Thrips pusillus Bagnall, 1926

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 middle region
Fig. 6: Sternites VI and VII
Fig. 7: Tergites IV and V
Fig. 8: Tergites VIII and IX
Fig. 9: Tergite VIII posteromarginal comb and tergite IX

Thrips pusillus causes damage on coffee and lemon, maize and other poaceous crops, particularly in the flowers, banana fruits and other crops. Both sexes fully winged. Body and legs mainly yellow, major setae dark; tergites II-VIII with a brown median patch, IX & X usually dark; antennal segments I & II yellow, III basally yellow and distally brown, IV yellow only at base, remaining brown; fore wings weakly shaded. Antennae 7-segmented; segments III & IV slightly constricted at apex and with forked sense cone, VII short (Fig. 1). Head wider than long; with 2 pairs of ocellar setae, pair I absent, pair III small and arising usually just within or on anterior margins of ocellar triangle; postocular setae I & III of equal length, setae II minute (Fig. 2). Pronotum with 2 pairs of posteroangular setae; posterior margin with 3 pairs of setae; anterior margin with 3-4 pairs of setae (Fig. 3). Mesofurca with spinula. Metanotal sculpture lines converging to posterior margin, transverse and curving at anterior; median setae longer than lateral setae and arising behind anterior margin; campaniform sensilla absent (Fig. 4). Mid and hind tarsi 2-segmented. Fore wing first vein usually with 3 (or 2) setae on distal half; second vein with a complete row of about 15 setae; clavus with 5 marginal setae, clavus terminal seta longer than subterminal seta (Fig. 5). Tergite II with 3 or 4 lateral marginal setae; tergites V-VIII with ctenidia present laterally (Fig. 7), on VIII posteromedial to spiracles; posterior margin of VIII with complete comb of long and slender microtrichia (Fig. 8 and 9); pleurotergites without discal setae. Sternite II with 2 pairs of marginal setae, III-VII with 3 pairs, the median pair on VII arising in front of margin; sternal marginal setae about as long as a sternite; sternites without discal setae (Fig. 6).
Male similar to female 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 and 2009).

Thrips pusillus is very similar to some other Thrips species - like Thrips nigropilosus, Thrips palmi and Thrips tabaci. Thrips pusillus has sternites and pleurotergites without discal setae (Thrips acaciae, Thrips brevisetosus, Thrips florum, Thrips gowdeyi, Thrips hawaiiensis and Thrips simplex, all of them have 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).
Inside this group most of the species have no alternating short and long postocular setae (in Thrips nigropilosus present), no campaniform sensilla on metanotum (only in Thrips palmi present), metanotal median setae that are longer than lateral setae (except for Thrips tabaci with shorter median setae), 1-3 distal setae on fore wing first vein (only Thrips tabaci with 2-6, usually 4, distal setae), 3 lateral marginal setae on tergite II (only Thrips palmi with 4 marginal setae), median setae of tergites II-VIII no more than 0.3 as long as median tergite length (except for Thrips nigropilosus with median setal pair unusually long and at least half as long as median length of tergite), tergites with one or without sculptured lines between median pair of setae (compared to Thrips nigropilosus with two or more transverse lines of sculpture extending medially across the tergites), and pleurotergites without many rows of fine microtrichia (present in Thrips tabaci). Furthermore, only Thrips nigropilosus is one of few members of the genus Thrips that produce short-winged adults. Compared to other three species in this group, the body color of Thrips palmi is pale without any brown markings on tergites, whereas others often exhibit at least some brown shadings medially on tergites. Thrips pusillus as well as Thrips palmi have the metanotal median area sculptured lines transverse at anterior, but longitudinal and mostly parallel on posterior half (compared to Thrips tabaci and Thrips nigropilosus with metanotal sculptured lines transverse at anterior, but forming equiangular or irregular longitudinal and large reticulations on posterior half).
Species of the 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 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 approximately two months 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
Crops: African eggplant, amaranth, avocado, banana, chillies, coffee, green gram, guava, Java plum, kale, karela, khat, lemon, maize, baby corn, mango, mobydick (Asclepia sp.), mulberry, okra, oleander, onion, papaya, passion fruit, Persian lilac (Melia azedarach), potato, red gram, tea, tobacco, watermelon.
Weeds: Achyranthes aspera, Amaranthus sp., Bidens pilosa, Lantana camara, Leonotis nepetifolia, Nycandra physalodes, Ocimum sp., Plectranthus faccichis, Senna longiracemosa, Sesbania sesban, Sonchus oleraceae, Strophanthus gratus (climbing oleander), Tagetes minuta, Tithonia diversifolia, Vernonia lasiopus.

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

Damage and symptoms
Thrips pusillus breeding particularly in the flowers and causes fruit spotting. Small circular spots appear on the surface of fruit, which gradually anlarge and blacken into oily, water-soaked lesions, sometimes followed by skin splitting which allows entry of pathogens (El-Bashir & Al-Zabidi 1985). Thrips pusillus along with Frankliniella williamsi was observed as a key pest of baby corn in Kenya (Nyasani et al. 2012).

Detection and control strategies
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Biogeography

Africa, Yemen. Angola (Nova Sintra), Cameroon, Ghana (Aburi), Kenya, Mozambique, Nigeria (Ibadan), Sierra Leone, South Africa (KwaZulu-Natal), Swaziland, Tanzania, Uganda, Zimbabwe.

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