Linear sedge shield bug - Rhopalimorpha (Rhopalimorpha) lineolaris

By N A Martin (2017)

Caption:

Classification

Phylum

Arthropoda

Class

Insecta

Order

Hemiptera

Family

Acanthosomatidae

Scientific name

Rhopalimorpha (Rhopalimorpha) lineolaris Pendergrast, 1950

Common names

Linear sedge shield bug

Biostatus and distribution

This endemic shield bug is present in the North and South Islands of New Zealand. The Linear sedge shield bugs are mainly found in on sedges and some grasses in open areas and in forests. They feed on the leaves, stems and seeds of these plants.

Conservation status: The Linear sedge shield bug is widespread in areas where sedges grow.

Life stages and annual cycle

Linear sedge shield bug overwinter as adults that shelter between leaves at the base of plants such as sedges and in detritus at the base of such plants. In spring they mate and lay eggs. There is a single generation per year. Nymphs are present in summer and new season adults appear in mid to late summer.

Adults are 7.5-9 mm long and about 2.5 times as long as wide. The body is coloured shades of brown with a central strong white line extending from behind the head to the tip of the scutellum. The dorsal surface of the head, thorax (middle part of the body) and the non-membranous part of the forewings is covered in small dark punctures. The antennae and the three pairs of legs are reddish brown. The long rostrum that holds the stylets used for feeding, is held between the legs when not used for feeding. Also on the underside is an abdominal spine that projects forward between the last pair of legs. When they mate the male and female are back to back with the male attached to the underside of the female.

The female lays batches of almost spherical eggs on green fruit or leaves of host plants. An egg batch typically has eight eggs, one for each ovariole. The surface of the egg is finely sculptured. A female lays several batches. The egg shell splits down the side during hatching.

The first instar (stage) nymphs stay by the eggs. They look like tiny wingless adults. The head and thorax are dark brown with a central pale line. The area around the scent glands is dark brown. There is a pair of pale grey-brown areas on the first abdominal segments. There are five nymphal instars. Nymphs go from one stage to the next by moulting, where the "skin" on the dorsal side splits and the next stage pulls itself out. The later nymphal instars are more darkly pigmented on the abdomen. The central while line extends from the thorax to the abdomen. There is also a pair of white lateral bands on the abdomen. The lateral edges of the mesonotum and metanotum (2nd & 3rd thoracic segments) are white. The antennae are pale brown with a mainly black terminal segment. The legs are pale brown. On the fourth and fifth instar nymphs wing buds can be seen. The wing buds on the fifth instar extend onto the abdomen.

A New Zealand entomologist, JG Pendergrast developed a method for rearing this insect. His 1952 paper reports that the developmental time from egg to adult is about 56 days: egg 7-9 days, 1st instar 8-10, 2nd instar 8-10, 3rd instar 9-10, 4th instar 9-12, 5th instar 10-18.

Walking and flying

The nymphs and adults have six legs (three pairs) that are used for walking. The adults have two pairs of wings. The front pair is modified as covers for the hind wings.

Feeding

Like other Hemiptera, the Linear sedge shield bug has sucking mouth parts. The long stylets, special shaped rods, are held in the rostrum. The Linear sedge shield bugs feed on plants. They feed on leaves and seeds of sedges and some grasses. During feeding the stylets are inserted into the plant. The mandibles hold the rostrum in place. The maxillae are inserted into the plant. They form two tubes, a narrow duct down which saliva is pumped into the plant, and a larger tube up which the partly digested food is sucked.

Drawing of an adult Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Des Helmore. © Drawing published in Fauna of New Zealand volume 35, figure 6. [Image: 2MK5]

Adult Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJZ]

Adult Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJL]

Underside of a male adult Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MK0]

Underside of a female adult Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJM]

A mating pair of Linear sedge shield bugs, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MK3]

Underside of a mating pair of Linear sedge shield bugs, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MK2]

Eggs of Linear sedge shield bugs, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae): note the faint ring at one end of each egg. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJN]

Eggs of Linear sedge shield bugs, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJR]

First instar nymphs of Linear sedge shield bugs, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae) by their egg shells. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJS]

