Dictyotus caenosus (Westwood)
The Brown shield bug or Brown stink bug is not commonly found in cotton. The habits of these bugs are not well known but they mainly feed on a range of grasses, bean crops and lucerne.
Identification: Adult bugs are shield shaped, matt brown and 7-8mm long. Newly hatched nymphs are orange with dark markings and a black head. As they grow they change colour to have a pale brown abdomen with transverse dark and pale markings at its centre.
May be confused with: The pest may be easily confused with the Glossy shield bug, a beneficial insect. The main distinguishing features of the Brown shield bug are the matt brown surface, shorter head and smaller eyes. Newly hatched nymphs are very similar in appearance to other shield bug nymphs until they grow and change colour.
Lifecycle: Pale cream eggs are laid in twin row rafts. There are 5 nymphal stages. Usually only one generation will develop per summer legume crop.
Damage: It has been shown that the Brown shield bug causes the least amount of damage of all bugs in the 'stinkbug’ complex, causing just ¼ of the damage caused by a Green vegetable bug.
Monitoring: The most effective way to check for the Brown shield bug is with a beat sheet. Populations are usually very patchy, so it is important that checking is carried out in as many sites across the field as possible.
Egg raft of the Brown Shield Bug. Eggs are initially cream coloured and are laid in double rows. 5mm long Photo: H. Brier
A large Brown Shield Bug nymph with a dark head and thorax, and a pale brown abdomen with transverse dark brown and pale markings at its centre. 4-5mm Photo: C. Mares
There has been no significant yield reductions reported from Brown Shield Bug infestations. 8mm Photo: J. Wessels