LEC 4: Pesticides

hi 2/14/25 2:26

What is the purpose of pesticide? What are they used for in agriculture?

• The purpose of pesticides: To kill or harm some form of life

• Pesticides are used to control various pests and disease carriers, such as mosquitoes, ticks, rats and mice 👈

• Pesticides are used in agriculture to control weeds, insect infestation and diseases

• There are many different types of pesticides; each is meant to be effective against specific pests

List 8 types of pesticides used in agriculture

• Herbicides

• Insecticides

• Fungicides

• Rodenticides

• Larvicides

• Molluscicides

• Bactericides

• Algacides 

What are the benefits of pesticides?👈

• Produces more crops on lesser land

• Prevents human/livestock diseases

• Controls plant-based diseases

• Keeps deforestation + soil erosion in check

• Helps gain food sufficiency

Do pesticides go away?

• Pesticides don’t just go away

• They persist in the environment where they remain and/or are transported over long distances + make their way into biological systems👈

What is bioaccumulation and biomagnification? 👈

• Bioaccumulation

  • Buildup of higher concentrations of toxins in organisms that cannot be excreted or broken down (non-biodegradable)

• Biomagnification

  • Buildup of toxins in organisms higher up

  • in the food chain (they ultimately have the most toxisn bc they eat the smaller ones)

What are some biological effects of pesticides? What does it depend on?👈

• Have diverse biological/physiological effects on the exposed organism

  • Neurological issues (eg, Parkinson’s disease), genetic defects, impacts on the endocrine system, and developmental disorders

    Specific types of cancer in some cases (eg, glyphosate exposure has been linked to non-Hodgkin’s lymphoma)

• Recall: Depends on the dose (how much), duration (timeframe of exposure) and frequency (how many exposure events)!

What are 3 ways of grouping pesticides? (classification based on..)

• Classification based on the mode of entry/action

• Classification based on pesticide function and the pest organism they kill (targeted)

• Classification based on the chemical composition of the pesticide --- the most common and useful method --- because this method gives the clue about the efficacy, physical, and chemical properties of pesticides👈

There are 4 classification Based on the chemical composition of the pesticides: explain these 2 Organochlorbines + Organophosphates - what do they target + what animals

• Organochlorines

  • The main effects of organochlorine pesticides are on the nervous system by interfering with different ion channels, namely GABA receptors

  • Are persistent and frequently can bioaccumulate in fat tissues of aquatic organisms such as fish and crustaceans
    

• Organophosphates

  • A group of synthetic chemicals that poison insects and mammals by damaging an enzyme in the body called acetylcholinesterase

    • Acetylcholinesterase: An enzyme that is critical for controlling nerve signals in the body

      • The damage to this enzyme kills pests and may cause unwanted side effects in exposed humans

  • These pesticides are non-persistent

  • However, organophosphates are more toxic to humans and other mammals than, for example, carbamates

There are 4 classification Based on the chemical composition of the pesticides: explain these 2: Carbamates + Pyrethrin + pyrethroids - what do they n where are they used

• Carbamates

  • Also work by inhibiting acetylcholinesterase

  • benefits to society, as

  • they protect and increase agricultural production,

  • protect human and animal health from insect-vector-mediated diseases

  • Overexposure of humans and animals to these pesticides often results in poisonings

• Pyrethrin and pyrethroids

  • Alter the activity of the sodium ion channels of nerves

  • Commonly used to control insects in various settings, including households, gardens, and agriculture

Pesticides vary in the number of species they control - describe broad-spectrum pesticides + narrow-spectrum pesticides

• Broad-spectrum Pesticides

  • Non-selective

  • Developed to kill a large range of pests (including beneficial ones)

  • Typically work by attacking the muscular or nervous system

    • eg, most organochlorines, organophosphates, pyrethroids

• Narrow-spectrum Pesticides

  • Selective 👈

  • Targets only the intended organism(s)

  • Designed to interact with a characteristic of the pest that is specific to that organism, such as a pheromone, hormone or physical feature (eg, molting/shedding)

    • eg, diacylhydrazines

Organochlorines + organophosphates are broad-spectrum - how many pests are they developed to kill?

