An insecticide is a pesticide that is used to kill, drive away or inhibit insects and their stages of development ( insecticidal effect). The terms insecticides or insecticides are synonymous. Insecticides are used in agriculture and forestry, to protect stocks and materials as well as in the hygiene sector and in private households. Some insecticides such as lindane (banned in the EU since 2007) are also used to treat parasitoses locally.
In the early days of human development, insect plagues were not uncommon. The plagues of locusts in Egypt were reported in wall paintings or in biblical texts. The use of sulfur as a crop protection against pests has been reported by Homer. Elemental sulfur mixed with oil was also used to combat insects by the Greeks and Romans. With Pliny the Elder, arsenic was used to fight insects. In China - as Marco Polo reported - arsenic was used against insects. In 1763 nicotine was discovered. In the 19th century, Schweinfurter Grün , an arsenic salt containing copper, was used as a remedy against insects and weeds. Other salts made from lead, iron, and mercury soon followed.
The first synthetic organic insecticide was Antinonnin ( dinitrocresol ) from Bayer in 1892. In 1938, the first effective phosphoric acid ester ( tetraethyl pyrophosphate ) was developed by Gerhard Schrader .
1939 by Paul Hermann Müller , the Dichlordiphenyltrichlorethan examined (DDT) as an insecticide. DDT found a very wide application in the fight against insects. It was not until much later that the adverse consequences such as poor biodegradability and accumulation in the fatty tissue of mammals became apparent . Between 1945 and 1950, other organochlorine compounds ( chlordane , lindane , aldrin , dieldrin ) were developed as insecticides. From 1972 many organochlorine compounds were banned because they accumulate in the fatty tissue of mammals in the food chain (see pesticides ). The insecticides aldrin, chlordane, dieldrin, DDT , endrin , heptachlor and lindane, known as “dirty sieves”, are now banned almost worldwide, for example by national, European or international (international) law ( Stockholm Convention ). The same goes for Mirex .
Another very important group of active ingredients is derived from the ingredients of the chrysanthemum flower - the pyrethrum . In the mid-1970s, very effective synthetic pyrethroids such as deltamethrin and permethrin came on the market as insecticides.
The active substance can be absorbed via the respiratory tract (respiratory toxins), the gastrointestinal tract (food toxins) or by touch (contact toxins).
In the case of all insecticides, there is a risk of resistance building up after prolonged administration. Therefore, one switches between different classes of active ingredients in crop protection.
Furthermore, one tries to meet only the harmful insects. Beneficial organisms such as predators (ladybugs) and pollinators (bees and bumblebees) should be spared.
Inhibition of nerve conduction
In the transmission of signals from nerve cells to downstream cells in muscles - and sometimes also in the brain - there is a synaptic gap between the individual cells in which the substance acetylcholine is responsible for the transmission of a nerve impulse. So that the signal transmission can be stopped again quickly, the acetylcholine is broken down again on the surface of the synaptic gap - the enzyme acetylcholinesterase is responsible for this in the synaptic gap .
Insects also have this kind of signal transmission. There are chemical pesticides that get into the synaptic cleft of an insect (or a person) through food, body contact ( contact poison ) or by inhalation, where they can deactivate the enzyme acetylcholinesterase. The substances include, for example, the phosphoric acid esters and carbamates.
By modifying the chemical structure and following the dosage instructions, the possible toxic effects during use (only for humans) can be significantly reduced. The phosphoric acid esters and carbamates are broken down in the environment after a few weeks, which means that their poisonous effect is only briefly harmful to insects; there is then hardly any risk for people when they eat food.
To treat acute poisoning with organophosphates, the poisoned person must be given atropine and an oxime ether such as pralidoxime iodide (2-PAM) or obidoxime chloride (toxoginin) as quickly as possible.
Important substance classes
Phosphoric acid ester
Phosphoric acid esters belong to an important class of insecticides.
By exchanging the oxygen bound to the phosphorus for sulfur ( thiophosphoric acid ester ), phosphoric acid esters are less toxic to mammals, and the use of methoxy groups instead of ethoxy groups reduces the toxic effect on mammals.
If a carbethoxy group is included, e.g. B. Malathion , it is converted in the liver of a mammal to a carboxy group, which is significantly less toxic, since the compound is easily excreted due to its water solubility. Such a process does not take place in insects, malathion retains its full poisonous effect for insects.
Important representatives are:
- Demeton (see Demeton-S and Demeton-O )
This substance class consists of compounds of the type RO – CO – NR 2 . There is also the group of oxime carbonates with the structure R 2 C = N — OCO — NR 2 .
Important representatives are:
Trade names of these active ingredients are Advantage, Gaucho, Provado, Biscaya and the like. a.
