INTERESTING INSECTS

By N A Martin (2017 revised 2018)

Banana silvering thrips, Banana thrips, Smilax thrips

Heliothrips bicinctus Bagnall, 1913

Heliothrips bifasciipennis Girault, 1926

The Banana silvering thrips, Hercinothrips bicinctus (Bagnal, 1919) is one of four species of the subfamily Panchaetothripinae in New Zealand. There are two other adventive species, Greenhouse thrips, Heliothrips haemorrhoidalis (Bouche, 1833), and Palm thrips, Parthenothrips dracaenae (Heeger, 1854) and one endemic species, Hangehange thrips, Sigmothrips aotearoana Ward, 1970. This subfamily is distinguished from other Thripidae by the dorsal surface of the head and prothorax being covered in reticulate sculpture. The maxillary palp is two segmented and the forewing has the first vein more or less fused to the costa. Another distinguishing feature of the four species in New Zealand is that they feed on mature or almost mature plant leaves.

This adventive species of thrips is widespread in New Zealand. It is found outdoors in many tropical and subtropical countries. It is found on native and adventive plants.

Conservation status: Widespread in the New Zealand on native and adventive plants in parks, gardens and native habitats. It may be regarded as a pest on some plants.

Life cycle of a plant feeding Terebrantia thrips. © Plant & Food Research Figure 8 from Crop & Food Research Infosheet No3-16. [Image: 2J2N]

Banana silvering thrips breed all year in Auckland, but are commonest in summer. They live mainly on the mature or almost mature leaves of their host plants as do the other three species of the subfamily Panchaetothripinae found in New Zealand.

Adults

Adults like the other active stages of Banana silvering thrips are relatively long and thin. The body is mainly brown and its surface is strongly sculptured and reticulate. The head has two antennae, two compound eyes and on the underside the mouth cone contains a pair of short maxillary stylets and a single stout mandible. The lateral margin of the head is relatively smooth. There are three pairs of brown legs and two pairs of wings that when not used for flying are held over the abdomen. The relatively narrow white forewings have two short dark bands. The tip of the abdomen contains the genitalia. There are males and females, though males are rare in greenhouses. The female also has an ovipositor for inserting eggs into leaves.

Eggs and larvae

Eggs are laid in either the upper or underside of the leaf depending on the plants species. A thin larva hatches from the egg. It is the shape of a tiny white wingless adult. Like the adult it has three pairs of legs, a pair of antennae and the same structures for feeding. There are two larval stages. Juvenile thrips, including prepupae and pupae go to the next stage by moulting. This involves the dorsal skin splitting and the next stage pulling itself out of the old skin. The second larva looks like the first larva and may become yellow-green coloured. The last two segments of the abdomen form a brownish cone with the anus at the tip. There are no setae (hairs) around the tip of the anus to help hold the faecal droplet. For this reason, the droplet frequently runs over the larva's body covering it with dark faecal matter.

Prepupa and Pupa

When the larva is fully grown it drops to the ground and hides in the litter or soil. Here it moults into the prepupa, the first of two non-feeding stages. The prepupa looks like a large larva with short wing buds. The tip of the abdomen has three pairs of spine-like setae, two pairs on segment 9 and one pair on segment 10. The prepupa moults into the pupa. The pupa has longer wing buds and the antennae are folded back over the head. It also has the six spines at the tip of the abdomen. It is assumed that the spines on the tip of the abdomen are used for defence. Both the prepupa and pupa can walk around.

Feeding and plant damage

Banana silvering thrips feed on mature or almost mature leaves rather than young rapidly expanding leaves. Larvae and adults use the stylets in their mouth cone to feed. They puncture plant cells with their single mandible and suck up the plant cell contents with their maxillary stylets. Their feeding kills the surface cells of the leaves creating distinctive pale areas of dead cells. The larvae carry a dark faecal droplet at the tip of the abdomen, that may run over the body or be flicked away at intervals.