• Broad-Spectrum:

  • developed to kill a large range of pests (including beneficial ones) aka non-selective pesticides

    • eg, organochlorines, organophosphates 👈

    • Most are lipophilic compounds = readily enter the tissues of organisms!

• Exposure to roundup (glyphosate) has been linked to the development of certain cancers in humans (eg, non-Hodgkin lymphoma)!

Are pyrethrin + pyrethroids broad spectrum agents?

• Pyrethrin and pyrethroids (synthetic derivatives of pyrethrin)

• Both are broad spectrum agents👈

  • Target a wide range of pests in both agricultural and non-agricultural settings

Are carbamates narrow-spectrum or broad?

• Narrow-Spectrum: 

  • aka selective pesticides, target only the intended organisms

    • eg, Diacylhydrazines

Explain the 2 sources of natural pesticides: organic + inorganic

• Organic Pesticides

• eg, pyrethrum, nicotine, neem oil, and all botanical pesticides are products of living organisms

  • Often, they are chemicals that plants and microbes use to protect themselves from parasites, predators, and pathogens

  • Organic pesticides are often lower in toxicity than older synthetic pesticides but this is not always the case. Organic does not necessarily equal low toxicity and environmentally safer.

• Inorganic Pesticides

  • eg, borates, silicates, and sulfur are minerals that are mined from the earth and ground into a fine powder

    • Some work as poisons and some work by physically interfering with the pest. Older "inorganics" included such highly toxic compounds as arsenic, copper, lead and tin salts

    • Current inorganic pesticides are relatively low in toxicity and have a low environmental impact

Explain the 3rd source of natural pesticides: Biorational pesticides. Included is a diagram that shows the similarities + differences in organic + inorganic compounds

• Biorational Pesticides

  • Have minimal impact on species for which they are not intended (called non-target species). Biorational pesticides include certain plant oils, insecticidal soaps, microbials (such as Bacillus thurengienesis and entomopathogenic nematodes), botanicals (made from plants) and insect growth regulators. The biorational pesticides should therefore be your first choice whenever a pesticide is needed

  • Refer to synthetic, organic, or inorganic pesticides that are both low toxicity and have a very low impact on the environment

What are natural pesticides? List 3 advantages + disadvantages.

• Plants produce many natural pesticides that they use for their own defense against insects and disease organisms 👈

• Advantages:

  • Eco-friendly

  • Safer for user

  • Very effective when used carefully

• Disadvantages:

  • Short-term activity

  • May be more expensive than older conventional pesticides

  • Less narrow-spectrum quality (especially when compared to newer synthetic pesticides)

• Chrysanthemum (shown above) contains a natural neurotoxin (pyrethrins) that attacks the nervous system of all insects without causing harm to birds and mammals

What are signal words for relative toxicity of pesticides? Caution, warning, danger

• Describes the acute (short-term) toxicity of a pesticide

  • The (toxicologically) appropriate signal word MUST appear on every pesticide label
    

• CAUTION: LD50 of greater than 500 mg/kg

  • Lowest degree of relative toxicity 
    

• WARNING: LD50 of greater than 50 to 500 mg/kg

  • Reflects an intermediate degree of relative toxicity 
    

• DANGER: LD50 of  50 mg/kg

  • Reflects highest degree of relative toxicity 

Signal words - toxicity of pesticides - Caution, warning, danger, danger-poison

Signal words for relative toxicity of pesticides blue graph

How does pesticide resistance develop?

• Pesticide resistance can develop over time when pesticides with the same mode of action (same way of affecting pests) are repeatedly applied in the same area
  

• Resistance occurs when a pesticide exhibits reduced effectiveness or no longer controls the pest population at the formerly effective rate 👈

How do insects develop resistance to insecticides (3)?

• Insects develop resistance to insecticides through a variety of mechanisms, including:

  • Mutations in genes that target insecticides

  • Increased detoxification

  • Behavioral changes👈

What is Genetical Modified Organisms (GMO) -what does it create

• A genetically modified organism, or GMO is a plant, animal, bacteria, virus or other organism whose genetic makeup has been modified in a laboratory using genetic engineering or transgenic technology

• This creates unique combinations of plant, animal, bacterial, and virus genes that do not occur in nature or through traditional crossbreeding methods

List some benefits + risks of GMOs