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

The western newer thrips, Frankliniella occidantalis (Pergande), has been p resent on Reunion Island since 1987. The tomato spotted wilt virus, which i s transmitted by F. occidentalis, was first observed on the island in 1991. Because of the strong threat to newer crops, we studied western flower thr ips dynamics at a newer farm (900 m elevation) from 1993 to 1997. The popul ation dynamics were monitored using sticky traps. The density of western ne wer thrips was studied through auto-correlograms and cross-correlograms wit h climatic data (temperature, relative humidity, rainfall). Thrips populati ons varied annually, typically due to temperature variation. Stepwise regre ssion allowed us to fit a model of density increment including 2 climatic p arameters: 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 ter ms for residuals. It appeared the western Bower thrips was present all year round on the site but density started to increase when temperatures reache d 15 degrees C. Nevertheless, the density decreased before the mean tempera ture reached its maximum. Heavy rainfall, involving submergence of pupae or high relative humidity, conditions which are favorable to an entomopathoge n, could explain this early decrease.