Entomology - Defences & Conservation

First line of defence for all insects

Hiding

Secondary external defences

• deimatic display

• physical defence

• chemical defence

• behavioural defence

6 forms of visual defence

1. Crypsis

2. Minimcry

3. Mimesis

4. Aposematism

5. Diematic display

6. Deflection marks

Crypsis

disruptive colouration and countershading

e.g. Mimas tiliae (Lime hawkmoth)

Mimicry

Appearing like other organisms

Batsian & Mullerian

Mimesis

Appearing like an inedible objects

e.g. orange-tip butterfly(Anthocharis cardamines)

Aposematism

Warning colouration (usually accompanied with chemical, physical or behavioural defences)

e.g. Tyria jacobaeae (Cinnibar)

Diematic display

Sudden display of bright colours or eye-spots

e.g. Inachis io (Peacock butterfly) or Cercopis vulnerata (Large yellow underwing)

Deflection marks

small eyespots

e.g. Deilephila elpenor (Elephant hawkmoth)

Batesian Mimicry

harmless organism mimic harmful

e.g. Hemaris tityus (Narrow bordered Bee hawkmoth) mimics bumblebees

Mullerian mimicry

multiple harmful species mimic one another

e.g. Many Hymenoptera have black and yellow stripes

Chemical defences

found in nearly all insects in some form - allelochemicals

Chemical defences are often associated with what visual defence?

Aposematism

Sources of chemical defences

• Metabolites

• Sequestered chemicals from the environment

Chemical defence compounds

• Steroids (e.g. cardenolides)

• cardiac glycosides (e.g. digoxin from foxglove

• enzymes

• terpenoids

• alkaloids

• quinones

• aromatics

What are the 4 mechanisms of chemical defence

1. passive exsistence (in haemolymph or urticating hairs)

2. secretion from limbs

3. active ejection

4. venom

Urticating hairs

• setae/spines along body containing toxins

• fracture when touched, releasing toxin - stinging sensation/ dermatitis erucism

Lepidopteran larvae (caterpillars) contain toxins that may be …

Haemolytic

Proteolytic

Contain hyaluronidase

Haemolytic toxin

destroys blood cells

Proteolytic toxin

destroys protein structures

Hyaluranidase

destroys connective tissue

Reflex bleeding

secretion of oily toxic haemolymph from leg joints as haemolymph has a bitter taste

Firefly (Lampyridae) chemical secretion defence

Lucibufagin

Cantharidin (Terenoid toxin)

Causes severe skin blistering and even death in humans

Produced in haemolymph

Red headed cardinal beetles chemical defence

Imbibe catharidin from oil beetles to enhance its own defence

Bombardier beetle chemical defence

Active ejection of boiling hot toxic chemicals (p-benzoquinones, hydrogen peroxide and enzymes) from glands on their posterior

Exploding ant species

Colotopsis explodens (gaster rupture)

Crematogaster inflata ( metapleural glands act as belt)

Aculeata venom defence

modified ovipositor into a stnger

Altruism in eusocial insects

Self sacrifice in the defence of the colony

What does venom typically consist of?

Cocktail of enzymes to produce immediate pain and tissue breakdown

Also releases an alarm pheromone

What species of Hymenoptera is the only one to die after stinging?

Apis melliforma (honeybees)

Barbed stinger gets stuck, pulling digestive tract, muscles and nerves out after stinging

3 forms of behavioural defence

1. Avoidance

2. Grooming (removes pathogens or parasites)

3. Basking in sun (UV kills microbes, elevated temp kills pathogens)

Thanatosis

death feigning (tonic immobility)

elicited by contact, restraint, and substrate vibrations

Faecal defence

Physical or chemical defence

e.g. Tortoise beetle (Chelymorpha alterons) covers itself

e.g. Termites (Coptotermes formosonus) incorporate faeces in nest wall to avert pathogens

Forms of physical defence

• Modified mouthparts

• Spiny legs

• Cuticular horns or spines

• Body shape to prevent dislodging from host

• Fungistatic compounds in epicuticle

What are the two elements to an insects immune response?

Cellular and Humoral

Cues of insect immune response

Pathogen surface molecules

What molecular cue allows the immune system to recognise a pathogen?

Pathogen associated molecular patterns (PAMPs)

Pattern recognition receptors (PRRs)

Glycoproteins on the surface of defence cells that bind to PAMPs

Examples of pathogen associated molecular patterns (PAMPs)

• Lipopolysaccharides (gram-neg only)

• Peptidoglycan

• Lipoteichoic acids (gram-pos only)

• Mannose

• Bacterial DNA and double stranded virus RNA

• Flagellin

• N-formylmethonine

Insect pathogen recognition receptors (PRRs)

• Immulectins (carbohydrate recognition domains)

• Haemolin (binds to surface of bacteria)

• Peptidoglycan recognition protein

• Toll and Toll-like receptors (bind to many ligands)

Innate immune responses

1. Phagosytosis

2. Nodule formation

3. Encapsulation

4. Melanisation

Damage associated olecular patterns (DAMPs)

function similar to pathogen associated molecular patterns

released by damaged or dying host cells

trigger cellular or humoral innate immune responses (e.g. phagocytosis)

