Spotting bugs

Description

Adult SB are green – brown, slender, and 11 – 15 mm in length. They are easily distinguishable from nymphs by the presence of wings. Initially eggs are pale green, which darken in colour and become translucent as they mature. Eggs are oval to slightly triangular in shape, measuring 1.7 mm long. Spotting bugs go through five instar stages. During the first stage, they are green and black and appear ant like and it is difficult to distinguish between each species. In later stages, they turn orange – brown or green. At maturity, A.lutescens have a noticeable pair of large black dots on their abdomen, which are encircled by a pair of prominent white bands, while A.nitida have a small pair of black dots on their abdomen, as well as black antennae, black knees and wing buds.

Spotting bugs can lay 150 eggs or more throughout their lifetime. Between November – March, eggs are primarily laid separately onto fruit, flowers, or leaves, before hatching within 6 – 7 days. During summer, the development from egg to adult takes about 42 days, although this is dependent on temperature and food on offer. Up to 3 – 4 generations can occur each year.

Signs of damage from SB can vary greatly between crops. Spotting bugs feed by piercing plant tissue with two pairs of slender tubes known as stylets, which suck juice from plant tissue. Whilst feeding, saliva enzymes are secreted into the tissues causing the breakdown of cells. This produces large areas of deep-set tissue breakdown, which forms lesions, often referred to as a ‘sting’ by growers. Lesions can appear as craters and ooze sap and the skin may crack as fruit matures. Blind stings are not visible unless fruit is peeled or cut into and small woody lumps can form under the fruit skin. In lychees damage is only visible by cutting open the fruit.

Premature fruit drop often occurs within days of SB feeding. Growing point damage, often visible as dieback, lesions, and abnormal growth, is common in papaya, mangos and custard apples. Flower damage causes the flower panicle to wilt and sometimes brown – black lesions may be seen on the petals. Spotting bugs can penetrate hard nut shells, such as macadamias, where they feed on the kernel often causing immature nuts to fall. Further damage produces shrivelled, deformed kernels, which often have mould present, making them unfit for consumption.

Spotting bug species are selective in their feeding habits, A. lutescens mainly feeds on fruit and new growth while A. nitida targets green fruit and flowers. Spotting bug damage can be confused with Queensland fruit fly (QFF) damage, the difference being that damage from QFF is usually accompanied by maggots in the fruit and the damage remains superficial.

Control

An integrated approach combining, cultural, biological and chemical controls will help achieve long term sustainable control of SB. Managing tree density, which increases light and allows groundcovers to proliferate, offers a habitat which encourages and supports natural enemies, therefore reducing damage from SB. Several egg parasitoid species help control SB by injecting their own egg into the eggs of SB, which consume the nymph.

Trials in macadamias have proven that SB can be reduced by limiting tree height to six metres, which enables spray equipment better access and coverage. Placement of orchards close to natural bushland inhabited by SB should be avoided, in particular rainforests, as SB will readily move from their native habitat into neighbouring orchards.

Monitoring SB can be difficult, as they are highly mobile and tend to inhabit the tops of trees. Growers should monitor bordering vegetation and hedges for SB. Pheromone traps are also useful.

Unfortunately, many of the insecticides used to control SB are broad spectrum and therefore affect beneficial insects. In contrast, Sivanto®Prime has minimal impact on many beneficial species including ladybird beetles, hoverflies, predatory mites, lacewings, honey bees and native stingless bees. It is also important to rotate insecticide groups to lower the risk of resistance developing.

Once SB populations exceed local thresholds, an application with an insecticide such as Sivanto® Prime or Bulldock® should be made. Sivanto® Prime is registered for banana spotting bug and fruit spotting bug in macadamias, avocados, mangoes and papayas. Bulldock is registered for the control of SB in avocados and macadamias.

References

Department of Primary Industries NSW (2019), ‘Managing fruit and banana spotting bugs in passionfruit’, The Passion Vine Spring 2019, Passionfruit Australia, FSB-BSB-4-page-Guide-1.pdf (passionfruitaustralia.org.au)

Huwer, R, Maddox, C, Bright, J, Hickey, M, Newton, I and Alt, S (2016), ‘Fruitspotting bugs 2016, NSW DPI management guide’, NSW Department of Primary Industries and Horticulture Innovation Australia, Fruitspotting Bugs 2016 (nsw.gov.au)

Queensland Government (2017), ‘Fruit-spotting bug’, Department of Agriculture and Fisheries, Fruit-spotting bug | Department of Agriculture and Fisheries, Queensland (daf.qld.gov.au)