Thrips brevisetosus (Trybom, 1912)

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 and VI
Fig. 7: Tergites VI-VIII
Fig. 8: Tergites VIII and IX

Thrips brevisetosus causes damage on flowers of Black Jack (Bidens pilosa) and amaranth. Both sexes fully winged. Body color brown; tibiae and tarsi yellow; antennae brown with III paler; fore wings uniformly light brown or shaded. Antennae 7-segmented; segments III & IV slightly constricted at apex and with forked sense cone (Fig. 1). Head wider than long; with 2 pairs of ocellar setae, pair I absent, pair III small and anterolateral to ocellar triangle; postocular setae minute (Fig. 2). Pronotum midline with transverse faint striae; without elongate setae; posterior margin with 3-4 pairs of setae; anterior margin with 4-6 pairs of setae (Fig. 3). Mesofurca with spinula. Metanotum median area sculptured lines with mainly equiangular reticulation; median setae shorter than lateral setae and arising well behind anterior margin; campaniform sensilla present (Fig. 4). Mid and hind tarsi 2-segmented. Fore wing first vein with 3 setae on distal half; second vein with a complete row of about 9-13 setae; clavus with 5 marginal setae and 1 discal seta, clavus terminal seta longer than subterminal seta (Fig. 5). Tergite II with 3 lateral marginal setae; tergites V-VIII with ctenidia present laterally (Fig. 7), on VIII posteromedial to spiracles; tergite VIII posterior margin with complete comb of small and irregular microtrichia (Fig. 8); pleurotergites without discal setae. Sternite II with 2 pairs of short marginal setae, III-VII with 3 pairs, the median pair on VII arising in front of or near margin; sternite II with 2-3 discal setae, III-VII with short discal setae varying in number from 13-17 in irregular transverse rows (Fig. 6).
Male similar to female in structure, but smaller.

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 brevisetosus is very similar to some other Thrips species - like Thrips acaciae, Thrips florum, Thrips gowdeyi, Thrips hawaiiensis and Thrips simplex. Thrips brevisetosus has sternites III-VII with at least 1 pair of discal setae and pleurotergites without discal setae (Thrips australis, Thrips microchaetus, Thrips subnudula and Thrips tenellus, all of them have sternites III-VII with at least 1 pair of discal setae and pleurotergites with discal setae; Thrips orientalis and Thrips parvispinus with 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).
Thrips brevisetosus is one of a few species in the genus Thrips and the only species inside this group that lacks 2 pairs of elongate pronotal posteroangular setae. Inside this group almost all species have the ocellar setae III on head arising on anterior margin of, or in front of, ocellar triangle, and the fore wing first vein with less than 5, mostly 3, setae on distal half (only Thrips simplex with ocellar setae III arising within ocellar triangle anterior to tangent of anterior margin of hind ocelli, and fore wing first vein with 6-10 setae on distal half), and most of them exhibit campaniform sensilla on metanotum (except for Thrips gowdeyi and Thrips simplex without metanotal campaniform sensilla). In Thrips brevisetosus as well as Thrips acaciae, Thrips gowdeyi and Thrips simplex the metanotal median setae arise behind anterior margin (in Thrips florum and Thrips hawaiiensis median setae arise at anterior margin). Like Thrips acaciae, the species has 7-segmented antennae (in Thrips gowdeyi and Thrips simplex antennae are 8-segmented; in Thrips florum and Thrips hawaiiensis antennae are 7- or 8-segmented), and a mainly equiangular reticulation on metanotal median area. Whereas in other species the metanotal median area exhibit transverse sculptured lines at anterior, but longitudinal or equiangular reticulations on posterior half (Thrips gowdeyi and Thrips simplex), longitudinal and parallel sculptured lines on posterior half (Thrips florum), or longitudinal and parallel sculptured lines or equiangular reticulations on posterior half (Thrips hawaiiensis). Furthermore, Thrips brevisetosus have pleurotergites not covered in microtrichia (like in Thrips florum and Thrips hawaiiensis; in Thrips acaciae, Thrips gowdeyi and Thrips simplex pleurotergites are covered in rows of fine microtrichia, situated on widely spaced lines of 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 placed on tergite VIII posteromedial to the spiracle, and all species have no ocellar setae I. 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 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
Amaranth, and weeds like Bidens pilosa (Black Jack), Leonotis nepetifolia, Senecio mannii, Tithonia diversifolia.

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

Damage and symptoms
-

Detection and control strategies
-

Biogeography

Africa. Cameroon, Congo (Lubero), Kenya, Uganda, Zambia.

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