The Green Vegetable Bug Nezara viridula

New Zealand Journal of Agriculture, Volume 79, Issue 6, 15 December 1949, Page 563

The Green Vegetable Bug Nezara viridula

By

R. A. CUMBER,

, Entomologist, Entomological Research Station,

Department of Scientific and Industrial Research, Nelson.

THE green vegetable bug Negara viridula L., a cosmopolitan insect, was first recorded as a pest in New Zealand in April, 1944, when specimens found attacking beans in the New Plymouth area were submitted by the Fruit Inspector of the Department of Agriculture. It had been reported as occurring in New Zealand by Kirkaldy in 1909, but in that instance the bug was confused with the native pentatomid Glaucias amyoti Wh., which may easily be mistaken for Negara. If the original record of Negara had been correct, it certainly would have manifested itself as a serious pest before 1944. Negara probably reached New Zealand in 1941.

IN 1946 Nezara was reported from mid-Northland, and now most areas north of Whangarei are affected to some degree by its depredations. It is found in the northernmost isolated settlements such as Te Hapua, indicating its powers of dispersal across what would appear to be unfavourable areas. Recent reports indicate moderate infestations in the Te Kaha area, Bay of Plenty. Apart from its powers of dispersal by flight, Nezara is spread in its nymphal stages during the distribution of flowers, fruit, and vegetables. The green vegetable bug belongs to that group of insects which grow by a succession of moults, the green adult emerging at the last moult. The immature stages or nymphs differ greatly from the adult in both colour and shape. When the bugs hatch from the eggs they are little larger than a pinhead and spherical. During immature stages they are brightly coloured, being marked with black, red, orange, yellow, and green. In the last of the nymphal stages two distinct colour forms occur, one of which is predominantly green, the other predominantly black, but intermediate colour forms also occur. The adult bug invariably is green during its active breeding period, but as winter approaches purplish-brown specimens may be found. The adult is shield shaped and, unlike the nymphal forms, has two pairs of fullyformed wings and can fly actively. Scent glands on the lower surfaces of the bugs produce an unpleasant odour, especially when they are handled roughly.

Two other bugs may be mistaken for Nezara in their immature and adult stages. The adults of both Nezara and the native Glaucias amyoti are about Jin. long, but Nezara has three white dots along the front margin of the central triangular plate; these dots are absent in Glaucias. The second bug which may be mistaken for Nezara is Cuspicona simplex Wlk., a native of Australia which has been introduced accidentally. Like Glaucias, it is a shinier green and does not have the three white dots, but the adults seldom exceed Jin. long.

Distribution and seasonal irregularities affect the number of generations and the time taken for each generation of Nezara. Probably in all areas in New Zealand the breeding cycle is interrupted during winter. Overwintering adults may emerge from hibernation and begin mating early in spring. About a week after mating the eggs are laid. The eggs, which are about the size of a pinhead, are deposited in groups in parallel rows glued firmly together and to the surface on which they rest. The groups, which usually consist of 60 to 80 eggs, are for the most part approximately round, but if laid on a narrow leaf, they may be drawn out into a strip four or five eggs in width.

Eggs are usually deposited on the lower surfaces of leaves. When first laid they are pale yellow, but as the embryo develops the eggs show a central pink spot which gradually spreads and darkens as hatching approaches. The incubation period is about 10 days. When ready to emerge the bugs push off the circular caps on the tops of the eggs and crawl out, leaving a raft of tiny clear cups. The young bugs, which are about l/10in. in diameter and brightly marked with orange and black, usually remain clustered together on or near the empty egg raft for several days. Before the adult bugs emerge the nymphs moult on five occasions, during which time they are brightly coloured. The life cycle of the bug is estimated to occupy about 8 weeks during the most favourable summer conditions of Northland. Here all stages of the bug are present for at least 6 months of the year, and probably at least two generations of the bug occur in addition to those -which over-winter. The adult bugs hibernate in long grass, foliage, and hedges. During the breeding season Nezara in all its stages feeds actively by pushing the fine sucking mouth parts into plant tissues and withdrawing the sap. No obvious mutilation accompanies their depredations, but growth stops and tissues already formed die away. Plants attacked include not only those which are grown commercially, but also weeds, grasses, and native shrubs. Nezara has been observed breeding very successfully in weedy, neglected gardens and alongside roads in areas which are miles from cultivated land.

