Australasian green shield bug - Glaucias amyoti
By N A Martin (2010, revised 2017)
Rhaphigaster amyoti Dallas, 1851
Nezara amyoti (Dallas, 1851)
Zangis amyoti (Dallas, 1851)
Zangis stali Schouteden, 1906
Biostatus and Distribution
This native shield bug is found throughout the North Island of New Zealand and Nelson and Marlborough on the South Island. It is also present in Australia, East Timor, Indonesia (West Timor), Palau and Papaua New Guinea. It occurs on host plants, a variety of trees and shrubs, in city gardens and parks as well as in native ecosystems.
Conservation status: Widespread, not threatened.
Life Stages and Annual Cycle
Australasian green shield bugs overwinter as adults that hide among tree and shrub leaves, but may be seen basking in the sun. Adults gather in suitable overwintering sites and on plants for breeding. They are probably attracted to each other by an aggregation pheromone (volatile chemical). Breeding usually occurs on plants with berries or fruit/seed heads. There are several generations per year. The overwintering adult females start laying eggs late spring. Each female lays several batches of eggs over several weeks, perhaps up to 8 weeks. This results in nymphs of all sizes being present at the same time. The resulting adults may mate and lay eggs until early autumn. Sometime during late summer the adult females cease laying eggs. This change is probably induced by a change in day length and perhaps by a combination of day length and temperature.
Eggs are laid in a cluster of up to 14, one for each ovariole. The eggs are tan coloured, but can be much paler. Just before egg hatch a dark T-shaped structure, the egg burster, develops at the top of the eggs and can sometimes be seen between the eye spots of the nymphs. The egg burster assists with pushing the top of the egg and is left attached to the egg shell.
Nymphs hatch from the eggs. First instar nymphs are like small, black, wingless adults and like other shield bugs, (Pentatomidae), the first instar nymphs cluster on and around the egg shells and do not feed. 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. As the insects progress through the nymphal stages, their colour changes from black to mostly green. In the later instars, the colour may vary from green to a dark colour. The 1st instar nymphs are almost circular, black with a pair of small white patches on the abdomen. It has black legs and black antennae. The 2nd instar nymph is similar in appearance, though the head is longer and the pair of white spots on the abdomen turn yellow as the nymph grows. The 2nd instar also pale areas on the lateral margins of the abdomen and the rostrum is very long, extending beyond the end of the abdomen, but as the nymph grows the rostrum extends less.
Third instar nymph are more variable in colour. The head and thorax may be black or have paler brown areas, lateral margins of the thorax may have extensive pale areas or be black. The abdomen may be black, brown or green, but has a pair of yellow spots and black around the scent glands, The 4th and 5th instar nymphs tend to be green coloured, though some have a dark head and thorax. Small wing buds can be seen on fourth instar nymphs. They are larger and more obvious on fifth instar nymphs. Adults emerge from fifth instar nymphs. Most egg laying ceases in late summer, but unhatched eggs and early instar nymphs have been seen in early May in Auckland.
Walking and flying
The nymphs and adults have three pairs of legs. The adults have two pairs of wings, the front pair is modified as a cover over the hind wings. Part of the forewing is coloured green, while the rest is membranous.
Like other Hemiptera, the Australasian green shield 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 berry or other suitable part of the plant. The stylets are then gradually pushed into the plant. The stylets form two tubes, one through which saliva is injected into the plant and a second through which plants juices are sucked up into the insect. Feeding of the Australasian green shield bug has not been studied, but it probably can use its saliva to digest the tissues of the plant.
Distinguishing green shield bugs,
Several shield bugs look similar to the Australasian green shield bug. The commonest is the green vegetable bug, Nezara viridula (Linnaeus 1758). It is a similar size to the Australasian green shield bug, but the adults have three white spots in a line between the wing insertions. Adults of the green potato bug, Cuspicona simplex Walker 1867, are smaller and have pointed ‘shoulders’. Nymphs of the green vegetable bug are differently patterned (see photographs), while the nymphs of the green potato bug start off grey and then become green.
Distinguishing shield bugs on Pittosporum trees
The Australasian green shield bug and the Pittosporum shield bug, Monteithiella humeralis (Walker 1868) may both be found on the same Pittosporum tree. Adults are easy to distinguish, Australasian green shield bugs are green whereas Pittosporum shield bugs are smaller and brown. The other life stages can be more difficult to tell apart.
Eggs of the two species are of similar size, but differ in colour. The eggs of the Australasian green shield bug are tan coloured, but may be paler, even off-white. The freshly laid eggs of the Pittosporum shield bug are pale green and turn white. In New Zealand the first instar (stage) nymphs of both species appear similar, black. They sit on their egg shells or stay close so enabling them to be identified by the colour of the eggs.
