INTERESTING INSECTS

By N A Martin (2015, revised 2018)

Green potato bug

This adventive shield bug comes from Australia and is found in the North and South Islands of New Zealand. It occurs on host plants, Solanum species, in crops, gardens and parks as well as in native ecosystems.

Conservation status: Widespread, living on some native plants and a minor pest of some vegetable crops.

The insect overwinters as adults. Adults appear to gather in suitable overwintering sites and on plants for breeding. They are probably attracted to each other by an aggregation pheromone (volatile chemical). Breeding may occur preferentially on plants with berries. The overwintering adult females start laying eggs late spring. Each female lays several batches of eggs over several weeks. Egg laying continues until late summer.

Eggs are laid in a cluster of up to 14, one for each ovariole. The eggs are white when first laid and then turn pale green. Just before eggs hatch the ‘egg burster’ can be seen. It is a dark T-shaped chiton structure that assists with pushing the lid of the egg. It appears as a dark rod between the eyespots of the nymph.

Nymphs hatch from the eggs. First instar nymphs are like small, black and grey, wingless adults. 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. As the insects progress through the nymphal stages their body and antennae change colour. The first instar is almost circular in outline. It has a black head and thorax, and the abdomen has black scent glands and red-brown speckles. The legs are black but the feet (tarsi) are pale. The antennae are brown with the terminal segment darker than the previous two. The second instar also has a black head, but it protrudes forward between the bases of the antennae. The thorax is pale with many black speckles and the abdomen is covered in brown and black speckles. The feet of the first two pairs of legs are black, while on the last pair the base of the femur (the long segment before the feet) and the feet are white. The terminal segment of the antennae is dark, with the basal quarter white, and the third segment from the end is white or brown. The brown antennae of the 3rd, 4th and 5th instars have a black terminal segment black with the basal quarter is white. The body of the 3rd, 4th and 5th instars is green with fine black speckles, the legs are pale brown.

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. In early summer, new eggs may be laid, but egg laying ceases in late summer. Depending on climate there may be 1-3 generations per year.

The length of the lifecycle (time from egg to adult) varies with temperature. McDonald and Grigg in New South Wales, Australia, found that at a constant temperature of 21°C, the time from egg to adult was 28.8 days (range, 28-30 days). The time in days for each life stage were: eggs 5 (5-6), first instar 3.6 (3-4), second instar 3.4 (3-5), third instar 3.8 (2-7), fourth instar 7.1 (4-10), fifth instar 7.3 (4-12).

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 it covers the hind wings. Part of the forewing is coloured green, while the rest is membranous.

Feeding

Like other Hemiptera, the green potato bug has piercing and sucking mouth parts. The long stylets, special shaped rods, are held in the rostrum. When it feeds 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 injects into the plant and a second through which plants juices are sucked up into the insect. Feeding of the green potato bug has not been studied, but it probably can use its saliva to digest the tissues of the plant.

Two adult green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) from above. Creator: Tim Holmes. © Plant & Food Research. [Image: 160G]

Underside of adult green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 160H]

A cluster of newly laid eggs of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) laid on a fruit of poroporo, Solanum aviculare (Solanaceae). Creator: DSIR Photographers. © Plant & Food Research. [Image: 160W]

A cluster of eggs of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) laid on a leaf of poroporo, Solanum aviculare (Solanaceae). Note the eye spots and the egg burster, a T-shaped structure. Creator: Tim Holmes. © Plant & Food Research. [Image: 160R]

Hatched eggs of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) laid on a leaf of poroporo, Solanum aviculare (Solanaceae). Note the T-shaped egg burster that remains attached to the eggshell. Creator: Tim Holmes. © Plant & Food Research. [Image: 160S]

Drawing of an adult green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae), the scale line equals 1 mm. (Drawing by Des Helmore published in Fauna of New Zealand Number 35, fig. 19). Creator: Des Helmore. © Landcare Research. [Image: 160X]

Drawing of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) nymphs. Creator: F. McDonald and Janice Grigg. © Drawings in General and Applied Entomology 12: 61-71, Figs 1-7. [Image: 160V]

Newly hatched nymphs of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) sitting on the eggshells. The eggs were laid on a fruit of poroporo, Solanum aviculare (Solanaceae). Creator: DSIR Photographers. © Landcare Research. [Image: 1611]

First instar nymph of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 160U]

Underside of a first instar nymph of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 160T]

Second instar nymphs of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae). Creator: DSIR Photographers. © Landcare Research. [Image: 160Z]

Second instar nymph of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) on a fruit of velvety nightshade, Solanum chenopodioides (Solanaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 160Q]

Second instar nymph of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae). Creator: DSIR Photographers. © Landcare Research. [Image: 1612]

Fourth instar nymph of the green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae), on leaf of Solanum chenopodioides (Solanaceae) from above. Creator: Tim Holmes. © Plant & Food Research. [Image: 160I]

Fourth instar nymph (lower) and fifth instar nymph (upper) of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 160J]

Fourth instar nymph (lower) and fifth instar nymph (upper) of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) on a leaf of velvety nightshade, Solanum chenopodioides (Solanaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 160L]

Side view of fifth instar nymph of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 160M]

Several shield bugs look similar to the green potato bug. It is the smallest of the three green shield bugs in New Zealand and has distinctive sharp protruding corners of the pronotum (first segment of the thorax).

