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Swan plant seed bug - Arocatus rusticus

By N A Martin (2017)

Classification

Phylum:
Arthropoda
Class:
Insecta
Order:
Hemiptera
Family:
Lygaeidae
Subfamily:
Lygaeinae
Scientific Name:
Arocatus rusticus (Stal, 1867)
  • Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Plant & Food Research
    Fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Plant & Food Research
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Common Names

Swan plant seed bug, Common Small Milkweed Bug, Parsonsia seed bug
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Synonyms

Tetralaccus rusticus Stal, 1867
Astacops caligatus Walker, 1872
Lygaeus subjectus Walker, 1872
Lygaeus singularis Walker, 1872
Lygaeus ruficoliliss Walker, 1872
Arocatus rusticus Stal, 1874

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Biostatus and Distribution

This adventive lygaeid bug from Australia is found throughout New Zealand on swan plant, Gomphocarpus species, and other plants in the family Apocynaceae including New Zealand jasmine, Parsonsia species. It occurs.

Conservation status: Widespread in gardens, parks and waste places and in native ecosystems on New Zealand jasmine, Parsonsia species.

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Life Stages and Annual Cycle

This bug from the Eastern part of Australia has one generation per year. Swan plant seed bugs over-winter as adults and have been found hiding under tree bark and in houses. Adults are most commonly found from November to March. Nymphs have been found from February to April, but may also be present in May when teneral (newly moulted) adults were found. Eggs are presumably laid in December and January.

Adults are found on young shoots, especially those with flowers and fruit. They are reddish-orange and black, and covered with fine grey down-like setae. Front part of the thorax, behind the head, is red and the underlying colour of the solid area of the forewings is red. The underlying colour of the underside is orange-red, but most of the head and thorax is covered with a grey ‘down’. The end of the abdomen has a pair of black spots on fourth and fifth segments. They have long black antennae that point forwards, a black, backward pointing rostrum that holds the feeding stylets and three pairs of black legs. The female has an ovipositor at the tip of the abdomen for inserting eggs into host plants.

Eggs are assumed to be laid into plant stems and seed pods of host plants. Nymphs hatch from the eggs. There are five nymphal stages, each is called an instar. Nymphs go from one stage to the next by moulting (changing their skin). During moulting, the skin on the dorsal side splits and the next stage pulls itself out of the old skin. The nymphs are like small adults, but without wings. The fifth instar nymph has a red body and like the adult has a black head, antennae, rostrum and legs. It also has black dorsal (top) side of the thorax and wing buds. Earlier instars have smaller wing buds. The fifth instar nymph is also covered in fine down-like setae, but it is not as obvious as it is on the adults. Adults emerge from fifth instar nymphs.

Walking and flying
Nymphs and adults have three pairs of legs. Adults have two pairs of wings, the front chitinised pair cover the membranous hind wings when not being used for flying. Most of the forewing is opaque orange-red and black, the rest is membranous and black.

Feeding
Like other Hemiptera, the Swan plant seed bug has piercing and sucking mouth parts. The long stylets, special shaped rods, are held in the rostrum. When it wishes to feed the bug moves the tip of the rostrum to a suitable part of the plant. The stylets are then gradually pushed into the plant. The inner two stylets (maxillae) form two tubes, one through which saliva is injected into the plant and a second through which plant juices are sucked up into the insect. Swan plant seed bug feeding has not been studied. They probably use their saliva to digest the plant cells in stems, leaves, fruit and seeds of host plants.

  • Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
    Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Side view of an adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Side view of an adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Plant & Food Research
    Fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Plant & Food Research
  • Underside of fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Underside of fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Side view of fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Side view of fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Top view of fourth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Nicholas A. Martin © Crop & Food Research
    Top view of fourth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Nicholas A. Martin © Crop & Food Research
  • Silhouette of a fourth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) showing the long rostrum stretching from the head down between the base of its legs.  Image: Nicholas A. Martin © Crop & Food Research
    Silhouette of a fourth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) showing the long rostrum stretching from the head down between the base of its legs. Image: Nicholas A. Martin © Crop & Food Research
  • Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) on a swan plant fruit.  Image: Nicholas A. Martin © Crop & Food Research
    Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) on a swan plant fruit. Image: Nicholas A. Martin © Crop & Food Research
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Recognition

The Swan plant seed bug is the only lygaeid in New Zealand that breeds on plants in the family Apocynaceae. The adults and nymphs are distinctively coloured in red and black. The adults also appear to be partly covered in a grey down.

  • Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
    Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Side view of an adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Side view of an adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Side view of fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Side view of fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Underside of fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Underside of fifth instar nymph of Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
  • Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) on a swan plant fruit.  Image: Nicholas A. Martin © Crop & Food Research
    Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) on a swan plant fruit. Image: Nicholas A. Martin © Crop & Food Research
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Natural Enemies

No natural enemies of the Swan plant seed bug are known in New Zealand. They may be caught by birds, spiders and predatory insects. In Australia Swan plant seed bugs are parasitised by a tachinid fly.

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Host Plants

The Swan plant seed bug lives on plants in the family Apocynaceae including Australian and New Zealand species of Parsonsia.

The female probably lays eggs in young stems and fruit. The adults and nymphs have piercing and sucking mouth parts which are inserted into the plant. When they wish to feed the bugs move the tip of their rostrum to a suitable part of the plant. Stylets are then gradually pushed into the plant. The inner pair of stylets (maxillae) form two tubes, one through which saliva is injected into the plant and a second through which plant juices are sucked up into the insect. Feeding by this insect has not been studied, but they probably use their saliva to digest the plant cells. No plant damage due to feeding has been observed, but as they probably feed on developing seeds, they will reduce the production of viable seeds.

Table: Host plants of the Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) from Plant-SyNZ database (5 March 2017). The reliability score shows the quality of evidence for the host association (1-10, 10=high).
Common Name(s)Scientific NameFamilyReliability IndexBiostatus
Cruel plant, Kapok vine, Moth plant, White bladder flowerAraujia horturum E.Fourn.Apocynaceae9naturalised
Bloodflower, Redhead cotton bushAsclepias curassavica L.Apocynaceae9naturalised
Swan plant, Narrow-leaf cotton bushGomphocarpus fruticosus (L.) W.T.AitonApocynaceae10naturalised
Swan plantGomphocarpus sp.Apocynaceae6naturalised
Oleander, Rose-bayNerium oleander L.Apocynaceae9naturalised
TweediaOxypetalum caeruleum (D.Don) Decne.Apocynaceae10naturalised
New Zealand jasmine, Small flowered jasmine, Akakaikiore, Akakiore, Kaikū, Kaikūkū, Kaiwhiria, Tōtoroene, TōtoroweneParsonsia capsularis (G.Forst.) R.Br.Apocynaceae10endemic
New Zealand jasmine, Akakaikiore, Akakiore, Kaihua, Kaikū, Kaiwhiria, Poapoa, Tautauā, Tawhiwhi, Tūtae-kererūParsonsia heterophylla A. CunninghamApocynaceae10endemic
 Parsonsia straminea (R.Br.) F.Muell.Apocynaceae9cultivated
  • Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) on a stem of Parsonsia sp. Image: Nicholas A. Martin © Crop & Food Research
    Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) on a stem of Parsonsia sp. Image: Nicholas A. Martin © Crop & Food Research
  • Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) on a swan plant fruit.  Image: Nicholas A. Martin © Crop & Food Research
    Adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae) on a swan plant fruit. Image: Nicholas A. Martin © Crop & Food Research
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Information Sources

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

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Acknowledgements

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

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Other Images

  • Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae).  Image: Tim Holmes © Crop & Food Research
    Underside of adult Swan plant seed bug, Arocatus rusticus (Hemiptera: Lygaeidae). Image: Tim Holmes © Crop & Food Research
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Suggested Citation

Martin NA. . Swan plant seed bug - Arocatus rusticus. Interesting Insects and other Invertebrates. New Zealand Arthropod Factsheet Series Number 77. http://nzacfactsheets.landcareresearch.co.nz/Index.html. Date Accessed. ISSN 1179-643X.

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