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Pheromone trapping


Pheromone trapping

Pheromone pitfall trap

Photo by Nicolas Fégeant, UGPBAN

Pheromone trapping is a technology that uses pheromones (chemical substances that are secreted by members of the same species to trigger specific responses) to attract insects to a trap. In banana plantations, pheromone traps are used against the banana weevil (Cosmopolites sordidus). The trap is baited with a pheromone that is specific to the weevil and attracts both sexes.

Weevils are also trapped by laying down pieces of pseudostem on the ground, but the effectiveness of these traps is variable. Moreover, the weevils can walk out unless the traps are baited with insecticide. Nevertheless, since pseudostem traps do not require buying traps and lures, they are still widely used, even in large commercial plantations.

Methodology

The main elements are the trap and the pheromone.

The trap

Container of a pitfall trap (photo by N. Fegeant, UGPBAN)
Container of a pitfall trap (photo by N. Fegeant, UGPBAN)

There are different kind of traps depending on the target insect. For weevils, a pitfall trap is generally used. It consists of a small yellow plastic box; to be visible from a distance. The container is buried in the ground. It can be empty or filled with soapy water. The cover closes the trap and holds the pheromone. A space between the two parts provides an entry for the weevils to fall in the trap. The opening is high enough for the weevils to pass through but limits the accumulation of residues.

The shape of the trap will be different if a biological control agent is added (see below) to allow the insect to escape after it has been contaminated.

The lure

The demonstration that the male weevil secretes a pheromone dates back to 1993[1]. Soon after, the main active ingredient (C11H20O2) was isolated and named sordidin[2]. The chemically synthetised sordidin (marketed as Cosmolure) used in pheromone traps is often mixed with isoamyle acetate. The pheromone attracts adult weevils within a 10 to 20 meter perimeter.[3]. Rain can interfere with the dispersal of the pheromone.

Uses

Pheromone traps have two main uses: monitoring population levels and controlling weevils by mass trapping. It is also recommended to trap the resisent weevils before planting a new plot.

Monitoring

Pheromone traps can be used to alert producers to the presence of the pest and to monitor the population before the infestation becomes serious. The recommended density is 4 traps per hectare[4]. Since pheromones only attract moving adult weevils, and as many as 75% of the weevils in a plots live inside a plant, it is important to prevent populations from getting out of control.

Mass trapping

Mass trapping is used to bring the weevils under control in heavily infested fields, in which case 16 traps per hectare placed 20 m apart are recommended. Computer simulations suggest that control is not improved when there are more than 16 traps per hectare[4]. It is also recommended to regularly check the traps (twice a month) in order to collect the trapped insects. A three-year study in 12 commercial banana plantations located on the Cariibean island of Martinique showed that the largest number of weevils were captured between the 40th and 80th month after planting and during the dry season[5] .

For a better control, trapping should be managed at the level of the plantation and take into account neighbouring plots (fallows or abandoned plots) that can be sources of weevils. To limit colonization from neighbouring plots, it is recommended to install a series of pheromone traps at the edge of the plot (1 trap every 20m).

Weevils parasitized by an entomophagic fungus (photo by N. Fegeant, UGPBAN)
Weevils parasitized by an entomophagic fungus (photo by N. Fegeant, UGPBAN)

Mass trapping within a fallow will improve weevil control and protect nearby fields from migrating adult weevils. In a study conducted in Guadeloupe, the number of weevil captures was highest 10 to 20 weeks into the fallow and decreased to zero after 9 months[6].

Coupling with biological control agents

Scientists are experimenting with biocontrol agents such as entomopathogenic fungi (Beauveria bassiana and Metarhizium anisopliae) and nematodes (Steinernema carpocapsae and Steinernema feltiae) to increase the efficiency of the traps. The weevils would enter the trap to get contaminated and then leave to in turn contaminate other weevils[4]. The technique is also being tested with thrips[7].

References

1. Budenberg, W.J., Ndiege, I.O. and Karago, F.W. 1993. Evidence for volatile male-produced pheromone in banana weevil Cosmopolites sordidus. Journal of Chemical Ecology 19(9):1905-1916.
2. Beauhaire, J., Ducrot, P.H., Malosse, C., Rochat, D., Ndiege, I.O. and Otieno, D.O. 1995. Identification and synthesis of sordidin, a male pheromone emitted by Cosmopolites sordidus. Tetrahedron Letters 36:1043-1046.
3. Tinzaara, W., Tushemereirwe, W. and Kashaija, I. 1999. The potential of using pheromone traps for the control of the banana weevil Cosmopolites sordidus Germar in Uganda. p.327-332. In: Frison, E.A., Gold, C.S., Karamura, E.B. and Sikora, R.A. (eds.). Proceedings of Workshop on banana IPM, Nelspruit (ZAF), 1998/11/23-28. Mobilizing IPM for sustainable banana production in Africa: Proceedings of a workshop on banana IPM. INIBAP, Montpellier (FRA).
4. Tixier, P., Vinatier, F., Cabrera Cabrera, J., Cubas, A.P., Okolle, J.N., Chabrier, C. and Guillon, M. 2010. Integrated pest management of black weevil in banana cropping systems. From Science to Field Banana Case Study Guide. ENDURE, Paris (FRA). 4p.
5. Duyck, P.F., Dortel, E., Vinatier, F., Gaujoux, E., Carval, D. and Tixier, P. 2012. Effect of environment and fallow period on Cosmopolites sordidus population dynamics at the landscape scale. Bulletin of Entomological Research 102(5):583-588.
6. Rhino, B., Dorel, M., Tixier, P. and Risède, J.M. 2010. Effect of fallows on population dynamics of Cosmopolites sordidus: toward integrated management of banana fields with pheromone mass trapping (p). Agricultural and Forest Entomology 12(2):195-202.
7. Control of red rust thrips of bananas posted on 18 November 2013 on the Wageningen UR website.

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This page is part of a series initiated by a grant from the Ministère français de l'agriculture, de l'agroalimentaire et de la forêt to the World Banana Forum.White