Spatial distribution of Scirtothrips aurantii Faure (Thysanoptera: Thripidae) and threshold level for one per cent. damage on citrus fruit based on trapping with fluorescent yellow sticky traps

Abstract

AbstractThe citrus pest Scirtothrips aurantii Faure shows a positive phototactic response to yellow surfaces, particularly fluorescent yellow with peak reflectance at about 525 nm. A fluorescent yellow sticky trap was devised. Impact of individuals on the trap surface was principally random. Taylor's power law gave a generalized value of 1·42 for slope of b. Widespread geographical locations gave similar values for biologically significant values of b. Habitat differences within one geographical area influenced b, which was highest in natural vegetation and lowest in certain citrus monocultures. Three traps per orchard (>5000 trees) were practicable, and produced statistically realistic results. The period during which S. aurantii can damage fruit was divided into a longer risk period and a shorter, central critical period. Where S. aurantii was present on the traps at less than nine individuals per set of three traps throughout the central critical period and 20 during the late risk period, the percentage of fruit so damaged as not to be of export grade was less than 1·0. This method of monitoring was sufficiently robust to allow for some human error in reading the traps under commercial conditions, and to permit variability in placement of the traps in the orchard.