Stenchaetothrips biformis (Bagnall)

Mound, Laurence A., 2011, Grass-dependent Thysanoptera of the family Thripidae from Australia, Zootaxa 3064 (1), pp. 1-40 : 34

Stenchaetothrips biformis (Bagnall)

( Figs 81–83 )

Bagnallia biformis Bagnall, 1913: 237

Thrips oryzae Williams, 1916: 353

Described originally from England on Phragmites , the synonym listed above was described from India on rice, Oryza sativa , and a further six synonyms are generally accepted as referring to the same species, the Oriental Rice Thrips ( Bhatti, 1982; Mound, 2011). This thrips is considered to be widespread across the Old World, from Australia to Europe, and also introduced to South America. In contrast, Vierbergen (2004) suggested that the “rice form”, from Asia and South America, is different from the form that lives on Phragmites in Europe, and discriminated these two as follows:

“rice form” - postocular setae I absent; antennal segments IV and V length/width ratios less than 1.9 and 1.8; pronotum with 8 discal setae; sternites IV–VI of female with pore plates;

“ Phragmites form” - postocular setae I usually present; antennal segments IV and V length/width ratios more than 2.4 and 2.0; pronotum with about 18 discal setae; sternites of female without pore plates.

The illustration accompanying the original description of oryzae indicates the presence of postocular setae I, contrary to Vierbergen’s “rice form”. Bhatti (1982) reported that “ syntypes ” of this species he studied had this pair of setae either present or absent, and the slide in the BMNH collection labelled “ TYPE ” has this pair of setae present. Moreover, six of the paratypes have one or both of these setae present, although both setae are absent in four other paratypes. None of these females has any sternal pore plates visible, although all of them are imperfectly cleared. Williams (1916: 355) stated “ Type in the British Museum” therefore the specimen labelled as “ TYPE ” should be considered the holotype according to the Code of Zoological Nomenclature. Of the type series of Bagnallia biformis , only one female and one male remain suitable for study (the other specimens are in a mountant that has turned black). The female, labelled Lectotype, has the left but not the right seta of postocular setae pair I, whereas the male has both of these setae. There is thus little support from the type specimens of the two nominal species for Vierbergen’s (2004) conclusion.

In Australia, this thrips has not been recorded from rice, but it is widespread in eastern Queensland on grasses in damp places, and a total of 22 slide-mounted individuals have been examined. Of these, seven lacked either one or both of postocular setal pair I, whereas 15 had both setae well developed. None of these specimens had more than eight pronotal discal setae, and none of the females had any sternal pore plates. Vierbergen (2004) stated that he had studied 18 specimens of the “rice form”, but all of these were from Surinam. Since this species is introduced to South America, it is likely that the introduced population will have gone through a genetic bottle neck, and thus exhibit a limited range of variation in comparison to that found in Asian populations. Bhatti (1982) summarised the variation exhibited by the rice thrips, within and between populations derived from various Asian localities as well as Europe. His interpretation of this as representing a single widespread species that breeds on various Poaceae in damp habitats, including rice, is here considered the most appropriate decision.

Figures

FIGURES 76 – 85. Grass living Thripinae. Monothrips cuspis 76 – 77: (76) sternites V – VII; (77) tergites VI – VIII. Monothrips flavus 78 – 79: (78) sternites V – VII; (79) tergites VI – VIII. (80) Stenchaetothrips bambusicola, head & thorax. Stenchaetothrips biformis 81 – 83: (81) antenna; (82) tergites VI – VIII; (83) head. Sten. bambusicola 84 - 85: (84) female sternites V-VII; (85) tergites VI – VIII.