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WHAT ARE PHEROMONES AND HOW CAN THEY BE USED FOR PEST CONTROL?

Here we take a look the use of pheromones (or more accurately, semiochemicals) for pest control, a segment of the industry that is likely to see growth in future years.

 

Most pest managers would have heard about pheromones, but what are they and how can they be used in pest control?

The ability to communicate through the use of chemicals is one of reasons insects have been so successful. The word ‘pheromone’ is often used to describe any chemical communication, but actually the word semiochemical is a more accurate term to describe chemicals used in communication. There are two main groups of semiochemicals: pheromones and allelochemicals (Figure 1).

 

Figure 1: Hierarchy of semiochemicals

 

The first group, pheromones, describe communication between individuals of the same species. There are two distinct types of pheromones: releasers and primers.

Releaser pheromones initiate immediate behavioural responses in insects upon reception. These are probably the group of semiochemicals most familiar to pest managers and include sex pheromones, trail pheromones, recruitment pheromones, alarm pheromones and aggregation pheromones.

Primer pheromones cause physiological changes in an animal – the chemicals affect the brain, which in turn stimulates the release of hormones which result in a physiological effect. Caste determination in social insects would be a classic example.

The second group of semiochemicals, called allelochemicals, and are used to describe communication between individuals of different species. Allelochemicals can be further broken down into three types:

 

  • Kairomones – chemicals that benefit the recipient of the signal. One example would be mosquitoes using carbon dioxide and other chemical cues to locate a potential host.
  • Allomones – chemicals that benefit the emitter of the signal. Defence secretions would be a good example of an allomone. The odours released by carnivorous plants to attract insects would be another.
  • Synomones – chemicals that favour both the emitter and recipient. A common example would be the odours released by flowers to attract pollinators; the plant benefits from pollination and the insect is rewarded by nectar.

 

Sometimes a chemical can be both a pheromone and a kairomone. For example, a predator may ‘eavesdrop’ on an intra-species chemical communication, such as a trail pheromone, to find its prey.

With semiochemicals able to have a profound e ect on insect behaviour, it is perhaps not surprising that there has been and continues to be significant research into how they can be utilised in pest control. A number of commercial products in the agricultural and pest control markets use semiochemicals.

These products fall into three categories: monitoring devices, traps and disruptors. Most pest managers would be familiar with the cockroach sticky traps as monitoring devices – a number of which use cockroach aggregation pheromones in their lure. In terms of traps, flies and mosquitoes have been the focus of much research; muscalure (Z-9-Tricosene), a house fly sex pheromone that attracts male flies, has been used in traps, baits and surface sprays. A range of mosquito traps on the market use a variety of kairomones as attractants. Often the decision as to whether a product is marketed as a monitoring device or a trap is determined by its effectiveness in decreasing the population.

Disruptors may be a less familiar type of product, but they are becoming increasingly common in agriculture and in managing stored product pests as they can be highly effective in reducing populations. They utilise sex pheromones, which are highly specific and can be detected by the target insect at very low concentrations – often a single molecule is enough to elicit a response. This is perhaps not surprising as male insects need to find females from a distance and fly up a concentration gradient to find them; as the amount of pheromone detected increases, the male knows it is getting closer to the source, and a potential mate.

Disruption devices work on the principle of flooding the area to be protected with the specific sex pheromone, making it impossible for males to find mates, thus preventing reproduction and suppressing the population. With a suitable slow-release mechanism they can keep the area protected for prolonged periods. With the pressures to reduce pesticide use, the utilisation of pheromone products in IPM programs is likely to become more prevalent.