Banana rust thrips

Scientific name

Chaetanaphothrips signipennis

Description of adult

The adult is slender, 1.5mm long, creamy yellow to golden brown with delicate feathery wings. The front margin of the wings is made up of a fringe of black hairs and, when at rest, these give the adult thrips a characteristic longitudinal black stripe down the middle of the abdomen. Two eye-like dark patches at the base of the wings are characteristic of adult rust thrips. These patches can be used to distinguish from the smaller males of the banana flower thrips.

Immature stages

Eggs are not visible to the naked eye. The wingless creamy white larvae are smaller but have the same shape as the adult. Pupae are white, 1mm in length, similar to the larvae and can crawl.

Life history

Eggs are laid just below the fruit or pseudostem surface. In summer, eggs hatch in about eight days. The larval period lasts about 8–10 days. The pupal stage lasts 7–10 days and is spent in the soil at the base of the plant.

Adults move back up to the plant and may live for many weeks forming colonies under leaf shelters on the pseudostem and in the bunches. A complete life cycle may take up to 3–months. Development is slower in winter.

Distribution

Rust thrips occur in coastal areas of Queensland and northern New South Wales.

Host range

This pest has been found in citrus and in some native plants but the main host is bananas.

Damage

Major and frequent.

Feeding by adult and nymphal stages causes the damage. The early symptoms appear as water-soaked smoky areas where the colonies congregate to feed and oviposit between touching or adjacent fruit. These areas then develop the typical rusty-red to dark brown-black discolouration.

Top hands are usually the most seriously affected. This pest produces distinctive localised damage that must not be mistaken as maturity bronzing. In severe cases the skin develops longitudinal cracks and damage may extend to cover most of the fruit surface.

This species is particularly troublesome in red soil areas, plant crops and where bunch bagging is not carried out. Fruit that develops during the warmer early months of the year is most at risk. The superficial damage does not reduce the fruit eating quality. However, 'rusty' fruit can be downgraded or rejected, depending on the severity of damage and the current market supply conditions.

Note: Rust thrips damage should not be confused with maturity bronzing, which produces a rusty reddish discolouration on the fingers. While it appears similar to rust thrips damage, maturity bronzing occurs on the exposed outer curve of the fruit and is not confined to areas where the fingers are touching.

Control

Examine 5–immature (one third to half filled) bunches per hectare for rust thrips on a fortnightly basis throughout the year.

Under heavy infestations, rust thrips can produce characteristic V-shaped rust coloured markings on pseudostems as a result of their feeding where the petiole meets the pseudostem. If these marking are observed, the presence of thrips should be confirmed by gently pulling the leaf petioles away from the stem and inspecting these sites with a x10 hand lens.

Cultural

Obtain thrips-free planting material and, if possible, hot water treat prior to planting out. Destroy all volunteer plants and old neglected plantations that harbour the pest and that could act as a source of thrips to spread to other plantings.

Sound (unbroken) bunch covers (which cover the full length of the bunch) do provide some protection if applied very early. These cannot be relied upon to fully protect fruit, particularly during severe infestations. Regular checking of fruit under the bunch covers is essential to ensure that damage is not occurring. Ensure treatments are applied immediately after detection to prevent further damage.

Biological

General predators such as lacewings and ladybird beetles exert some control over rust thrips on the plant, and ants may be effective in removing some of the pupae in the soil.

Chemical

Chemical control should be directed at both the soil-dwelling pupal stage and the adults and larvae on the fruit and plant. Failure to control the pest at both sites will result in continuous reinfestation, especially during the hot, humid periods of the year.

• Soil treatments: The treatments aimed at banana weevil borer in September/October will provide temporary control of rust thrips.
• Fruit and plant treatments: All bunches, the pseudostem and the suckers should be sprayed with an approved pesticide. This control method can disrupt beneficial insects so exercise caution.
• Bunch treatments: Pesticide injection for scab moth provides early bunch protection against rust thrips. Extended protection up to harvest should then be provided by 1–insecticide application to the bunch or by the application of the recommended length of SusCon ribbon at the time the bunch cover is applied.

Chemical registrations and permits

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