How Does Malathion Work? Properties, Benefits, and Applications
Malathion is a broad-spectrum organophosphate acaricide and insecticide also known as mercaptothion, maldison, and carbophos (that is used to kill mites and ticks). Considerably less toxic to humans compared to parathion, malathion can be suited for the control of garden and household insects and is essential in the control of boll weevils, mosquitoes, lice, and fruit flies.
Properties
Malathion is given as a colourless yellow-brown liquid having a characteristic unpleasant odour. Malathion iupac id is 4004. Generally, it can be prepared by combining O and O-dimethyl phosphorothioate with diethyl maleate. It is also soluble in most of the organic solvents except paraffin hydrocarbons. Practically, it insoluble in water and is readily decomposed by alkalies. The malathion chemical acts by binding to the enzyme acetylcholinesterase (AChE) at nerve endings, causing the neurotransmitter acetylcholine (ACh) to be disrupted, eventually leading to death.
Mechanism of Action
Malathion is a compound that inhibits acetylcholinesterase, which is a large family of chemicals. When this is injected into the target organism, it binds irreversibly to the serine residue in the cholinesterase enzyme's active catalytic site. The phosphoester group is then tightly bound to the cholinesterase and irreversibly deactivates the enzyme, resulting in a rapid build-up of acetylcholine at the synapse.
Production Method
Malathion can be produced by the addition of dimethyl dithiophosphoric acid to either diethyl fumarate or diethyl maleate. The compound is chiral but can be used as a racemate.
Mix Ratio for 55% Malathion for Killing Bedbugs
Generally, while malathion is considered as an exterior pesticide, there are a few formulations, which are labelled interior use, with certain label restrictions. In the U.S.A., the product is not labelled at all for the treatment of bedbugs. The other issue with malathion is the fact that, generally, it can be sold as a malathion oil emulsion and holds a nasty odour. Malathion, that being said, is still considered as an effective treatment of malathion insecticide against bedbugs that have developed a tolerance to the pyrethrin and pyrethroid in a few areas.
In the United States, the last labelled use for bedbug control happened in 1965, a time when lindane, chlordane, D.D.T., and other insecticides were in wide use. At that time, the label suggested a concentration ranging from 0.5% to 1.0%, which would be achieved by mixing a single ounce ranging from 55% with 50–100 ounces of water (also, kerosene was a listed vehicle for malathion, but certainly it should not be used inside the home).
There are many other malathion insecticides, which are considered more appropriate for bedbug control, and they should be readily available for purchases either at hardware or home supply stores. The other suggested treatment is using the ethanol diluted in water is as a topical treatment, but it kills only bedbugs which are sprayed directly with it, and after it dries, it does not have a residual effect.
Most of the websites that cover the bedbug's information recommend hiring a professional pest control company to treat the premises for bedbugs since the local populations tend to develop some resistance to chemical treatment quickly and fairly.
Malathion Uses
Let us see some of the malathion insecticide uses.
Malathion Pesticide Use
Malathion is given as a pesticide, which may be used widely in residential landscaping, agriculture, in public health pest control programs such as mosquito eradication, and also in the public recreation areas. And, in the U.S., it is known to be the most commonly used organophosphate insecticide.
In the 1980s, a malathion mixture containing corn syrup was used to battle the Mediterranean fruit fly in California and Australia. Whereas, in the United States and Canada, starting in the early 2000s, malathion was sprayed in several cities to combat the West Nile virus.
Malathion was also used over the last two decades regularly during the summer to kill mosquitoes. However, homeowners were allowed to exempt their properties in the case if they chose. Today, Winnipeg is the only major city in Canada with a program of ongoing malathion adult-mosquito-control.
Medical Use
In low doses (0.5% preparations), malathion can be used as a treatment for:
Body lice and head lice. Malathion is also approved by the United States Food and Drug Administration for the treatment of pediculosis. It is effectively claimed to kill both the adult lice and eggs, but in fact, it has been shown in the United Kingdom, studies to be only 36 percent effective on the head lice and less so on their eggs. This specific low efficiency was observed when malathion was applied to lice found on schoolchildren in the Bristol region of the United Kingdom, and it is believed by some to be caused by the lice developing resistance to malathion.
Scabies
Some of the preparations of malathion include Prioderm, Derbac-M, Quellada-M, and Ovide.
