Estimation of the immigration time of Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) adults in citrus orchards as a function of the total effective temperature

Scirtothrips dorsalis adults generally immigrate into citrus orchards immediately after emerging from other suitable host plants surrounding the orchards; however, a method to predict adult immigration time has not yet been established. In this study, I examined the relationship between immigration time and total effective temperature for S. dorsalis using trap data collected every few days. The investigation was performed in eight citrus orchards in Shizuoka Prefecture from early May to mid-September in 1999, 2000, and 2001. The total effective temperature was calculated using data from meteorological stations located near the orchards. In each orchard, a positive linear relationship was observed between total effective temperature (y) and the generation number (x) at each immigration peak. The slope and y-intercept of the regression lines did not differ significantly among five orchards in the central district of Shizuoka Prefecture; after pooling the entire data, the linear relationship could be expressed as y=70.67+314.92x (n=84, r2=0.989, p<0.001). In two of the three orchards in the western district of Shizuoka Prefecture, the regression lines did not differ significantly in their slope (using the same equation form).