Banana weevil borer
Bruno Pinese & Rod Elder, Department of Primary Industries and Fisheries
Figure 1. Banana
weevil borer larva, pupa and adults
Adult
Adult weevils are about 10- 12mm long, hard shelled and have the pronounced snout typical of weevils. The newly emerged weevil is reddish brown but soon becomes uniformly dull black. The weevils are nocturnal and hide during the day in or around corms or under moist areas near the plant and in the trash. Unusually sluggish in their movements they feign death when disturbed and seldom fly. Natural spread is very slow. Dispersal is primarily by the introduction of infested suckers and bits for planting.
Immature stages
Eggs are laid singly in a shallow pit at the base of the pseudostem. They are elongate, oval, about 2 mm long and pearly white. The eggs are very hard to find because the oviposition site becomes covered by congealed sap. The soft, creamy-white, stout (up to 10 mm in length), legless larvae have a distinctly curved body, are swollen in the middle and have a hard brown head. Pupae are about the same size as the larvae. Inside the white pupal skin the structure of the future adult with its snout, wing buds, legs and antennae is visible.
Life history
An average life cycle is completed in 12 weeks in north Queensland. The eggs hatch in 8 days. The larvae immediately burrow into the corm and after four moults lasting a total of 3 to 14 weeks depending on temperature, pupate close to the surface of the corm. The short (8 day) pupal period is followed by the emergence of the reddish-brown adult. The pre-oviposition period has been found to be variable and may extend to 40 days. Adults are long lived.
Two peaks in adult emergence and activity have been noted; the first in spring during September and October, and the second in March and April. These peaks are particularly evident in South-east Queensland where activity almost ceases in Winter. In North Queensland, where winter temperatures are higher activity continues throughout the year although at a reduced rate in winter. In North Queensland, dry conditions greatly reduce adult activity, whereas rainfall may be a major factor in increasing adult activity (as determined by adult weevil borer traps).
Distribution
Throughout coastal Queensland and New South Wales, associated with cultivated and wild bananas.
Host range
Hosts include members of genus Musa including banana (M. sapientum) and abaca (M. textilis).
Management
Importance
Usually minor and frequent in northern Queensland but has a greater impact in southern areas; It can become an important pest in poorly managed plantations.
Damage
The larvae tunnel within the corm that lies below the soil surface. When there are large populations, most of the corm tissue and a short distance up the pseudostem may be tunnelled. This tunnelling weakens the plant and renders it susceptible to 'blowdown' in windy weather. Heavy infestations interfere with the movement of nutrients to the plant, and plants appear unthrifty. In severe cases the young suckers whither and fail to develop.
In some situations it is difficult to determine if weevils are the main cause or a symptom of plantation decline, since other factors (primarily burrowing nematodes) may be contributing to poor growth. Because of slower growing conditions, in South-east Queensland, this pest can become a major pest, reducing plant growth and causing extensive plant fall outs.
The economic impact of weevil borer varies considerably with rate of growth of the plant. In northern Queensland, populations are rarely of economic importance and only neglected or poorly managed plantations suffer losses of production that can be attributed to this pest. In southern Queensland, where it is difficult to maintain a high level of plantation hygiene, plant growth is slower due to cooler conditions and where plantations are maintained for many years, the economic significance is much higher leading to yield losses. Typical symptoms of a severe infestation are reduced plant growth, choking of the bunch in the pseudostem, yellow leaves and weak or dying suckers.
The development of insecticide resistance to cyclodienes, and subsequently to the organophosphates, has increased the potential threat of weevil borer.
Action level
At monthly intervals during March to April and September to October monitor populations using 100 mm thick pieces of cut pseudostem as baits during periods of adult activity. At other times 6 weekly intervals would be sufficient. The pseudostem material selected for making baits should be taken from the lower part of the stem of freshly harvested plants. Place at least 20 baits at the base of 20 randomly selected plants and with the cut surface in full contact with the soil after removing any weeds and debris. They should be covered with leaf material to prevent drying out. Count weevils after 3 to 4 days and treat if the average count is greater than 2 adult per trap (in south east Queensland) ie greater than a total of 40 adults over 20 trap baits. In northern Queensland an average count above 4 per trap would be more appropriate. Concentrate baits in known 'hot spots'.
Adult weevil activity increases during warm and/or wet weather and decreases during cold and/or dry conditions. Consequently, weevil borer numbers at baits placed during adverse conditions may not accurately reflect actual population levels.
Regular monitoring of adults will give information on weevil borer trends that can be useful in targeting the correct time for treatment. Chemical control measures will achieve the best result if applied during periods of high adult activity, because more weevil borers will come in contact with the lethal dose of insecticide.
Control methods
Cultural
It is essential to use weevil free planting material. Ideally, planting material should be obtained from weevil-free blocks, plant nurseries or from tissue-cultured plantlets.
When replanting into old banana land, all banana residues must be destroyed and the land left to fallow for at least 6 months after all residues have rotted down to prevent carry over of adults.
Ensure good plantation hygiene by removing all trash from the area around plants and suckers by raking all leaves into the interrow. Cut up all fallen and harvested plant pseudostems to increase the rate of breakdown and destroy breeding sites. This is more important in South-east Queensland where breakdown is slower due to lower temperatures and drier conditions.
Biological
A large range of general predators including ants, beetles and cane toads assist in reducing weevil borer numbers.
Chemical
Apply strictly in accordance with label directions. Select the most appropriate for your area based on known chemical resistance history.
Recommended chemicals
chlorpyrifos, cadusafos, bifenthrin, fipronil, oxamyl, prothiofos, terbufos. Note: This information was correct at the time of publication. However, it is the user's responsibility to ensure that registered agricultural chemicals are used in accordance with legal requirements. (See Further information). Always read the label.
Further information
- Infopest CD-ROM contains current national information on registered agricultural chemicals and is available from Infopest, DPI&F, GPO Box 46, Brisbane, Qld. 4001.or by email from infopest@dpi.qld.gov.au
- Agrilink Tropical Banana Information Kit provides information on all aspects of growing and marketing tropical bananas in Queensland. It is available from the Agrilink website or office (phone 1800 677 640) or the DPI&F Shop On-line.
- For information on Tropical Banana production contact the DPI&F Business Information Centre on 13 25 23 (local call) (8am to 6 pm Monday to Friday); E-mail callweb@dpi.qld.gov.au .
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries, Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last updated 04 February 2004
