Frankliniella williamsi Hood, 1915

Thripinae, Thripidae, Terebrantia, Thysanoptera

Figures

Fig. 1: 8-segmented antenna, segments III and IV with forked sense cone, terminal segments VI-VIII
Fig. 2: Head dorsal with ocellar triangle
Fig. 3: Pronotum
Fig. 4: Meso- and metanotum
Fig. 5: Fore- and hind wing, fore wing distal region
Fig. 6: Meso- and metasternum
Fig. 7: Sternites II and III
Fig. 8: Sternite VII
Fig. 9: Tergite VIII with posteromarginal comb

Frankliniella williamsi breeds in the leaf axils of young plants of maize and other grasses. Both sexes fully winged; body color yellow, antennal segments VII & VIII and distal half of VI brown; fore wings pale. Antennae 8-segmented; segments III & IV with forked sense cone, segment VIII about twice the length of antennal segment VII (Fig. 1). Head wider than long; 3 pairs of ocellar setae present, pair III about as long as distance between hind ocelli and arising just within anterior margins of ocellar triangle; postocular setae pair I present, pair IV distinctly shorter than distance between hind ocelli (Fig. 2). Pronotum with 4-5 pairs of elongate setae (1 pair anteromarginally, 1 pair anteroangularly, 2 pairs posteroangularly and 1 pair of moderately elongate posteromarginal submedian setae) (Fig. 3). Metanotal median area transverse at anterior and with irregular equiangular or longitudinal reticulations on posterior half; median setae longer than lateral setae and arising at anterior margin; campaniform sensilla present (Fig. 4). Mesofurca with spinula (Fig. 6). Mid and hind tarsi 2-segmented. Fore wing with 2 complete rows of veinal setae (Fig. 5). Tergites V-VIII with paired ctenidia laterally, on VIII anterolateral to spiracle; posteromarginal comb on VIII with long and fine, closely spaced microtrichia on broadly triangular bases (Fig. 9). Sternites III-VII without discal setae, except sternite II with 1 or 2 long discal setae medially (Fig. 7); median setae of sternite VII arising at or close to posterior margin (Fig. 8).
Male similar to female but smaller; tergite VIII with complete comb of long slender microtrichia, IX with median pair of setae shorter than lateral pair; sternites III-VII with small oval glandular area, sternite II with 1 or 2 discal setae medially, sternite VII with toothed craspedum on posterior margin.

The genus Frankliniella Karny, 1910
This genus is mainly known from the New World and contains about 230 species, many of them from the Neotropics (Mound & Marullo 1996, Cavalleri & Mound 2012). Some species are widely known as crop pests - Frankliniella occidentalis, Frankliniella intonsa, Frankliniella schultzei (all of them vectors of tospoviruses) and Frankliniella williamsi. The members in this genus are sometimes quite difficult to separate from one another and the classification has been in flux with many species later synonymized in association with color variations. They mostly have 3 pairs of well developed ocellar setae, 8-segmented antennae with segments III and IV having forked sense cones, usually 4-5 pairs of elongate pronotal setae (1 pair anteromarginally, 1 pair anteroangularly, 2 pairs posteroangularly, and 1 pair of moderately elongate posteromarginal submedian setae S2 which are longer than median seta S1), metanotal median setae arising at anterior margin, when present wings with complete rows of setae on the wing veins, paired ctenidia laterally on tergites V-VIII with those on VIII anterolateral to the spiracles, no discal setae on sternites, and the males are generally smaller and paler than the females (Mound & Marullo 1996; Stannard 1968).

Compared to other members of the genus, Frankliniella williamsi has 1 or 2 median discal setae in addition to marginal setae on the sternite II (Frankliniella borinquen, Frankliniella occidentalis and Frankliniella schultzei without discal setae on sternite II), postocular setae IV distinctly shorter than distance between hind ocelli (in Frankliniella borinquen as well as Frankliniella schultzei the length of postocular setae IV are about as long as distance between hind ocelli; in Frankliniella occidentalis postocular setae IV longer), tergite VIII always with a complete comb of long and fine, uniform spaced microtrichia on broadly triangular bases (in Frankliniella borinquen and Frankliniella occidentalis the comb on tergite VIII is complete, but in Frankliniella borinquen with short microtrichia arising from triangular bases and in Frankliniella occidentalis with short or long microtrichia arising from triangular bases; in Frankliniella schultzei posteromarginal comb of microtrichia weakly developed or complete absent). Frankliniella williamsi as well as Frankliniella occidentalis and Frankliniella borinquen with ocellar setae III arising on anterior margin of or just within anterior margin of ocellar triangle, and campaniform sensilla on metanotum normally present (only Frankliniella schultzei with ocellar setae III arising very close together between anterior margins of hind ocelli, and without metanotal campaniform sensilla). Frankliniella williamsi as well as Frankliniella occidentalis and Frankliniella schultzei have a simple pedicel of antennal segment III, and an antennal segment VIII that is longer than segment VII (only Frankliniella borinquen has the pedicel of antennal segment III swollen, with edged ring surmounted by a distinctive swelling and a slightly flared collar, and antennal segment VIII equal in length to or shorter than segment VII). In Frankliniella williamsi and Frankliniella schultzei ocellar setae III on head are about as long as distance between hind ocelli (in Frankliniella occidentalis ocellar setae III are about as long as distance between external margins of hind ocelli; in Frankliniella borinquen as long as distance between midpoint of hind ocelli).
Species of the genus Frankliniella are similar to species of Thrips, Stenchaetothrips, Microcephalothrips abdominalis, Larothrips dentipes and Fulmekiola serrata, in having tergites V-VIII which bear a pair of ctenidia laterally, but in these species ctenidia of the tergite VIII arranged posteromedial to the spiracle, whereas species of Frankliniella have ctenidia on tergite VIII placed anterolateral to the spiracle.

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 one 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).The life-cycle from egg - adult at 24°C and 86% RH ranged from 23-28 days. Fecundity ranged from 58.3 - 64.9 eggs/female. Unmated females produced fewer eggs and offsprings were all male (Wechakit and Ketavan, 2010).

Host plants
Mainly Poaceae, also other crops and weeds.
Crops: babycorn, beans (French beans, peas), capsicum, cassava, chillies, coriander, maize, onion, red gam, rice, sorghum, wheat. soy bean, peanut and cotton.
Weeds: Bidens pilosa, Tithonia diversifolia.
This species was found to infest babycorn intercropped with French beans in Kenya (Nyasani et al. 2012).

Vector capacity
Maize chlorotic mottle virus. MCMV is the only species in the genus Machlomovirus (family Tombusviridae) and Frankliniella williamsi is one among the vectors of this disease. It transmits the disease in a non-persistent manner (Nelson et al. 2011).

Damage and symptoms
Feeding on young leaves results in streaks on the leaves of maize.

Detection and control strategies
-

Biogeography

Widespread in tropical and subtropical countries around the world: Asia, Australia, New Zealand, Central and South America, North America. Kenya and Uganda.

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