Scirtothrips dorsalis adults generally immigrate to citrus orchards after propagation on suitable host plants that grow near the orchards; however, it is not clear when these thrips immigrate. In this study, the time of S. dorsalis adult immigration to citrus orchards was examined in relation to their occurrence on surrounding host plants. The investigation was carried out in citrus orchards and the surrounding fields of the following three plants: tea groves, bigleaf podocarp trees, and Japanese pear trees. The average number of adults emerging from these four plant fields gave six or seven peaks from May to early September, notwithstanding the small number of adults emerging from the citrus orchards. The peak periods of trap catch in citrus orchards coincided with those of adult emergence from the fields of four plants. The peak periods of adult S. dorsalis density on citrus fruits and shoots coincided with those of trap catch in citrus orchards. These results demonstrated that S. dorsalis adults immigrated to citrus orchards immediately after emerging from other suitable host plants surrounding the orchards.
The seasonal prevalence of the citrus red mite and its predators on Satsuma mandarin trees was surveyed by nakedeye observation and the beating method in three commercial groves in Shizuoka Prefecture in 2003 and 2004. Of the predators, only phytoseiid mites were caught mainly by beating, and their population dynamics were synchronized with those of the citrus red mite from June to September. Most adult females of phytoseiid mites caught by beating belonged to the species Neoseiulus californicus. Furthermore, one population of N. californicus caught from a surveyed grove showed development and oviposition on the eggs of the citrus red mite as well as the Tetranychus urticae eggs under experimental conditions. These results indicate that an indigenous population of N. californicus in conventionally controlled citrus groves in central Japan has the ability to suppress the population of P. citri on Satsuma mandarin.
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 yϭ70.67ϩ314.92x (nϭ84, r 2 ϭ0.989, pϽ0.001). 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).
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