Chirothrips Haliday

Minaei, Kambiz & Mound, Laurence, 2010, Grass-flower thrips of the genus Chirothrips (Thysanoptera: Thripidae), with a key to species from Iran, Zootaxa 2411, pp. 33-43 : 34-38

Chirothrips Haliday

Thrips ( Chirothrips ) Haliday, 1836. Type species: Thrips ( Chirothrips ) manicata Haliday. Chirothrips Haliday : Amyot & Serville, 1843.

Agrostothrips Hood, 1954 . Type-species A. guillarmodi Hood. syn nov.

Chirothrips is one the largest genera in the Thripidae , with more than 50 species listed worldwide ( Mound, 2009). Hood described Agrostothrips for a single new species taken from grasses at two sites in South Africa and one site in Uganda, and distinguished this genus from Chirothrips on three character states:

1. Antennal segment II external margin not prolonged;

2. Antennal segments III–IV with sensorium forked;

3. Abdomen slender and acuminate.

Bhatti (1990) indicated that, by themselves, these characters were not sufficient to warrant recognition of a separate genus. However, he added two further character states in order to distinguish Agrostothrips , and he then included four species in that genus: Chirothrips ah Girault, Chirothrips atricorpus Girault , Chirothrips meridionalis Bagnall , and A. guillarmodi . The two additional characters proposed were:

4. Craspedum on posterior margin of tergites and sternites comprising elongate plates;

5. Eyes “lack differentiated facets” (this state was not defined, but presumably refers to pigmented facets).

Considering these five characters, it is clear that the third listed, the shape of the abdomen, is not a useful distinction because it cannot be defined satisfactorily. Moreover, the fifth character is incorrect, because ah, atricorpus and meridionalis all usually have several pigmented eye facets ventrally, in the same pattern as C. manicatus . The first character would appear to be well defined, but it applies to only two of the four species. Both atricorpus and guillarmodi have the second antennal segment almost symmetrical ( Fig. 5 ), but ah and meridionalis have this segment projecting laterally ( Figs 4, 6 ). The symmetrical shape of the second antennal segment is certainly interesting and probably plesiotypic, but a few other species of Chirothrips are known to have this segment only weakly asymmetrical, such as C. watanabei from Japan.

The second character state indicated above also seems clearly defined, but it is not consistent across the four species. Although in guillarmodi the sensoria on segments III and IV are forked, in meridionalis the sensorium on segment IV is forked but that on III is simple, and in ah and atricorpus the sensoria on segments III and IV are simple. Thus the only character remaining to define Agrostothrips from Chirothrips is the form of the craspedum on the posterior margins of the tergites and sternites.

In guillarmodi the tergites and sternites bear a series of closely approximated, but independent, elongate lobes. The tergites of ah, atricorpus and meridionalis all bear a craspedum that comprises rounded lobes (Fig. 23), unlike the elongate lobes of guillarmodi . Moreover, in these species although each of the lobes is independent on some segments, they are broadly fused at the base to form a continuous structure on the more posterior segments, and in ah this lobed tergal craspedum is often weakly developed or even absent. Among other Chirothrips species there is considerable variation in the form of the tergal craspeda. Many species have a more or less continuous and weakly lobed tergal craspedum, as in manicatus (Fig. 20), but other species have very different structures, such as a series of independent small, triangular lobes in pretorianus (Fig.22), or a series of widely and evenly spaced microtrichia-like teeth in molestus (Fig. 24).

On the sternites, the lobed craspedum of ah, atricorpus and meridionalis also takes a rather different form from that found in guillarmodi , in that the lobes are long, slender and widely-separated ( Fig. 16, 19 ). Moreover, hamatus and falsus have slender independent lobes laterally that are similar to the lobes of meridionalis , but are small or absent medially ( Fig. 18 ). Many species of Chirothrips lack any craspedum on the sternites, including frontalis, kurdistanus , and pretorianus , but others, including manicatus , molestus , and aculeatus , have a series of tubercles on the sternal posterior margins ( Fig. 17 ) that vary from prominent to insignificant, partly in relation to body size.

The four species, ah, atricorpus , guillarmodi and meridionalis , are unusual within the genus Chirothrips in having fully winged males ( Mound & Palmer, 1972), and it is possible that they represent a species-lineage from the Afro-tropical Region. Masami Masumoto has pointed out (in litt., 2009) that the metathoracic preepisternum is reduced in those Thripinae species that are related to Chirothrips . In typical species of Thripinae , including Limothrips cerealium ( Fig. 12 ), this sclerite is broadly band-like, with parallel or slightly tapering sides, extending laterally around the anterior margin of the meta-episternum. However, in the available species of Chirothrips and Arorathrips this sclerite is reduced to a pointed triangle, of varying size among species ( Fig. 15 ). In ah, atricorpus , and meridionalis the metathoracic pre-episternum is intermediate in condition, extending from the triangular base for a short distance ventro-laterally as a narrow, and irregularly sclerotised strip ( Figs 13, 14 ).

Each of the four species placed by Bhatti in Agrostothrips seems to retain one or more characters in a plesiotypic state. However, given the wide range of variation in the posterior margins of the sternites and tergites indicated here, and also the lack of consistency in other character states including antennal sensoria, there seems little support for placing these four species into a genus separate from Chirothrips . Thus, Agrostothrips is here placed into synonymy.

Generic diagnosis: Head variably prolonged in front of eyes, smaller than pronotum; usually with at least three pairs of ocellar setae, and four pairs of postocular setae; maxillary palps 3-segmented. Antennae 8- segmented; segment I without median dorsal apical setae; II usually projecting laterally; III–IV with sensorium simple, rarely forked. Pronotum trapezoidal, with two pairs of posteroangular setae. Mesonotum with median pair of setae situated medially, anterior campaniform sensilla present. Metanotum with two pairs of setae near anterior margin, campaniform sensilla present. Prosternal ferna divided medially; basantra rugose, triangular; prospinasternum transverse, narrow. Mesothoracic sternopleural sutures complete; meta pre-episternum reduced, not broadly band-like. Meso and metasternal furca without spinula. Forewings slender, first vein with long gap in setal row, two distal setae; second vein with four to five setae arranged irregularly; clavus with about four veinal and one discal setae. Tarsi 2-segmented. Abdominal terga without ctenidia; terga I–VIII with varied posteromarginal craspedum, VIII without comb; sterna without discal setae, craspeda present or absent; sterna II with two pairs of posteromarginal setae, III–VII with three pairs. Male generally similar to but smaller than female, usually micropterous, with sternal pore plates.

FIGURES 20–25. Chirothrips tergites. (20) manicatus V–VI [Victoria]. (21) aculeatus IV–V. (22) pretorianus III–IV. (23) meridionalis IV–V. (24) molestus III. (25) kurdistanus I–II.

Figures

FIGURES 1 – 6 Chirothrips species. (1) adults emerged from pupae within grass seeds. Chirothrips heads 2 – 6: (2) aculeatus; (3) africanus; (4) ah; (5) atricorpus; (6) meridionalis.

FIGURES 12 – 19. Chirothrips and Limothrips species. (12) Limothrips cerealium, meta pre-episternum arrowed. (13) C. meridionalis pteronota. (14) C. ah meta pre-episternum arrowed. (15) C. manicatus meta pre-episternum arrowed [Victoria]. Abdominal sternites: (16) C. meridionalis IV – V; (17) C. manicatus III – IV [A. C. T.]; (18) C. hamatus IV – V; (19) C. ah VI.