jeudi 28 mars 2019

145- Alternatives to pesticides -4- Sexual confusion


This name may seem barbaric or laughable for the uninitiated. Yet it is a real revolution in the concept of crop protection.

This technique, developed in the 1980s and first developed on vines and fruit production, was later extended to a large number of crops.

The principle is particular:
In lepidoptera, and in several other arthropods, males and females find each other for mating by olfactory signals released into the air.
Specifically, in the case of Lepidoptera, mature females produce a pheromone, a volatile substance that they release into the air, and which is intended to allow males to locate them.

Males have very sensitive olfactory receptors that allow them to locate the pheromone, and to follow the path to find the origin.
When the males find the females, the mating takes place, the females lay fertilized eggs from which the caterpillars, their larvae, will be born, which will feed on the crop by doing damage, until they are able to metamorphose to become breeding adults in their turn.

The technique of sexual confusion consists in diffusing in the fields to be protected, a large amount of sexual pheromone of the harmful insect, by installing a large number of diffusers.
Males are unable to follow a clear olfactory path. They do not find the females, the fertilization does not take place, so there are no eggs or larvae that can do damage to crops.
The crop is protected by preventing the harmful species from developing there.

In fact, this technique is not perfect because chance meetings can take place.
The species is not threatened, but its damage is negligible.
These chance meetings do not represent any agricultural risk, except in certain cases of very excessive (or invasive) presence of the pest. In these rare situations, it may be necessary to supplement the confusion with one or more insecticide sprayings, until the regulation of the populations is sufficient. It's usually pretty fast.
One of the problems of monocultures is the abnormal increase in certain phytosanitary problems, due to the concentration of a single plant species, which never occurs in Nature.
For this reason, among other things, the concern for the respect of biodiversity has become so important in recent years, as well as the many efforts made on farms.
Sexual confusion prevents the abnormal multiplication of the same species.

However this technique is operational for protection against certain insects, especially Lepidoptera, but there are still many against which the technique has not yet been developed.
The determination of the exact composition of the "pheromonal bouquet" of each species is a very long research task. Once determined, it is necessary to find the way to manufacture it, to develop an operational diffusion system (type of diffuser and density per hectare), then to test it to check its effectiveness, and its absence of side effects.

Side effects are usually negligible because each pheromone is specific to a single species, so that males and females can find each other, without the risk of crossing with other species.

In the 80s, I had the opportunity to participate development trials in orchards, in the south of France, of the first technique of sexual confusion against the Oriental fruit moth (Cydia molesta), by a pioneering Australian society. I can certify that it works.
The usual manipulation of the diffusers was that I was impregnated with pheromones, and I was followed by a troop of males, inevitably disappointed when they realized that I was only a vulgar human!
"I'm not the one you believe!"

It should be pointed out that, while this technique is a real alternative to the use of pesticides, it does not, in any way, respond to the stated desire of one part of the civil society to go out of synthetic chemistry.
Indeed, all licensed and available diffusers on the market are filled with synthetic pheromone, copy of natural pheromones (otherwise it would not work). This is called biomimicry. They are produced in chemical plants quite similar to all the chemical plants in the world.
In fact, given the amount of pheromones needed for this technique to work, it's totally inconceivable to extract it from breeding females.

But this technique represents in my opinion a real revolution in the way of conceiving the phytosanitary protection of crops:
We don't try to kill the insect, we try to prevent its population to reach levels of presence that turn it into a nuisance.
It's totally different, and it opens the door to a real change of thought.
We don't need to protect a crop that is not threatened.
But we must be able to prevent aggression from occurring.

This paradigm shift opens the door to other techniques, more natural than sexual confusion, and seeking a similar result in other ways.
We will talk about it again.


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