Second instar nymphs of both species are also similar. Later instars of the pittosporum shield bug are black or dark brown with paler brown areas. Australasian green shield bug 3rd, 4th, and 5th instar nymphs may be green, though some have a dark head and thorax, and the abdomen is much paler.
Eggs of the Australasian green shield bug may be parasitised by two species of tiny wasp belonging to the family Platygasteridae. Trissolcus oenone, a native wasp, parasitises several native shield bugs. Another egg parasitoid, Trissolcus basalis (Wollaston 1858), was released into New Zealand in 1949 for control of green vegetable bug, Nezara viridula (L.). It also parasitises eggs of other shield bugs including Australasian green shield bug. When this wide host range was discovered in the 1960s, it was regarded as beneficial, because at that time protection of crops was regarded as more important than protecting native insects. Eggs parasitised by T. basalis turn black.
In 2010 Stephen Thorpe discovered in New Zealand a braconid wasp parasite of the green vegetable bug, Nezara viridula. The parasitoid, Aridelus rufotestaceus Tobias, 1986 (Braconidae) is known to parasitize nymphs of green vegetable bug. In laboratory experiments in Italy, nymphs of several sizes and adults were parasitised. In 2016, it was reared from Australasian green shield bug nymphs. The female wasps lay eggs in nymphs and may be adults. When the parasite larva is fully grown, it emerges from the nymph and spins a white cocoon in which it pupates. The adult cuts the cap of the cocoon and climbs out.
|Scientific Name||Common Name||Classification||Enemy Type||Reliability Index||Biostatus|
|Aridelus rufotestaceus Tobias, 1986||Shield-bug nymphal parasitoid (Wasp)||Hymenoptera: Braconidae||parasitoid||10||adventive|
|Trissolcus basalis (Wollaston, 1858)||Green vegetable bug egg parasitoid (Wasp)||Hymenoptera: Platygasteridae||parasitoid||10||adventive|
|Trissolcus oenone (Dodd, 1913)||Native shield-bug egg parasitoid (Wasp)||Hymenoptera: Platygasteridae||parasitoid||10||native|
Host plants of the Australasian green shield bug include a variety of native and naturalised trees and shrubs. Adults and juveniles feed by inserting a stylet into the plant and sucking plant sap and berries. Sometimes they may also be predaceous.
|Common Name(s)||Scientific Name||Family||Reliability Index||Biostatus|
|Coprosma ×cunninghamii Hook.f.||Rubiaceae||10||endemic|
|Tree coprosma, Mamangi, Mamangi||Coprosma arborea Kirk||Rubiaceae||10||endemic|
|Shining karamu, Kakaramu, Kakarangu, Karamu, Karamuramu, Karangu, Patutiketike||Coprosma lucida J.R.Forst. & G.Forst.||Rubiaceae||10||endemic|
|Large seeded coprosma, Kakaramu, Kakarangu, Karamu, Karamuramu, Karangu||Coprosma macrocarpa Cheeseman||Rubiaceae||10||endemic|
|Taupata||Coprosma repens A.Rich.||Rubiaceae||10||endemic|
|Glossy karamu, Kakaramu, Kakarangu, Karamu, Karamuramu, Karangu||Coprosma robusta Raoul||Rubiaceae||10||endemic|
|Cabbage tree, Giant dracena, Grass palm, Palm lily, Sago palm, Ti, Kauka, Kiokio, Kouka, Ti, Ti awe, Ti kouka, Ti para, Ti pua, Ti rakau, Whanake||Cordyline australis (G.Forst.) Endl.||Asparagaceae||9||endemic|
|Broadleaf, Huariki (fruit), Kapuka, Maihihi, Papauma, Paraparauma, Tapatapauma||Griselinia littoralis Raoul||Griseliniaceae||10||endemic|
|Akakopuka, Akapuka, Puka, Pukatea||Griselinia lucida G.Forst.||Griseliniaceae||10||endemic|
|Shrubby haloragis, Toatoa||Haloragis erecta (Banks ex Murray) Oken||Haloragaceae||9||endemic|
|Ivy, English ivy||Hedera helix L.||Araliaceae||9||naturalised|
|Chinese privet, Small-leaf privet||Ligustrum sinense Lour.||Oleaceae||10||naturalised|
|Australian ngaio, Boobialla, Tasmanian ngaio||Myoporum insulare R.Br.||Scrophulariaceae||10||naturalised|
|Ngaio||Myoporum laetum G.Forst.||Scrophulariaceae||10||endemic|
|Black maire, Maire, Maire raunui, Pau||Nestegis cunninghamii (Hook.f.) L.A.S.Johnson||Oleaceae||9||endemic|
|New Zealand passion flower, New Zealand passionfruit, Aka, Akakaiku, Akakohia, Akakuku, Akatororaro, Kahia, Kohia, Kupapa, Pohue, Popohue, Kaimanu||Passiflora tetrandra Banks ex DC.||Passifloraceae||10||endemic|
