Effect of solitary and group rearing on demographic parameters of Stethorus gilvifrons (Col.: Coccinelidae) feeding on Tetranychus urticae

Stethorus gilvifrons is one of the most important monophagus predators of Tetranychus urticae. In this study, demographic parameters of S. gilvifrons were compared between solitary and group (5 pairs of the predator) rearing systems feeding on different developmental stage of T. uricae at 27±1°C temperature, 60±10% RH and a photoperiod of 16:8 h. L:D. In order to start experiments, 120 eggs (< 24 h. old) were selected randomly from the laboratory culture of S. gilvifrons for each treatment. The data were analyzed based on the age-stage, two-sex life table theory. Developmental times of the incubation period, larval, pupal, and total immature stages of S. gilvifrons were 3.92±0.08, 6.52±0.14, 2.98±0.06, 13.59±0.14 days, respectively, in solitary rearing system. In the case of group rearing, developmental time of S. gilvifrons for the mentioned developmental stages were 3.51±0.06, 6.85±0.21, 2.85±0.11, and 13.18±0.21 days, respectively. Moreover, estimated values of intrinsic rate of increase (r), finite rate of increase (λ), mean generation times (T), net reproductive rate (R0) and Gross reproduction rate (GRR) were (0.1219; 0.1455 day-1), (1.1297; 1.1567 day-1), (30.23; 19.88 day-1), (39.92; 18.08 offspring/individual), (265.38; 88.37 females/female/generation), respectively in solitary and group rearing systems. According to the obtained results, demographic parameters of the S. gilvifrons were affected by the number of the individuals in the arena, and population growth was less in the group rearing system, in comparison with solitary rearing condition. These findings can be useful for improving mass rearing of S. gilvifrons and biological control programs of Tetranychids.