Research

The effect of Eugenol in Syzar

The effect of Eugenol Aromatic substances play an important role in the life of all kinds of organisms. Plants are no exception. They use their scents for various purposes, and a plant may therefore smell differently in different situations. The smell is not always perceivable by the human nose, but we have managed to establish it by means of sophisticated equipment.

Repellent or attractive. The plant uses the aromatic substances among other things to attract insects for fertilisation, but also for defence purposes. A plant can use aromatic substances to show that it is menaced by an insect. The natural enemies of such a pest are then attracted by the scent, so that the plant can start a direct defence.

Apart from an attracting effect, scents may also have a repellent effect on pests. A scent may be attractive to one pest, but not at all to another.

Our product Syzar is based on the repellent effect of the aromatic substance called Eugenol. Eugenol is often found in plants, but it is especially known from cloves. The repellent effect is very strong for the leaf miner fly. However, the leaf miner fly can only smell the Eugenol when it is close to the treated leaves. If the female leaf miner fly is looking for food or for suitable places to lay eggs, it will encounter the scent of Eugenol each time it is close to the leaf, and her movements will become very faltering. It is driven from one plant to another to find a suitable place to feed and lay her eggs. If the crop is well treated with Syzar, the fly will hardly be able to find a suitable place, so it will feed less. This results in fewer spots on the crop.

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Study of the black vine weevil

At the end of the summer, the black vine weevil is a common sight, and is very easy to recognise. He is black and has a very clear snout, and is indeed a member of the snout beetle family. The weevils live from mid-May to the end of August, and cause a lot of damage to leaves in particular in that period.

In August especially, the weevils are often found in houses, sheds and greenhouses, where they are looking for a suitable place to lay their eggs. This is the most important egg laying period for the females, and they hatch reasonably quickly, so that the larvae can be found in the ground in the period from mid-July to mid-October. During this period, they can do a great deal of damage to the roots.

The larvae hibernate from October on, and become active again in spring (around the end of March). Upon wakening, they soon pupate and the weevil crawl out of their pupa in May.

In the past year, DeruNed has made efforts to influence the development of these weevils using Alsa. Tests were undertaken, at a hosta grower for example, for this purpose, with a dosage of 1 litre of Alsa per hectare, repeated weekly. The Alsa was administered systemically in the plant, i.e. via the feed water, in order that the Alsa would be absorbed.

After 4 weeks' treatment, an extensive search was carried out for damage, weevils and any larvae. They were no longer found, and later in the summer too, there were still no weevils in the crop. We were also not able to find any larvae in the ground. Following the success of these tests, we plan to undertake many more tests this year, in order to be able to give good advice on treatment.

Interaction between insects and plants

Interaction between organisms is generally brought about by aromatic substances. The pheromones are of course well known in insects, because of the important role they play in finding a partner for reproduction purposes. Insects can also use aromatic substances to find nutrition from a great distance however, and they are attracted by specific aromatic substances of certain plants. Others actually repel these insects, and it is often a combination of various aromatic substances which makes an insect decide whether or not to visit a certain crop.

All insects are looking for vitamin B, amino acids and minerals, which are found in all plants. It is particularly the availability of these substances which plays an important role. The surface with possible hairs and waxy layers form a barrier for insect access, though the adaptations which the insect itself can make to overcome these barriers are also important of course.

Aromatic substances are also vital to plants. To begin with, scents (and colours) attract insects to the flowers to pollinate them, and plants also secrete aromatic substances if they are damaged by insects or other pathogens. These aromatic substances attract the natural enemies of whatever is attacking the plants. And so the plant has added protection against pathogens. It's also possible that these substances play a role between the plants themselves, helping them warn each other that attackers are present. While this has never been proven, scientists are certainly taking this possibility seriously. Plenty of research will be required on this matter and it is currently being carried out.

