Pheromone traps, lure insects to their end… with scents!

Biological control against pest insects is all the rage, and pheromone traps are proving to be effective and natural solutions. Previously, only professionals would use these traps. But they’re slowly are making their way into family gardens and orchards.

Note that a single trap can’t protect against all attacks. Here, you’ll read how and when to use these special kinds of traps.

So, what are pheromones exactly?

Before understanding what a pheromone trap is, let’s dive back to our schoolday lessons. Remember what pheromones are? No? Here’s the answer: they are chemical molecular substances produced by animals, especially insects. In a word, “scents”. They essentially allow them to communicate and send messages to other individuals of their species.

For insects, key pheromones trigger interactions between males and females to enable mating and reproduction. Other pheromones are related to territory, while others still broadcast the presence of interesting food. Another set of scents transmit alert messages when danger lurks…

How do pheromone traps work?

In biological control, the most effective lure are sexual pheromones. These are used in traps. In practice, the traps release fake, synthetic pheromones, that would normally be secreted by females during mating season to attract males . Males are therefore tricked and trapped instead of meeting up with females.

Without males, females can’t reproduce. For species with high reproduction rates, traps greatly reduce numbers for that generation. Furthermore, these traps allow gardeners to know when the breeding period begins and ends.

There are two types of pheromone traps:

• The funnel or water pheromone trap: pheromones are released from a capsule placed in a funnel sealed with a lid (see main picture at top). The funnel is filled with water and males drown in it, exhausted by their flight.
• Sticky plate or delta pheromone trap: this triangle-shaped device resembles a tent in which a sticky plate serves as a floor. Males stick to it.
• Collar-shaped traps are placed around trees against processionary caterpillars.

There are also chromatic traps, often yellow or blue. These two colors attract certain insects.

Pros and cons of pheromone traps

Widely used in organic farming, pheromone traps offer many advantages:

• They help avoid the use of chemical or synthetic products, which may be organic today, but aren’t fully harmless for soil and water.
• These traps target a specific pest population and normally have no impact on other more beneficial species.
• They are very easy to set up and use.
• Capsules work for 4 to 6 weeks and can be used in all weather conditions. The trap itself is reusable year after year.

The only disadvantage they have is that they’re actually good at annihilating a pest species. Yes, you have to be a very zen gardener!

Indeed, one could argue that even insects who eat our fruits and young vegetable shoots are also useful and contribute to the great cycle of life. Other gardeners prefer to trust helper fauna by planting plants that attract birds, certain mammals like hedgehogs, or reptiles such as lizards.

What are the target pest insects?

There are different types of pheromone traps, specific to particular species. In general, it’s primarily butterfly (Lepidoptera) and fly (Diptera) that are targeted.

In the vegetable garden

• carrot fly (Psila rosea)
• leek moth (Acrolepiopsis assectella)
• bollworm of cabbage and tomato (Noctuidae)
• tomato leafminer (Tuta absoluta)
• pea moth (Cydia nigricana)
• click beetle (Agriotes sp.)

In the orchard

• cherry fly (Rhagoletis cerasi)
• Mediterranean fruit fly (Ceratatis capitata)
• codling moth of apples, plums, and pears (Cydia pomonella)
• olive fly (Dacus Oleae)
• oriental fruit moth of peach (Cydia molesta)

In the ornamental garden

• processionary caterpillar
• red palm weevil (Rhynchophorus ferrugineus) 
• boxwood moth (Cydalima perspectalis)
• horse-chestnut leaf miner (Cameraria ohridella).

How do pheromone traps work?

Pheromone traps must be placed as close as possible to vulnerable plants to be fully effective. Therefore, in a vegetable garden, the trap is set among the vegetables, about 2 feet (60 cm) above so that insects get trapped during their flight.

In the orchard or decorative garden, pheromone traps are hung in the heart of the tree, at a human’s height.

The number of traps needed varies. It is generally easy to compute from information on the packaging.

When to use them?

Herein lies the main difficulty! Indeed, when to install pheromone traps is entirely dependent on the breeding period of each insect. But, in general, they are set from the early months of spring, when the temperature is sufficiently warmed. It is indeed at this time that insects emerge from hibernation to fly.

For fruit trees, it is advised to wait until the end of blooming so as not to disturb pollination.

They should remain in place until the end of summer since some insects have multiple generations. Generally, pheromone capsules inserted into the traps work for 4 to 6 weeks. Therefore, plant to replace them after that span of time.

→ Also read:

• Natural tips to protect the garden against pests
• Fruit fly: Control and treatment
• Diatomaceous earth against garden pests