Introduction - What is a Weed?
Insect traps for monitoring and control
Insect traps are useful tools for monitoring insect populations to determine the need for control or the timing of control practices. In some instances, attractants and traps also can be used to control insect populations directly by mass trapping or mating disruption. Mass trapping is most likely to be effective when the density of the target pest is low and immigration into the trapped area is minimal, as is the case in restricted environments (e.g. greenhouses).
Insect traps consist of a visual (colour, shapes and light) and/or chemical (scent) attractant to attract the target insect, plus a device to capture the insect once it arrives. Most insect traps either use glue to immobilise insects or have funnel structures to prevent them from escaping.
Coloured sticky traps (blue, yellow or white) or water traps
They are useful for monitoring adult insects in the nursery or field.
- Yellow sticky traps and water traps have been used for monitoring adult leafminers, whiteflies, aphids (winged forms) and thrips among other insect pests. Thrips are also attracted to white and blue. As the yellow colour attracts many insect species, including beneficial insects, use yellow sticky traps only where necessary. Coloured traps can be easily made at home (see below).
- Water traps are also useful for trapping aphids thrips and leafminer immatures that drop to the soil to pupate. Sticky and water traps need to be checked regularly; the trapped insects should be identified and counted and the traps serviced.
The sticky boards have to be changed, or the water replenished, once they are covered by insects, dust and/or debris, otherwise they will not be effective.
Light traps
They can be used to catch moths such as armyworms, cutworms, stemborers and other night flying insects. Light traps are more efficient when placed soon after the adult moths start to emerge but before they start laying eggs. However, light traps have the disadvantage of attracting a wide variety of insects. Most of the attracted insects are not pests. In addition, many insects that are attracted to the area around the light traps (sometimes from considerable distances) do not actually fly into the trap. Instead, they remain nearby, actually increasing the total number of insects in the immediate area.
Pheromone traps
A scent lure may smell like food to an insect pest or, more frequently, like pheromones. Many insects, release an odour to signal their readiness for mating, specially the females (sex pheromones), or to attract other insects (male and females) from the same species (aggregation pheromones). These odours can be reproduced in a laboratory. This material is then applied to a rubber cap or other device and the scent is released slowly over several weeks, attracting the insects to the collection device.
Several types of pheromones traps have been developed for monitoring and mass trapping African bollworms, cutworms, fruit-flies, etc. and are widely used. However, in East Africa pheromone traps are, in the rule, not locally available, and imported ones are not affordable to smallholder growers.
Because pheromone traps are so effective and specific, they are useful for mass trapping pests. For that purpose, numerous traps have to be placed throughout a pest's environment, so that enough insects are trapped to substantially reduce the local population and limit the damage it causes. When aggregation pheromones are used to attract adult beetles of both sexes, traps may reduce the feeding damage caused by the adult insects and reduce reproduction by capturing adults before they lay eggs. When sex pheromones are used to capture moths, success depends upon capturing males before mating occurs. Pheromone lures must be changed on a regular schedule.
