🐞 Chemical Control and Pesticide History

Chemical control is a core pillar of insect pest management in which pesticides are used strategically to reduce pest populations when monitoring and threshold-based decisions justify intervention.

Chemical Control and Pesticides

Chemical Control: Management of insect pests using chemical pesticides is termed as chemical control. Pesticides: Chemicals which are used to kill pests.

History of Insecticide Development

Year Chemicals

900 - Arsenites in China (Inorganic compound)

1690 - Tobacco used in Europe (Plant/natural product)

1787 - Soaps used in Europe

1867 - Paris Green in US

1874 - DDT synthezized by Zeidler

1883 - Bordeau in France

1925 - Dinitro compounds (First synthetic organic insecticide)

1932 - Thiocyanates

1939 - DDT insecticidal property discovered by Paul Muller of Switzerland .

Paul Muller awarded Nobel Prize in 1948 for discovering insecticidal property of DDT

1941 - BHC in France and UK (in 1942) (BHC is presently called as HCH)

1944 - Parathion ( Organo phosphate ) discovered by Gerhard Schrader in

Germany

1945 - Chlordane (Cyclodian compound) in Germany

1947 - Carbamate insecticides in Switzerland

1962 - Rachel Carson’s Silent Spring appears (US) (This is not a chemical. The

book ‘ Silent Spring’ created awareness about ill effects of pesticides)

1967 - First JH mimic (Juvenile Hormone mimic) used in US (Insect growth

regulator)

1970 - Development of synthetic pyrethroids (UK) (Fast degradation) (Effective

at very low doses)

1980 - Discovery of avermectins (derived from bacteria). Effective at low dose.

Fast degradation.

1990 - Discovery of newer groups like (1) Neonicotinoids (Imidacloprid),

similar to natural nicotin, (2) Spinosyns (e.g. Spinosad) derived from actinomycet

TOXICITY PARAMETERS

Toxicity of a given chemical to an organism can be measured using various parameters as listed below.

LD50 or Median lethal dose

LD50 is defined as the amount of insecticide per unit weight which will kill 505 of the particular organism or insect. LD50 usually expressed as mg/kg body weight or g/larva or adult insect.

LC50 or Median lethal concentration

Defined as the concentration of insecticide required to kill 50% of the given organism or insect. This is used when the exact dose per insect is not known, but the concentration is known. LC50 is expressed in PPM (1/1,000,000) or Percentage (1/100)

LT50 (Median lethal time)

LT50 is defined as the time required to kill 50% of the population at a certain dose or concentration.

LT50 expressed in hours or minutes. LT50 is used in field studies and also for testing insect viruses (NPV).

4. KD50: Median knockdown dose Dose of insecticide or time required to 5. KT50: Median knockdown time knockdown 50% of the insects

KD50 and KT50 are used for evaluating synthetic pyrethroids against insects.

6. ED50: Median effectivedose These terms are used to express the 7. EC50: Median effective concentration effectiveness of insect growth

regulators (IGR)

ED50 and EC50 are defined as the dose or concentration of the chemical (IGR) required to affect 50% of population and produce desired symptoms in them.

Toxicity terms used to express the effect on mammals

1. Acute toxicity : Toxic effect produced by a single dose of a toxicant

2. Chronic toxicity : Toxic effects produced by the accumulation of small amounts of the toxicant over a long period of time

3. Oral toxicity : Toxic effect produced by consumption of pesticide orally

4. Dermal toxicity : Toxic effect produced when insecticide enters through skin

5. Inhalation toxicity : Toxic effect produced when poisonous fumes of insecticide are inhaled (fumigants)

Other terms : Acute oral, Acute dermal, Acute inhalation toxicity, etc.

Ideal Qualities of an Insecticide

An ideal insecticide should posses the following qualities Kill the target insect effectively and quickly Be less toxic to natural enemies Be less toxic to honey bees, soil microorganisms Be less toxic to fishes and mammals Less hazardous and less toxic during handling or accidental consumption by human

beings Quickly degradable in environment and should be less persistent (Residues should be

very less) Should not cause resurgence of the target insect (i.e. Increase in population of target

insect) e.g. Chlorpyriphos causes resurgence of BPH on rice. Should not cause outbreak of secondary pest on a minor pest by killing the natural

enemies Should have a complex mode of action against which resistance development will

take more time. e.g. Azadirachtin from neem tree has complex action Should have a longer storage life or shelf life It is advantageous to select an insecticide which can kill a relatively broad spectrum of

target pests It should be cost effective (High benefit/Cost ratio) and safe to use (High benefit/Risk

ratio)

Various generations of insecticides

Year

1939-1942

Compounds

BHC and DDT

Generation

First generation insecticide

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 1970s Synthetic pyrethroids

Summary Cheat Sheet

• Chemical control uses insecticides and related pesticides to reduce pest populations rapidly.

• The history of chemical control shows the transition from early inorganic compounds to synthetic modern insecticides.

• Chemical control is effective but must be used judiciously because overuse can cause resistance, resurgence, and environmental harm.

• Review core concepts, definitions, and field-level application points from this lesson.

• Prioritize economic threshold-based decisions and integrated management logic where relevant.