The nymphs are grey or green, and the antennae of the second to fifth instar nymphs have a white ring on the antennae. The commonest in New Zealand is the green vegetable bug, Nezara viridula (Linnaeus 1758), which is similar in size to the to the Australasian green shield bug, Glaucias amyoti (Dallas 1851).

Adults of the green vegetable bug have three white spots in a line between the wing insertions and the nymphs are distinctly patterned (see photo). The smaller nymphs of the Australian green shield bug are black, later instars have a green abdomen with black scent glands. Some final stage nymphs have a green thorax. None have a white ring on the antennae.

Adult green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae); note the angular projections of the prothorax. Creator: DSIR Photographers. © Landcare Research. [Image: 1610]

Fourth instar nymph (lower) and fifth instar nymph (upper) of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 160J]

Adult (left) and late instar nymphs of Green vegetable bug, Nezara viridula (Hemiptera: Pentatomidae). The green vegetable bug is a pest of vegetable, flower and nut crops. Creator: Bruce Given. © Ministry of Agriculture and Fisheries. [Image: 3C9]

Dorsal (top) view of Australasian green shield bug, Glaucias amyoti (Hemiptera: Pentatomidae); Note the absence of any white spots in a line. Creator: Tim Holmes. © Plant & Food Research. [Image: 3BU]

Third and fourth instar nymphs of Australasian green shield bug, Glaucias amyoti (Hemiptera: Pentatomidae). Creator: DSIR photographers. © Landcare Research. [Image: 3C4]

Green form of a fifth instar nymph of Australasian green shield bug, Glaucias amyoti; note the prominent wing buds. Creator: DSIR photographers. © Landcare Research. [Image: 3C3]

Dark form of a fifth instar nymph of Australasian green shield bug, Glaucias amyoti (Hemiptera: Pentatomidae) feeding on Coprosma berries; note the prominent wing buds. Creator: DSIR photographers. © Landcare Research. [Image: 3C5]

No predators or pathogens are known.

Parasitoids

Eggs of the green potato bug may be parasitized by three species of tiny wasps. Two belong to the family Platygasteridae. Trissolcus oenone, a native species, parasitizes several native shield bugs. Another egg parasitoid, Trissolcus basalis (Wollaston 1858), was released into New Zealand in 1949 to control green vegetable bug, Nezara viridula (L.). It also parasitizes eggs of other shield bugs, including the Australian green shield bug, Glaucias amyoti, and the green potato bug, Cuspicona simplex. 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 parasitized by T. basalis turn black.

The third, an unnamed species, belongs to the genus Acroclisoides sp.in the family Pteromalidae. It has distinctive black spots on its forewings.

In Australia, two species of flies (Diptera: Tachinidae) and a parasitic wasp (Hymenoptera: Braconidae) kill fifth instar nymphs and adult green potato bugs.

Black eggs of green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) showing that they have been parasitized by the Green vegetable bug egg parasitoid, Trissolcus basalis (Hymenoptera: Platygasteridae); note the tydeid mites hiding amongst the eggs. Creator: DSIR photographers. © Landcare Research. [Image: 3C6]

Eggs of Green potato bug, Cuspicona simplex (Hemiptera: Pentatomidae) with black at the top showing that they have been parasitized by the Native shield-bug egg parasitoid, Trissolcus oenone (Hemiptera: Pentatomidae): note that some eggs have not been parasitized. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2KK7]

Dead and live adult Acroclisoides sp. (Hymenoptera: Pteromalidae) after emerging from eggs of Schellenberg's soldier bug, Oechalia schellenbergii (Hempitera: Pentatomidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2S4U]

Host plants of the green potato bug are native and naturalised species of Solanum including potatoes and tomatoes. Adults and juveniles feed by inserting the stylets into the plant and sucking plant sap and berries.

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.

Cameron PJ 1989. Nezara viridula (L.), green vegetable bug (Hemiptera: Pentatomidae). In: Cameron PJ, Hill RL, Bain J, Thomas WP eds. 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.

Coombs M, Khan SA 1997. New parasitoid/host records for Australian Pentatomidae, Tachinidae and Braconidae. Australian Entomologist 24: 61 - 64.

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 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: 1-326.

McDonald FJD, Grigg J 1980. The life cycle of Cuspicona simplex Walker and Monteithiella humeralis (Walker) (Hemiptera: Pentatomidae). General and Applied Entomology 12: 61-71.

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.

Dr Fred McDonald for permission to use his drawings published in General and Applied Entomology 12: 61-71, Figs 1-7.

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 August 2018, NA Martin. Parasitoid list updated, photos of Acroclisoides sp added

1 February 2018. NA Martin. Captions for parasitised egg photos updated

1 August 2017, NA Martin. Photo of parasitised eggs added.