In Australia two species of Cotton Stainers are occasional pests, the Cotton Stainer (Dysdercus cingulatus) and the Pale Cotton Stainer (Dysdercus sidae), which is generally the most common. They tend to be more common late season in crops that have had low spray regimes.
Identification: Adult Pale Cotton Stainers are 12mm long with brown and black or red and black backs. There is a small black spot near the centre of each forewing. There is a black triangular marking ahead of the centre of the back, and black markings occur across the front of the thorax and on the head. The underside is yellow-green with red and black markings. Small nymphs are yellow, becoming red and black as they mature.
May be confused with: Other species that may be confused with Pale Cotton Stainers are the Seed Eating Bug (Graptostethus servus) and the Red Eyes Bug (Leptocoris mitellata). However the Pale Cotton Stainer wings are generally dark (rather than being orange) and have a distinct dark spot.
Lifecycle: Batches of about 100 creamy white eggs are laid in shallow depressions in the soil. Young Pale Cotton Stainers moult through five nymphal stages before reaching adulthood. Two days after the final moult, adults will begin to mate.
Damage: Adults and nymphs feed on cotton seeds. Damage to young bolls often results in black spots on bolls and warty growths on the inside of the bolls. Young seeds may be damaged. However, Pale Cotton Stainers are unusual as they can damage bolls of all stages, even those almost mature. On older bolls (>20 days old) there are no visible signs of feeding on the boll coat. However, if damaged bolls are opened, small black puncture marks can be seen on the inside of the boll wall. The lint of damaged bolls often becomes yellow or brownish, possibly due to the entry of fungi which stain the lint and cause ‘tightlock’ where bolls do not fluff out. Damaged locks of the bolls tend to adhere to the boll coat if the locks are removed rather than coming out freely. The larger end of the seeds, which is closest to the outside of the developing boll often shows dark brown damaged areas if the seeds are cut in half. Damaged seeds are unable to complete the development of fibres. If sufficient bolls are damaged loss of yield, and reduced fibre quality can occur. Even on open bolls, Pale Cotton Stainers will sometimes feed on the exposed seed and will occasionally lay eggs inside open bolls. The germination success of damaged seed can be substantially reduced. Female Pale Cotton Stainers are more damaging than the smaller males or mating pairs.
Monitoring: The abundance of Pale Cotton Stainers and the prevalence of boll damage should be checked weekly once bolls are present. The best way to sample this pest is to use a beat sheet, being aware that they are often more abundant lower in the canopy. Boll damage can be assessed by cutting open bolls of varying ages and examining these for browned, dried damage areas. Confirmation that it is Pale Cotton Stainer damage can be achieved by cutting seeds in half and checking for damaged areas.
Control: Several broad spectrum insecticides are registered for control – their use should be considered carefully as they can disrupt natural enemies which may flare populations of other pests. As there is no resting stage in the Pale Cotton Stainer’s lifecycle, cultural controls between cotton seasons, especially limiting access to alternate food sources such as volunteer or ratoon cotton and exposed fuzzy seed will assist greatly in delaying population development.
Natural Enemies: A range of natural enemies such as Tachinids (parasitic flies) and predatory bugs (e.g.Assassin bugs) have been recorded in Africa. The role of natural enemies in the control of developing populations of Pale Cotton Stainers in Australia has not been studied.
