FNZ 10 - Tubulifera (Insecta: Thysanoptera) - Morphological and Diagnostic Characters
Mound, LA; Walker, AK 1986. Tubulifera (Insecta: Thysanoptera). Fauna of New Zealand 10, 144 pages.
(
ISSN 0111-5383 (print),
;
ISBN 0-477-06784-0 (print),
).
Published 22 Sep 1986
ZooBank: http://zoobank.org/References/0C947CDE-29D0-411A-8AB1-E16C06255989
Morphological and Diagnostic Characters
Heming (1970a, b, 1971, 1972, 1975, 1978, 1980) has discussed many aspects of thrips morphology and functional anatomy, and Priesner (1965) produced an extended introductory account of this subject. The following notes are intended simply as a guide to those structural features of Phlaeothripidae which are referred to in the descriptions and keys given below.
Morphological features of the adult are illustrated and labelled in Figure 1; the immature stages are illustrated in Figures 2-6.
Head
Although typically compressed dorsoventrally, the head in Tubulifera is sometimes considerably deeper than in Terebrantia. This can result in considerable changes in apparent shape due to coverslip pressure on specimens mounted for study on microscope slides. The head varies from more than twice as long as wide to slightly wider than long. The anterior margin is sometimes prolonged in front of the compound eyes, and in a few species bears one or more pairs of stout setae. The compound eyes are usually rounded and well developed, but are sometimes reduced to a few facets, or prolonged ventrally, or even greatly enlarged, such that the head is holoptic. Most species have a single pair of major postocular setae, and a pair of major postocellar setae may also be present; further major setae may be developed laterally on the cheeks. Three dorsal ocelli are present in macropterae, but frequently these are reduced or absent in micropterae and apterae.
Ventrally the mouth cone varies from very long and pointed, reaching across the mesosternum, to short and rounded. Differences in the shape of the mouth cone in dorsal view are due in part to whether it is directed ventrally or posteriorly. The right mandible is not developed, although the left one is long and stout. The paired maxillary stylets have complex, coadapted apices and fit together to form a feeding tube, but this varies considerably in length and thickness. In Idolothripinae, which ingest whole fungal spores, the maxillary stylets are 5-10 µm in diameter, whereas in Phlaeothripinae they are more slender, 2-3 µm. In Sophiothrips the stylets are exceptionally short and restricted to the mouth cone, whereas in many species the stylets extend deeply into the head, often as far as the compound eyes. In many Phlaeothripidae a pair of elongate, dark structures is visible lateral to the maxillary stylets; these are referred to as the maxillary guides, and in Haplothrips are clearly joined anteriorly by a maxillary bridge. The antennae usually have eight segments, but several unrelated species have the terminal segments VII and VIII fused to give a seven-segmented condition. Segments III-VIII usually have one or more emergent, pale trichomes as well as a number of setae.
Thorax
In most Phlaeothripidae three sclerites are visible dorsally on the prothorax: the large pronotum, and two small epimeral sclerites posterolaterally. In a few species the epimeral sutures are not developed. Typically there are five pairs of major pronotal setae - anteromarginals (am), anteroangulars (aa), midlaterals (ml), epimerals (ep), and posteroangulars (pa); in addition, some species have a pair of posteromarginals developed medially.
Ventrally on the prothorax there is usually a pair of weakly developed sclerites just behind the mouth cone, the praepectus (or praepectal plates), which should not be confused with the smaller cervical sclerites. Behind the praepectus are a pair of probasisternal sclerites and a small median sclerite, the spinasternum. Behind this is a transverse, often boat-shaped sclerite, the mesopraesternum, just in front of the mesoeusternal border. In many species there is a pair of longitudinal sutures laterally on the metasternum, the metathoracic sternopleural sutures, which extend posteriorly from the mesothoracic coxal cavities.
Dorsally the structure of the mesonotum and metanotum depends on the degree of wing development. Macropterae have the mesonotum rhomboid, often with a pair of major setae laterally, and the metanotum elongate with one or more pairs of median setae. In apterae both these sclerites may be reduced and transverse.
Legs
The fore tarsi are always one-segmented. The inner margin is often more or less drawn out into a small or large tooth, particularly in males, and ventrally the apex of the segment is prolonged into a claw-like hook, or hamus. The fore femora are often swollen, particularly in large males, and on the inner margin near the base there appears to be in all species a small, trichobothrium-like sense organ. The middle and hind tarsi may be of one or two segments, and the hind tibiae are often elongate, with one or more long setae on the external margin.
Wings
In Tubulifera the wings are completely different in structure from those of Terebrantia. The fringing wing-cilia, although similar in general appearance, are probably not homologous, because unlike the socketed, seta-like cilia of Terebrantia they are solid, microtrichia-like extensions of the wing membrane itself. On the posterior margin of the forewing, distally, a few of the cilia are frequently duplicated. No wing veins are developed (cf. Terebrantia), and the only setae are two to four sub-basal setae on the forewing. Moreover, when closed the wings lie flat over each other on the abdomen.
In fully winged individuals (macropterae) the wings extend to the apex of the abdomen. However, short-winged or wingless individuals (micropterae and apterae) are common in many species, and the wing morphs are often not completely distinct from each other. A few species have the wings progressively reduced, giving rise to hemimacropterae. More frequently wingless individuals may have a small wing bud present, and even bearing a seta, despite the absence of axillary sclerites. For these reasons the distinction between apterae and micropterae is sometimes arbitrary.
Abdomen
When referring to tergal and sternal setae the median pair is designated B1 the submedian pair B2 the next pair B3 etc.
The abdomen comprises nine visible segments plus the tube (segment X). The first segment is reduced to a small sclerite dorsally, the pelta, which is often more or less bell-shaped but is sometimes reduced and rarely transverse. Tergites II-VII frequently bear one or two pairs of curved or sigmoid wing-retaining setae. These vary in size and shape, and in a few species are broadly expanded rather than acute. Individuals with reduced wings may have the wing-retaining setae reduced or absent. Tergite VIII bears a pair of spiracles laterally, and tergite IX bears three pairs of elongate posteromarginal setae, of which B2, is often short and stout in male Phlaeothripinae.
Ventrally the sternites bear a variable number of small discal setae and usually three pairs of posteromarginal setae. In males, sternite VIII frequently has a glandular area medially which is variable in size and shape between species. A few species (e.g., of Plectrothrips, Hoplothrips) when viewed by phase-contrast microscopy have curiously iridescent reticulate areas on the median sternites; these too may be glandular in function.
The tube varies greatly in shape; it may be almost conical, or short and parallel-sided, or very long and tubular. Apically a series of setae arises in a circle around the anus, but only a few species have any setae well developed laterally on the tube. Males have the base of the tube, ventrally, emarginate where the aedeagal complex is evaginated. The structure of the male genitalia is discussed by Heming (1970b), but few species other than those related to Haplothrips have the aedeagus developed into a distinctive, elongate structure which can be used to distinguish between species. The female ovipositor is an eversible, chute-like structure derived from the hind margin of sternite VIII (Heming 1970a).