Adult Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Night-scented Jessamine, Cestrum nocturnum (Solanaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J5K]

Adult Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Night-scented Jessamine, Cestrum nocturnum (Solanaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J5J]

Drawing of head of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) showing the reticulate body sculpture and the relatively smooth lateral edges of the head. © Drawing published in Fauna of New Zealand Number 1. Figure 8. [Image: 2J63]

Drawing of the forewing of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) showing the veins setae (hairs) and pigmentation. © Drawing published in Fauna of New Zealand Number 1. Figure 150. [Image: 2J62]

Ventral (under) side of the tip of the abdomen of a female Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): microscope slide preparation of the showing the toothed ovipositor that makes holes in leaves for eggs. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2JTK]

Dorsal (upper) side of the tip of the abdomen of a male Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): microscope slide preparation of the showing the genitalia. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2JTL]

First and second instar (stage) larvae of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Tecomanthe speciosa (Bignoniaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2J60]

First and second instar (stage) larvae of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Night-scented Jessamine, Cestrum nocturnum (Solanaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J5H]

First and second instar (stage) larvae of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Night-scented Jessamine, Cestrum nocturnum (Solanaceae): note the faecal material on the abdomen. Creator: Tim Holmes. © Plant & Food Research. [Image: 2J5F]

Second instar (stage) larvae of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Night-scented Jessamine, Cestrum nocturnum (Solanaceae): note the conical shape of the segments at the tip of the abdomen (black arrow). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J5I]

Microscope slide preparation of a larva of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): note the short conical terminal segments of the abdomen. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J67]

Dorsal (upper) side of the tip of the abdomen of a larva of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): microscope slide preparation of the tip of the abdomen showing the pigmentation and shape of the terminal segments, the lack of setae at the tip of the abdomen and the stigma (opening to breathing tube) on abdominal segment 8 (black arrow). Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J65]

Ventral (under) side of the tip of the abdomen of a larva of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): microscope slide preparation of the tip of the abdomen showing the pigmentation and shape of the terminal segments, the lack of setae at the tip of the abdomen. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J64]

Dorsal (upper) side of larva of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): microscope slide preparation with black arrows pointing to the stigmata (opening to breathing tubes) of the the thorax (left) and first abdominal segment (right). Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J66]

Prepupa of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Night-scented Jessamine, Cestrum nocturnum (Solanaceae): note the short wing buds. Creator: Tim Holmes. © Plant & Food Research. [Image: 2J5G]

Microscope slide preparation of a prepupa of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): note the short wing buds and spine-like setae at the tip of the abdomen. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J69]

Dorsal (upper) side of the middle part of a pupa of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): microscope slide preparation showing the wing bud with a row of about 22 setae (hairs) on the outer edge of the wing bud. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J68]

Dorsal (upper) side of the tip of the abdomen of a prepupa of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): microscope slide preparation showing the three pairs of spine-like setae on segment 9 and 10. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J6B]

Side view of the tip of the abdomen of a prepupa of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): microscope slide preparation showing the spine-like setae on segment 9 and 10. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J6A]

Banana silvering thrips are found on mature or almost mature leaves of host plants with typical thrips feeding damage. With the aid of a strong magnifying glass, they can be distinguished from the other three species in the subfamily Panchaetothripinae. The dorsal surface of the head and prothorax of adults of the New Zealand species in this subfamily is strongly sculptured and reticulate.

Adult Banana silvering thrips, Hercinothrips bicintus body is dark brown and it has narrow wings with dark and pale areas. The wings are similar to those of the Hangehange thrips, Sigmothrips aotearoana but different from Palm thrips, Parthenothrips dracaenae, that has broad wings. Adult Banana silvering thrips and Hangehange thrips are best distinguished by the shape of the head. The lateral margins of the head of the Hangehange thrips have prominent angular projections whereas the lateral margins of the banana silvering thrips head appear smooth. The Greenhouse thrips, Heliothrips haemorrhoidalis, has white bases to its wings and white legs, whereas the Hangehange thrips has brown legs.

Colonies of Banana silvering thrips can easily distinguished from colonies of two species of Panchaetothripinae. Only adults and larvae are present on leaves in colonies of Banana silvering thrips and Hangehange thrips, whereas colonies of Greenhouse thrips, Heliothrips haemorrhoidalis, and Palm thrips may have prepupae and pupae present as well as adults and larvae.

