Sustainable and low-cost traps help control the main banana pest

Researchers from Embrapa Mandioca e Fruticultura (BA) adapted sustainable and low-cost traps that help control the beetle Cosmopolites sordidus, transmitter of the rhizome borer, or banana borer, the main crop disease in Brazil. The traps consist of pieces of pseudostem or rhizome cut from already harvested banana plants — the rhizome is the part below the ground, the true stem of the banana tree — that attract the insect by its odor. Another advantage is that the wedge-type trap can be used in an organic production system, whether or not associated with biological control with beauveria bassiana, a fungus that can parasitize insects, killing or disabling them.

The banana borer vector

An insect that measures approximately 11 cm long by 5 cm wide in adulthood is the main pest of banana and plantain crops (terra type banana trees) in all Brazilian regions. Due to the rhizome borer or banana borer, losses can reach up to 80% of production.

Active at night and commonly known as banana mole, the Cosmopolites sordidus It spends the day in humid and shaded environments, next to tussocks and cultural remains scattered across the banana plantation soil. “This insect has a nocturnal habit. We can say that it lives freely because it is not confined to the rhizome of the banana tree”, explains entomologist Marilene Fancelli, a researcher at Embrapa who has studied monitoring the insect for more than 20 years.

The severe attack on plants occurs precisely in the larvae phase, affecting the emission of roots, impairing the absorption of water and nutrients, weakening the plants and making them more sensitive to tipping over – a problem that is accentuated in plane trees due to their larger size – and to penetration of pathogenic microorganisms, capable of producing infectious diseases in their hosts under conditions favorable to their survival and development.

Monitoring via traps

To combat the banana moleque, Embrapa's solution comes from work in the public domain with the increase of a new possibility, sustainable and using resources available on rural properties. “We use long-standing knowledge that the adult insect is attracted to the odors of the plant: the pseudostem or the cut rhizome. The adult insect is always looking for a new host to develop and begin the infestation cycle. Based on this information, traps were developed to monitor adult insects and all dynamics in terms of population monitoring were based on the number of insects found in the traps”, says Fancelli.

The control level varies from two to five insects per trap, with a maximum of five in the case of older banana plantations. The best-known monitoring traps are of the cheese and tile type, which have these names due to their shape, but evaluations carried out by Embrapa since 2015 in plane tree cultivation in the lower-southern region of Bahia demonstrate the superiority of another trap, shaped like a wedge, which contributed 40% of the insects captured in the area, with the other two types capturing 30% each.

Technical publication

The results were published in Technical Communiqué 166, with the authors being Juliana Silva Queiroz, at the time a fellow at Embrapa Mandioca and Fruticulture, researchers Marilene Fancelli, Maurício Antonio Coelho Filho and Carlos Alberto da Silva Ledo and César Guillén Sánchez, professor at the University of Costa Rica, at the time a researcher at Corporación Bananera Nacional (Corbana).

Trap types

The tile-type trap is made with the pseudostem of the banana tree, which is the part that is above ground level and is cut at around 60 centimeters in height. By splitting this stem lengthwise, two traps are obtained. “When this material is harvested, the cut part remains on the ground, we invert its position and the insect will be attracted to the trap and remain in that cut part in contact with the odors of the banana tree”, explains the researcher.

The traps are made with already harvested banana trees. They are more attractive after they reach the flowering phase and after harvesting as well, which is why the attractiveness of this material is greater for the insect. It is recommended to cut the most basal part of the plant, which is the material that is most humid. These tiles have to be located at the base of the clump on the side of the banana tree that has not yet produced the bunch”, he continues.

According to literature data, the cheese trap is around ten times more attractive than the tile trap and must be done within 15 days of harvesting so that it can maintain adequate humidity to attract adult insects. The researcher describes the process: “A very low cut is made at the level of the rhizome, around 15 centimeters high. It is a partial cut so that the piece of pseudostem still remains attached to the lower part of the rhizome. It will open like a mouth, leaving about 10% of the area still uncut. This way, you can even place a support to encourage the release of gases that attract insects.”

The sandwich trap is produced by placing the two parts obtained by cutting the pseudostem one on top of the other in a horizontal position at the base of the banana clump. “There is then one tile at the bottom and another at the top. The attracted insects will stay between one slice and another”, reports Fancelli.

How to carry out monitoring

To carry out monitoring, the producer must distribute 20 traps per hectare and return to the locations one week and two weeks after distributing the traps, count the number of insects found in each trap and add up all that he found and divide by the number of traps. “Then it has a population average in the first assessment and in the second assessment. It calculates the average of these two evaluations and has the population average in the banana plantation, in the lot or in the evaluated plot. If the average is more than five adults, he is already losing, he is already suffering losses, so he needs to start controlling it”, advises Marilene.

The wedge trap is adapted from a version developed in Costa Rica, and considered the most efficient for population monitoring and control of the rhizome borer. Entomologist César Guillén Sánchez uses traps in Costa Rica as a method to determine insect populations and possible control alternatives. “I evaluated these traps mainly for Cavendish and Gros Michel bananas. In the case of plane trees it is a little different, as there is not always a lot of freshly harvested plants available to make traps. In this case, I use the recently harvested plants that are present and complete the remaining ones with other types of traps, which are also efficient when there is not enough material available”, he comments.

The wedge trap must be made with plants harvested within a maximum of 15 days. Initially the pseudostem must be lowered to a height of 50 cm and then two cuts are made in the pseudostem approximately 15 cm above the ground in a horizontal V shape. The upper cut must form a 45° angle to the lower cutting surface, parallel to ground level. “As it has more exposure area in relation to the rhizome, it managed to attract more insects than the other traps we tested”, he reports.

Agronomist Tiago Struiving, a consultant for large banana farms in the north of Minas Gerais, has been a fan of the wedge trap for years. “For monitoring, we normally make a small number of baits, 30 to 50 per hectare. When it is for control purposes, we bait the area as much as possible to reduce the insect population,” he explains.

For Struiving, the main advantages are the practicality and longevity of the trap: “In everyday life, it is more practical to make than the cheese and tile type and apparently the wedge has a longer period of attractiveness”.

Insect development phases

O Cosmopolites sordidus It has four stages of development: egg, larva, pupa and adult. Females lay eggs singly in small holes opened on the periphery of the rhizome, close to soil level. Three to four days later, larvae are born and begin building galleries both inside and on the periphery of the rhizome, feeding on the rhizome tissue.

The larval phase lasts between 30 days and 45 days and is quite severe for the plant which, in general, presents reduced development, yellowing of the leaves and subsequent drying, lack of fruiting and, especially in young plants, death of the apical bud, which would generate the vertical growth of the plant. At the end of this time, the pupa is formed, which is located on the periphery of the rhizome but no longer feeds. The pupal stage lasts about seven days, after which the adult emerges, a black beetle.