Chemical Pest Control Methods and Their Formulations, Biology tutorial

What is a Pest? 

1) Pest is any animal that is destructive, noxious or bothersome to man or his welfare.

2) A pest is any organism that takes place in big numbers and conflict with man's wellbeing, expediency and profit.

3) A pest is an organism that harms man or his property appreciably or is probable to do so (Woods, 1976).

4) Pests are organisms that compel burdens on human population by causing: 

  • Damage to crop plants, forests and ornamentals.
  • Exasperation, injury and death to domesticated animals and humans.
  • Demolition or value depreciation of the stored products.

5) Chemical Pest Control is the administration and management of pests by employing chemical pesticides 

6) Pesticides are the chemicals which are employed to kill the pests.

History of Insecticide Development:

Year

Chemicals

900

Arsenites in the China (that is, Inorganic compound)

1690

Tobacco employed in Europe (that is, Plant or natural product)

1787

Soaps utilized in Europe

1867

Paris Green in the United States

1874

DDT made by Zeidler

1883

Bordeau in the France

1925

Dinitro compounds (that is, first synthetic organic insecticide)

1932

Thiocyanates

1939

DDT insecticidal assets discovered by Paul Muller of Switzerland.

1941

BHC in France and UK (in year 1942) (BHC is at present termed as HCH)

1944

Parathion (that is, Organophosphate) discovered through Gerhard Schrader in Germany.

1945

Chlordane (that is, Cyclodian compound) in the Germany

1947

Carbamate insecticides in the Switzerland 

1962

Rachel Carson's Silent Spring comes into view

1967

First JH mimic (that is, Juvenile Hormone mimic) utilized in US

1980

Discovery of the avermectins (derived from the bacteria).

1990

Discovery of the newer groups such as (a) Neonicotinoids (Imidacloprid), alike to natural nicotin, (b) Spinosyns (example: Spinosad) derived from the actinomycet 

Ideal Qualities of an Insecticide:

An ideal or perfect insecticide must encompass the given qualities: 

1) Kill the target insect efficiently and rapidly.

2) Be less poisonous to natural enemies. 

3) Be less toxic to soil microorganisms and honey bees.

4) Be less poisonous to mammals and fishes.

5) Less dangerous and less poisonous all through handling or accidental utilization by human beings.

6) Speedily degradable in atmosphere and must be less persistent (that is, Residues must be extremely less).

7) Must not cause resurgence of the target insect (that is, Increase in population of target insect) example: Chlorpyriphos causes resurgence of the BPH on rice. 

8) Must not cause outbreak of secondary pest on the minor pest through killing the natural enemies.

9) Must encompass a complex mode of action against which resistance growth will take more time. Example: Azadirachtin from neem tree consists of complex action.

10) Must encompass a longer storage life or shelf life 

Various Generations of Insecticides:

S/N

Generation

Year

Compounds

1.

First generation insecticide

1939-1942

DDT and BHC

2.

Second generation insecticide

1944-1947

Organophosphates and Carbamate

3.

Third generation insecticide

1967

Hormonal insecticides, JH mimic insect growth regulators

4.

Fourth generation insecticide

1970

Synthetic pyrethroids 

Pesticide Groups

Pesticides are usually categorized into different groups based on the pest organism against which the compounds are employed, their chemical nature, mode of entry and mode of action. 

1) Based on organisms:

  • Insecticides: Chemicals employed to kill or control the insects. Example: Endosulfan and Malathion. 
  • Rodenticides: Chemicals fully employed to control rats. Example: Zinc phosphide.
  • Miticides or Acaricides: Chemicals employed to control mites on crops or animals. Example: Dicofol 
  • Avicides: Chemicals employed to repel the birds. Example: Anthraquionone 
  • Molluscicides: Chemicals employed to kill the snails and slugs. Example: Metaldehyde 
  • Nematicides: Chemicals employed to control nematodes. Example: Ethylene dibromide 
  • Fungicides: Chemicals employed to control plant diseases caused due to fungi. Example: Copper oxy chloride. 
  • Bactericide: Chemicals employ to control the plant diseases caused due to bacteria. Example: Streptomycin sulphate 
  • Herbicide: Chemicals employed to control weeds. Example: 2, 4, - D 

2) Based on mode of entry:

  • Stomach poison: The insecticide applied in the leaves and other portion of the plant if ingested, act in the digestive system of the insect and bring about death. Example: Malathion. 
  • Contact Poison: The toxicant that brings about death of the pest species through means of contacts. Example: Fenvalerate. 
  • Fumigant: Toxicant enters in vapor form to the tracheal system (that is, respiratory poison) via spiracles. Example: Aluminium phosphide 
  • Systemic poison: Chemicals if applied to plant or soil are absorbed through foliage (or) roots and translocated via vascular system and cause death of insect feeding on plant. Example: Dimethoate. 