Third instar nymphs of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae) on leaves of Giant umbrella sedge, Cyperus ustulatus (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJP]

Fourth instar nymph of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae) on a leaf of Giant umbrella sedge, Cyperus ustulatus (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJX]

Third instar nymph of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJY]

Fifth instar nymph of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJW]

Fifth instar nymph of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJQ]

Underside of a fifth instar nymph of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJV]

Fifth instar nymph of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae) on a seed head of Niggerhead, Carex secta (Cyperaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJT]

Recognition

Both the adults and nymphs of the Linear sedge shield bug and the Obscure sedge shield bug, Rhopalimorpha (Rhopalimorpha) obscurus are similar in appearance, but live individuals can be identified.

Adults

Adults of both species are about 7.5-9.5 mm long. The Linear sedge shield bugs are about 2.5 times as long as wide, while the adult Obscure sedge shield bugs are narrower, about 3 times as long as wide. They are similarly coloured. The best distinguishing character is the width of the central white line on the mesonotum and scutellum. It is wider and whiter in the Linear sedge shield bug. Whereas black punctures almost cover all of the line on the Obscure sedge shield bug.

Nymphs

While the nymphs of Linear sedge shield bug are covered in a fine pubescence, it is not easy to see on live insects. The best character is the pair of dark brown oval areas on the third abdominal segment. They are rounded on their inner edge and have a pale spot near their lateral edge.

The nymphs of Obscure sedge shield bugs lack the pubescence. The dark brown oval areas on the third abdominal segment are invaginated on the inner margin and they lack the pale spot laterally.

Drawing of an adult Obscure sedge shield bug, Rhopalimorpha (Rhopalimorpha) obscura (Hemiptera: Acanthosomatidae). Creator: Des Helmore. © Drawing published in Fauna of New Zealand volume 35, figure 5. [Image: 2MLD]

Adult Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJZ]

A mating pair of Linear sedge shield bugs, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MK3]

Adult Obscure sedge shield bug, Rhopalimorpha (Rhopalimorpha) obscura (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2ML4]

A mating pair of Obscure sedge shield bugs, Rhopalimorpha (Rhopalimorpha) obscura (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MKA]

Drawing of a fifth instar nymph of the Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae): note the clear spot in the dark oval area on the 3rd abdominal segment (arrow). Creator: Des Helmore. © Drawing published in Fauna of New Zealand volume 35, figure 23. [Image: 2MK4]

Drawing of a fifth instar nymph of the Obscure sedge shield bug, Rhopalimorpha (Rhopalimorpha) obscura (Hemiptera: Acanthosomatidae): note the pale invagination internal edge of the dark oval area on the 3rd abdominal segment (arrow). Creator: Des Helmore. © Drawing published in Fauna of New Zealand volume 35, figure 22. [Image: 2MLC]

Fifth instar nymph of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJU]

Fifth instar nymph of Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MJW]

Fifth instar nymph of Obscure sedge shield bug, Rhopalimorpha (Rhopalimorpha) obscura (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MKX]

Fifth instar nymph of Obscure sedge shield bug, Rhopalimorpha (Rhopalimorpha) obscura (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MKD]

Natural enemies

Three natural enemies of the Linear sedge shield bug are known.

Parasitoid

The egg parasite, Trissolcus maori Johnson, 1991 (Hymenoptera: Platygasteridae) is known on this shield bug and two other shield bugs in the family Acanthosomatidae.

Predators

Two birds have been recorded feeding on this shield bug. There may also be eaten by other birds and by predatory insects.

Table: Natural enemies of Forest shield bug, *Oncacontias vittatus* (Hemiptera: Acanthosomatidae), from Plant-SyNZ database (26 October 2017). The reliability index shows the quality of evidence for the host association (0-10, 10=high quality).
Scientific Name	Common Name	Classification	Enemy Type	Reliability Index	Biostatus
Trissolcus maori Johnson, 1991	(Wasp)	Hymenoptera: Platygasteridae	parasitoid	10	endemic
Gymnorhina tibicens (Latham, 1801)	Magpie (Bird)	Passeriformes: Cracticidae	omnivore	10	adventive
Sturnus vulgaris Linnaeus, 1758	Starling (Bird)	Passeriformes: Sturnidae	omnivore	10	adventive

Host plants

The adults and nymphs feed on the developing seeds and leaves of sedges and some grasses. Adults will also feed on ripe seeds, especially during winter.

