Frankliniella occidentalis (Pergande, 1895)

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 wing and fore wing distal region
Fig. 6: Tergite VIII with posteromarginal comb and tergite IX
Fig. 7: Tergite VIII, lateral region with stigma and ctenidia
Fig. 8: Tergites IX and X
Fig. 9 and 10: Female feeding on a bean leaf (Phaseolus vulgaris)

Frankliniella occidentalis breeds on a wide range of plants, in flowers and on leaves, and causes serious crop losses both through feeding damage and as an important vector of tospoviruses. Both sexes fully winged; body color variable from yellow to brown, but widespread pest strain usually mainly dark yellow with brown areas medially on each tergite; antennal segments II & VI-VIII brown, III-V yellow with apices variably brown; legs mainly yellow washed with brown; fore wings pale with dark setae. Antennae 8-segmented; segments III & IV with forked sense cone, segment VIII longer, about 1.5 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 external margins of hind ocelli and arising on or just within anterior margins of ocellar triangle; postocular setae pair I present, pair IV longer 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). Mesofurca with spinula. 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). Mid and hind tarsi 2-segmented. Fore wing with 2 complete rows of veinal setae (Fig. 5). Tergites V-VIII with paired ctenidia laterally, ctenidia sometimes weakly developed on IV, on VIII anterolateral to spiracle (Fig. 7); posteromarginal comb on VIII complete, with short to moderately long microtrichia arising from triangular bases (Fig. 8). Sternites III-VII without discal setae; median setae of sternite VII arising at or close to posterior margin.
Male similar to female but smaller and paler; tergite VIII without marginal comb; IX with median pair of dorsal setae shorter than lateral pair; sternites III-VII with transverse glandular area.
Second instar larva white, antennae weakly shaded, tergite IX not with shaded transverse band extending just anterior to major setae; tergites with transverse rows of small, weakly developed, linear plaques, dorsal setae all blunt; tergite IX campaniform sensilla wide apart, almost anterior to setae S2, posterior margin with complete row of well-developed teeth.

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).

Frankliniella occidentalis is very similar to Frankliniella borinquen with differences in the shape of pedicel of antennal segment III (Frankliniella borinquen has a pedicel swollen, with edged ring surmounted by a distinctive swelling and a slightly flared collar; Frankliniella occidentalis as well as Frankliniella schultzei and Frankliniella williamsi with a simple pedicel), and length of terminal antennal segment (Frankliniella borinquen with antennal segment VIII equal in length to or shorter than segment VII; other three species with antennal segment VIII longer than segment VII). In Frankliniella occidentalis, ocellar setae III on head are about as long as distance between external margins of hind ocelli and in Frankliniella borinquen as long as distance between midpoints of hind ocelli, whereas in Frankliniella schultzei and Frankliniella williamsi they are about as long as 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 are longer and in Frankliniella williamsi distinctly shorter than distance between hind ocelli). In Frankliniella occidentalis, Frankliniella borinquen and Frankliniella williamsi ocellar setae III arising on anterior margins of or just within anterior margins 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). As in Frankliniella borinquen, females of Frankliniella occidentalis with a complete posteromarginal comb of short microtrichia arising from triangular bases on tergite VIII (but in Frankliniella occidentalis microtrichia short or long). In constrast, Frankliniella williamsi tergite VIII with posteromarginal comb of long and fine, closely spaced microtrichia on broadly triangular bases, and Frankliniella schultzei comb weakly developed or absent. Compared to Frankliniella williamsi which has 1 or 2 median discal setae in addition to marginal setae on sternite II, other species of Frankliniella possess sternite II without median discal setae.
Species of Frankliniella are similar to species of Thrips, Stenchaetothrips, Microcephalothrips abdominalis, Larothrips dentipes and Fulmekiola serrata, in having tergites V-VIII with pairs 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 anterolateral to the spiracle.

Life history
Dependent on temperature, life cycle from egg to adult can range from 15 (30°C) to 44 (15°C) days, and adults can live for 28 to 71 days. The number of eggs that an adult thrips can lay range from 24 to 96 and there can be 12-15 generations in constant warm temperatures such as in greenhouses (OEPP/EPPO 1989). Different diets have effects on the oviposition rate (Kumm & Moritz 2010; Steinbach et al. 2012). Male killing bacteria, like Wolbachia were not detected in Wester Flower Thrips (WFT) (Kumm & Moritz 2008).

