Banana flower thrips

Thrips hawaiiensis

Small, slender-bodied active insects are readily seen moving on the surface of young banana fruit, particularly near the 'bell' or male end of the new bunch. Adult females (1 mm) are distinctly coloured - bright orange and black - and are usually found under bracts or inside flowers.

Males (0.75 mm) are pale straw-coloured and are usually found on the outer surface of the bracts. Adult thrips have characteristic wings; the transparent wings have a fringe of hairs around the outside edge standing out in the same plane as the wing. They are easily seen with a x10 hand lens.

The immature stages are wingless, smaller than adults and are pale, almost transparent.

The life cycle, which is completed on the bunch, takes about three weeks. Eggs are laid just below the surface on young fruit and on the bunch stalk. Two active nymphal stages are followed by two or three pupal stages before the adult stage.

Found throughout the banana-growing districts.

Thrips have a wide host range.

Banana flower thrips are major pests in South East Queensland and northern New South Wales and minor in northern Queensland.

Thrips cause corky scab, which is primarily a problem in the drier banana-growing areas. In northern Queensland thrips are active throughout the year. Fruit harvested in winter or spring is usually the most affected, indicating that the period of greatest activity is after the wet season.

Fruit damage is caused by feeding and oviposition. Feeding damage results in slightly raised areas on the fruit that are grey-brown to grey-silver at first. They develop to form the corky raised areas of brown corky scab. Damage is confined in most cases to the outer curve of the fruit, particularly near the cushion end where the fruit finger joins the bunch stalk.

In severe infestations, damage can spread to other areas of the fruit. Bottom hands (closest to the male flower) are most at risk, but in severe cases, damage can extend to cover most of the bunch.

Oviposition on young fruit produces minute raised spots with a dark central tip on the fruit surface. This damage has little economic importance since it becomes almost unnoticeable as the fruit develops and matures.

No direct relationship between thrips numbers and subsequent damage is evident indicating that other factors, apart from pest numbers, are important in determining fruit damage.

Biological
A range of predatory bugs, ladybird beetles and lacewings assist in reducing thrips populations.

Cultural
Removal of the male 'bell' where adult thrips move after all hands are exposed, may help in reducing thrips populations. This approach has not been evaluated. Evidence from observations and growers' reports suggest that overhead irrigation prevents corky scab in most situations.

Chemical
Bunch injection with insecticide to control scab moth has been very successful in preventing corky scab development in northern Queensland. Treatments should concentrate on bunches which emerge during the period of maximum thrips activity (usually December to March), or at other times if previous experience has demonstrated a different activity period.

Throat applications to the emerging bunch have only proved partially successful. Cover sprays are not recommended because of disruption to beneficial species.

Chemical registrations and permits
Check the Australian Pesticides and Veterinary Medicines Authority chemical database and permit database for chemicals registered or approved under permit to treat this pest on the target crop in your state or location. Always read the label. Always observe withholding periods.