3) Based on mode of action:

  • Physical poison: Toxicant that brings about death of the insect through exerting a physical effect Example: Activated clay.
  • Protoplasmic poison: Toxicant accountable for precipitation of the protein. Example: Arsenicals. 
  • Respiratory poison: Chemicals that inactivate respiratory enzymes. Example: hydrogen cyanide. 
  • Nerve poison: Chemicals restrain impulse conduction. Example: Malathion. 
  • Chitin inhibition: Chemicals restrain or inhibit chitin synthesis. Example: Diflubenzuron. 

 4) Based on chemical nature:

1) Inorganic pesticides: In this, inorganic chemicals employed as insecticides. Example: Fluorine, Arsenic, Sulphur, lime sulphur (Insecticides) and zinc phosphide (Rodenticide).

2) Organic pesticides: Organic compounds (comprised by C, H, O and N mostly) 

  • Hydrocarbon oil (or) Petroleum oil: Example: Coal tar oil, kerosene and so on. 
  • Animal origin insecticides: Example: Nereistoxin extracted from the marine annelids - commercially accessible as cartap and padan.
  • Plant origin insecticides: Nicotine from the tobacco plants, pyrethrum from Chrysanthemum flowers, Rotenoids from the roots of Derris and Lonchocarpus, Neem - Azadirachtin, Pongamia glabra, Garlic and so on.
  • Synthetic organic compounds: Such organic chemicals are synthetically generated in laboratory.

Pesticide Formulations:

Pesticides are not generally applied in pure form (or active ingredient) as they are highly toxic and quantity accessible for application is low and therefore they are diluted by means of inert materials such as talc (or) with water joining with other materials like wetting agents, solvents, stickers and so on. The ultimate product is the formulated pesticide and it is prepared for use.

Types of Formulations:

According to the mode of application, the kinds of formulation are as illustrated below: 

I) For dry application directly from container:

1) Dusts (D): The technical material (that is, active ingredient) is mixed by a carrier like clay (that is, attapulgite, Kaolin and ash), organic flour (or wood bark), pulverized minerals (such as, sulphur, talc, lime and gypsum). The size of particle will be less than 100 and it must pass via 200 mesh sieve. Dusts are cheaper and simple to use. Though, they are least efficient and cause wind drift leading to the poor deposit on surface; they are highly toxic to advantageous insects. 

2) Granules (G): Granules are made through applying liquid insecticides to coarse particle of the porous material such as clay, corn cobs or walnut shells. The quantity of active ingredient ranges from 2 to 10 per cent. They are extremely safer to apply than dusts.

II) For spraying after mixing with water:

1) Wettable Powders (WP):  It comprises of active ingredient mixed by inert dust and a surfactant which mixes readily by water and forms a short-term suspension. WPs are much more concentrated than dusts, having 15 to 95% active ingredient. Frequent agitation is needed to keep the insecticides in suspension. WPs generally cause less phytotoxicity than ECs. WPs must never be employed without dilution. 

2) Emulsifiable Concentrates (EC): It consists of a toxicant, a solvent and an emulsifier having a stabilizing agent. If EC is mixed in water, it provides emulsion - droplets of oil having the insecticide dispersed in water. Emulsifier turns the water-insoluble toxicant to water-soluble and it yields a stable milky solution if diluted with water. Whenever applied, the solvent evaporates rapidly leaving the toxicant from which water as well evaporate. 

3) Soluble Powders (SP):  Soluble powder comprises of finely ground solid material that dissolve in water or several other liquid making true solutions. 

4) Flowable (F): Flowable is the pesticide formulation in which the active ingredient is wet milled having a clay diluents and water. Flowables should be continually agitated to prevent the insecticide from emerging of suspension and settling. 

5) Ultra Low Volume Concentrates (ULV): They are special type of high concentrate solutions and are applied devoid of dilution having special aerial or ground equipment to generate very fine spray.

III) For application as gas or vapor:  

1) Fumigants: Fumigants are the pesticides in the form of poisonous gases which kill when absorbed or inhaled. Most of the fumigants are liquid and are mixtures of two or more gases. 

2) Smoke generators: They are employed in the form of coil-like strips having pyrethrum, oxidant and wood dust for the control of mosquitoes. If ignited, such coils discharge vapors. 

3) Aerosols:  Aerosol includes a small amount of pesticide which is driven via a fine opening through a chemically inactive gas under pressure if the nozzle is triggered or by burning toxicant or vaporizing it with that. The toxicant is hanged as minute particle (0.1 to 50 w/w) in air as a fog or mist. It comprises of toxicant (2 percent), solvent (10 percent), knockdown agent (2 percent) and propellant (86 percent).

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