Hercinothrips bicinctus (Bagnall, 1919)

Panchaetothripinae, Thripidae, Terebrantia, Thysanoptera

Figures

Fig. 1: 8-segmented antenna, segments III and IV with forked sense cone and segment V, terminal segments V-VIII
Fig. 2: Head dorsal with ocellar triangle
Fig. 3: Head and pronotum
Fig. 4: Meso- and metanotum
Fig. 5: Fore wing and fore wing distal region
Fig. 6: Tergites II and III
Fig. 7: Tergites III-VI
Fig. 8: Tergites VIII and IX
Fig. 9: Tergites IX-XI

Hercinothrips bicinctus causes leaf and fruit damage to a range of crops, including bananas. Both sexes fully winged. Body brown; head yellow sub-medially, also abdominal segments 9 and 10; tarsi and tibiae, antennal segments I and III-VIII yellow; fore wings pale, lightly shaded at base, with 2 short dark brown transverse bands, extensive pale area medially distinctly longer than the pale apex of wing. Antennae 8-segmented; segments III and IV with sense cone forked and extending well beyond apex of segment, VIII more than twice as long as VII (Fig. 1). Head finely reticulate, with cheeks convex, sharply constricted to basal neck (Fig. 2). Pronotum finely reticulate; with several pairs of moderately long discal setae (Fig. 3). Mesonotum not divided medially. Metanotum with weakly defined reticulate triangular area medially; median setae long (Fig. 4); 1 pair of campaniform sensilla present; metafurca elongate and Y-shaped. Mid and hind tarsi 2-segmented. Fore wing first vein close or fused to costal vein; fore wing with complete row of setae on both longitudinal veins; costal cilia longer than setae, posteromarginal cilia wavy (Fig. 5). Tergites reticulate; median tergal setae minute (Fig. 6 and 7); lateral fourth of tergites I-VIII with a posterolateral comb of short wedge-like teeth which are produced into long needles on VIII (Fig. 8); tergite X with longitudinal split almost complete (Fig. 9).
Male lighter than female; with 3 pairs of spine-like setae on tergite IX; sternites III-VII with very small circular glandular area.

The genus Hercinothrips Bagnall, 1932
About 10 species recognised in this genus, all originally from Africa, a few are recorded as crop pests and are now widespread around the world. They can be distinguished from each other by differences in the color pattern of the body and the fore wings (Wilson 1975). Unlike the species of most Panchaetothripinae genera, the members of Hercinothrips have 2-segmented tarsi, and both veins of the fore wings bear complete rows of long setae. All of them have 8 antennal segments, antennal segments III and IV with forked sense cone, fore wings banded and with posterior fringe undulated.

The species is similar to Hercinothrips femoralis which has antennal segments VI-VIII dark brown, fore wings with a short submedian pale area, when present, no longer than the pale apex of wing, no triangular area medially on metanotum. Whereas Hercinothrips bicinctus possesses antennal segments VI-VIII yellow, fore wings with an extensive pale area medially distinctly longer than the pale apex of wing, and a weakly defined reticulate triangular area medially on metanotum.
Unlike the species of most Panchaetothripinae genera, members of Hercinothrips have 2-segmented tarsi (like in Monilothrips kempi and Panchaetothrips noxius), and complete rows of long setae on both veins of the fore wing (like in Monilothrips kempi and Selenothrips rubrocinctus). Monilothrips kempi differs from species of Hercinothrips in having no reticulate sculpture on head and pronotum except for the collar, no constriction posteriorly on head, but having 2 pairs of elongated pronotal setae and a distinct occipital ridge. Compared to Hercinothrips, Panchaetothrips noxius has a distinct occipital ridge and a pronotum without strong sculpture, the fore wing first vein setal row is incomplete, the second setal row is absent, costal setae on fore wing are about twice as long as wing width, all fore wing setae dark, comb of microtrichia on tergite VIII absent, and tergite X elongate and tubular. In contrast to Hercinothrips, Selenothrips rubrocinctus has a pronotum with transverse striate sculpture, a dominant sculptured triangle medially on metanotum, uniformly dark brown fore wings, costal setae on fore wing which are about twice as long as wing width, and a complete comb of microtrichia on tergite VIII.

Life history
As with other thrips species the life cycle from egg to adult is dependent on temperature. The tiny eggs are laid just into the plant tissue. The larvae hatch after 7 or 8 days and the larval stages lasts about 10 days after which the second larvae and propupae move down into the soil to pupate. Adults emerge after a further 7 to 10 days Pinese & Piper 1994).

Host plants
Crops: African nightshade, banana, eggplant, potato.
Weeds: Acanthospermum hispidum.

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

Damage and symptoms
Feeding by these thrips causes silver speckling of green fruit (hence the common name of the insect), particularly on green bananas (Faure 1957). Silvery or brown patches covered with small black spots found on the fruits. The skin of severely infested fruit may crack, and this allows secondary rots to attack the fruit (Hill 1983). The adults and larvae feed also on mature leaves, and the pupae are found on leaves.

Detection and control strategies
Clean cultivation with effective management of weeds such as Acanthospermum hispidum which can harbour Banana thrips could reduce their incidence. Appropriate bunch treatment at the time of bunch pruning with botanicals such as pyrethrum and neem or covering of bunch are useful.

Biogeography

Pantropical, widespread in the Old World tropics from Africa, Australia, New Zealand, Europe (originally from Africa and established in the tropics and subtropics where greenhouse plants are grown). Kenya, South Africa (KwaZulu-Natal: Richards Bay, Eshowe, Durban, Ifafa Beach, Port Shepstone; Eastern Cape: Somerset East, Port St. Johns; Western Cape: Knysna, Mossel Bay, Hermanus, Cape Town, Cape Peninsula), St. Helena, Uganda.

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