Hypsithocus hudsonae Bergroth, 1927
Alpine shield bug, Black alpine shield bug
Biostatus and distribution
The Alpine shield bug is endemic to New Zealand's South Island where it is found in the alpine areas of central and western Otago. It is the only New Zealand shield bug that cannot fly. Its abundance and annual cycle in these areas is not known. Its host plants are also unknown.
Conservation status: This flightless New Zealand shield bug has a restricted distribution in Southern alpine areas and there is a lack of knowledge of its host plants. DoC classify the species 'At Risk, Naturally Uncommon'.
Life stages and annual cycle
Little is known of the annual cycle of the Alpine shield bug. The flightless adults have been found from November to February and large nymphs from December to February. It is likely that the Alpine shield bug over-winters as adults, male and females. Eggs are probably laid in spring and early summer. Nymphs develop during late spring and summer with the first new season adults emerging in mid to late summer. Mating may occur both in summer and spring. The insects appear to live close to the ground and their dark colour enables them to absorb the heat from the sun and warm rocks more efficiently and thus grow faster.
The adults are about 7-9 mm long. The head, thorax, short forewings and abdomen are dark brown with small dark punctures. There is a thin pale edge on the body. The male external genitalia are visible from above. The underside of the body is black as are the legs and rostrum. The tarsi on the three pairs of legs are brown. The brown antennae have a paler colour on the basal half of the final segment. The black rostrum extends to the base of the last pair of legs and holds the stylets used for feeding.
The eggs have a white finely sculptured shell. Before hatching they are a creamy colour. Shortly before hatching red eyes can be seen and a black T-shaped structure, the egg burster, that is used to push up the lid of the egg.
The nymphs that hatch from the eggs are like small, dark, wingless adults. There are five nymphal instars (stages). 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 first instar nymphs are dark grey with fine black punctures. The edge of the thorax and head are black and there are black areas on the centre of the abdominal segments typical of shield bugs. Two of these black areas surround the scent glands. The first instar nymphs stay by their eggs after hatching. The second instar is black with tiny white setae (hairs). The edge of the thorax and abdominal segments are white and black. The legs are black. The Third instar nymphs are similarly coloured, but the edges of the thorax and abdominal segments are white or pale brown. The antennae are coloured like the adults. The fifth instar nymph has wing buds that extend over the first two abdominal segments. The body is dark brown and covered in small black punctures. Near the edges are tiny white specks.
The dark colour of the adults and nymphs facilitates the absorption of heat from the sun and hot stones, rocks and soil.
Walking and Dispersal
The nymphs and adults have six legs (three pairs) that are used for walking. The adults cannot fly. They have reduced forewings and no hind wings. Strong winds may carry adults to new areas that may by chance be suitable for breeding and the establishment of a new colony.
Like other Hemiptera, the Alpine shield bug has sucking mouth parts. The long stylets, special shaped rods, are held in the rostrum. The Alpine shield bugs feed on plants. 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.
The first instar nymphs stay by their eggs after hatching and apparently do not feed.
The reduced size of the forewings and lack of hind wings distinguishes the Alpine shield bug from all other shield bugs in New Zealand including the Alpine brown soldier bug, Cermatulus nasalis hudsoni that has full sized forewings.
The nymphs of the Alpine shield bug are darkly coloured and covered in fine punctures. They do not have the distinct markings that are on the abdomen of other brown coloured nymphs. There antennae are also distinct with a dark grey basal half and a pale orange-brown area on the last segment.
No natural enemies of the Alpine shield bug are known. It may be eaten by some alpine birds and predatory insects. Like other New Zealand shield bugs, its eggs may also be parasitised by tiny wasps.
Adults and large nymphs have been found associated with low growing alpine plants. Marie-Claud Lariviere suggested that a shrub, Veronica odora (Plantaginaceae), was a likely host plant while Brian Patrick suggested to me that these ground dwelling shield bugs are probably associated with cushion plants such as Abrotanella inconspicua and Raoulia species, but not shrubs. Some careful research is needed to discover their host plants.
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.
Why is an alpine insect flightless?
At first it seems a bit strange that an insect that lives in mountainous areas has lost the ability to fly. Surely flying is a good way to get from one mountain ridge to another. If the insect has special habitat requirements, then there is a risk that a flying insect could be blown away from suitable habitats and not be able to easily find alternatives. Not being able to fly and keeping close to the ground of suitable habitats may encourage successful breeding.
A similar argument is used to explain why insects on remote islands tend to be poor fliers or flightless.
What are the host plants of the Alpine shield bug?
This important information for a wingless species with restricted distribution. At present no definitive host plants have been identified. Identification of host plants will require careful observations of feeding by nymphs and/or adults ideally under natural conditions. The parts of the plant as well as species should be recorded. It is a good idea to collect voucher specimens of the plants used as food, and deposit the plant specimens in an appropriate collection. Once the parts of plants that are used for food have been identified, then other plants can be tested in cages.
Brian Patrick thinks that these ground dwelling shield bugs are probably associated with cushion plants such as Abrotanella inconspicua and Raoulia species, but not shrubs.
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.
Brian Patrick for information about plants associated with the Alpine shield bug.
Tom Saunders (University of Auckland) and Sophie Hunt (Plant & Food Research) for making available Alpine shield bugs for photographing and information about their collection.
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.