There are different types of traps that can be used to catch insects. Traps are usually used for monitoring insect populations, but some traps can also be used to for controlling pests.
The efficiency of traps depends partly on the mobility of the insects. Therefore traps are usually more effective in catching adult insects.
When traps are used for monitoring, this is often done to predict outbreaks of a pest species and to assist the farmer in making decisions. But care should be taken in the interpretation of results. A sudden increase in insects caught in a trap does not always mean that an outbreak will occur. Farmers will have to use data from traps in combination with other observations to make crop management decisions.
Farmers should experiment with traps in their own fields to increase their understanding of pest populations and to learn how to use traps as a monitoring tool.
When traps are used as a tool to control pests, it should be understood that trap efficiency is related to population density.
Some common traps that are often used to catch insects are: sticky traps, light traps and pheromone traps. Other types of traps include those that are used to kill or capture rodents (mice, rats).
Yellow sticky traps
A number of insect species (aphids, whitefly, flea beetles, some moths) are attracted by yellow color. If a yellow colored card is placed in a crop field, these flying insects will attempt to land on it. Covering the surface with a non-drying glue or with grease will immobilize and kill these insects.
Yellow sticky traps are efficient to monitor population densities of day-flying insects that respond to the yellow color. They can also be used as a control measure for these insects, but that requires placing a large number of traps inside the field.
Besides pest insects, the yellow sticky traps will also attract certain beneficial insects (wasps, flies). When using these traps this will have to be carefully observed. If it becomes obvious that the traps are catching large numbers of beneficial insects it is better not to use the traps.
Light traps
Light traps make use of a light source to attract night-flying insects. They are especially useful to monitor certain species of moths. Catching moths in the light trap will tell the farmer that is time to start searching for eggs or caterpillars in the field.
Different light sources can be used, ranging from simple oil lamps to different types of electric bulbs. Special light sources called black-light have been developed and are particularly efficient because of the type of light they emit. They should be considered in situations when other light sources (houses, street lights) are competing with the traps.
While the light source attracts the insects, the traps need another device to kill or capture them. Often this is a container with water that is placed under the light source. The moths that circle around the light will drop in the water and can be counted the next morning. It is recommended to add a bit of soap to the water. Instead of water, it is also possible to use sticky plates.
Light traps are generally used a monitoring tools and will not have much impact as a control measure. Daily observation of traps will show that not only pest insects but also some natural enemies may be caught. If the traps appear to kill large numbers of beneficial insects it is better to take out the traps.
Pheromone traps
Pheromones can be used as a bait to attract certain insects (especially moths) and catch them in a trap. Usually these traps use a sticky surface to catch the insects, but others use containers filled with water or other liquids to catch them.
Most pheromones are “sex pheromones”. These are chemicals released by female moths to attract a male partner. As a consequence the traps will only catch male moths and usually of only one species. To catch other species, different pheromones will have to be used.
Pheromone traps are very useful for monitoring a specific pest species and will often detect low population densities. However, the traps are not very efficient for controlling pests.
A disadvantage of the pheromone traps is that the chemicals are often expensive and not easily available. On the other hand, they have the advantage that they only attract the pest and will not kill beneficial insects.
