Astrothrips Karny, 1921

Rachana, Remani R., Mound, Laurence A. & Rayar, Shashikant G., 2019, Tryphactothripini of India (Thysanoptera, Thripidae, Panchaetothripinae), with identification keys and a new record of Opimothrips, ZooKeys 884, pp. 43-52 : 43

Astrothrips Karny, 1921

Astrothrips Karny, 1921: 239. Type species Heliothrips globiceps Karny, 1913.

Notes.

This genus was based originally on a single species that had been described from a single female collected in New Guinea, but four generic synonyms are listed in ThripsWiki (2019).

It is an Old World genus that is restricted to tropical countries, with two species from Africa and 10 distributed between Pakistan and New Guinea ( ThripsWiki 2019). These are leaf-feeding thrips, with the occasional adult found in flowers, and although adults have been taken from a wide variety of plants, suggesting the possibility of polyphagy, larvae remain unknown for most of the described species. The many published host-plant associations (Table 1 ) involve more than 30 plant families, with little indication of any specificity. These records are based on the collection of one or more adults from any given plant, and thus may involve a flying adult simply resting on a plant surface without feeding. Possibly these records are more of a measure of the dispersive behavior of adults, rather than an indication of the plants on which they might breed. Moreover, most of the species are known from few specimens. This combination of small sample size and lack of biological information leads to a lack of confidence in the relatively trivial structural differences that have been used to distinguish some of the species. The species of Astrothrips from India were reviewed by Bhatti (1967), with many clear illustrations in the form of line drawings, and Ananthakrishnan and Sen (1980) provided a further key to the species from India but without illustrations.

Diagnosis.

Small, dark brown, strongly reticulate Panchaetothripinae usually with banded fore wings bearing stout veinal setae. Antennae with 5-8 segments, sense cones on III and IV forked or simple. Head with conspicuous raised reticulate sculpture, setae all small, ocellar area sometimes elevated; maxillary palps bi-segmented. Pronotum transverse, strongly sculptured with some raised reticulation. Mesoscutum usually deeply notched; metascutum with prominent triangle. Tarsi 1-segmented. Fore wing slender, both longitudinal veins with prominent setae; costal setae shorter than costal cilia; posteromarginal cilia wavy. Tergite II of abdomen with anterior margin strongly constricted, and anterolaterally with a group of prominent strongly recurved microtrichia; tergites III–VII with transverse reticulation on anterior half; VIII with no posteromarginal comb; X divided longitudinally. Male smaller, sternites with or without slender, deeply curved, pore plates.

Antennal segmentation.

The 8-segmented condition of antennae is considered plesiotypic for the family Thripidae ( Zhang et al. 2019). However, among some Panchaetothripinae genera, including Astrothrips , there are species with the distal segments fused in different combinations, such as segments VI+VII or VII+VIII, or sometimes VI–VIII or even V–VIII forming a terminal group. As a result of this fusion the number of apparent segments is reduced to seven, six, or even five. It is important to recognise that reduction in the number of segments is not necessarily a shared apomorphy, because the 7-segmented condition could arise by fusion of either VII+VIII or by VI+VII ( Zhang et al. 2019).

Species recognition.

Species level taxonomy in this genus is based on some relatively trivial character states, each of which may have been observed on very few specimens. Stannard and Mitri (1962) described aureolus from only two females and distinguished this new species from globiceps and parvilimbus . The three diagnostic characters selected by the authors (shape of antennal segment III, colour of costal setae, body colour) are now considered to be variable among more recently collected specimens. Some other character states used by authors to distinguish species in this genus have been found to be more variable with the discovery of more specimens. Bhatti (1967) described stannardi as having the major sense cone on antennal segment VI surpassing the apex of the antenna, but this has been found to be untrue on various specimens of the species collected from South India and Thailand. Wilson (1975) in his key to species treated stannardi in the group with five or six antennal segments, but in the main text under that species, he states that there are seven segments; this confusion is repeated by Ananthakrishnan and Sen (1980). Subsequent identifications that are based solely on such original descriptions may not be reliable. The male of aureolus has been unknown, but a male identified as this species from Timor Leste (in ANIC) has U-shaped pore plates on sternites IV–VII as in stannardi . Similar problems are involved in host-plant associations. For example, Bhatti (1967) described lantana from two females, but Wilson (1975) mentions weekly collections from Lantana camara near the type locality without finding this thrips. In contrast, Kudô (1995) identified three females from Nepal as lantana that were taken from a species of Quercus and an unidentified tree.