W11: Invertebrate Physiology (Physiology Of Resistance: Insect Immunity & Insecticides) [Dr. Blair] Flashcards
Main pathogens that attack insects? (4)
- Fungi.
- Viruses.
- Nematodes.
- Bacteria.
Term used to refer to these pathogens?
Entomopathogens.
What is the infection route of viruses?
Infection route is through consumption/being eaten.
What is the infection route of bacteria?
Infection route is through consumption/being eaten.
Which pathogens enter/infect an insect via consumption/being eaten? (2)
- Viruses.
- Bacteria.
What are the infection routes of nematodes/parasitic nematodes? (2)
- Natural openings like the mouth, anus & spiracles.
- Cutaneous penetration, through direct penetration through the insect’s cuticle.
What are the infection routes of fungi? (2)
- Cuticular penetration, through penetration into an insect’s cuticle (outer shell).
- Respiratory infection, where insects inhale fungal spores through their spiracles.
Insect immune system attributes? (4)
- Innate immune system.
- Immediate but non-specific response.
- Pre-programmed response to certain pathogens but no immunological memory.
- Not adaptive.
Mammalian immune system attributes? (3)
- Innate & adaptive responses.
- Respond to certain pathogens with immunological memory.
- Quicker & efficient in future exposures.
Types of insect immunity? (3)
- Physical barriers/response.
- Cellular response.
- Soluble response.
Physical response?
= the exoskeleton (chitin) & gut/tracheal linings act as physical barriers to keep pathogens in or out.
Physical barriers in the insect immune system? (2)
- Exoskeleton (chitin acts as the first line of defence).
- Gut/tracheal linings.
Cellular response?
= insect immune system defends insect through immune cells (hemocytes) found in the haemocoel.
Hemocytes is equivalent to what in humans?
White blood cells.
Immune cells?
= molecules that fight pathogens.
Soluble response?
= where immune cells such as enzymes, melanin & peptides (defensin/attacin) help the insect fight off pathogens.
What about insect wounds?
In the case of insect wounds such as punctured wounds, hemocytes act as platelets and become black due to melanin which contains pigment.
What about the more severe wounds like loss of limbs?
In the case of limb losses, hemocytes and melanin work together to clot the wound, but limb regeneration can occur if the insect is in the juvenile stage (instar/nymphs) and not in the adult stage.
Is limb regeneration possible?
Yes, but it depends on when the insect loses the limb. If an insect loses the limb as a juvenile (instar/nymph) it is possible due to its ability to molt. If an insect loses the limb as an adult it is impossible due to its inability to molt.
Anything else: Parasitoid wasps?
= unique group of wasps that lay eggs on or within a host organism, especially caterpillars and beetles, and ultimately kill the host as the developing larvae feed on the host’s body for sustenance.
Pesticides?
= chemical/biological agents that are used to control/eliminate pests like insects or other organisms that damage crops, spread disease, or cause harm to livestock or humans.
Pesticides attributes? (2)
- Globally high manufacture & usage of insecticides.
- Help manage populations in agriculture & disease vectors.
Types of pesticides? (4)
- Insecticides.
- Herbicides.
- Fungicides.
- Rodenticides.
Pesticide type that we will focus on?
Insecticides.
Insecticide?
= type of pesticide that targets insects by disrupting vital processes like the nervous system or growth.
Insecticides attributes? (3)
- Have 1000s of formulations (names) with active ingredients.
- Depending on formulation it will have a mode of action (MoA) of killing the insect.
- Are dangerous to health, use as guided.
Eg of a common insecticide?
DOOM.
DOOM attributes? (4)
- Active ingredient is pyrethroids.
- MoA is neurotoxic.
- Use it as suggested.
- Strip colour on product indicates the product’s toxicity.
Types of insecticides modes of action? (3)
- Neurotoxins.
- Growth regulators (IGR).
- Biological insecticides.
Neurotoxins?
= interfere with nervous system pathways/signalling, causing overexcitement, paralysis and ultimately death of the insect.
Neurotoxins attribute?
Often used in malaria-control sprays.
Growth regulators (IGRs)?
= interfere with the natural growth/development (larvae) of the target insect by mimicking hormones like the Juvenile hormone/chitin inhibitors to prevent maturation or development, and ultimately death.
Biological insecticides?
= derived from natural organisms (bacteria/fungi/viruses).
Biological insecticides attributes? (2)
- More targeted than typical chemical insecticides.
- Can be Bt maize where when insects ingest the toxin, it leads to its death.
Eg of Biological insecticides?
Bt Maize.
Explain Bt Maize eg?
Bacillus thuringiensis (Bt) produces crystalline (Cry) proteins that are toxic to Lepidoptera when ingested to deter them from damaging maize/crops.
Aren’t we at risk if there are toxic proteins in Bt Maize?
No, it is harmless to humans.
The picture on pesticides around the world?
Represents how pesticide use has increased drastically as we have to feed the increasing population & prevent disease
Issues with using pesticides excessively?
It has non-target effects such pollution, where pesticides may enter/infiltrate into the soil, water, air and other plants through the wind. Therefore, some are banned such as Paris green & DDT.
Egs of banned pesticides? (2)
- Paris Green.
- DDT.
The Physiology of Resistance process?
As the same pesticide is applied over time from the first generation to later generations of pest insects, pest insects become more resistant to the pesticide over time.
Ways that insects can become resistant to insecticides? (3)
- Metabolic intoxification.
- Target-site mutation.
- Behavioural response.
Metabolic intoxification?
= when enzymes detoxify/break down the insecticide before it reaches its target site or lethal levels.
Target site mutation?
= when mutations can prevent the insecticide from binding, this often eliminates an entire group of insecticides (MoA).
Behavioural response?
= when insects alter their behaviour to avoid exposure to the insecticide.
How do we solve this issue of insecticide resistance by insects? (3)
- Manufacturing new formulations.
- Rotation of insecticide types/MoA.
- Integrated management through using both biological & chemical controls.
Super summary? (3)
- Immunity (innate immune system, hemocytes).
- Insecticides (modes of action, extensive usage = resistances).
- Resistance (various forms of resistance, metabolic/mutations/behaviour).
