Harlequin bug in apple orchards
The harlequin bug, Dindymus versicolor, is a native Australian plant bug. It was documented as a pest of pome and stone fruit in the 1950s. However, between then and the 1990s, the use of synthetic insecticides might have suppressed harlequin bug numbers to the point where it was no longer considered a significant pest. Since the mid-1990s, orchardists have reported increasing harlequin bug activity. This is likely due to changes in crop protection chemistry and pest management strategies.
Pest identification
The adult harlequin bug is about 12 mm long and is very conspicuous. The head and inner margins and tips of the forewings are black, and the thorax and base of the forewings are reddish-orange. The underside of the body is tinged with yellow or green and has some red and black markings.
The harlequin bug develops through 5 immature stages (instars) and is often found swarming in large numbers on native tree trunks, trellises, hail netting posts and in sheds. Mating adults can be seen moving in pairs, joined at the abdomen and facing in opposite directions.
Damage
The harlequin bug is a sap-sucker that uses a proboscis (needle-like mouthpart) to pierce the skin of the host plant tissue. On fruit, this feeding results in slight depressions on the skin of the apple and is associated with the browning of the underlying flesh. The damage could be easily confused with that of boron deficiency (cork disorder).
Monitoring
Common orchard weeds such as Malva spp. (marshmallow), Rumex spp. (dock) and Polygonum aviculare (wire weed) are known hosts and should be the focus of monitoring and weed control programs. Inspect weeds, timber stacks, trellises, netting structures and nearby native bush for harlequin bug colonies.
Management
Cultural and physical: the severity of damage in some orchards seems to be associated with the bugs having easy access to the trees via weed growth within the tree row and/or canopy, low-growing branches, nearby trellis posts or wires and irrigation tubes.
Due to the harlequin bug's association with certain weed species, controlling weeds in the orchard will help reduce the likelihood and intensity of infestations. Particular attention should be given to removing and controlling common orchard weeds in the Malva (marshmallow), Rumex (dock) and Polygonum (wireweed) genera.
Removing sheltering sites such as timber stacks and other rubbish from within the orchard should also help reduce bug numbers.
Biological: there are no known biological control agents for the harlequin bug.
Chemical: as there are no chemicals registered for controlling harlequin bug in orchards in Australia, managing this pest is dependent on using cultural practices.
