A pheromone is not always a single substance

In practice, we often encounter the idea that a pheromone is one specific chemical compound that reliably attracts the target insect species. However, the reality is more complex. In a large proportion of insect species, a pheromone is not made up of a single molecule, but rather a precisely defined mixture of several substances in a specific ratio.

It is precisely this combination that determines whether an insect responds to the signal – or completely ignores it.

How insects distinguish the “correct” signal

The olfactory apparatus of insects is extremely sensitive, but at the same time highly selective. The antennae contain various types of chemoreceptors, each of which responds to a different type of molecule (e.g. alcohol, aldehyde, acetate).

Only when:

• several correct components are present,
• in the correct ratio,
• and in the correct temporal and spatial context,

does a complete signal arise in the insect's nervous system, triggering a typical behavioural response – for example, flight towards the pheromone source.

Multi-component pheromones as a species barrier

One of the main reasons why pheromones consist of several components is to prevent interspecies mating. In nature, related species that live in the same environment and are active during the same period often occur.

The differences between their pheromones may lie in:

• the composition of the blend,
• the ratio of individual components,
• or the presence of so-called synergists or inhibitors.

Even a small deviation in the ratio may cause a pheromone to stop working – or start attracting another species.

Example from practice: one pheromone, multiple species

An interesting fact is that the same chemical substance may occur in the pheromones of several insect species. However, what is decisive is not the component itself, but its combination with other components.

Therefore, it is not true that:

“When we know the main active substance, we know the entire pheromone.”

In practice, this means that simplified or “abbreviated” pheromone blends may have:

• lower effectiveness,

• a shorter range or undesirable incidental catches.

   

The importance of component ratios

With multi-component pheromones, the precise ratio of individual substances is crucial. This ratio is:

• species-specific,
• often optimized by evolution,
• and verified in practice through field tests.

A change in the ratio can lead to:

• reduced attractiveness,
• changes in insect behaviour,
• or a complete loss of effect.

Therefore, the development of a high-quality pheromone is always a combination of chemical analysis and biological testing.

Impact on pheromone traps and monitoring

The use of correctly formulated multi-component pheromones is of crucial importance for:

• accurate population monitoring,
• reliable determination of the onset of swarming,
• effective mass trapping.

Conversely, poor-quality or simplified blends can lead to erroneous conclusions and incorrect decisions in stand protection.

Conclusion

Multi-component pheromone blends are not a complication, but a necessity. They reflect the biological reality of insect communication and ensure high species selectivity as well as effectiveness.