If adults are absent, colonies of Banana silvering thrips and Hangehange thrips can be distinguished if you have access to a binocular microscope. Look at the tip of the abdomen of the larvae. The Hangehange thrips larvae have long setae, but the banana silvering thrips larvae have no setae around the opening. This is the reason larvae are more likely to be covered by dark faecal matter. If the last two abdominal segments are visible, the terminal segment of the banana silvering thrips is almost conical whereas the segment in Hangehange thrips is almost as wide at the tip as it is at the base.

Adult Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Night-scented Jessamine, Cestrum nocturnum (Solanaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J5K]

Drawing of head of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) showing the reticulate body sculpture and the relatively smooth lateral edges of the head. © Drawing published in Fauna of New Zealand Number 1. Figure 8. [Image: 2J63]

Drawing of the forewing of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) showing the veins setae (hairs) and pigmentation. © Drawing published in Fauna of New Zealand Number 1. Figure 150. [Image: 2J62]

First and second instar (stage) larvae of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Tecomanthe speciosa (Bignoniaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2J61]

Second instar (stage) larvae of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae) on underside of a leaf of Night-scented Jessamine, Cestrum nocturnum (Solanaceae): note the conical shape of the segments at the tip of the abdomen (black arrow). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J5I]

Microscope slide preparation of a larva of Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae): note the short conical terminal segments of the abdomen. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J67]

Adult Hangehange thrips, Sigmothrips aotearoana (Thysanoptera: Thripidae) on upper side of a leaf of Hangehange, Geniostoma ligustrifolium (Loganiaceae): note the sharp lateral projections on the head (white arrow). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J3X]

Drawing of head of Hangehange thrips, Sigmothrips aotearoana (Thysanoptera: Thripidae) showing the reticulate body sculpture and the angular lateral edges of the head. © Drawing published in Fauna of New Zealand Number 1. Figure 9. [Image: 2J4R]

Drawing of the forewing of Hangehange thrips, Sigmothrips aotearoana (Thysanoptera: Thripidae) showing the veins setae (hairs) and pigmentation. © Drawing published in Fauna of New Zealand Number 1. Figure 153. [Image: 2J4Q]

First and second instar (stage) larvae of Hangehange thrips, Sigmothrips aotearoana (Thysanoptera: Thripidae) on upper side of a leaf of Hangehange, Geniostoma ligustrifolium (Loganiaceae): note the long anal setae in the faecal droplet of the thrips on the right. Creator: Tim Holmes. © Plant & Food Research. [Image: 2J40]

Microscope slide preparation of a larva of Hangehange thrips, Sigmothrips aotearoana (Thysanoptera: Thripidae): note long setae at the tip of the abdomen. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J4G]

Adult Palm thrips, Parthenothrips dracaenae (Thysanoptera: Thripidae) on the upper side of a leaf of Pigeonwood, Hedycarya arborea (Monimiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J2U]

Adult and prepupa of Palm thrips, Parthenothrips dracaenae (Thysanoptera: Thripidae) on leaf of Three Kings cabbage tree, Cordyline obtecta (Asparagaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J2R]

Larvae of Palm thrips, Parthenothrips dracaenae (Thysanoptera: Thripidae) on the upper side of a leaf of Pigeonwood, Hedycarya arborea (Monimiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2J2Y]

Pupa of Palm thrips, Parthenothrips dracaenae (Thysanoptera: Thripidae) on a leaf of Tecomanthe speciosa (Bignoniaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2J33]

Dorsal (upper) side of the tip of the abdomen of a larva of Palm thrips, Parthenothrips dracaenae (Thysanoptera: Thripidae): microscope slide preparation showing the setae (hairs) with expanded tips and the round stigma (opening to breathing tube) on abdominal segment 8 (black arrow). Creator: Nicholas A. Martin. © Landcare Research. [Image: 2J39]

Adult Greenhouse thrips, Heliothrips haemorrhoidalis (Thysanoptera: Thripidae) on the underside of a leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2JVH]

Larvae of Greenhouse thrips, Heliothrips haemorrhoidalis (Thysanoptera: Thripidae) on the underside of a leaf of Small-flowered mistletoe, Ileostylus micranthus (Loranthaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2JUV]

Adult and juvenile Greenhouse thrips, Heliothrips haemorrhoidalis (Thysanoptera: Thripidae) on the underside of a leaf of Puka, Meryta sinclairii (Araliaceae): note the colour of the larvae, prepupae and pupae. Creator: Tim Holmes. © Plant & Food Research. [Image: 2JUY]

