W11: Invertebrate Physiology (Physiology Of Resistance: Insect Immunity & Insecticides) [Dr. Blair]

Question 1

Main pathogens that attack insects? (4)

Answer 1

• Fungi.
• Viruses.
• Nematodes.
• Bacteria.

Question 2

Term used to refer to these pathogens?

Answer 2

Entomopathogens.

Question 3

What is the infection route of viruses?

Answer 3

Infection route is through consumption/being eaten.

Question 4

What is the infection route of bacteria?

Answer 4

Infection route is through consumption/being eaten.

Question 5

Which pathogens enter/infect an insect via consumption/being eaten? (2)

Answer 5

• Viruses.
• Bacteria.

Question 6

What are the infection routes of nematodes/parasitic nematodes? (2)

Answer 6

• Natural openings like the mouth, anus & spiracles.
• Cutaneous penetration, through direct penetration through the insect’s cuticle.

Question 7

What are the infection routes of fungi? (2)

Answer 7

• Cuticular penetration, through penetration into an insect’s cuticle (outer shell).
• Respiratory infection, where insects inhale fungal spores through their spiracles.

Question 8

Insect immune system attributes? (4)

Answer 8

• Innate immune system.
• Immediate but non-specific response.
• Pre-programmed response to certain pathogens but no immunological memory.
• Not adaptive.

Question 9

Mammalian immune system attributes? (3)

Answer 9

• Innate & adaptive responses.
• Respond to certain pathogens with immunological memory.
• Quicker & efficient in future exposures.

Question 10

Types of insect immunity? (3)

Answer 10

• Physical barriers/response.
• Cellular response.
• Soluble response.

Question 11

Physical response?

Answer 11

= the exoskeleton (chitin) & gut/tracheal linings act as physical barriers to keep pathogens in or out.

Question 12

Physical barriers in the insect immune system? (2)

Answer 12

• Exoskeleton (chitin acts as the first line of defence).
• Gut/tracheal linings.

Question 13

Cellular response?

Answer 13

= insect immune system defends insect through immune cells (hemocytes) found in the haemocoel.

Question 13

Hemocytes is equivalent to what in humans?

Answer 13

White blood cells.

Question 14

Immune cells?

Answer 14

= molecules that fight pathogens.

Question 15

Soluble response?

Answer 15

= where immune cells such as enzymes, melanin & peptides (defensin/attacin) help the insect fight off pathogens.

Question 16

What about insect wounds?

Answer 16

In the case of insect wounds such as punctured wounds, hemocytes act as platelets and become black due to melanin which contains pigment.

Question 17

What about the more severe wounds like loss of limbs?

Answer 17

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.

Question 18

Is limb regeneration possible?

Answer 18

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.

Question 19

Anything else: Parasitoid wasps?

Answer 19

= 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.

Question 20

Pesticides?

Answer 20

= 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.

Question 21

Pesticides attributes? (2)

Answer 21

• Globally high manufacture & usage of insecticides.
• Help manage populations in agriculture & disease vectors.

Question 22

Types of pesticides? (4)

Answer 22

• Insecticides.
• Herbicides.
• Fungicides.
• Rodenticides.

Question 23

Pesticide type that we will focus on?

Answer 23

Insecticides.

Question 24

Insecticide?

Answer 24

= type of pesticide that targets insects by disrupting vital processes like the nervous system or growth.

Question 25

Insecticides attributes? (3)

Answer 25

• 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.

Question 26

Eg of a common insecticide?

Answer 26

DOOM.

Question 27

DOOM attributes? (4)

Answer 27

• Active ingredient is pyrethroids.
• MoA is neurotoxic.
• Use it as suggested.
• Strip colour on product indicates the product’s toxicity.

Question 28

Types of insecticides modes of action? (3)

Answer 28

• Neurotoxins.
• Growth regulators (IGR).
• Biological insecticides.

Question 29

Neurotoxins?

Answer 29

= interfere with nervous system pathways/signalling, causing overexcitement, paralysis and ultimately death of the insect.

Question 30

Neurotoxins attribute?

Answer 30

Often used in malaria-control sprays.

Question 31

Growth regulators (IGRs)?

Answer 31

= 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.

Question 32

Biological insecticides?

Answer 32

= derived from natural organisms (bacteria/fungi/viruses).

Question 33

Biological insecticides attributes? (2)

Answer 33

• More targeted than typical chemical insecticides.
• Can be Bt maize where when insects ingest the toxin, it leads to its death.

Question 34

Eg of Biological insecticides?

Answer 34

Bt Maize.

Question 35

Explain Bt Maize eg?

Answer 35

Bacillus thuringiensis (Bt) produces crystalline (Cry) proteins that are toxic to Lepidoptera when ingested to deter them from damaging maize/crops.

Question 36

Aren’t we at risk if there are toxic proteins in Bt Maize?

Answer 36

No, it is harmless to humans.

Question 37

The picture on pesticides around the world?

Answer 37

Represents how pesticide use has increased drastically as we have to feed the increasing population & prevent disease

Question 38

Issues with using pesticides excessively?

Answer 38

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.

Question 39

Egs of banned pesticides? (2)

Answer 39

• Paris Green.
• DDT.

Question 40

The Physiology of Resistance process?

Answer 40

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.

Question 41

Ways that insects can become resistant to insecticides? (3)

Answer 41

• Metabolic intoxification.
• Target-site mutation.
• Behavioural response.

Question 42

Metabolic intoxification?

Answer 42

= when enzymes detoxify/break down the insecticide before it reaches its target site or lethal levels.

Question 43

Target site mutation?

Answer 43

= when mutations can prevent the insecticide from binding, this often eliminates an entire group of insecticides (MoA).

Question 44

Behavioural response?

Answer 44

= when insects alter their behaviour to avoid exposure to the insecticide.

Question 45

How do we solve this issue of insecticide resistance by insects? (3)

Answer 45

• Manufacturing new formulations.
• Rotation of insecticide types/MoA.
• Integrated management through using both biological & chemical controls.

Question 46

Super summary? (3)

Answer 46

• Immunity (innate immune system, hemocytes).
• Insecticides (modes of action, extensive usage = resistances).
• Resistance (various forms of resistance, metabolic/mutations/behaviour).