Hemiptera : Pentatomidae : Nezara viridula
Green Vegetable Bug (Nezara viridula) is a sap-sucking pest with a worldwide distribution that was first reported in Australia in 1916. Green Vegetable Bug can now be found in all Australian states and territories. It is a significant pest in eastern Australia from south-eastern Queensland, through New South Wales, to northern Victoria.
Green Vegetable Bugs release a smelly defensive fluid when threatened, which gives rise to a common name used overseas for this bug – ‘Green Stink Bug’. Confusingly, the insect known in Australia as ‘Green Stink Bug’ is the native bug Plautia affinis. It’s important to know that common names may indicate different insects to different people, but a scientific name is only used for a single insect by all scientists everywhere.
Sap-sucking pests such as Green Vegetable Bugs can be a problem if you allow their numbers to build up. The secret to pest control is to keep an eye on your plants so that you can spot pest incursions early. Regular monitoring, along with the prevention and control methods outlined here, will ensure that a major infestation of Green Vegetable Bugs is avoided.
If you enjoy gardening in the morning that is a great time to watch for late stage nymphs and adult bugs basking in the sun. For this to work you will need to know what Green Vegetable Bug adults and nymphs look like (see Description).
Prevention is always better than cure. There are a number of measures that you can take to prevent or minimise damage by Green Vegetable Bugs (see How to Prevent Green Vegetable Bugs Appearing). A simple technique is to keep your garden as weed free as possible, because Green Vegetable Bugs breed in a number of weed species.
If control is necessary, treat with Yates Baythroid Insect Killer for Gardens. This product can only be used on ornamentals, broccoli, Brussels sprouts, cabbage, cauliflowers or tomatoes. Ensure you spray foliage thoroughly when bugs are seen or if they reappear.
Whatever control measures you take against Green Vegetable Bugs, you need to be persistent - especially if you live in an area where there are multiple generations of bugs per year. There is help at hand - a couple of parasites have been introduced to help control Green Vegetable Bugs and they are very effective (see Natural Enemies). You can encourage them by having lots of flowering plants available for them to have a feed of nectar.
Green Vegetable Bug is an introduced sap-sucking pest that is a member of the ‘shield bug’ family Pentatomidae.
Adult Green Vegetable Bugs are green, shield-shaped bugs, approximately 15 mm long. They can be distinguished from similar looking bugs by the three small yellow spots in a line across the top edge of the triangle on their backs. Green Vegetable Bugs overwinter as adults. In areas that experience cold winters, hibernating adult bugs change from green to brown in colour. In areas with less severe winters, the overwintering adults remain green but inactive.
Green Vegetable Bug eggs are about 1 mm long and slightly drum-shaped. When viewed from the side, the eggs appear to be elongated but circular when viewed from above. The eggs are initially creamy yellow in colour but become reddish prior to hatching.
Nymphs vary considerably in colour – they are initially orange but then change to black or green with white, cream, yellow and red markings on their back. Confusingly, fourth and fifth stage nymphs have two colour forms each. Nymphs become greener in colour as they progress through a series of moults, until the final moult when they become completely green.
The Green Vegetable Bug develops through a life cycle of gradual metamorphosis – egg to nymph to adult.
Females lay up to 120 eggs at night in a raft shaped formation on the underside of leaves. As the eggs are laid they are smeared with a glue-like liquid that sticks the eggs to the leaf, and eggs to each other.
The eggs hatch into first stage (1st instar) nymphs that cluster together around the egg shells. When the first stage nymphs moult into the second and the third stage, those nymphs also cluster together for safety. The nymphs disperse around the plant once they moult to the fourth stage. Nymphs moult once again to a fifth stage that has obvious wing buds, and then a final time to the adult stage.
The entire life cycle takes about two months to complete and there may be as many as three generations per year, depending on the climate.
Adult bugs are strong flyers and will fly away when disturbed, and they may also release a foul smelling defensive fluid. Late stage nymphs and adult green vegetable bugs bask on the sunny side of plants, especially in the morning.
Image above: 3rd, 4th and 5th Green Vegetable Bug instars