Three pupae of Greenhouse thrips, Heliothrips haemorrhoidalis (Thysanoptera: Thripidae) on the underside of a leaf of Whau, Entelea arborescens (Malvaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2JUD]

Microscope slide preparation of a larva of Greenhouse thrips, Heliothrips haemorrhoidalis (Thysanoptera: Thripidae): note the short terminal segment of the abdomen and short anal setae (hairs). Creator: Nicholas A. Martin. © Landcare Research. [Image: 2JVK]

No natural enemies of the Banana silvering thrips have been recorded in New Zealand. It is probably eaten by spiders and insect predators. There may also be an egg parasitoid.

The Banana silvering thrips prepupae and pupae live in the litter or soil. They both have six spines-like setae at the tip of their abdomen. It is assumed that these spines are used for defence.

The Bananan silvering thrips feed on adventive, cultivated and native plants. They feed on mature or almost mature leaves of trees, shrubs and herbs. The adults and larvae may feed on either side of leaves. In a recent publication, it was reported that in New Zealand, it had been found on 52 species of plants, of which 15 were indigenous. It was the only one of the four species in the subfamily Panchaetothripinae in New Zealand to live on plants in the families Compositae, Convolvulaceae and Solanaceae.

Feeding and plant damage

Banana silvering thrips feed on mature or almost mature leaves rather than young rapidly expanding leaves. Larvae and adults use the stylets in their mouth cone to feed. They puncture plant cells with their single mandible and suck up the plant cell contents with their maxillary stylets. Their feeding kills the surface cells of the leaves creating distinctive pale areas of dead cells. The larvae do carry a dark faecal droplet at the tip of the abdomen, which at intervals runs down over their body. There are usually dried black faecal droplets on leaves where the thrips have been feeding.

Underside of a leaf of Coastal coprosma, Coprosma repens (Rubiaceae) with damage from feeding by Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae). © All rights reserved. [Image: 2SAS]

Upper side of a leaf of Coastal coprosma, Coprosma repens (Rubiaceae) with damage from feeding by Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae). © All rights reserved. [Image: 2SAT]

Underside of a leaf of Coastal coprosma, Coprosma repens (Rubiaceae) with feeding damage and larval Banana silvering thrips, Hercinothrips bicinctus (Thysanoptera: Thripidae). © All rights reserved. [Image: 2SAU]

Reproduction and Parthenogenisis in Thysanoptera

In Thysanoptera, females are diploid (2 sets of chromosomes) and males are haploid (one set of chromosomes). Males are produced from unfertilised eggs. This type of reproduction is called Arrhenotoky. The proportion of males to females in a population is variable. In Palm thrips this appears to be related to temperature. In a warm greenhouse (25-28°C) there are very few males, 6-7 per 100 females, while in a cooler greenhouse (18-20°C) there are more males. Where there are very few or no males, females can reproduce without fertilisation. This is called Thelotoky, form of parthenogenesis. In populations where there are very few males there are probably two types of female present, Arrhenotokous and Thelotokous.

Palm thrips is the first species from the Thysanoptera order that was found to be capable of thelytokous parthenogenetic reproduction. This characteristic is contained in the Latin name of the genus, Parthenothrips.

Lewis T. 1973. Thrips their biology, ecology and economic importance. Academic Press, London, UK. Pp. 1-349.

Martin NA. 2016. Distinguishing feature of immature stages of Panchaetothripinae (Thysanoptera: Thripidae) known in New Zealand. New Zealand Journal of Zoology 43 (4): 1-8.

Martin NA. 2017. Host plants of Panchaetothripinae (Thysanoptera: Terebrantia: Thripidae) in New Zealand. New Zealand Journal of Zoology 44 (1): 1-8.

Martin NA, Mound LA. 2004. Host plants for some New Zealand thrips (Thysanoptera: Terebrantia). New Zealand Entomologist. 27: 119-123.

Mound LA, Walker AK. 1982. Terebrantia (Insecta: Thysanoptera). Fauna of New Zealand. 1: 1-113.

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.

Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.

1 December 2018. NA Martin. Changed symbol used for apostrophes.

1 August 2018. NA Martin. Photos of damage to Coprosma repens added.