Banana flower thrips Thrips hawaiiensis
General information and management
Occurrence and seasonality
Banana flower thrips are common in banana flowers and among the fingers of newly emerged hands. This pest is found anywhere bananas are grown but its damage is more significant in the less humid, warm and dry climate of South East Queensland and northern New South Wales. Flower thrips are active throughout the year, with increased activity in January through to April. However, as long as flowers are present they can continuously breed.
Description and life cycle
Female flower thrips cause the most damage. They are 1mm long with a pale brown head and thorax and have a black abdomen. They are generally found sheltering under the bracts or inside the flowers. Male flower thrips are smaller (about 0.7mm long), uniformly cream coloured and tend to occur on the outer surface of the bracts.
Adults and nymphs are found on newly emerged bunches and invade the fruit early when the bunch is still covered by its bracts. Recent work has found that flower thrips are present very early in bunch development, inside the bell whilst it is still upright. Flower thrips breed all year round if flowers are present and migrate progressively down the bunch as bracts lift. The lifecycle takes about three weeks in summer, with full development from the egg to the adult taking place on the bunch or in other parts of the plant.
Damage to fruit is the result of superficial scarring caused by feeding and ovipositing (egg laying). Oviposition damage resembles minute raised pimples on the young immature fruit skin. These have a dark raised centre and can be confirmed by lightly touching the raised area with the fingertips.
Extensive feeding damage causes a ‘corky scab’, a slightly raised grey corky skin covering. This damage is usually confined to the lower hands (flower thrips damage increases on lower hands as populations increase as they move down the bunch, if it is untreated). Usually, it is first noticeable on the outer whirl, where the neck meets the cushion, but can extend to the outer curve of the fruit.
If flower thrips damage is being picked up in the packing shed, the best solution would be to speak to your bell injectors, revise training and ensure that bell injections are being performed correctly (right time and right position).
Flower thrips damage is easy to find in the shed, but it is also possible to find it out in the field. Monitoring for early detection of flower thrips can be done by examining bells of bunched plants every time you’re in the paddock. When large numbers of flower thrips are present, they cause bract-feeding patterns which are ‘lace-like’ in appearance and are lighter than the mauve bracts. These are more pronounced at trimming (when flower thrips populations are highest) and although bunches may already have damage, it gives you an early indication of high pest pressure allowing you to revise training with bell injectors, approximately 12 weeks earlier if assessing damage at harvest in the shed.
Chemical control is best achieved with correct bell injection. Flower thrips can make their way between the bracts into the bell and damage very young fruit before bell injection. Therefore, to limit the extent of this damage, the timeliness of bell injection is important. Inject bells whilst still upright. Increase the frequency of bell injecting during warmer months to account for increased plant growth (if possible, as short as every 4-5 days and extending out to every 7 days in winter). Always check the APVMA website for current chemical registrations before use. Below are insecticides currently registered (March 2023) and permitted for bell injection to control flower thrips.
A range of predatory bugs, predatory mites, ladybird beetles and lacewings can assist in reducing the build-up of flower thrips. Choosing chemical products that are less likely to kill these beneficial insects may assist in suppressing background pest populations.