5 examples of types of cells involved in cellular immune response

1. Haemocytes

2. Prohaemocytes

3. Apidohaemocytes

4. Plasmatocytes

5. Granular cells

Haemocytes

direct role in healing

Prohaemocytes

essentially stem cells

Adipohaemocytes

fat storage cells

2 most important cells involved in cellular immune response

Plasmocytes and Granular cells

Plasmocytes

• phagocytose pathogens

• perform spreading behaviour

• work in wound healing and encapsulation

Granular cells

• nodulation and encapsulation

• wound healing

• no spreading behaviour

Phagocytosis

engulfing a small number of small invadors

performed by plasmocytes

Nodule formation

engulfment of lots of small pathogens - separating them from the haemolymph

performed by haemocytes

melanisation is a knock-on effect

Encapsulation

Similar to nodule formation but 1 large invader rather than many small

performed by granular cells and plasmatocytes

melanisation is a knock-on effect

Wound healing

triggered by damage associated molecular patterns (DAMPs)

performed by granular cells and plasmatocytes

What do granular cells do in wound healing?

rupture at wound site, forming a soft clot gel-like substance

WHat do plasmatocytes do in wound healing?

attracted by granular cells and bind underneath the soft clot, cleaning up the wound

How is a wound healed after the formation of a soft clot?

• hard clot forms by phenyloxidases

• epidermal cells migrate over the clot and repair cuticle

Humoral immune response

a primary and secondary response mediated by noncellular macromolecules

Primary humoral response

activation of cascades of constitutive proteins in haemolymph

e.g. prophenoloxidase (ProPO) cascade

Secondary humoral response

transcriptional activation of defence proteins

very specific to pathogen as is built in response to arrival

e.g. induction of anti-microbial proteins

Humoral effectors derived from body fat

• Antimicrobial peptides (AMPs)

• opsins (melanisation of clotting)

• catalase (limits reactive oxygen produced)

• tranferrin (reduces free iron for microbial proliferation)

• lysosome (hydrolyses link in bacterial walls)

Melanisation

Phenoloxidase cascade synthesises melanin

What is produced as by-products in melanisation (Phenoloxidase cascade)?

Toxic quinone intermediates, reactive oxygen and nitrogen species

How is Phenoloxidase stored?

In an inactive form proPhenoloxidase stored in circulating haemocytes

Released in response to wounding or PAMPs

How is proPhenoloxidase activated into Phenoloxidase?

proteolysis through action of specific serine protease

What happens to the toxic by-products of melanin production?

Reactive oxygen and nitrogen intermediates (e.g. peroxide) cause oxidative damage to pathogens directly or indirectly

Anti-microbial peptides (AMPs)

Catatonic peptides with less than 100 amino acid residues

AMphipathic structure

Generate pore in membrane of target and disrupts functioning

Synthesised in body fat in response to infection

What activates the transcription of anti-microbial peptides in the presence of gram negative bacteria?

Immune deficiency signalling pathways

Peptidoglycan recognition proteins (a form of pathogen recognition receptor)

What activates the transcription of anti-microbial peptides in the presence of gram positive bacteria?

Toll signalling pathway

What are the 4 groupings of anti-microbial peptides?

1. Defensins

2. Cecropins

3. Attacins

4. Diptericin

Defensins

form of anti-microbial peptide

Lyse bacteria cells by formation of membrane channels

Cecropins

form of anti-microbial peptides

Kill many but not all gram positive and negative bacteria by creating membrane channels

Attacins

form of anti-microbial peptide

Only attack gram negative bacteria

Prevent cell division by inhibiting biosynthesis of outer membrane proteins

Diptericin

form of anti-microbial peptide

Only attack limited range of gram negative bacteria

Disrupt cytoplasmic membrane

Around how many British insects are listed as endangered, rare, scarce or threatened?

2000

How many insects have been evaluated by the IUCN and how many described insects species are there?

Around 6000 species evaluated

Over 1million described species

How many species are deacribed as data deficient by the IUCN?

1702

Why are many species classed as data deficient?

• difficult to identify populations

• difficult to acheive public funding

• higher funding is provided to more attractive species

Why is it hard to establish conservation methods for insects?

• understanding threats can be incredibly difficult

• poplations are generally very changing (e.g. seasonal)

• Sub-species often not described

• prominent interspecific relationships making methods complex

• funding

• requirements are different for different lifestages

• metapopulation

How have humans effected insect populations?

• habitat destruction

• invasive species introduction

• biological control of crop ‘pests’

• pathogen spread

• GMO crops

• climate change

Light pollution

Artificial light at night

effects daily or seasonal photoperiod, vital in insects synchronisation of physiological and behavioural processes with the environment

Phototactic

attracted to light

Problems causes by artificial light at night

1. fatal attraction

2. amplifies polarisation - effects oviposition especially in species with aquatic larvae

3. disrupts light based communication and signalling (Lamprydae)

4. disrupts navigational signals

5. disrupts circadian rhythms - ecological mismatch

Problems caused by noise pollution

1. alters detection and processing of acoustic cues

2. impairs ability to respond to predator or prey signals

3. reduces accuracy of prey/host location in predators and parsitoids

Oxidative pollutants

Ozone, nitric oxide and carbon dioxide

• change odour profiles of food, oviposition sites and floral plumes

• therefore alters feeding, mating, oviposition, ability to locate prey and decreased pollination

Metal chemical pollution

changes ingestion, locomotor and reproductive behaviours

Parasiticides and pesticides

cause outbreaks of pests due to loss of natural enemies

loss of diversity in freshwater

reduced nutrient cycling

What is best practices to aid conservaition of insects?

• more research on the species and its functioning

• more traditional management (e.g. orchards)

• habitat restoration and enhancement

• replanting of food items and removal of non-native species

• education