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Semiochemicals beginner’s guide: Types and how to use

Theme: Basics of biocontrol

Theme: Biocontrol agents

Overview

Semiochemicals definition

Semiochemicals can be used in pest management to control and monitor pests. They do not directly kill pests. Instead, they interfere with their communication and change or disrupt the pest’s normal behaviour. To control pests, some of these bioprotection products require the use of traps.

Semiochemicals are natural chemical compounds emitted by animals or plants into the environment. These compounds can either be extracted from the organism or synthetically produced to mimic the natural compound. Organisms use semiochemicals to communicate with each other.

You can use these products in bioprotection alongside biopesticides like microbials and natural substances.

Some examples of semiochemicals used in bioprotection are:

There are two types of semiochemicals based on who they affect:

  • Pheromones: compounds that are emitted by an organism that affect members within the same species. 
  • Allelochemicals: compounds that are emitted by an organism that affect other species.
A semiochemical pheromone dispenser attached to a branch
A semiochemical (pheromone) dispenser attached to a branch to disrupt the reproduction of sweet corn pests. Credit: Eugene E. Nelson via Bugwood.org

Types of semiochemicals

Pheromones

The majority of semiochemical products contain pheromones. These are compounds that insects emit to communicate with each other. Indeed, pheromones carry messages that can affect their behaviour and interactions. For example, insects can emit pheromones to signal the presence of a mate, food source, or even a threat to other individuals of the same species.

Pests can ‘read’ the message transported by the pheromone. This leads to a behaviour change and is a way to control them.

Semiochemical products can contain different pheromones. The most important ones are:

  • Sex pheromones signal the presence of a mate. Usually, female insects emit these pheromones to signal their presence and attract males. 
  • Aggregation pheromones usually indicate a place to go to, where insects can find food, for example. They usually attract males and females.  
  • Trail pheromones can transmit information like food quality or food location. Social insects like ants emit this type of pheromones.
  • Pherogen Spray FAW® (BR) is based on sex pheromones that prevent males from finding females to mate. As a result, the population gets smaller.
  • Pherodis® (KE) is another product containing sex pheromones that attract males of the tomato leaf miner. To control the pest, the product works in combination with a trap.
A semiochemical pheromone dispenser attached to a delta sticky trap placed in a field
A pheromone dispenser attracting adults of the tomato leaf miner in a delta trap. © CABI

Allelochemicals

Allelochemicals are compounds emitted by an organism that members of a different species can recognize, unlike pheromones that are only understood within the same species.

There are different types of allelochemicals such as kairomones. They usually come from plants and are attractants. They are mainly useful for monitoring pests as part of Integrated Pest Management.

  • Bio Broca® (BR) is a semiochemical that contains a kairomone. It can manage the coffee berry borer. In this case, the kairomone imitates the smell of ripe coffee fruits and attracts females of the pest. By using Bio Broca® together with a trap, you can monitor the level of coffee berry borer infestation and decide when to act.

Semiochemicals in pest management

Semiochemicals interfere with the behaviour of a pest, allowing its capture or repulsion. There are three main ways semiochemicals interfere with a pest’s behaviour:

  • Attraction: the semiochemical acts as a lure and attracts the pest towards it, where you can trap it.
  • Mating disruption/confusion: the semiochemical confuse and disorient the pest. This prevents the pest from finding potential mates. As a result, the pest cannot reproduce, and the pest population decreases.
  • Repulsion: some semiochemicals push pests away from crops, preventing them from damaging them.
A semiochemical pheromone dispenser hanging from an olive tree
A pheromone dispenser for mating disruption in an olive tree. Credit: Esmat M. Hegazi, University of Alexandria via Bugwood.org

How to use semiochemicals

The application of semiochemicals usually depends on the formulation and the mode of action of the product. Typically, you can load semiochemicals inside dispensers that slowly release the product into the environment. Dispensers can be vials, small pouches, rubber tubing, capsules, etc.

  • For example, Caps. Tuta absoluta® (ES, PT) are capsules that release a pheromone, which attracts the tomato leaf miner. The capsules can be inserted inside a trap to catch attracted individuals.

You must apply semiochemical dispensers strategically in the field in order to make them effective. Sometimes, you must combine them with a trapping system to control or monitor a pest. As the compounds emitted by the dispenser only reach a certain distance around it, several dispensers are usually needed to cover an entire field. However, the requirements are specific to each product and type of semiochemical, so this is why you should always refer to the product label for a correct application.

You can apply semiochemicals for two purposes:

  • Direct control: the semiochemicals can help kill the pest or interfere with its reproduction. The main ways to control pests are:
    • Mass trapping and attract-and-kill: you can place the semiochemical dispenser in a trap or use a semiochemical that already comes with a trap, like sticky traps coated with a pheromone. Hence, the lured pest is either removed from the population (mass trapping) or killed (attract-and-kill).
    • Mating disruption: you need to place the sex pheromone dispensers strategically in the field.
  • Indirect control: semiochemicals do not directly control the pest but can help take additional measures to manage it.
    • Detection/Monitoring: you can use pheromones or kairomones-baited traps to detect or estimate the density of a pest population. This helps in choosing the right moment to control it.
      Read more about the use of pheromone traps for pest monitoring.
A semicohemical pheromone dispenser placed in a sticky trap with dead moths glued on the trap
Adults of the codling moth caught in a trap with a capsule emitting a pheromone. Credit: Whitney Cranshaw, Colorado State University via Bugwood.org

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