Thrips australis (Bagnall, 1915)

Thripinae, Thripidae, Terebrantia, Thysanoptera

Figures

Fig. 1: 7-segmented antenna, segments III and IV with forked sense cone, terminal segments V-VII
Fig. 2: Head dorsal with ocellar triangle
Fig. 3: Pronotum
Fig. 4: Meso- and metanotum
Fig. 5: Fore wing and fore wing distal region
Fig. 6: Sternites V-VII
Fig. 7: Tergites VIII and IX
Fig. 8: Tergites VII-XI

Thrips australis causes damage particularly on the flowers of gum tree (Eucalyptus sp.) and other Myrtaceae. Both sexes fully winged. Body color highly variable, commonly yellow with yellow legs, and with brown area medially on tergites II-IX, and abdominal segment 10 largely brown; antennal segment I white, III yellow, remaining segments largely brown; fore wings pale with dark setae and hind margin shaded; some individuals more extensively dark brown, but many individuals pale with little or no brown shade except distal antennal segments. Antennae 7-segmented; segments III & IV slightly constricted at apex with short forked sense cone, segment VI bullet-shaped, segment VII short (Fig. 1). Head wider than long; with 2 pairs of ocellar setae; pair I absent, pair III arising just within anterior margins of ocellar triangle close to fore ocellus; postocular setae I & III as long as ocellar setae pair III (Fig. 2). Pronotum with 2 pairs of moderately elongate, stout posteroangular setae; posterior margin with 3-4 pairs of setae; anterior margin with 3-5 pairs of setae (Fig. 3). Mesofurca with weak spinula. Metanotum with mainly equiangular reticulation medially; median setae arising well behind anterior margin; campaniform sensilla present (Fig. 4). Mid and hind tarsi 2-segmented. Fore wing first and second vein with almost complete row of closely set setae; clavus with 6 marginal setae, clavus terminal seta longer than subterminal seta (Fig. 5). Tergite II with 4 lateral marginal setae, of which the 2 anterior setae are equal in length; tergites V-VIII with ctenidia present laterally, on VIII posteromedial to spiracles; posterior margin of VIII with comb incomplete or with short craspedum medially but represented by about 8 short teeth laterally (Fig. 7 and 8); pleurotergites commonly with 5-9 discal setae. Sternite II with 2 pairs of marginal setae, III-VII with 3 pairs (Fig. 6), median marginal setae on VII arising at posterior margin; sternal discal setae ranging from 3 on II to 30 on VII, in irregular double rows.
Male similar to female in structure, but smaller and paler; tergite VIII without comb; tergite IX with 4 setae close set in a transverse row, S1 slightly shorter than S2 setae, bases slightly closer to S2 than to each other; sternites III-VII with small transverse glandular area anterior to about 10 discal setae.

The genus Thrips L., 1758
There are nearly 300 species currently recognized in the genus Thrips making this genus one of the largest taxa within the order Thysanoptera. The genus was redefined progressively during the 1970's (see Mound et al. 1976), to include many species previously placed in Taeniothrips. The genus Thrips now includes a range of species, some with the antennae 7-segmented, others 8-segmented, and a few with the number of segments varying between 7 and 8. Similarly, some species have few setae on the fore wing first vein, whereas others have a complete row of setae on this vein. The species with a complete setal row on the first vein were placed from some taxonomists in the genera Isothrips or Isoneurothrips. However, all of the species in Thrips have the following character states: antennal segments III & IV with forked sense cone, absence of ocellar setae I, pronotum with 2 pairs of elongate posteroangular setae, paired ctenidia laterally on the tergites V-VIII, tergite VIII ctenidium arising posterior to the spiracle (in contrast to species of the genus Frankliniella). Other character states, such as number of antennal segments, number of setae on the fore wing veins, and number of discal setae on the abdominal sternites are variable between species (Mound & Masumoto 2005; Nakahara 1994; Palmer 1992). Identification keys are available for the species of this genus from many parts of the world. Of particular importance is the published key by Mound (2010) for members of the genus Thrips from Afro-tropical region as well as previous Lucid keys from Moritz et al. (2001, 2004, 2009).

