Chirothrips pretorianus Hood, 1953

Thripinae, Thripidae, Terebrantia, Thysanoptera

Figures

Fig. 1: 8-segmented antenna, segments II-V (III and IV with simple sense cone), terminal segments V-VIII
Fig. 2: Head ventral with anterior tentorial arms
Fig. 3: Head dorsal with ocellar triangle
Fig. 4: Trapezoidal pronotum
Fig. 5: Prothoracic sternite region
Fig. 6: Meso- and metanotum
Fig. 7: Meso- and metasternum
Fig. 8: Pro,- meso- and metanotum, male (micropterous)
Fig. 9: Fore- and hind wing, fore wing distal region
Fig. 10: Sternites VI and VII
Fig. 11: Tergites VI-VIII
Fig. 12: Tergites VIII-XI

Chirothrips pretorianus damages forage grasses and other Poaceae like sorghum and maize. Female macropterous; body, antennae and legs brown, tarsi paler; fore wings light brown and weakly shaded. Antennae 8-segmented; segment II asymmetric with prolonged external margin bearing a apical sens-area, III & IV with stout simple sense cone (Fig. 1). Head small and prolonged in front of eyes; with 3 pairs of ocellar setae, pair III anterolateral to fore ocellus (Fig. 2 and 3). Pronotum trapezoidal; with 2 pairs of elongate posteroangular setae (Fig. 4 and 5). Meso- and metafurca with well-developed lateral flanges, but without median spinula (Fig. 7). Metanotum irregularly reticulate; median pair of setae shorter than lateral pair and arise behind anterior margin; campaniform sensilla present (Fig. 6 and 8). Mid and hind tarsi 2-segmented; fore tibia not prolonged around fore tarsus. Fore wing pointed at apex; first vein with 2 or 3 setae on distal half; second vein with 5 or 6 setae (Fig. 9). Tergites with weak lines of sculpture medially; posterior margins with a series of independent small, triangular lobes; ovipositor moderately developed and bearing rows of teeth (Fig. 11 and 12). Sternites with 3 pairs of marginal setae, median pair on VII arise in front of margin; posterior margins without craspedum (Fig. 10).
Male micropterous (Fig. 8) and similar to female; sternites III-V with small circular glandular area.

The genus Chirothrips Haliday, 1836
Chirothrips currently includes about 45 to 50 species worldwide. Zur Strassen (1960) provided an identification key and catalogue of this genus for over 50 species, and Bhatti (1990) created six new genera for these species originally placed in the genus Chirothrips, and one of these, Arorathrips, is discussed in comparison to Chirothrips. Chirothrips appears to be a genus of Holarctic species, whereas Arorathrips is from the New World with a typical reduced mesothoracic endofurca. This genus has consistent characters that include small heads, short antennae with 8 segments, antennal segment II mostly expanded laterally (except in this key for Chirothrips guillarmodi), and a trapezoidal pronotum with 2 pairs of long posteroangular setae.

The species can be distinguished from other species of the genus Chirothrips by antennal segment II which is asymmetric with prolonged external margin bearing a apical sense area. Whereas Chirothrips manicatus as well as Chirothrips frontalis have a asymmetric antennal segment II with prolonged external margin bearing an exactly terminal small seta at tip, Chirothrips ah has a very slender and acute, slightly hook-shaped projection of the second antennal segment which bears a small sensorium at its apex, in Chirothrips guillarmodi antennal segment II is symmetric, and in Chirothrips meridionalis it is not strongly produced on outer margin, but drawn out into a sharply pointed angle. Compared to other species, in Chirothrips pretorianus the tergites have a craspedum with a series of independent small, triangular lobes (tergites of Chirothrips manicatus bearing a continuous craspedum with margin of weakly and rounded lobes; Chirothrips frontalis with a complete craspedum of unbroken border or flange at the posterior margin; Chirothrips ah and Chirothrips meridionalis with broadly rounded independent lobes fused at bases into continuous craspedum; Chirothrips guillarmodi with closely approximated but independent elongate lobes). Chirothrips pretorianus as well as Chirothrips frontalis with no sternal craspedum, whereas Chirothrips manicatus with sternites with entire posterior margin and a series of distinctive tubercles, Chirothrips ah and Chirothrips meridionalis with a craspedum of independent small pointed lobes, and Chirothrips guillarmodi with closely approximated but independent elongate lobes. Chirothrips pretorianus and most of Chirothrips species ocellar setae III arranged anterolateral to fore ocellus, and metanotal median setae are shorter than the lateral pair and arising behind anterior margin (except for Chirothrips ah with ocellar setae III on anterior margins of ocellar triangle and median metanotal setae which are distinctly longer than lateral metanotal setae and arising at anterior margin; Chirothrips guillarmodi and Chirothrips meridionalis with metanotal median setae arising at anterior margin). Moreover, the species have tergites II-VIII discal campaniform sensilla situated in front of the discal setae S1 but somewhat farther apart than the setae (as well as Chirothrips manicatus and Chirothrips frontalis). Chirothrips ah, Chirothrips guillarmodi and Chirothrips meridionalis have tergites II-VIII discal campaniform sensilla that placed between the discal setae S1 and S2 or posteriorly.
Species of the genus Chirothrips are similar to Arorathrips mexicanus, but Arorathrips mexicanus has a greatly reduced mesothoracic furca (furcal pits widely separated), fore tibia prolonged at apex around the external margin of the first fore tarsal segment, and tergites II-V with transverse row of small tubercles along antecostal ridge. Whereas all species of the genus Chirothrips have furcal pits on mesosternum fused in the middle line, fore tibia not prolonged around fore tarsal segment, and the sculpture of antecostal ridge on tergites II-V is more or less elongated. Compared to described species of Chirothrips, Arorathrips mexicanus has the sternite VII median posteromarginal setae arising at margin, whereas in species of Chirothrips these setae arise in front of posterior margin.