The preferred form of application in this group of substances is seed dressing . In this way, an impairment of beneficial organisms is to be prevented and the effective range is to be limited to feeding insects. Due to procedural errors in production and sowing, however, there were repeated mass deaths of bee colonies and beneficial organisms, so that this economically successful group of substances has come under fire and products with these active ingredients have been partially banned.
Because of their high persistence , representatives of the neonicotinoids run the risk of accumulation in soils and surface waters.
Active ingredients without inhibition of acetylcholinesterase
Pyrethroids are chemical compounds derived from the pyrethrins found in chrysanthemums .
Pyrethroids such as deltamethrin are about 400 times more toxic to insects than pyrethrin. The pyrethroids act on the ion channels of nerve cells in the conduction of stimuli.
Important representatives are:
Pyrethroids break down better outdoors than indoors. For example, permethrin is only 10% degraded after 3 months under indoor conditions, which means that long-term contamination is to be expected.
Pyrethroids are fat soluble and can potentially build up in human adipose tissue. They also have a weak toxic effect, which is manifested by nausea, vomiting, headache, dizziness.
Other active ingredients
Another active ingredient that also acts on the sodium ion channel is indoxacarb , which is one of the voltage-dependent sodium channel blockers.
Another group of substances are the avermectins . These compounds act on the chloride ion channel of nerve conduction. They are obtained by fermentation and are therefore very expensive.
Another group of substances affects the development of insects in the larval stage. Here the biosynthesis of the chitin shell is influenced. Benzoylureas such as diflubenzuron inhibit chitin biosynthesis. Other active ingredients such as fenoxycarb and pyriproxyfen act as analogs to the juvenile hormone and prevent the larva from developing into adult animals.
In 2017, 17,652 tons of insecticides (including acaricides and pheromones ) were sold in Germany . According to figures from 2013, the top-selling insecticide classes include the neonicotinoids (27%), pyrethroids (16%), organophosphates (11%), diamides (8%), avermectins (7%) and the phenylpyrazoles / fipronil (5%) .
According to a study published in Germany in the spring of 2015 , the concentration found for half of all insecticides detected in bodies of water worldwide was higher than it should be according to the official approval process. The incumbent President of the German Federal Environment Agency warned that smaller bodies of water in particular are highly polluted and that they are not monitored enough.
The cotton production consumes 24 percent of all insecticides.
About the described synthetically produced there are of course, z. B. insecticides obtained on the basis of fungi ( Paecilomyces fumosoroseus ), roundworms (Nematoda), bacteria (Bacteria) ( Bacillus thuringiensis , produces Bt toxins ) and viruses . A list of higher plants from which insecticides are obtained can also be found in the article Crop Plants .
|substance||Substance group||Parent plant (organ, content)||effect|
|nicotine||alkaloid||Nicotiana tabacum , Nicotiana rustica (leaves 5–14%)||Food, contact and respiratory toxins (lethal dose in humans over 500 mg)|
|Anabasine||alkaloid||Anabasis aphylla (leaves 1–2.6%)|
|Piperine||alkaloid||Piper nigrum (seeds) and other plants||Synergist (practically non-toxic to vertebrates)|
|Veratridine alkaloids ( cevadine , veratridine )||alkaloid||Schoenocaulon officinale (seeds 2–4%), Veratrum album , Veratrum viride (root)||selective contact and food poison (also poisonous for humans)|
|Ryanodine||Diterpene derivative||Ryania speciosa (wood 0.16-0.2%)||Oral food poison (gastric poison), selective effect (low vertebrate toxicity)|
|Wilfordin||alkaloid||Tripterygium wilfordii (root)||selective food poison z. B. for storage pests (low vertebrate toxicity)|
Quassin , Neoquassin
Quassia amara (wood)
Picrasma excelsa (wood)
|Selective effect (no toxic effect on vertebrates)|
|Sesamin||Crystalline fraction of sesame oil (0.25%)||Sesamum indicum (seeds)||Synergist (very low vertebrate toxicity)|
|Rotenone ( Elliptol , Sumatrol , Malacol , Deguelin , Toxicarol )||Rotenoids||
In addition, 57 plants from 5 families
|Contact poison, food poison (lethal dose in humans 2000–3000 mg)|
|Pyrethrin, cinerin, jasmoline||Pyrethrins||Chrysantheum cineriaefolium , Chrysantheum roseum , Chrysantheum carneum (flowers 0.7–3%)||Contact poison (practically non-toxic to vertebrates)|
- Pest Control
- Broad spectrum insecticide
- Insect repellent
- Herbal defense against herbivores
- Agricultural aviation
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