Host plants
Polyphagous, feeds on all plant parts i.e., flowers, fruit, seeds, stems and leaves of numerous plant material such as vegetables, fruits, potted flowering plants and nursery stock.
Crops: African nightshade, amaranth, babycorn, beans (broad bean, common bean, French bean, hyacinth bean, Lima bean), beet root, broccoli, cabbage, capsicum, cassava, chillies, courgettes, cucurbit, dolichos, eggplant,export flowers (Ornithogalum arabicum, Eryngium sp., Lupinus sp., Gomphocarpus semilunatus (mobydic)), kale, leek, maize, onion, papaya, peas, potato, pumpkin, squash, red gram, thorn apple, tomato, wild sunflower, wheat.
Weeds: Achyranthes aspera, Ajuga remota, Bidens pilosa, Chenopodium sp., Conyza bonariensis, Crotolaria sp., Datura suaveolens, Erlangea calycina, Galinsoga parviflora, Nycandra physalodes, Senna didymobotrya, Sonchus oleraceus, Tagetes minuta, Tithonia diversifolia.
Feeding and oviposition preference experiments with Frankliniella occidentalis indicated that Cucurbita pepo and G. parviflora may serve as potential sources of WFT outbreaks within French bean fields of Kenya (Nyasani et al. 2012b).

Vector capacity
Tomato spotted wilt virus (TSWV)
In East Africa Frankliniella occidentalis vector Tomato Spotted Wilt Virus on tomato and cucurbits (Wangai et al. 2001; Ramkat et al. 2006; Ramkat et al. 2008).
Impatiens necrotic spot virus (INSV)
Groundnut ringspot virus (GRSV)
Tomato chlorotic spot virus (TCSV)
Chrysanthemum stem necrosis virus (CSNV)
Also known to transmit Fusarium moniliforme (a fungus that causes ear rot of corn) and Erwinia amylovora (fire blight bacteria).

Damage and symptoms
Deformation of young seedlings and fruit and discoloration, silvering and bleaching of leaves, flowers and fruit. Fruits scarred very early in development causing disfigurement as fruit expands.

Detection and control strategies
Frankliniella occidentalis are attracted to both yellow and blue sticky traps, which could be used for effective monitoring of their dynamics in the field. They are also attracted to semiochemicals such as the aggregation pheromone (Hamilton et al 2005) and the flower based kairomones (Teulon et al 2007; Muvea, 2011).
Intercropping French bean with baby corn/ Irish Potato/ Sunflower at ratio of 1: 4 reduced the incidence of thrips and enhanced the marketable yield by nearly 50% (Nyasani et al. 2012a).
The biological agent Amblyseius swirkii (Acari: Phytoseiidae) have been used to control Frankliniella occidentalis on sweet pepper in Turkey (Kutuk et al. 2011). Other natural enemies used for their management include Neoseiulus cucumeris (=Amblyseius cucumeris), Amblyseius degenerans, Hypoaspis miles and Hypoaspis aculeifer (Acari: Laelapidae), the minute pirate bug Orius insidiosus (Hemiptera: Anthocoridae), the entomopathogenic or insect-killing nematode Steinernema feltiae (Nematoda: Steinernematidae), and the entomopathogenic fungus Beauveria bassina (Cloyd 2009). Metarhizium. anisopliae isolate ICIPE 69 was found to be effective against both the larvae and adults of Frankliniella occidentalis (Niassy et al. 2012b). This fungus is compatible with imidacloprid or thiamethoxam (Niassy et al. 2012c). Metarhizium anisopliae isolate ICIPE 69 developed for thrips management, is fully registered and already commercialized in Ghana under the name of Campaign®, and is being registered in several other African countries (Mozambique, Ethiopia, Kenya and South Africa) (Ekesi et al. 2011). A semiochemical-baited autoinoculation device treated with Metarhizium anisopliae for control of Frankliniella occidentalis on French bean is currently under development (Niassy et al. 2012a).

Biogeography

Originally from the South Western States of the USA, the western flower thrips is now widespread around the world. It has become established in areas with a Mediterranean climate, but in colder areas it is found in greenhouses. It is not a pest in the lowlands of the wet tropics, although it is sometimes abundant at high elevations in such countries, including Kenya and Malaya. In Africa the pest is reported from Kenya, Tanzania, Egypt, Algeria, Tunisia, South Africa (Gauteng: Krugersdorp; Limpopo: Letsitele; Western Cape) Zimbabwe, Uganda and Reunion islands.

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