Arthropod Defenses

a Glimpse at

Some Chemical Defenses• Types

Class I: cause some direct harm to predator. E.g. toxic venom, caustic liquid, explosive gas, etc. (often accompanied by aposematic coloration) Class II: discourage feeding. E.g. toxic haemolymph, noxious odors

• Sources (Where do they come from?)– Host plants, prey, mother

• Deployment (At what stage are they used?)– Egg, larva or nymph, pupa, adult

• Application (How are they used?)– Bite, sting, squirted, oozed, gassed, passive-internal

Aposematically colored bugs.

Aposemitism: self-advertising, usually through color, that an organism is poisonous or can harm a predator in a way that benefits the survival of the bearer. The effect may be long-lived if the predator learns avoidance, thus protecting other prey. Aposematic colors are usually some combination of red, yellow, & black. Aposemitism may also be involved in mimicry complexes.

A caterpillar with urticating hairs advertised with aposematism.

Many darkling beetles and stinkbugs emit foul-smelling quinone-laden gas.

Cinnabar moth larvae, exotic biocontrol agents of tansy ragwort, sequester toxic chemicals from the plant for their own defense.

Gullen & Cranston 2005

Bombardier beetles (Brachinus spp.)shoot an explosive noxious blastwhen disturbed.

(Hydrogen peroxide + hydroquinones from secretory tissue) + enzymes from wall of reservoir => valve release => explosion in reaction chamber. Near-boiling hot gas is ejected with an audible “pop”. Text box 14.3

Gullen & Cranston 2005

Role of cantharadin in certain pyrochroid beetles. (Neopyrochroa flabellata). Text box 14.4

Defensive chemical in prey protects eggs of next generation.

Environmental acquisition +horizontal transmission +vertical transmission of an multi-function defensive toxin (cantharidin).

Male: defensive protectant aphrodesiac

Female: defensive protectant nuptial gift

Egg: defensive protectant

PATH OF TOXIN: Environment (prey?) => male => courtship/nuptial gift => selection by female => female acquisition through mating => transfer to eggs => egg protection.

“harmful” models

“harmless” mimics

Types of Defense• Against Physical Forces

Threats Dehydration, Drowning, Freezing, Radiation, Wind (blowing

away)

• Against Biological Forces Threats

Microbes Parasites Predators

Strategies Passive Active

Important Points• Virtually all arthropods have adaptations for defense.• Certain adaptations may be both defensive and serve some other function, e. g. flatness of fleas.• Apparent defensive adaptations against humans per se are incidental.

Insect Defence Against Biological Enemies

Disappearing, (Out of Sight - Out of Mind)

hiding, dropping

running, hopping, flying

Costumes:

crypsis & camouflage

mimesis

Passive Resistance, Discouraging the Attacker

Chemical

toxic haemolymph

secretion of noxious compounds

urticating hairs

Morphological

tough, slippery, spiny cuticle

autotomy (part behavioral)

removable scales, hairs

“backwards” appearance

Behavioral

feigning death

Scare Tactics (Morphological/Behavioral)

eyespots

aposemitism

Active Resistance, Resisting attack or Fighting Back

Educatively Injuring the Attacker

slow-acting toxins

bites & stingsKilling the attacker

Collective Strategies, Special Adaptations of Social Species

confusion effects

nest blocking

mass counter-attack

bluff attack

Visual Defenses(Physical Appearance)

• MimicryTrue Mimicry

Batesian

Mullerian

Mimesis & Startle Effect

• Crypsis

• Warning coloration

Some Morphological/Mechanical Defenses

• Tough or Slippery Exoskeleton• Odd shape• Special structures

– Spines (passive or active poking)– Claws (for hanging on to substrate)– Scales (slippery)– Expendable Wing Surface (detachable)– Jumping legs or other springy devices (escape)– Stings (behavioral)

Defense?

Advanced necrosis from brown recluse spider bite. Not the primary function of the defensive adaptation (venom).

Behavioral Strategies

• Passive– Hiding - often with Mimicry, Mimesis, Crypsis– Timing of Development– Migration & Diapause– Autotomy

• Active– Aggressive defense (entails one or more special weapons)– Escape– Startle– Death-feigning

Special Defense Strategies of Gregarious & Social species

(most are mixed strategies)

• Protective Nest

• Large Numbers => startle/confusion effect

• Massive counter-attack, e.g. stinging

• Sophisticated “alarm/attack” signaling

• Soldier caste (specialized for defense)

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