The Rutherglen bug is a widespread, small native sap-sucking insect. Adult Rutherglen bugs are often found on cotton but they do not tend to feed and are unable to reproduce on the crop. They are important pests of sunflower and also attack other field crops, fruit crops and weeds. Starving nymphs can occasionally cause damage to border areas of cotton adjacent to sunflower crops that have started to desiccate. If this damage coincides with other stresses, such as water stress, control may be required.

Identification: Adults are 3-4mm long, mottled grey-brown-black, and have clear wings folded flat over the back. Nymphs are wingless, with a reddish-brown, pear-shaped body.

Lifecycle: Females lay up to 400 eggs, singly or in small groups on the soil surface, or in flower heads of crops and weeds. The 1mm long eggs are creamy but turn amber, hatching about a week after being laid. The small reddish brown, wingless nymphs are pear shaped. Wing buds appear in the fourth and fifth nymph stages. Egg to adult takes about 4 weeks, with the life of an adult being another 4 weeks in warm weather. Several generations occur between spring and autumn. Adults and late stage nymphs overwinter in plant debris on the soil surface, and the presence of fallen seed from prior crops, especially sunflowers or canola, can greatly increase survival through winter and can lead to large numbers in the following spring placing nearby seedling cotton crops at risk.

Host range: They breed on many weeds, particularly mat-like weed growth at ground level eg pigweed, thistles, capeweed, fleabane and cudweed. Rutherglen bugs thrive when winter and early spring conditions favour these weeds, followed by a dry late spring that forces bugs to migrate from dying weeds to surrounding crops. Field crops that are commonly attacked include sunflowers, linseed, canola, wheat, sorghum, safflower and lucerne, as well as horticultural crops.

Damage: Occasionally very hungry Rutherglen bugs may survive through winter in cotton fields and feed on cotton seedlings, causing damage. This unusual situation can occur where cotton crops follow sunflowers (from the previous summer). The bugs maintain their populations on fallen sunflower seeds and migrate to cotton as the seedlings emerge. They suck the cotton seedlings dry resulting in an establishment problems and gappy stands. This situation can also arise in fields with poor hygiene where weeds act as a winter host. They can also build in some winter crops such as canola and then move into adjacent seedling cotton in the spring. There have been no reports of damage to squaring or flowering cotton and they are unlikely to be a threat to mature cotton. If high bug numbers are found in cotton, monitoring plant growth and fruiting will detect any damage. Look for damage by cutting fruit open to check for blackened stamens in squares and staining of the seeds in young bolls.

Control: Rutherglen bugs can be controlled by removing the weeds they use as hosts and by ploughing a deep furrow around the crop, preventing wingless bugs from migrating from weeds.

 
Adult Rutherglen bugs are often found on cotton but they do not tend to feed and are unable to reproduce on the crop. This bug is pictured on sorghum. 4mm Photo: K. Power

 
This image shows the top and underside of rutherglen bug adults (left) and nymphs (right). Photo: QDPI

 
The most common field crop attacked by the rutherglen bug is sunflowers. Photo: M. Dillon