Insects and plants. Natural repellents and toxins

you are: Insects and plants

Manufacture of enough of food for all population of the Earth reaching already and now 4 billion and growing with speed of 1,8% year, demands intensive agriculture in which very important role play insektitsidy and herbicides. Plants have some protective mechanisms, and insects in something are vulnerable, and the person, obviously, can exploit both that and another. Works are in this area generally at a stage of research or only are developed, so to their practical appendix while is far; and still new, more effective preparations will receive, possibly, a wide circulation already in the near future. However, until then while it has not occurred, it is necessary to use others insektitsidami though they and not quite meet those requirements which are shown to an ideal preparation. Such preparation should:

1) to kill only that organism for which he is intended (organism-target);

2) to be cheap, simple in manufacturing and convenient in circulation;

3) not to render toxic action on the person and pets not to pollute environment;

4) quickly to break up before nontoxical connections. Many synthetic connections do not break up for the reason that their chemical structure has no analogue in the nature and consequently microorganisms are not capable to split them. It is necessary to search for an exit in that at creation of new pesticides to use as model any natural connections; in flora and insects have many substances which can be applied to decrease in number of population of insects-wreckers.

The substances Containing in much plants doing plants inedible, do not represent in this sense of special value because spraying by them does not provide enough reliable and long protection; they can effectively influence an insect only in a role endogennyh components of plants. However such two substances of a phytogenesis, namely piretrin (monoterpen) and rotenon (flavonoid) (fig. 15.5), nevertheless have found application in quality insektitsidov. At spraying of plants by these substances insects perish; except that, they can be received from plants in enough, i.e. To make on sale. Piretrin receive from a camomile, Pyrethrum, cultivated in Africa specially for this purpose. Both piretrin, and rotenon, being natural connections, possess at least one distinctive feature: they decay bacteria and are not for long kept in the environment. Unfortunately, piretrin it is unstable as well to ultra-violet radiation so it can decay still before will have time to work; recently, however, it was possible to achieve essential success - synthetic derivatives piretrina, proof to ultra-violet radiation and consequently representing much more powerful insektitsidy have been received. Bacteria, fortunately, distinguish and decompose as well these synthetic derivatives piretrina; hence, it is possible to consider that we in some measure managed to carry out an object in view - to create ideal insektitsid. However, these connections operate on different kinds of insects neizbiratelno and, means, it is necessary and to improve them further.

Most likely, the most reliable way to creation ideal insektitsida is connected with the account of features of life cycle of the insect. The chemical preparation, poisonous for an insect, most likely will appear poisonous and for the person as the metabolism of an insect and the person is in general similar. Other business the systems regulating development in insects and at the person: these systems differ very strongly and consequently influence should be directed on them. First of all it is necessary to establish, whether connections interesting us influence those stages of life cycle which are peculiar only to insects, and whether they operate specifically only on one kind of insects. At such approach to this problem three possible ways of its decision are outlined. Transition from one stage of development to another is subordinated at insects to the hormonal control. The juvenilnyj hormone (fig. 15.6) suppresses transformation of a larva into an adult insect. That this transformation has occurred, level juvenilnogo a hormone should go down. Vulnerability a metamorphosis of insects is defined by that the insect, irrespective of its age, cannot make posterity until its transformation into the adult form is finished.

In some plants the substances rather close reminding juvenilnye hormones of insects contain. For the first time this fact has been noticed, when it was found out that larvae of bug Pyrrhocoris apterus cannot finish transformation into the adult form if to grow up them on paper napkins from any paper made in the USA. So, it was found out that in coniferous trees, and first of all in a balsam fir (Abies balsamea), the special effective substance - juvabion (fig. 15.6) contains. Similar substances can quite protect plants from variety of insects. Spraying insects juvenilnym a hormone, it would be possible, obviously to prevent their reproduction. As for lack of the adult form the following generation cannot appear, the  destruction of the larvae processed by this hormone, would mean full eradication of the wrecker or anyway sharp reduction of its number (if any larvae managed to avoid contact to a preparation).

Other possible influence has opposite character. Two substances possessing ability to suppress secretion juvenilnogo of a hormone are found in known ornamental plant Ageratum and to cause premature transformation nepolovozrelyh larvae in the abnormal adult form - in tiny sterile imago. Having learnt to allocate these substances from plants or to synthesise them, we would receive in the order harmless to the person insektitsidy as their action is directed on system juvenilnogo a hormone which is available only for insects. Is at them and one more advantage, consisting that they transform gluttonous larvae in mature individual who more any more are not fed on plants that also promotes crop savings. We, of course, cannot expect from similar insektitsidov strictly selective action, however it is quite probable that known degree of selectivity concerning this or that group of insects is inherent in all of them. insektitsidov this type it is necessary to consider as obvious advantage and that circumstance that stability to them at insects, obviously, cannot develop, in the same way as there can not be at insects a stability to own hormones. Insektitsidnye substances from Ageratum cause also in insects a condition reminding hibernation. If to spray such insektitsidami crops by then when their action will stop, the crop will be sberezhen and it is cleaned, and in the winter the frost will kill wreckers. Similar systems of protection against insects are represented to us by something new, however plants almost for certain use them since the oldest time as insects did at all times them essential harm.

Among secondary metabolitov plants also there are the substances, capable to influence life cycle of insects. A number is found out in the most different plants fitoekdizonov - the connections simulating ekdizony, or hormones of a moult of insects. It was more recently found out that these derivatives of steroids contain in plants in rather significant amounts; at fern Polypodium, for example, on their share it is necessary to 2% of dry weight of a rhizome. Quite often one any kind of plants has a whole set of related connections of this kind. Efficiency of these connections in protection of plants against insects-wreckers remains while under doubt as at skarmlivanii by their insect of any effect it is not observed. There is an assumption that in the presence of some other natural substances of fitoekdizo th get ability to get through kutikulu an insect. However the role fitoekdizonov in natural protection of plants requires proofs.