Selenothrips rubrocinctus (Giard, 1901)

Panchaetothripinae, Thripidae, Terebrantia, Thysanoptera

Figures

Fig. 1: 8-segmented antenna, segments III and IV with forked sense cone, terminal segments V-VIII
Fig. 2: Head dorsal with ocellar triangle
Fig. 3: Head and pronotum
Fig. 4: Meso- and metanotum
Fig. 5: Meso- and metasternum
Fig. 6: Fore- and hind wing, fore wing distal region
Fig. 7: Tergites VI and VII
Fig. 8: Sternites VI and VII
Fig. 9: Tergites VIII-XI
Fig. 10: Adults, male and female

Selenothrips rubrocinctus is a leaf-feeding thrips on cashew, cocoa, mango and many other plants. Both sexes fully winged. Body blackish brown; tarsi and apices of tibiae yellow; antennal segments brown except for III & V yellow in basal half, IV yellow at base and apex, VII & VIII grey; fore wings uniformly dark brown with black setae. Antennae 8-segmented; segments III & IV constricted into neck at base and apex, and with sense cone long and forked, sensorium on VI extending beyond antennal apex, III-V with long dorsal setae (Fig. 1). Head with transverse reticulation, cheeks sharply constricted to basal neck; 3 pairs of ocellar setae, pair III arise on anterior margins of ocellar triangle (Fig. 2). Pronotum with transverse lines of sculpture; no prominent posteroangular setae, but 1 pair of moderately long anteromarginal setae (Fig. 3). Mesonotum transverse reticulate; without median division. Metanotum with median triangle enclosing transverse lines of sculpture; with 1 pair of setae medially and 1 pair of campaniform sensilla (Fig. 4); metathoracic furca elongate and Y-shaped (Fig. 5). Mid and hind tarsi 1-segmented. Fore wing first vein close to or fused to costal vein; fore wing with long costal setae about twice as long as wing width medially; first and second vein with complete row of widely spaced setae; posteromarginal cilia undulated (Fig. 6). Tergites with lateral thirds reticulate; III-VIII with median setae longer than distance between their bases (Fig. 7); VIII with many discal microtrichia and a complete comb of long microtrichia (Fig. 9); tergite X without longitudinal division. Sternites with 3 pairs of long median setae (Fig. 8).
Male similar to female; sternites III-VII with small oval glandular area on antecostal ridge; tergite IX with 3 pairs of prominent stout and thorn-like setae (Fig. 10).

The genus Selenothrips Karny, 1911
There is only one species recognized in this genus. The area of origin of Selenothrips rubrocinctus is not clear, either Africa or South America, but is now found throughout the tropics. Typical features of this genus are long setae on antennal segments, and segments III and IV constricted apically and basally. Antennal segment III and IV each with a long forked sense cone. 2 rows of long dark stout veinal setae on the uniformly dark brown fore wings. Head constricted to a basal neck, but without a transverse ridge dorsally (Mound & Kibby 1998).

The heavily dark brown fore wings distinguish this species from most other panchaetothripinae. The genus Selenothrips is similar to the monobasic African genus Xestothrips, with dark fore wings too, but Xestothrips glabratus lacks strong sculpture on the head and pronotum, the occipital ridge on head is conspicuous, the fore wing first vein with the setal row widely interrupted on middle third, and the fore wing costal setae are always at most as long as wing width. Selenothrips rubrocinctus has a strongly sculptured head and pronotum, a indistinct occipital ridge on head, a complete row of evenly placed setae on both veins of the fore wings, and fore wing costal setae at middle of wing are up to twice as long as wing width medially. The shape of the head, legs, and anntennae gives indications of similarity with Caliothrips, but Selenothrips differs in the head constricted posteriorly, the transverse striated pronotum, and the abdominal microtrichia and complete comb on tergite VIII. Just as Selenothrips rubrocinctus, also Panchaetothrips noxius and Monilothrips kempi have fore wing costal setae up to twice as long as wing width, but both species differs by the distinct occipital ridge on head, the pronotum without strong sculpture, light brown fore wings with pale sub-base, the 2-segmented tarsi, and the absence of posteromarginal comb of microtrichia on tergite VIII. Furthermore, Monilothrips kempi has the surface of head not strongly reticulated except for occiptal collar on head, the pronotum with 2 pairs of elongated setae, and the metanotum without dominant or weakly sculptured triangle medially. In Panchaetothrips noxius the fore wing first vein setal row is incomplete and the second vein setal row is absent.

Life history
Selenothrips rubrocinctus is a slow moving insect requiring prodding to take a few steps across the leaf. The eggs inserted into the leaf tissue; hatching takes about 12-18 days. The larvae have three red-colored bands developed from internal pigmentation. Thus is the reason for the common name ´red-banded cacao thrips´. Larval period lasts 6-10 days and pupal period 3-6 days, so that incubation time from egg to adult can take 3-5 weeks dependent upon seasonal temperatures. Adults, larvae and pupae occur together on leaves (Hill 1983).

Host plants
Polyphagous, mainly on cacao, also on avocado, cashew, guava, mango, orange, pear.

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

Damage and symptoms
The damage is associated with older leaves, where the lower leaf surfaces are darkly stained, rusty in appearance, and with numerous small, shiny black spots of excreta; leaf edges are curled (Hill 1983).

Detection and control strategies
It is preyed upon by a large assortment of natural predators such as spiders and mites (Wasmannia auropunctata), lacewings (Chrysopidae), predatory thrips (Franklinothrips tenuicornis, Franklinothrips vespiformis), and predatory bugs (Termatophylidea maculata), especially minute pirate bugs (Orius thripoborus) (Chin & Brown 2008; Dennill 1992; McCallan 1943). The wasp parasite Goetheana shakespearei from the Gold Coast and Java attacks many species of thrips but its principle host is Selenothrips rubrocinctus, which it is able to control (Dohanian 1937).
Chemical controls are not always necessary for this thrips, as natural controls are apparently effective most of the time (Denmark & Wolfenbarger 1971).

Additional notes
This species is particularly common on weak or damaged host plants, taking advantage of nutritional abnormalities by feeding on the leaves. Populations increase particularly when plants are water stressed (Fennah 1965).

Biogeography

Widespread in tropical and subtropical countries. Cameroon, Congo, Ghana, Ivory Coast (Le Banco), Kenya (Coastal Province), Nigeria, Sierra Leone, South Africa (KwaZulu-Natal: Port Shepstone, Richards Bay; Mpumalanga: Nelspruit, White River, Brondal), Tanzania, Togo (Lomé), Uganda (Kampala).

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