Flowers, developing seed, growing points, and foliage are attacked. The developing seed in legumes is particularly attractive to the bugs; pods become shrivelled and distorted and little seed formation occurs. This is particularly noticeable in beans. Fruits which are attacked become mottled and discoloured and fall prematurely. Included in plants noticeably attacked in Northland are beans of all types, peas, Dolichus, clovers, tomatoes, potatoes, native solanaceous plants, tree tomatoes, mustard, cabbages, cauliflowers, turnips, silver beet, pumpkins and marrows, maize . and sweet corn, grapes, banana passion fruit, rhubarb, ana thistles. Damage to peaches has also been reported. Control Measures Two parasites are known to control Nezara. One of these, a small hymenopterous egg parasite, Microphanurus basalis Woll. (Scelionidae) , has recently been introduced into New Zealand. It is hoped that the other, a fly Trichopoda • pennipes Fabr. ' (Tachinidae) , will be introduced later. Microphanurus is a wasp-like insect

about l/25in. long. It lays its eggs in those of Nezara and the adult parasite? hatches out about 3 weeks latdr. Early , this year several hundred of the egg parasite were received from Mr. F. Wilson, Division of Economic Entomology, Canberra, Australia. (The parasite was introduced into Australia from Egypt in 1934.) A temporary breeding station was set up in the Bay of Islands, where conditions appeared to be favourable for the work, and there some 48,000 parasites were bred by the?: writer. The main areas of liberation* were Awanui, Kaitaia, Paihia, Kawakawa, Whangarei, New Plymouth, and Te Kaha (near Opotiki). In three of the northern areas where liberations were made subsequent examinations showed parasitised egg masses and emerging parasites at the liberation sites. The success of these liberations cannot be assessed for some time. ,If a measure of control is obtained, it is likely to be more noticeable in the warmer coastal areas. Results of spray trials carried out by the Department of Agriculture in New Zealand are not yet available. Recent experiments with D.D.T. dusts

and sprays in Australia gave promising results. Weekly spraying with 0.2 per cent. D.D.T. in a suitable solvent has given satisfactory control. Sprays are more effective against the immature stages of the bug. The adults, in addition to being more resistant, are able to fly and readily move from place to place. As the bugs breed and hibernate in rough wastage areas and spread rapidly in the adult stage, destruction of hibernation sites and hand picking have limitations as control measures. However, the destruction of possible hibernation sites, the burning of old infested plants, and the destruction by hand of adults and nymphs, particularly those found early in the season, can all aid in reducing the Nezara population. * Assistance in field work and parasite liberations was given by W. Delf, Paihia, A. A. Sneddon, Maori Affairs Department, Opotiki, and officers of the Department of Agriculture at Kaitaia, Whangarei, New Plymouth, Kaikohe, and Tauranga.

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Artificial Teal lor Starting Calves on Bucket

A DEVICE for starting calves on the bucket which does away with hours of back-bending and saves fingers from being bitten has been devised by Mr. G. Macpherson, of Kaitaia, Northland. It consists of a piece of milking-machine claw rubber passed through a weighted fishing-net cork which floats well down in the milk. The calf draws milk through the upper end of the rubber which, by being subjected to ■ heat, is moulded to teat shape and is softened so that it gives a spongy feel when in the calf's mouth. Mr. Macpherson has found that calves seldom need to be started on this device more than, once and that after • a week it can be removed and the calves will drink straight from the bucket without noticing the absence of the artificial teat. Mr. Macpherson used large staples to weigh the cork down in the: milk, and the weight of the staples also prevents the calf from lifting the float out of the bucket. Staples are arranged so that they .prevent the cork from splitting (see diagram) : . , Corks used for making the device, as far as possible, should be free of air holes. Mr. Macpherson has found that if corks are scalded daily they will last for several seasons. ' ’ ■ '