Thrips australis is very similar to some other Thrips species - like Thrips microchaetus, Thrips subnudula and Thrips tenellus. Thrips australis has sternites III-VII with at least 1 pair of discal setae and pleurotergites with discal setae (Thrips acaciae, Thrips brevisetosus, Thrips florum, Thrips gowdeyi, Thrips hawaiiensis and Thrips simplex, all of them have sternites III-VII with at least 1 pair of discal setae and pleurotergites without discal setae; Thrips orientalis and Thrips parvispinus, both have discal setae on sternites III-VI, but not on sternite VII, and without discal setae on pleurotergites; Thrips nigropilosus, Thrips palmi, Thrips pusillus and Thrips tabaci, all of them have sternites and pleurotergites without discal setae).
Inside this group Thrips australis is the only species which has the fore wing first vein with setal row almost complete (in other three species the fore wing first vein with a wide gap before distal group of setae), and the metanotal sculpture with mainly equiangular reticulation (in Thrips microchaetus and Thrips tenellus sculptured lines are transverse at anterior, but longitudinal and parallel on posterior half; Thrips subnudula with sculptured lines transverse at anterior, but forming equiangular or irregular longitudinal reticulations on posterior half). Furthermore, in Thrips australis ocellar setae III arising on or just within anterior margins of ocellar trinagle (in Thrips microchaetus and Thrips tenellus ocellar setae III arising outside ocellar triangle and lateral to fore ocellus; in Thrips subnudula ocellar setae III arising close together behind first ocellus within the triangle). Most of the species have campaniform sensilla on metanotum (in Thrips tenellus absent), pleurotergites without many rows of fine microtrichia (only in Thrips subnudula present), and sternites III-VI with 3 pairs of posteromarginal setae (except for Thrips subnudula with 5-7 pairs of posteromarginal setae). In Thrips australis as well as Thrips subnudula tergite VIII posteromarginal comb is absent medially (compared to Thrips microchaetus and Thrips tenellus with complete posteromarginal comb of microtrichia on tergite VIII). The species differs from most other Thrips-species by the number of marginal setae on fore wing clavus, because only three species have more than 5 marginal setae on fore wing clavus: Thrips australis with 6, Thrips subnudula with 5-7, and Thrips acaciae with 5-8 marginal setae. The remaining have always 5 marginal setae on clavus. Furthermore, outside the group Thrips australis is similar to Thrips parvispinus and Thrips orientalis in having the fore wing first vein with an almost complete setal row, and the metanotal median sculpture with mainly equiangular reticulation.
Species of the genus Thrips are similar to species of Stenchaetothrips, Microcephalothrips abdominalis, Larothrips dentipes and Fulmekiola serrata because of tergites V-VIII bear a pair of ctenidia laterally, which on tergite VIII situated posteromedial to the spiracle, and all species have no ocellar setae I on head. In contrast to species with craspedum on tergites II-VII (Microcephalothrips abdominalis, Larothrips dentipes and Fulmekiola serrata), species of Thrips and Stenchaetothrips have no posteromarginal craspedum on tergites and sternites. Species of the genus Thrips as well as Fulmekiola serrata and species of Stenchaetothrips have 2 pairs of elongate posteroangular setae (Microcephalothrips abdominalis with 2 pairs of moderately elongate pronotal setae and Larothrips dentipes without elongate setae). Compared to the species of Thrips, Microcephalothrips abdominalis, and Larothrips dentipes, which have ocellar setae II on head much shorter than or about as long as III, Fulmekiola serrata and species of Stenchaetothrips have ocellar setae II much longer than III, and sternites always without discal setae.

Life history
As with other thrips species the life cycle from egg to adult is dependent on temperature. The full cycle can take about 15 days (Lewis 1973) to over a month. Adults may live for more than one month producing several generations in one year depending on seasons. With greenhouse temperatures the developmental time from egg to adult can decrease to about one week.

Host plants
Particularly gum tree (Eucalyptus sp.).
Crops: Acacia sp., banana, capsicum, carrot, citrus, flax, French bean, sunflower, tomato.
Weeds: Lantana sp., Pentanisia ouranogyne.

Vector capacity
None identified, but possible mechanical distribution of phytopathogenic fungi and bacteria.

Damage and symptoms
-

Detection and control strategies
-

Additional notes
Breeding particularly in the flowers of white and yellow flowered species of Eucalyptus, but also in other Myrtaceae with similar colored flowers. This species has not been reported as a major pest but has been introduced around the world where ever Eucalyptus has been distributed. It can produce very large populations, and adults will then disperse and be found in the flowers of many different plants (Mound 2010).

Biogeography

Worldwide: Cyprus, Palestine, North and South Africa, Japan, Australia, Brazil. Egypt (Montazah), Kenya, Malawi, Morocco, South Africa (Limpopo: Zebediela; Western Cape: Mossel Bay, Stellenbosch), Tunisia (Skanés, Sahline), Zimbabwe.

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