Life history
As with other thrips species the life cycle from egg to adult is dependent on temperature. The full cycle can take less than a week 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).

Host plants
Poaceae: forage grasses, maize, sorghum.

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

Damage and symptoms
All species in this genus Chirothrips breeding in grass flowers, sometimes their larvae and especially pupae are transported around the world within commercial grass seed.

Detection and control strategies
-

Additional notes
The precise host-plant on which this species breeds is not clear, but like all members of the genus Chirothrips the females lay eggs in the young flowers of certain grasses. Each larva apparently feeds within, and subsequently pupates within a single floret.

Biogeography

East, South and South West Africa. Botswana (Tuli Block area), Kenya, Lesotho (Mamathes), Mozambique (Umbeluzi - southwest of Maputo, Machava - near Maputo), South Africa (Gauteng: Pretoria - 4500 ft., Kameeldrif, Silverton, Pretoria Salt Pan; Limpopo: Ratomba - 21 miles east of Louis Trichardt 3150 ft., Pietersburg - 4100 ft., Mokopane - 4500 ft., Zebediela - 3400 ft., Modimolle - 4600 ft., Bela Bela, Satara - Kruger National Park; Mpumalanga: Nelspruit - 2350 ft., Komatipoort - Baberton District 1000 ft., Sabie - Pilgrim's Rest District 4500 ft., Lydenburg - 5000 ft., Loskop Dam, Bethal - 5600 ft.; North West: Buffelspoort - near Rustenburg 4000 ft., Rietspruit - Marico district 3500 ft.; Free State: Heilbron - 5100 ft., Bethlehem - 5300 ft., Bloemfontein - 4500 ft.; Western Cape: Longridge - north of Plettenberg Bay, Heidelberg - 300 ft., Ceres - in the Michelľs Pass 1000 ft., Worcester - 790 ft., Kleinmond, Smitswinkel Bay, Witteberge - 2100 m; Northern Cape: Kgalagadi Transfrontier National Park; Eastern Cape: Kidds Beach, Grahamstown - 1700 ft., Balfour - west of Seymour 2100 ft., Coldstream), Uganda, Kenya (Embu), Zimbabwe (Chegutu, Mutare, Birchenough Bridge - 1500 ft., Lutope Pools - on Bubye River).

Bhatti JS (1990). On some genera related to Chirothrips (Insecta: Terebrantia: Thripidae). Zoology (Journal of Pure and Applied Zoology). 2 (4): 193-200

Hood JD (1953). Two new species of Chirothrips new to Africa (Thysanoptera, Thripidae). Revue de Zoologie et Botanique Africaines. 47 (1-2): 108-119

Lewis T (1973). Thrips: their biology, ecology and economic importance. Academic Press Inc., London Ltd., 349 pp

Minaei K & Mound LA (2010). Grass-flower thrips of the genus Chirothrips (Thysanoptera: Thripidae), with a key to species from Iran. Zootaxa. 2411: 33-43

Nakahara S & Footit RG (2012). Review of Chirothrips and related genera (Thysanoptera: Thripidae) of the Americas, with descriptions of one new genus and four new species. Zootaxa 3251: 1-29

zur Strassen R (1958). Studies in African Thysanoptera, 1. Journal of the Entomological Society of Southern Africa. 21 (2): 333-353

zur Strassen R (1959). Studies in African Thysanoptera, 2. Journal of the Entomological Society of Southern Africa. 22 (1): 174-198

zur Strassen R (1960). Key to and catalogue of the known species of Chirothrips Haliday, 1836 (Thysanoptera: Thripidae). Journal of the Entomological Society of Southern Africa. 23 (1): 144-176

zur Strassen R (1960). Catalogue of the known species of South African Thysanoptera. Journal of the Entomological Society of Southern Africa. 23 (2): 321-367

zur Strassen R (1967). Studies on the genus Chirothrips Haliday (Thysanoptera: Thripidae) with description of new species. Journal of the Entomological Society of Southern Africa. 29: 23-43