Insect Defences

Question 1

What is considered the first line of defence from predators?

Answer 1

hiding

Question 2

1. visual defences

Answer 2

predator avoidance strategy

• crypsis - disruptive colouration + countershading
• mimicry - appearing like another organism
• mimesis - appearing like an inedible object
• aposematism - warning colouration
• deimatic display - sudden display of bright colour/eye spots
• defection marks - small eyespots

is overlap between different kinds of visual defence

Question 3

batesian vs mullerian

Answer 3

batesian - fake toxic

mullerian - real toxic

Question 4

chemical defences

Answer 4

• defensive compounds - produced in nearly all insects (allelochemicals)
• vary in size + volatility, chemical class, mechanism of action
• may contain substances that increase effectiveness
• insects often brightly- coloured (aposematism)
• strong, unpleasant odors
• sources - metabolites or sequestered from environment (e.g. food plants)
• compounds incl steroids (e.g. cardenolides), cardiac glycosides (e.g. digoxin from foxglove), enzymes, terpenoids, alkaloids, quinones, aromatics

Question 5

Defensive chemical compounds may:

Answer 5

a) exist passively in Haemolymph or urticating hairs
b) be secreted from limbs
c) be actively ejected or exploded from body
d) occur as venom + administered via sting

Question 6

a) passive toxins - haemolymph

Answer 6

in wings of adult wings or larvae of Lepidoptera

usually accompanied w/ warning colouration

Question 7

a) passive toxins - urticating hairs

Answer 7

• insects may have setae/spines along body containing toxins from poison gland cells
• hairs fracture when touched and toxins spill out onto body surface causing stinging sensation or dermatitis erucism
• Lepidopteran larval toxins may be haemolytic (destroying blood cells), proteolytic (destroying protein structures) or contain hyaluronidase (destroys connective tissue)

e.g. caterpillars

Question 8

b) secreted from limbs

Answer 8

• common among Coleoptera such as ladybirds (Coccinella), bloody-nosed beetles (Timarcha), rove beetles (Paederus)
• usually secrete toxic oily haemolymph from leg joints
• haemolymph has bitter taste - causes predators to spit out insect
• known as reflex bleeding

Question 9

d) venom

Answer 9

evolved from ovipositor in some Aculeata (Aprocrita: Hymenoptera)

Eusocial spp display altruistic beh in defence of colony (loss of stinger causes death)

venom contains cocktail of enzymes to produce immediate pain, inflammation + tissue breakdown

releases alarm pheromone

Barbed stinger gets lodged in flesh + continues to pump driving stinger further in and releasing venom

sting consists of two barbed lancets on either side of stylus

sting drawn in by barbed slides - move alternately up and down stylus

when bee stings, it cannot pull the barbed stinger out - leaves stinger + part of abdomen + digestive tract, + muscles + nerves

Honey bees only species of bees to die after stinging - massive abdominal rupture kills bee

Question 10

Thanatosis - death feigning

Answer 10

• tonic immobility
• anti-predator tactic not requiring movement
• insect may fall to ground, tuck in legs or antennae
• remain for some time
• common among beetles
• elicited by contact, restraint + substrate vibrations

Question 11

physical defences

Answer 11

• modified mouthparts + spiny legs = defensive
• some cuticular horns or spines can be used to deter predator
• body shape can be used to prevent dislodging from their hosts
• many insects make retreats
• primary physical-chemical barrier to infection
• fungistatic compounds in epicuticular waxes can inhibit development of some pathogens
• fungistatic, compounds incl fatty acids, melanin
• virulent pathogens are able to overcome these barriers