Thrips imaginis Bagnall

Mound, Laurence A. & Masumoto, Masami, 2005, The genus Thrips (Thysanoptera, Thripidae) in Australia, New Caledonia and New Zealand, Zootaxa 1020 (1), pp. 1-64 : 29-31

Thrips imaginis Bagnall

Thrips imaginis Bagnall, 1926: 111

Thrips imaginis apicalis Bagnall, 1926: 111

Thrips fortis Bagnall, 1926: 109

Thrips shakespearei Girault, 1927a: 1 syn.n.

Neophysopus io Girault, 1927a: 1

Neophysopus aureolus Girault, 1928c: 3

Aptinothrips apertus Kelly & Mayne, 1934: 33

Diagnosis: Body colour variable, sometimes yellow but frequently bicoloured with abdomen brown and head and thorax paler; antennal segments I, III and base of IV yellow; legs yellow; forewings pale. Antennae 7­segmented; ocellar setae III arise within ocellar triangle close to first ocellus ( Fig. 38 ). Pronotum with 4–5 posteromarginal setae, external postero­angular seta shorter than inner seta ( Fig. 38 ). Metanotum irregularly reticulate medially ( Fig. 41 ), median setae well behind anterior margin, campaniform sensilla present. Forewing first vein with 3 or 4 setae on distal half. Abdominal tergite II with 3 lateral setae; tergite VIII comb represented by a few teeth laterally; sternites III–VII with 15– 25 discal setae, pleurotergites with 1–3 discal setae ( Fig. 40 ).

Male yellow, pleurotergites without discal setae.

Comments: T. shakespearei was inadvertently placed as a synonym of T. tabaci by Mound & Houston (1987). This error is clear from the discussion by these authors in referring to the presence of sternal discal setae – a character state never found in T. tabaci . The holotype of T. shakespearei is severely damaged; not only are the head and pronotum detached, but the shrunken abdomen is at the margin of the coverslip and has been partially cut away, presumably when someone decided to clean off excess balsam from the slide with a knife. This species is further discussed below under the newly described species, T. safrus .

Breeding: The Plague Thrips , T. imaginis , is one of the most abundant and widespread insects across the southern half of Australia. It is highly polyphagous, occurring in large numbers in the flowers of native as well as introduced plants such as Echium . Populations increase early in Spring and are particularly large in summer in the flowers of alpine plants of the south eastern mountains. The Plague Thrips sometimes causes damage through feeding in the flowers of apple trees, grape vines and strawberries. However, despite much early literature ( Evans, 1932; Andrewartha & Birch, 1952) there are no modern studies on the biology or economic importance of this species. The large populations can at times constitute a public annoyance or even health hazard, when large numbers of individuals crawl through the filters of air conditioners and enter buildings. Adults vary greatly in colour, some females being brown or bicoloured whereas others are yellowish white. The palest forms occur during hot weather in summer, and these have been found around Perth in Western Australia as well as Adelaide in South Australia. Around Canberra, the palest forms have been found in the white flowers of Sophora in mid­summer, and the darkest forms in the blue flowers of Echium in spring, but the cause of the variation in body colour remains unknown.

Distribution: An Australian endemic, this species is widespread in southern Australia including Tasmania, but records from further north than Latitude 27° on this continent are likely to refer to the new species described below as T. safrus , the Northern Plague Thrips . A few specimens of T. imaginis have been seen from New Zealand ( Mound & Walker, 1982), and this species is also recorded from New Caledonia ( Bournier & Mound, 2000), but the only specimen available from that territory during the present studies represents T. safrus . As indicated above in the Introduction, the failure of this polyphagous insect to establish in other countries remains an enigma.

Relationships: T. imaginis is sister­species to T. safrus described below, and these two appear to be closely related to T. unispinus and possibly also to T. australis , although molecular data are needed in order to confirm the available morphological evidence.

Figures

FIGURES 38–47. Thrips species. T. imaginis 38–41: (38) Head & pronotum; (39) Sternites VI–VII; (40) Pleurotergites IV–VI; (41) Meso­metanota. T.safrus (42) Pleurotergites IV–VI. T. insignis (43) Meso­metanota. T. knoxi 44–48: (44) Head & pronotum; (45) antennal segments IV–VIII; (46) Sternites III–IV; (47) Meso­metanota; (48) tergites VII–VIII.