Systematic significance of antennal segmentation and sense cones in Thripidae (Thysanoptera: Terebrantia)

Abstract

Variation is discussed concerning the number of antennal segments in adults, and the number of their sense cones, among 182 of the 289 genera of Thripidae. Brief comments are also made concerning antennal structure and sensoria among the other seven terebrantian families. The plesiotypic condition for Thysanoptera is 9-segmented antennae, but fusion between various segments leads to a reduction in number to as few as five segments, and such fusion occurs in unrelated species. In Thripidae, antennal segment III never bears more than one sense cone, but the distribution of sense cones on segments IV–VIII varies and is tabulated. On antennal segment IV, species in nearly all Panchaetothripinae genera and more than half of Thripinae genera have two sense cones, but genera of Dendrothripinae and Sericothripinae bear only one on this segment. The differing patterns of segmental fusion that occur in Thripidae are discussed in association with the number of sense cones on VI–VIII; species with 7, 8 or 9 segmented antennae almost always lack a sense cone on the terminal segment. It is concluded that the number of antennal segments is subject to irregular homoplasy, and is thus sometimes an unreliable indicator of relationships.

Phylogenetic analysis of the Taeniothrips genus-group, with revision of the species of Ctenothrips and Vulgatothrips (Thysanoptera, Thripinae)

“…1. Antennae segment number: 9-segmented antennae is considered plesiomorphic in Thysanoptera (Mound et al 1980), but in Thripidae the number of antennal segments is unreliable as an indicator of relationships (Zhang et al 2019a). Among the species involved in this analysis, most are 8-segmented, but Smilothrips productus and Ctenothrips dissimilis have 7-segmented antennae, and an occasional specimen of C. distinctus has antennal segments VII-VIII partly fused.…”

Tryphactothripini of India (Thysanoptera, Thripidae, Panchaetothripinae), with identification keys and a new record of Opimothrips

“…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).…”

Reduced antennal segmentation in a new species from Iran of the genus Aeolothrips (Thysanoptera: Aeolothripidae)

“…The number of antennal segments in adults of the different families and genera in the insect order Thysanoptera varies between five and nine. The plesiotypic number is considered to be nine (Zhang et al 2019), and fossil thrips reported to have 10 to 15 segments (Tong et al 2019) are generally considered to be aberrations in which the terminal segment bears transverse striae. The 9-segmented condition occurs particularly amongst species that exhibit several other characters in a plesiomorphic state, including all Melanthripidae, two genera of Merothripidae, also most species of Fauriellidae, Stenurothripidae, Heterothripidae, and Aeolothripidae (Mound et al 1980).…”

“…The 9-segmented condition occurs particularly amongst species that exhibit several other characters in a plesiomorphic state, including all Melanthripidae, two genera of Merothripidae, also most species of Fauriellidae, Stenurothripidae, Heterothripidae, and Aeolothripidae (Mound et al 1980). Curiously, members of a few genera of Thripidae (Palmer & Mound 1985;Minaei 2012) also have nine antennal segments, but this is considered a reversion from the 8segmented condition that is assumed to be plesiomorphic for that family (Zhang et al 2019). Variation between eight and nine segments occurs in the genus Anaphothrips, and within that genus a few species exhibit intraspecific variation in antennal segmentation (Mound & Masumoto 2009).…”