INTERESTING INSECTS

By N A Martin (2015, revised 2017)

Tri-horned treehopper

Centrotus trispinifer Fairmaire, 1846

Acanthucus [sic] trispinifer (Fairmaire, 1846)

Acanthuchus gracilispinus Stål, 1869

This adventive treehopper from Australia is found in both the North and South Islands of New Zealand. It occurs on host plants in city gardens and parks as well as in native ecosystems where it feeds by sucking juices from plant stems.

Conservation status: Not threatened; widespread.

There is little information about the annual cycle of this insect in New Zealand. In Auckland nymphs have been found in winter and nymphs and adults in summer.

Adults are black in colour with three prominent spines on the dorsal surface of the pronotum (hardened plate covering the first segment of the thorax behind the head). The head with its bulging eyes is almost covered by the pronotum, which has two golden patches, just behind the head and above the base of the legs. The central dorsal spine of the pronotum extends backwards as a curved ridge partially covering the wings. The black anterior wings have a few pale patches towards their tips and cover the posterior wings. The female probably inserts eggs into stems of host plants.

Nymphs hatch from eggs, and are initially wingless, coloured green or grey, with a large thorax bearing forward pointing spines dorsally. The body tapers to a long tail. 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. Small wing buds can be seen on the fourth and fifth instar nymphs. Adults emerge from fifth instar nymphs.

Feeding and honeydew

Like other Hemiptera, the tri-horned treehopper has sucking mouth parts. The long stylets, special shaped rods, are held in the rostrum. When feeding the bug moves the tip of the rostrum to the stem on which it is sitting. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (or nutrient transport vessels) of the plant. Tri-horned treehoppers suck the plant’s sap which is high in sugars and low in other nutrients. The treehoppers excrete the excess sugary liquid, which is called honeydew. The nymphs have a long extension to the abdomen that is normally retracted into the body. When the nymphs excrete honeydew, these terminal segments are extended and they flick the honeydew droplets away from the insect.

Side view of tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on stem of Coprosma repens (Rubiaceae), with empty nymphal skin behind recently emerged adult. Creator: Tim Holmes. © Plant & Food Research. [Image: 15H2]

Frontal view of an adult tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on stem of Coprosma repens (Rubiaceae), with the empty nymphal skin behind. Creator: Tim Holmes. © Plant & Food Research. [Image: 15H5]

Top view of adult tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on stem of Coprosma repens (Rubiaceae), with empty nymphal skin behind. Creator: Tim Holmes. © Plant & Food Research. [Image: 15H4]

Nymph of tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on leaf petiole of Coprosma repens (Rubiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15GX]

Nymph of a tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on a stem of Coprosma repens (Rubiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15GZ]

Nymph of a tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on a leaf petiole of Coprosma repens (Rubiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15H0]

Dead preserved nymph of tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), with last two abdominal segments (arrow) extended for honeydew excretion. Creator: Tim Holmes. © Plant & Food Research. [Image: 15H6]

The tri-horned treehopper is the only species of the family Membracidae in New Zealand. The adults have three prominent spines on the dorsal surface of the thorax (middle body) and overall black colour. The nymphs are also distinctive with prominent forward pointing dorsal spines on the thorax and a long tapering body.

Adult tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on stem of Coprosma repens (Rubiaceae), the empty nymphal skin is behind. Creator: Tim Holmes. © Plant & Food Research. [Image: 15H3]

Nymph of a three-spined bug tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on a stem of Coprosma repens (Rubiaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15GY]

Dorsal (top) view of tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on stem of Muehlenbeckia complexa (Polygonaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 29GR]

Side view of tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on stem of Muehlenbeckia complexa (Polygonaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 29GS]

Side view of young nymph of tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on leaf of Calystegia tuguriorum (Convolvulaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 29GT]

Side view of young nymph of tri-horned treehopper, Acanthuchus trispinifer (Hemiptera: Membracidae), on leaf of Calystegia tuguriorum (Convolvulaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 29GU]

No natural enemies of the tri-horned treehopper are reported in New Zealand but birds, spiders and other insects are likely generalist predators.

Host plants include a variety of native and naturalised trees, shrubs and climbers.

The treehoppers excrete the excess sugary liquid, which is called honeydew. The nymphs have a long extension to the abdomen that is normally retracted into the body. When the nymphs excrete honeydew, these terminal segments are extended and the flick the honeydew droplets away from the insect.

In New Zealand nymphs of this species are solitary, though several may be on the same branch. No ants have been seen attending the nymphs in New Zealand, however, in Australia, the nymphs of other species of Membracidae may be attended by ants that feed on the honeydew.

Lariviere M-C, Fletcher MJ, Larochelle A 2010. Auchenorrhyncha (Insecta: Hemiptera): catalogue. Fauna of New Zealand 63: 1-228.

Larivière, Marie-Claude (ed.) 2005 (and updates): Checklist of New Zealand Hemiptera (excluding Sternorrhyncha). The New Zealand Hemiptera Website, NZHW 04.

Larivière, M.-C.; Fletcher, M.J. 2004 (and updates): The New Zealand leafhoppers and treehoppers (Hemiptera: Auchenorrhyncha): web-based identification keys and checklist. The New Zealand Hemiptera Website, NZHW 02.

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.

1 August 2017. NA Martin. Host plant table updated.