Science - February 24, 2005

Luring banana weevils to their death

The scent traps that are used in Central America to catch banana weevils are not so effective in East Africa. This pest can probably be better controlled by introducing a pathogenic fungus into the pheromone traps where the banana beetles are lured that is then spread among the population, according to the PhD research done by William Tinzaara from Uganda.

The banana weevil (Cosmopolites sordidus) wreaks havoc in banana fields over the whole world. The larvae of the beetle eat their way through the underground root system of the banana plant, cutting off the sap flow and sometimes killing the plant. Tinzaara devoted his research to examining environment-friendly ways of controlling the weevil using pheromone traps.

Pheromone traps are fairly successful in Central America. The traps contain the pheromone sordidin, to which both male and female weevils are attracted in large numbers. There is now even a synthetic version of the weevil pheromone available, Cosmolure+, and this is used on banana plantations, where an average of four traps per hectare are laid to trap the weevils in large numbers.

Tinzaara carried out field tests in Uganda using the traps, but they were far less effective. The weevil population declined by far less than in Central America and damage to the corms was hardly reduced at all. Professor Arnold van Huis of the Laboratory of Entomology, and also a supervisor of Tinzaara, thinks it has to do with the different conditions in East Africa. ‘The situation in Uganda is very different from Central America. In the banana republics you have plantations, whereas the ways in which bananas are grown in Uganda are far less uniform.’

Using pheromone traps as a direct form of pest control would therefore seem to be less suitable in East Africa. However, the traps can be used indirectly as a way to spread the pathogenic fungus Beauveria bassiana, which can be used for biological weevil control. The fungus spores are added to the pheromone in a trap. The weevils that enter the trap pick up the fungus and then spread it among fellow weevils.

Van Huis: ‘This is an effective form of pest control, because the fungus works selectively. You can also increase the attractiveness of the pheromone traps by including rotting banana material – the combination of these together with the pheromone is irresistible for the weevils.’ A sandwich PhD student is now doing further research in Uganda on this promising form of pest control. / GvM

William Tinzaara receives his PhD on 25 February. His promotors are Professor Arnold van Huis and Professor Marcel Dicke of Entomology.