Temporal analysis of western flower thrips (Thysanoptera: Thripidae) population dynamics on reunion island

The western newer thrips, Frankliniella occidantalis (Pergande), has been present on Reunion Island since 1987. The tomato spotted wilt virus, which is transmitted by F. occidentalis, was first observed on the island in 1991. Because of the strong threat to newer crops, we studied western flower thrips dynamics at a newer farm (900 m elevation) from 1993 to 1997. The population dynamics were monitored using sticky traps. The density of western newer thrips was studied through auto-correlograms and cross-correlograms with climatic data (temperature, relative humidity, rainfall). Thrips populations varied annually, typically due to temperature variation. Stepwise regression allowed us to fit a model of density increment including 2 climatic parameters: ln (R) at lag = 0 and H at lag = -3 (with R for rainfall, and H for relative humidity; 1 lag = 15 d) and auto-regressive moving average terms for residuals. It appeared the western Bower thrips was present all year round on the site but density started to increase when temperatures reached 15 degrees C. Nevertheless, the density decreased before the mean temperature reached its maximum. Heavy rainfall, involving submergence of pupae or high relative humidity, conditions which are favorable to an entomopathogen, could explain this early decrease.