8.10); and at 80 prey density (28.52 ± 1.02). The current study provides a critical insight into these variables that are crucial in the predatory performance of their prey, and are successful parameters in establishing a specific predator-prey interaction. This is a useful parameter for figuring out a specific predator-prey interaction in the wild. All the above mentioned factors will affect how well D. indicus performs as a predator in the field.