Feeding

Like other Hemiptera, the Linear sedge shield bug has sucking mouth parts. The long stylets, special shaped rods, are held in the rostrum. During feeding the stylets are inserted into the plant. The mandibles hold the rostrum in place. The maxillae are inserted into the plant. They form two tubes, a narrow duct down which saliva is pumped into the plant, and a larger tube up which the partly digested food is sucked.

Table: Host plants of the Linear sedge shield bug, *Rhopalimorpha lineolaris* (Hemiptera: Acanthosomatidae) from Plant-SyNZ database (10 November 2017). The reliability score shows the quality of evidence for the host association (1-10, 10=high).
Common Name(s)	Scientific Name	Family	Reliability Index	Biostatus
Bent grass, Browntop, Browntop bent	Agrostis capillaris L.	Gramineae	6	naturalised
Meadow foxtail	Alopecurus pratensis L.	Gramineae	6	naturalised
Grey sedge	Carex divulsa Stokes	Cyperaceae	10	naturalised
Australian sedge, Bergalia tussock	Carex longebrachiata Boeckeler	Cyperaceae	10	naturalised
Niggerhead, Makura, Mārū, Mātā, Mātātā, Pūkio, Pūrei, Pūreirei, Pūrekireki	Carex secta Boott	Cyperaceae	10	endemic
Swamp sedge	Carex virgata Sol. ex Boott	Cyperaceae	10	endemic
Snow tussock, Snow grass	Chionochloa sp.	Gramineae	5	endemic
Umbrella sedge, Puketangata	Cyperus eragrostis Lam.	Cyperaceae	10	naturalised
Coastal cutty grass, Cyperus, Giant umbrella sedge, Toetoe, Toetoe upokotangata, Toetoe whatu-manu, Toetoe whatu-pākau, Upokotangata	Cyperus ustulatus A.Rich.	Cyperaceae	10	endemic
Cocksfoot	Dactylis glomerata L.	Gramineae	10	naturalised
Fescue tussock, Hard tussock	Festuca novae-zelandiae (Hack.) Cockayne	Gramineae	6	endemic
Knobby clubrush, knotted sedge, Leafless sedge, Turf rush, Wīwī	Ficinia nodosa (Rottb.) Goetgh., Muasya & D.A.Simpson	Cyperaceae	10	indigenous, non-endemic
Cutty grass, Tarangarara, Tarangārara, Tatangi, Toetoe kiwi, Toetoe mātā, Toetoe ngaungau, Toetoe tara-ngārara	Gahnia lacera (A.R. Rich.) Steud.	Cyperaceae	10	endemic
Yorkshire fog	Holcus lanatus L.	Gramineae	9	naturalised
Common rush, Leafless rush, Soft rush	Juncus effusus L	Juncaceae	10	naturalised

Information sources

Lariviere M-C. 1995. Cydnidae, Acanthosomatidae, and Pentatomidae (insecta: Heteroptera): systematics, geographical distribution, and bioecology. Fauna of New Zealand. 35: 1-107.

Lariviere M-C, Larochelle A. 2004. Heteroptera (Insecta: Hemiptera): catalogue. Fauna of New Zealand. 50: 1-330.

Pendergrast JG. 1952. Studies on the biology of pentatomid bugs of the genus Rhopalimorpha Dallas (Heteroptera). Transactions of the Royal Society of New Zealand 80(2): 143-153.

Pendergrast JG. 1960. Nymphs of the genus Rhopalimorpha Dallas (Hemiptera, Acanthosomidae). Transactions of the Royal Society of New Zealand 88(1): 141-147.

Acknowledgements

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

Other images

Underside of a male adult Linear sedge shield bug, Rhopalimorpha (Rhopalimorpha) lineolaris (Hemiptera: Acanthosomatidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MK0]

INTERESTING INSECTS

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