Modeling Thermal Developmental Trajectories and Thermal Requirements of the Ladybird Stethorus gilvifrons

SIMPLE SUMMARY: The ladybird Stethorus gilvifrons is an important natural enemy of herbivorous two-spotted spider mites, Tetranychus urticae. Here, we modeled the effect of temperature, which is the most significant abiotic environmental factor, on the development and thermal thresholds of S. gilvifrons. Thermal parameters and developmental trajectories were estimated by fitting two linear and 20 non-linear models to experimental data measured at seven temperature regimes ranging from 15 to 38 °C. Our findings demonstrate that S. gilvifrons is able to complete development at a broad range of temperatures and is well-adapted to temperatures occurring in temperate, Mediterranean, and subtropical climates. The thermal development models presented here represent a significant step towards an in-depth evaluation of S. gilvifrons as a biological control agent of T. urticae under different temperature regimes. The models can be used to predict the phenology of this predator, to forecast its population dynamics in the field, and to optimize mass-rearing efforts. ABSTRACT: The development rate of the predatory ladybird, Stethorus gilvifrons (Mulsant), fed on Tetranychus urticae Koch, was determined at 15, 20, 25, 27, 30, 34, and 38 °C. The total development time from egg to adult emergence for females was estimated to be 61.4, 31.6, 14.4, 13.3, 12.5, and 11.7 days, respectively. The development time decreased with increasing temperature from 15 to 34 °C, but all eggs failed to hatch at 38 °C. The lower temperature threshold (T(0)) for the entire development period and the thermal constant (K) for female S. gilvifrons were estimated to be 11.64 °C and 194.50 degree-days (DD) using the common linear model, and 11.96 °C and 187.87 DD using the Ikemoto and Takai model, respectively. Data were fitted to 20 non-linear development rate models and the thermal thresholds (T(min) and T(max)) and optimal temperature (T(opt)) were estimated. Among non-linear models, the Briere-2 and Ikemoto and Takai linear model provided adequate descriptions of the temperature-dependent development of S. gilvifrons. The upper-temperature threshold was estimated to be about 44 °C using the Logan-10 non-linear model. The estimated thermal development characteristics can be used to predict the occurrence and the population dynamics, as well as to improve the mass rearing and release, of S. gilvifrons for the biological control of T. urticae.