Thermal requirements and phenology modelling of a <i>Drosophila suzukii </i>population: implications for pest risk under a changing climate

Drosophila suzukii (spotted-wing drosophila) is an invasive pest causing significant economic losses in soft-skinned fruit crops globally. This study presents comprehensive temperature-dependent life table data and phenology models for an African D. suzukii population collected in Kenya. Developmental time, mortality, fecundity, and adult longevity were assessed under constant temperatures from 12 to 30 °C. Using Insect Life Cycle Modelling (ILCYM) software, linear and nonlinear models were applied to characterise the effects of temperature on life history traits. Additionally, spatial risk indices including Establishment Risk Index (ERI), Generation Index (GI), and Activity Index (AI) were mapped globally for current and future (2061–2080) climate scenarios. The models revealed developmental thresholds of 6.87–34.05 °C (egg-larva) and 9.13–31.97 °C (pupa), with optimal development and reproduction occurring between 20–27 °C. Mortality rates increased at thermal extremes, with minimal mortality near 19.9 °C. Peak intrinsic rate of natural increase (rm = 0.276 day-¹) and finite rate of increase (λ = 1.317) were observed at 27 °C, while population growth declined sharply above 30 °C. Mapped spatial risk indices indicate a largely unchanged pattern between current and future projections, with high risk areas in tropical regions and localised changes in intensity and also distribution. These findings are consistent with other studies which have also indicated that temperature-driven phenology influences the spatial risk patterns of most insects. Given the recent invasion and ongoing spread of D. suzukii in Africa, integrating empirical data with mechanistic modelling provides a robust framework to anticipate invasion risk and optimise surveillance and control under changing climatic conditions.