Toxicity
Malathion is more highly toxic to the bees and other aquatic invertebrates, beneficial insects, and a few species of fish, notably largemouth and bluegill bass. Also, it is of moderate toxicity to the birds.
FAQs on Malathion: Key Concepts, Uses, and Mechanism
1. What exactly is Malathion?
Malathion is a man-made organophosphate insecticide. It is chemically classified as a dithiophosphate and is widely used for its broad-spectrum activity against various insects. It was first introduced in the 1950s and is known for its relatively low toxicity in mammals compared to other organophosphates.
2. What are the main uses of Malathion?
Malathion is primarily used to control a wide range of insects in various settings. Its main applications include:
- Agriculture: To protect fruits, vegetables, and other crops from sucking and chewing insects like aphids and spider mites.
- Public Health: In large-scale mosquito control programs to combat diseases like West Nile virus and malaria.
- Gardening: For use in home gardens on ornamental plants, shrubs, and trees.
- Veterinary & Domestic: To control fleas and ticks on pets and livestock, as well as in household pest control products.
3. How does Malathion work to kill insects?
Malathion functions as a neurotoxin by inhibiting the enzyme acetylcholinesterase (AChE). In a healthy nervous system, AChE breaks down the neurotransmitter acetylcholine. By blocking AChE, Malathion causes a buildup of acetylcholine at the nerve synapse, leading to continuous nerve stimulation, paralysis, and ultimately the death of the insect.
4. Is Malathion harmful to humans and other mammals?
Yes, Malathion can be harmful if exposure is high enough. It is a neurotoxin for mammals as well, but it is significantly less toxic to them than to insects. Symptoms of acute poisoning in humans can include nausea, dizziness, confusion, and in severe cases, respiratory paralysis. Following safety guidelines during application is crucial to minimise risk.
5. Why is Malathion generally considered safer for mammals than for insects?
The selective toxicity of Malathion is due to differences in metabolism. Mammals possess high levels of the enzyme carboxylesterase, which effectively detoxifies Malathion into harmless byproducts before it can be converted to its more toxic form, malaoxon. Insects have much lower levels of this enzyme, allowing the toxic conversion to occur, making the compound lethal for them.
6. What is the role of Malaoxon in Malathion's insecticidal action?
Malathion itself is not the primary toxic agent. In insects, it undergoes a metabolic process called oxidative desulfuration, which converts it into its oxygen analog, malaoxon. Malaoxon is a much more potent inhibitor of the acetylcholinesterase (AChE) enzyme than Malathion. This conversion is what makes Malathion a highly effective insecticide.
7. What are the key chemical properties of the Malathion molecule?
Malathion (C₁₀H₁₉O₆PS₂) is an organothiophosphate ester. Its key properties include:
- Structure: It contains a central phosphorus atom bonded to two methoxy groups, a sulfur atom (thiono group), and a succinate ester side chain.
- Solubility: It has low solubility in water but is soluble in many organic solvents.
- Appearance: In its pure form, it is a colourless liquid, but technical-grade Malathion is often a brownish-yellow liquid with a garlic-like odour.
- Stability: It is relatively stable in neutral or slightly acidic conditions but hydrolyzes (breaks down) quickly in alkaline (high pH) environments.
8. What happens to Malathion in the environment after it is applied?
Malathion is considered a non-persistent pesticide. In the environment, it breaks down relatively quickly through several processes:
- Hydrolysis: It is broken down by water, especially in alkaline conditions.
- Photolysis: Sunlight can contribute to its degradation.
- Microbial Action: Soil microorganisms metabolise and break down the chemical.
9. How does Malathion's mechanism differ from that of a pesticide like DDT?
Malathion and DDT have fundamentally different mechanisms of action.
- Malathion: As an organophosphate, it is an enzyme inhibitor. It blocks acetylcholinesterase, leading to nerve overstimulation.
- DDT: As an organochlorine, it is a nerve channel modulator. It forces sodium ion channels in nerve cells to stay open, causing continuous nerve firing, spasms, and paralysis.
10. Can insects develop resistance to Malathion?
Yes, insect populations can develop resistance to Malathion over time. Resistance typically occurs through genetic mutations that enhance the insects' ability to detoxify the chemical. For example, some resistant strains may produce higher levels of enzymes like carboxylesterase or have a modified form of the acetylcholinesterase (AChE) enzyme that is less sensitive to inhibition by malaoxon.
