Green vegetable bug
Due to their widespread distribution, ability to rapidly reproduce, and potential to quickly cause damage green vegetable bugs (GVB), also known as green stink bugs and green shield bugs, are considered one of the most damaging sucking pests of Australian pulse crops. Hosts include soybeans, mungbeans, navy beans, adzuki beans, cotton, sunflower, maize, peanuts, linseed, common brassicas, cereal crops and many other horticultural crops. Green vegetable bugs tend to be more widespread in warmer areas.
Description
Adult bugs are shield shaped, bright green in colour and measure 13 – 15 mm long. They have three distinct white spots between their shoulders and emit a foul odour when disturbed. Occasionally, yellow or orange variations can be found. Eggs are round, cream-yellow in colour when first laid, later turning orange prior to hatching. Eggs which have been parasitised appear black in colour. Newly hatched nymphs are 1.5 mm long, wingless, round – oval shaped and can be orange, brown or black in colour, changing to green as they approach their adult stage. The presence of wing buds becomes visible during their fifth instar.
Green vegetable bugs typically infest summer legume crops at flowering time when they commence feeding and lay their eggs in batches of 50 - 100 on the underside of leaves. At temperatures of 25°C, eggs will generally hatch after six days. Nymphs go through five instar stages before reaching maturity, which usually takes about 30 days. There can be 3 – 4 generations per year, this being dependent on climate and temperature. In tropical areas GVB breeding is continuous, whilst in temperate areas adults overwinter by taking shelter in cracks and crevices. High mortality of GVB occurs when temperatures exceed 35°C.
Green vegetable bugs have thin, long needle like mouthparts, which they use to suck nutrients out of the seed. Nymphs require the nutrients from the seed to complete their development and usually reach a damaging size by mid podfill. Injury to young pods results in shrivelled seeds and reduced yields. While damage to seeds in older pods causes blemishing, rendering them difficult to grade and reduces seed quality. Injury to buds and flowers can also occur and puncture wounds from feeding allows the entry of fungi and bacteria into the seed pod. Summer legumes remain at risk from GVB until seeds are too hard to penetrate. Often podding only lasts long enough for one generation to develop in crop, however GVB populations are mobile and can move to later plantings, in which case populations can escalate to high levels.
Control
A combination of cultural and chemical control techniques should be implemented to control GVB. Avoid planting consecutive summer legume crops, as GVB can move from earlier to later plantings enabling populations to grow. Try and prevent combining cultivar and sowing times which lengthen the duration of flowering and podding. Control weedy species around crops which may act as an alternative host to GVB and do not plant susceptible crops close to older infested crops.
Several natural enemies may help control GVB, including the parasitic wasp Trissolcus basalis which parasitises eggs turning them black. Nymphs may be attacked by ants, spiders or predatory bugs, while the fifth instar and adults are parasitised by the tachinid fly. For this reason, minimising the use of broad spectrum insecticides to preserve natural predator populations is important.
Crops should be monitored twice a week from budding until prior to harvest. Ideally, sampling should take place early - mid morning when GVB are in the top of the crop canopy. The most efficient method of sampling for pod sucking bugs is beat sheet sampling.
Green vegetable bugs should be controlled prior to nymphs reaching a damaging size, ideally during early pod fill.
References
Jackson, G, Mua, M and Tsatsia, H (2017), ‘Green vegetable bug’, Pacific pests and pathogen fact sheet, Australian Centre for International Agricultural Research, Green vegetable bug (098) (lucidcentral.org)Queensland Government (2017), ‘Green vegetable bug’, Department of Agriculture and Fisheries, Green vegetable bug | Department of Agriculture and Fisheries, Queensland (daf.qld.gov.au)
Queensland Government (2019), ‘Green vegetable bug’, Business Queensland, Green vegetable bug | Business Queensland
The Seed Collection (2020), ‘How to protect beans, peas, tomatoes and other crops from the Green Vegetable Bug’, The Seed Collection, How to Protect Crops from the Green Vegetable Bug | The Seed Collection