Aromatic substances are only required in very small amounts for them to be noticed by the organisms which are sensitive to them. We people can smell certain substances even when the concentration in the air is only 0.001 ppm. Yet we cannot detect other substances at all. The same occurs with insects. Their sensitivity to aromatic substances depends very strongly on the organism, and plants and animals have geared themselves to that during evolution. Plants have developed repellent substances for example, against the insects found in their normal ecosystem. If these plants are moved to other parts of the world, they suddenly become susceptible to the same insects. A good example of this is the Neem tree, which is originally only found in Burma. There, the tree has adapted well to would-be attackers, and has produced repellents and even insecticides to deal with all the insects which attack it there. In Burma therefore, the tree is no longer bothered by these insects. Now that it's been imported elsewhere in the world however, the tree has proven sensitive to all kinds of diseases, including many insects. Some of the insects can even be found in Burma, but they have evolved slightly differently and are not sensitive to the aromatic substances excreted by the neem tree. There are many such examples in which changes in ecosystems can have important consequences for both the interaction between plants and insects and for the natural regulation process.

Secondary defences of the plant

The plant has a number of systems in order to ensure it won't be damaged. The most important of these is of course the waxy cuticle layer and the bark. We have also seen that aromatic substances play an important role in an insect's choice to visit a plant. These are the primary defence systems of a plant. When a plant is at risk of damage, it produces different substances again in order to shake off its attackers. This includes not only insecticide type substances and growth inhibitors but also aromatic substances. These are secondary defence systems. They are local, which means that the root can have a different secondary system to the stem or the leaf. This can have strange consequences.

A bulb of garlic is capable of producing anti-mould substances for example. These are stored in the bulb and only released when there is a risk of it becoming affected. Many plant-sucking insects apparently also detest this scent. In nature, they won't encounter it, because it's contained within the garlic bulb. If we extract this aromatic substance from the bulb and add it to the feed water of the garlic plant, the scent is released around the plant and insects such as thrips and whiteflies will be repelled. They will flee from this scent, even though thrips are normally a very common problem for garlic !!!!

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Decomposition of organic material

In nature, organic material will be reconverted into useful products for other living organisms. Many of these products will serve as food for plants but also animals (and people), bacteria, moulds and viruses can live off them.

A number of processes are possible in order to reconvert the (generally dead) organic material.

Microbial conversion

This type of conversion is very common, and makes use of oxygen. The bacteria (and sometimes moulds) which use oxygen can make optimum use of the available nutrients. These micro-organisms use the nutrients for manufacture of their own building blocks and for production of energy. Part of the nutrients is therefore lost.

If there is no oxygen present, then rotting takes place, which is incomplete decomposition of the organic material. In such conversions, all kinds of by-products can be formed which may be harmful for other organisms (e.g. plants). The micro-organisms can extract much less energy from the same volume of organic material and will therefore have to convert more organic material for their energy supply. They will also need more organic material for their development. The growth of these micro-organisms is often relative to the conversion rate of the organic material. They therefore grow much slower than micro-organisms growing in the presence of oxygen.

Enzymatic conversion

If the enzymes used by the micro-organisms for conversion of organic material are isolated and then deployed separately, the same full decomposition can take place without extracting oxygen from the environment. In many cases, oxygen is not essential for direct conversion.

In time, the enzymes fail to work because the decomposition products have an inhibiting effect on the enzymes. The reaction will no longer take place after a while.

Conversion by micro-organisms and enzymes.

If both enzymes and micro-organisms are deployed to decompose organic material, the added enzymes will do most of the work. They will become less effective in time however, due to the inhibiting effect of the decomposition products. The micro-organisms can immediately absorb these decomposition products and ensure that the inhibition ends. Due to both of them being present, decomposition will be accelerated, while the oxygen supply in this area only depends on the growth of the micro-organisms. In the case of very explosive growth, the oxygen will become depleted; in all other cases, sufficient oxygen will be diffused to this area.

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