POPULATION-DYNAMICS OF FRANKLINIELLA SPECIES (THYSANOPTERA, THRIPIDAE) THRIPS AND PROGRESS OF SPOTTED WILT IN TOMATO FIELDS

The population of Frankliniella thrips, as monitored by captures on st icky traps, developed quite differently in 1990 compared to 1989. The first thrips in 1990 arrived 10 days earlier, increased at a 22% faste r rate, and reached an asymptotic level that was nearly twice as high as the thrips in 1989. Despite the substantial differences in the thri ps populations between the 2 years, the incidence of spotted wilt in t omatoes was low (<9%) both years. Although the thrips were present dai ly in the crop, the disease seemingly developed in only one-three sepa rate monocycles. These monocycles were not correlated with apparent ge nerations of thrips nor with specific weather events. The sigmoidal cu rves for the cumulative number of trapped thrips over time were fit we ll by the Weibull model with shape parameters of c = 2.16 and 2.55 for fields 1 and 2 in 1989 and c = 3.32 and 2.81 for the two fields in 19 90. Three generations of migrating thrips apparently occurred in each season as detected by waves of increased numbers of thrips when the po pulation curves were linearized. The diseased plants occurred mostly a t random in the fields, which was evidence that the primary source of dispersal was by immigrating thrips. Polycyclic development undoubtedl y was prevented in these commercial fields by weekly application of in secticides. Additional tactics are needed to prevent movement into tom ato fields of viruliferous thrips that develop on hosts outside the fi elds.