Thrips acaciae Trybom, 1910

Thripinae, Thripidae, Terebrantia, Thysanoptera

Figures

Fig. 1: 7-segmented antenna, segments III and IV with forked sense cone, terminal segments VI and 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: Meso- and metasternum
Fig. 7: Sternites V and VI
Fig. 8: Tergites VI and VII
Fig. 9: Tergites VIII and IX
Fig. 10: Tergites IX-XI

Thrips acaciae causes damage particularly on flowers of Acacia, coffee, Diospyros sp. (ebony), mango, sweet potato and fabaceous forage plants. Both sexes fully winged. Body color brown; fore tibiae and tarsi yellow; antennal segments I & II brown, III mainly yellow, IV & V yellow at base, VI & VII brown; fore wings brown shaded with base paler. 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 arising on anterior margin or outside of ocellar triangle (Fig. 2). Pronotum with many transverse sculpture lines not closely spaced; about 40 discal setae; 2 pairs of moderately elongate posteroangular setae (about 0.3 as long as pronotum); posterior margin with 4-5 pairs of setae; anterior margin with 4-6 pairs of setae (Fig. 3). Metanotum median area sculptured lines with mainly equiangular reticulation, medially with longitudinal row of large slightly elongate reticles; median setae longer than lateral setae and arising behind anterior margin; campaniform sensilla present (Fig. 4). Mesofurca with spinula (Fig. 6). Mid and hind tarsi 2-segmented. Fore wing first vein with 2-5 (mostly 3) setae on distal half; second vein with a complete row of about 9-13 setae; clavus with 5-8 marginal setae and 1 discal seta, clavus terminal seta longer than subterminal seta (Fig. 5). Tergite II with 4 lateral marginal setae; tergites V-VIII with ctenidia present laterally (Fig. 8), on VIII posteromedial to spiracles; tergite VIII posterior margin with weak but complete comb of small and irregular microtrichia (Fig. 9 and 10); pleurotergites without discal setae, but with weakly dentate or slender microtrichia on widely spaced lines of reticulation. Sternite II with 2 pairs of marginal setae; III-VII with 3 pairs of marginal setae (Fig. 7), the median pair on VII arising in front of posterior margin; sternite II with 2-3 discal setae, III-VII with 14-24 short discal setae in two irregular rows.
Male similar to female in structure, but smaller and paler; tergite VIII with no marginal comb; tergite IX with transverse row of 4 equally-spaced setae medially; sternites III-VII with transverse glandular area anterior to row of discal setae.

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 acaciae is very similar to some other Thrips species - like Thrips brevisetosus, Thrips florum, Thrips gowdeyi, Thrips hawaiiensis and Thrips simplex. Thrips acaciae 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).
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). Most of them exhibit campaniform sensilla on metanotum (except for Thrips gowdeyi and Thrips simplex without metanotal campaniform sensilla), and 2 pairs of elongate pronotal posteroangular setae (except for Thrips brevisetosus without elongate pronotal setae). In Thrips acaciae as well as Thrips brevisetosus, 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). As Thrips brevisetosus, the species have always 7-segmented antennae (in Thrips gowdeyi and Thrips simplex antennae are always 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), always 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 acaciae possesses rows of fine microtrichia on pleurotergites, situated on widely spaced lines of reticulation (as in Thrips gowdeyi and Thrips simplex; in Thrips brevisetosus, Thrips florum and Thrips hawaiiensis these rows of microtrichia are absent). Outside this group, also Thrips tabaci and Thrips subnudula have pleurotergites covered with rows of fine microtrichia.
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 on tergite VIII lie 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 species of Thrips, and 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
Polyphagous.
Crops: Acacia sp., African spiderplant, coffee, Diospyros sp. (ebony), maize, mango, sweet potato.
Weeds: Ajuga remota, Aspilia pluriseta, Bothriocline longipes, Crotalaria pycnostachya, Erlangea calycina, Galinsoga parviflora, Indigofera hilaris, Lantana camara, Lantana trifolia, Lessertia brachystachya, Senecio diversifolius, Tagetes minuta, Vernonia lasiopus.

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

Damage and symptoms
-

Detection and control strategies
-

Biogeography

Africa. Botswana (Kalahari, Kooa Pan), Cameroon, Congo (Rutshuru), Kenya, Namibia (Kalahari), South Africa (Gauteng: Pretoria; Limpopo: Limpopo: Zebediela Estates, Mokopane, Satara - Kruger National Park; North West: Rietspruit - Marico district; KwaZulu-Natal: Mtubatuba, Amatikulu, Dukuduku Forest, Richards Bay; Cape Provinces), Sudan, Tanzania (Rufigi River), Uganda (Kampala, Morogoro, Mpumumpu, Rubaja).

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