Retithrips syriacus (Mayet, 1890)

Panchaetothripinae, Thripidae, Terebrantia, Thysanoptera

Figures

Fig. 1: 8-segmented antenna, segments III and IV with forked sense cone and segment V
Fig. 2: Head dorsal with ocellar triangle
Fig. 3: Head ventral with sclerotised ommatidia and fore tentorial arms
Fig. 4: Pronotum
Fig. 5: Meso- and metanotum
Fig. 6: Meso- and metasternum
Fig. 7: Fore wing and fore wing basal region
Fig. 8: Tergites II-VII
Fig. 9: Tergites I-V
Fig. 10: Tergites V-IX
Fig. 11: Tergites VII-X

Retithrips syriacus breeds on and damages the leaves of a wide range of plants, including castor beans, cassava, cotton, grapes, and persimmon. Both sexes fully winged. Body shape distinctive, with pterothorax unusually broad. Body dark brown; tarsi yellow; antennal segments III & IV basally pale, distally yellowish brown, segment V almost white; fore wings grey with brown swellings. Antennae 8-segmented, but segments VI-VIII sometimes without dividing sutures; III & IV each with forked sense cone that lacks basal stem and arises in large pit (Fig. 1). Head wider than long; ocelli on conical projection: posteromedian area reticulate, sculptured reticles with internal markings (Fig. 2). Compound eyes ventrally with 6 dark pigmented facets (Fig. 3). Pronotum exceptionally short (Fig. 4). Mesonotum without longitudinal division. Metanotal reticulate triangle broad, with 1 pair of setae near posterior (Fig. 5); metafurca elongate and Y-shaped (Fig. 6). Mid and hind tarsi 1-segmented. Fore wing broad, with 3 swellings along costal margin; fore wing first vein close to or fused to costal vein; costa without cilia; posteromarginal cilia straight (Fig. 7). Tergites II-X with median reticulated groove; 1 pair of large median setae on II-VIII, arising on sides of median reticulated groove (Fig. 8 and 9); VIII with complete posteromarginal comb of long strong microtrichia (Fig. 10); tergite X with median depression V-shaped, and small setae; sternal marginal setae small (Fig. 11).
Male similar to female; sternites III-VIII each with a large transverse glandular area.

The genus Retithrips Marchal, 1910
2 species are included in this genus. One of these, Retithrips syriacus, is polyphagous and widespread in the tropics, and is sometimes considered a minor pest. Both species have unique thrips characters. The genus is described as having a wide body with heavy reticulate sculpture, antennae are thick and 8-segmented with forked sense cones on segments III and IV and with the segments appearing connected and without sutures. The fore wings are wide with a few veinal setae on the first vein, and near the costal margin of the fore wing there are 3 evenly distributed swellings (Mound & Marullo 1996).

Retithrips syriacus is a distinct species and differs from other Panchaetothripinae due to the fore wings bearing anteromarginally 3 curious blister-like callosities, the exceptionally broad pterothorax and abdomen, and the minute setae on tergite X. It is closely related to Phibalothrips peringueyi and Rhipiphorothrips miemsae. With all of them it agrees in having minute costal setae and no cilia on anterior margin of fore wings, straight no undulated cilia on posterior margin of fore wings, uniformly pale or light brown fore wings, and a dominant or weakly sculptured triangle medially on metanotum. Compared to both other species, Retithrips syriacus has polygonal reticles on head and pronotum with distinct internal wrinkles (other species without internal wrinkles), the shape of the metothoracic furca is elongate and Y-shaped (other species with V-shaped metathoracic furca), and a complete posteromarginal comb of microtrichia on tergite VIII (others without or comb only laterally). Unlike Phibalothrips peringueyi, Rhipiphorothrips miemsae and Retithrips syriacus have 8-segmented antennae with forked sense cone on segments III & IV, whereas Phibalothrips peringueyi has 7-segmented antennae with simple sense cone on segments III & IV. Compared to both other species only Phibalothrips peringueyi has a distinctive tergal sculpture forming a series of hair clamp-like arches on the antecostal ridges. Only Rhipiphorothrips miemsae bears a strong irregular reticulate and rugose sculpture on the head and pronotum, and has a complete longitudinal division medially on mesonotum.

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 to over a month and adults may live for more than one month producing several generations in one year depending on seasonal weather (Lewis 1973). With greenhouse temperatures the developmental time from egg to adult can decrease to about one week.

Host plants
Polyphagous.
Crops: avocado, cassava, castor beans, coffee, cotton, Eucalyptus spp., grapes, mango, persimmon, rose, walnut, Pomegranate.

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

Damage and symptoms
This species is generally found feeding on the leaves of its host plants. Heavy infestation results in the leaves getting almost completely bleached, filled with excreta and presenting a sickly appearance and finally drying up (Ananthakrishnan 1971).

Detection and control strategies
The eggs are parasitized by Megaphragma priesneri (Hymenoptera: Trichogrammatidae) and the later stages by Thripobius hirticornis (Hymenoptera: Eulophidae) (Priesner 1964).
The anthocorids Orius albidipennis and Orius niger are found to predate on Retithrips syriacus (Falamarzi et al. 2009).

Biogeography

Pantropical, Asia, Central and South America, Europe, North America, Africa. Congo, Egypt (Cairo), Ghana, Kenya, Libya, Malawi, Morocco, Mozambique, Nigeria, Senegal (Fété Olé), Somalia, South Africa (Gauteng: Pretoria), Sudan, Tanzania, Togo (Cacaveli), Uganda. It has also been recently reported in Tunisia (Elimem et al. 2011).

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