Temporal dynamics of Scaphoideus titanus populations: from annual occurrence patterns to changing climate suitability assessments
Abstract: A previously published model based on a time-varying distributed delay with attrition is used to simulate, at three different temporal scales (one, five and fifty-two years), the dynamics of the invasive grape leafhopper Scaphoideus titanus Ball in vineyards located in Southern and Western Switzerland. The model was parameterized with laboratory and field data. Built on population theory principles and driven by daily temperature maxima and minima and grapevine plant phenology it satisfactorily represents annual and multiannual occupancy patterns and hence, is concluded to have satisfactory predictive and explanatory capabilities. The simulations representing canopy occupancy by non-diapausing eggs, nymphs and emerging adults are particularly useful for tactical purposes including the timing of monitoring operations and insecticide applications. The simulations representing canopy occupancies by diapausing eggs, non-diapausing eggs, nymphs and adults are useful for strategic purposes. Growers and extensionists should be aware that rather stable occupancies are maintained once an area suitable for development is invaded and no management operations are undertaken. The simulations by the validated model representing long term dynamics could be useful for strategic purposes, policy design and research work. Namely, the model produces an index that represents the climate suitability of a region for colonization by S. titanus. A temporal coincidence was observed between a climate that lifted the temperatures by about 1 °C shift at the end of the 1980s and an abrupt change of the index at the Locarno-Magadino and Geneva sites. If verified at other locations, the climate suitability may have little changed after the introduction and hence, the colonized areas remained relatively constant. At the end of the 1980s, however, new areas were successfully colonized, presumably as a result of now favorable climate conditions and a sufficient dispersal ability of S. titanus. Extensionists and policy makers could take note of a future invasion and prepare growers for dealing with a new pest.