|Kaikaro, Karo, Kihihi||Pittosporum crassifolium Banks & Sol. ex A.Cunn.||Pittosporaceae||10||endemic|
|Lemonwood, Kihihi, Tarata||Pittosporum eugenioides A.Cunn.||Pittosporaceae||10||endemic|
|Black matipo, Kaikaro, Kohuhu, Kohukohu, Koihu, Kowhiwhi, Mapauriki, Pohiri, Powhiri, Rautawhiri, Tawhiri||Pittosporum tenuifolium Sol. ex Gaertn.||Pittosporaceae||10||endemic|
|Golden tainui, Gum-digger's soap, Kumarahou, Kumararaunui, Papapa||Pomaderris kumeraho A.Cunn.||Rhamnaceae||10||endemic|
|Coastal five finger, Houmapara, Houpara, Houparapara, Kokotai, Oho, Parapara, Whauwhau||Pseudopanax lessonii (DC.) K. Koch||Araliaceae||10||endemic|
|Cattley guava, Cherry purple guava, Purple guava, Strawberry guava||Psidium cattleyanum Sabine||Myrtaceae||10||cultivated|
|Seven-finger, Kohi, Kotete, Patate, Patate, Pate, Patete||Schefflera digitata J.R.Forst. & G.Forst.||Araliaceae||10||endemic|
|Bullibul, Bullibulli, Large kangaroo apple, Popopo, Poroporo, Poroporotanguru||Solanum laciniatum Aiton||Solanaceae||10||non-endemic|
|Flannel leaf, Kerosene plant, Tobacco weed, Wild tobacco tree, Woolly nightshade||Solanum mauritianum Scop.||Solanaceae||10||naturalised|
|European linden||Tilia ×europaea L.||Malvaceae||9||cultivated|
|Hebe, Shrub speedwell, Veronica, Speedwell, Koromiko||Veronica sp.||Plantaginaceae||6||endemic|
|New Zealand oak, Kauere, Puriri||Vitex lucens Kirk||Labiatae||10||endemic|
Although Australasian green shield bugs are primarily vegetarian they occasionally feed on other insects.
|Scientific Name||Common Name||Classification||Reliability||Biostatus|
|Caliroa cerasi (Linnaeus, 1758)||Pear and cherry slug||Hymenoptera: Tenthredinidae||10||adventive|
Why Stink bugs
Pentatomidae are often called stink bugs because when handled they emit a strong smell. The nymphs have prominent glands on the upper (dorsal) side of their abdomen, while adults have glands between the bases of their legs. The chemicals may deter predators and cause other bugs to drop to the ground, but some of the chemicals produced may also act as aggregation pheromones.
What triggers egg development in the spring and cessation of egg production in the autumn. Australasian green shield bugs overwinter adults that hide among tree and shrub leaves, but may be seen basking in the sun. It is not known if they feed during this time. At some point in the spring they start feeding and eggs start developing in the ovaries of the females. In Auckland eggs may be found in late November. Overwintering adults could be collected and kept under different day length regimes to determine the environmental trigger for egg production.
In late summer, egg laying ceases. Is this caused by decreasing day length affecting the adults already laying eggs or those that have not started? Is the trigger a specific day length or decreasing day length?
Cameron PJ 1989. Nezara viridula (L.), green vegetable bug (Hemiptera: Pentatomidae). In: Cameron PJ, Hill RL, Bain J, Thomas WP ed. A. review of biological control of invertebrate pests and weeds in New Zealand 1874 to 1987, Technical Communication No. 10. Wallingford, England, UK, CAB International. Pp. 111-114.
Cumber RA 1964. The egg-parasite complex (Scelionidae: Hymenoptera) of shield bugs (Pentatomidae, Acanthosomidae: Heteroptera) in New Zealand. New Zealand Journal of Science 7 (4): 536-554.
Lariviere M-C, Larochelle A 2004. Heteroptera (Insecta: Hemiptera): catalogue. Fauna of New Zealand 50: 1-326.
Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.
Shaw SR, Salerno G, Colazza S, Peri E. 2001. First record of Aridelus rufotestaceus Tobias (Hymenoptera: Braconidae: Euphorinae) parasitizing Nezara viridula nymphs (Heteroptera: Pentatomidae) with observations on its immature stages and development. Journal of Hymenoptera Research. 10: 131-137.
Eric Scott for helpful suggestions.
The New Zealand Plant & Food Research Institute Limited (Plant & Food Research) for permission to use photographs.
12 December 2016. NA Martin. Natural Enemies Table: corrected biostatus collumn
1 June 2016. NA Martin. Annual cycle: updated and added extra photos. Recognition: rewritten and added extra photos. Natural enemies: updated, extra photos. Prey: added. Research project added.