Scirtothrips dorsalis (Thysanoptera: Thripidae): Scanning Electron Micrographs of Key Taxonomic Traits and a Preliminary Morphometric Analysis of the General Morphology of Populations of Different Continents

ABSTRACT The chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) is an emerging pest of many economically important vegetable and ornamental crops grown in the United States. Accurate identification of this pest is a fundamental requirement in development of effective quarantine and management strategies. Using scanning electron microscopy, high resolution images of important taxonomic traits of this pest were produced, which will aid research, regulatory and extension personnel to identify this pest. High resolution images were obtained for identifying characters of S. dorsalis including tergites with antecostal ridges; head with 3 pairs of ocellar setae, metanotum presenting longitudinal striations with medially located pair of setae; veins of forewing presenting widely spaced setae; segment VIII with complete posteromarginal comb of microtrichia; and sternites lacking discal setae but covered with rows of microtrichia except in the antero-medial region. Further, a preliminary comparison of morphological traits of S. dorsalis populations from different geographical regions was conducted, which can help in understanding the phenotype of this pest. Specimens of S. dorsalis were obtained from 5 distinct geographical regions: New Delhi, India; Shizouka, Japan; Negev, Israel; St. Vincent and Florida in the United States. Fourteen morphological characters of each population of S. dorsalis were measured and compared among the 5 populations. No significant differences were observed between the body lengths of the various S. dorsalis populations, which ranged from 0.85 mm (Negev) to 0.98 mm (Florida). When comparing 12 morphological characters, we found no significant differences among New Delhi, St. Vincent, Negev and Florida populations. However, when S. dorsalis populations of these 4 regions were compared with Shizouka, significant differences were detected for either 2 or 5 morphological characters depending on the population, suggesting the Japan population is more robust i.e., longer and wider mesothorax and metathorax, and wider abdomens. Also, the mean lengths of body size among different populations did not vary directly or inversely with latitude.

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