ENT201 - Exam 1

Trilobites - key characteristics

• Arthropods

• Extinct

• Marine

• Lived in ancient oceans 550-250 million years ago

Horseshoe crab - evolutionary relation

Closely related to spiders

Horseshoe crab - medical significance

Their bright blue blood is harvested to test medical supplies for bacterial contamination

Arthropods - key characteristics

• Jointed appendages

• segmented bodies

• bilateral symmetry

Amber

• Fossilized tree resin

• Preserves trapped organisms in great detail

• Only gemstone that burns

Typical age of amber insect fossils

30-60 million years old

Appearance of the first insects

Tiny, wingless, soft-bodied organisms that moved from water to land around 420 million years ago

Insect flight emergence timeline

Around 300 million years ago, with the ancestors of dragonflies and mayflies

Earliest recorded human-insect interaction artwork

Cave drawings around 6,000 BC showing humans collecting honey from bees

Aristotle’s contribution to zoology

Known as the father of Zoology; wrote Historia Animalium

Theophrastus

Ancient Greek scholar who was the first to catalog insect crop pests

Pliny the Elder

Roman author who dedicated Book 11 of his work Historia Naturalis to insects

John Sperling’s 1661 estimate of species

• Estimated at around 40 beetles

• 50 caterpillars

• 70 flies

• over 100 butterflies

• All in Zoolgia Physica

John Ray’s 1700 global insect estimate

Estimated that there were approximately 10,000 total insect species in the world in Historia Insectorum

Linnaeus

Established the formal binomial system of nomenclature in Systema Naturae (10th ed., 1758)

Biological definition of a species

One or more populations of interbreeding individuals that produce fertile, reproductively isolated offspring

Number of identified insect species

1,000,000 named and identified species

silk cultivation history

Cultivated for 6,000 years in Asia

True classification of ladybugs

• Beetles (order Coleoptera), not true bugs

Griffinflies

Extinct giant flying insects

• closely related to modern dragonflies

First animal group to achieve flight

Insects (one of only four animal groups to ever achieve true flight)

Evolutionary advantage of insect flight

Allows small organisms to exploit scattered resources and traverse large distances efficiently

Timeline for present-day insect species presence

Many modern insect species were present by the mid-Tertiary period (~25-30 million years ago)

Horseshoe crab structural trait shared with trilobites

A hard, protective chitinous exoskeleton

Timeline for modern insect relatives

Most modern insect relatives were present before the Jurassic period (~180 million years ago)

A fraction of all living species that are arthropods

2/3 of all identified species

Fraction of all identified species that are insects

1/2 of all identified species

Number of Insects per Human on Earth

200,000,000

Phylum Arthropoda

• Segmented bodies

• Jointed appendages

• Chitinous exoskeleton

• Bilateral symmetry

Bilateral symmetry

Only one plane of symmetry divides the body into two identical halves

Class #1 crustacea

• A class of primarily aquatic arthropods

• 4 antennae and 10 limbs

• Lobsters, crabs, shrimps

Physical reason crustaceans can grow to large physical sizes

Because they live in water, buoyancy makes them weightless, relieving gravitational constraints

Class #2 Chilopoda

• Centipedes

• 100 legs

• Multi-segmented predatory arthropods

• 1 pair (2 legs) per segment

• Fangs and venom

Dietary habits and ecological role of centipedes

All are venomous predators that hunt arthropods, lizards, small rodents and birds

Class #3 Diplopoda

• Milipedes

• 1000 legs

• herbivorous/detrivorous

• Arthropods

• Rounded bodies

• 2 pairs (4 legs) per segment

Defensive mechanisms used by Class Diplopoda (Milipedes)

Rolling into a tight ball, utilizing barbed hairs, producing chemical defenses such as cyanide

Primary ecological function of milipedes in ecosystems

• Detritivores

• Feed on decaying plant material and fungi

Class #4 Arachnida

• Spiders, scorpions, ticks, mites

• 8 legs

• 2 body regions

• no antennae

• presence of pedipalps

Class #5 Insecta

• 6 legs

• 3 body regions

• 2 antennae

• external mouthparts

• 0,2, or 4 wings

Body regions in Class Insecta

3 body regions:

• head, thorax, abdomen

Linnaeus

• Established a modern system of binomial nomenclature in Systema Naturae

Mnemonic for taxonomic rank hierarchy

King Philip Cried ‘Oh For Goodness Sake’

KINGDOM

PHYLUM

CLASS

ORDER

FAMILY

GENUS

SPECIES

Benefit of binomial nomenclature over common names

Provides precise, globally standardized identification regardless of local language or common names

Language traditionally used for scientific naming of new species

Latin

Two components that make up a binomial scientific name

1. The genus (capitalized)

2. The specific species (lowercase)

all italicized

Structural advantage hollow tube design in insect exoskeletons

A metal tube or cylinder provides greater structural strength against bending compared to a solid rod of equal weight

Inelasticity of hardened exoskeleton

Once an insect’s exoskeleton completely hardens and tans, it cannot stretch or expand further.

Basement membrane function

A non-cellular layer that separates the internal body cavity (hemolymph) from the epidermal cells

Three main layers of insect cuticle from innermost to outermost

Endocuticle —> exocuticle —> epicuticle

Endocuticle

• Soft, flexible

• Non-tanned matrix of chitin and protein

• Flexible but non-stretching

Exocuticle

• Hardened, rigid layer

• Formed when protein, chitin, and phenolics cross-link into sclerotin

Epicuticle

• Prevents water loss by forming a thin, waterproof layer of protein, wax and cement

The primary reason insects require a waterproof epicuticle

• Due to their high surface-area-to-volume ratio

• Body water is their most precious and easily lost resource

Resilin

An extraordinarily elastic, rubbery protein found in joints, wing hinges, and jumping mechanisms

Setae function in bees

Branched hair like sturcutres that catch and hold pollen grains during foraging

Defensive adaptation of setae in certain caterpillars

Hiding stinging or venomous spines under setae to deter predators

Chitin

a large natural sugar (polysaccharide) polymer that forms the structural backbone of insect cuticles

Chemical resistance of chitin

Highly resistant to degradation by dilute acids and alkalis

Three advantages of an exoskeleton

1. Prevents water loss

2. Physical protection against predators/pathogens

3. High strength-to-weight ratio

Three major disadvantages of an exoskeleton

1. Limits the ultimate physical body size

2. Decreases flexibility/freedom of movement

3. Requires a dangerous molting process

Reason molting poses a extreme danger to insects

• Shedding the old exoskeleton leaves the insect soft, immobile and defenseless against predators

Most abundant biogenic organic polymer on Earth

Cellulose

Biological role of cellulose in plants

Provides structural support for plant cell walls and stems

Presence of an exoskeleton in internal insect structures

• Cuticle lines interval invaginations, including the foregut, hindgut, and tracheal respiratory tubes

Sclerotin

A rigid, tanned protein complex formed by cross-linking proteins, chitin, and phenolics in the exocuticle

Wax layer location and function within epicuticle

• Situated in the epicuticle

• Serves as the primary barrier preventing evaporative water loss

Physical reason exoskeletons constrain maximum insect body size

As body size increases, exoskeleton weight increases exponentially, becoming too heavy for interval muscles to move on land

Insect body segment organization

20 total segments in 3 body regions

Insect head structure

• A hard capsule formed by the fusion of 6 segments

• Acts as the sensory and feeding center

• Insect mouth parts: Appendages modified to form mouthparts

Compound eye structure

• A mosaic of hexagonal subunits or facets aligned with light-sensing cells

• Some can see colors —> violet, blue, green, and yellow, but cannot see red

Insect motion detection speed

Insects detect movement significantly faster than human eyes can

Ocelli

• Simple eyes consisting of a single facet

• Senses light and some movement

Plumose antennae function

Feather-like antennae designed to maximize surface area to detect female pheromones

Chewing mouthparts layout

Original insect layout: labrum, 2 mandibles, maxillae, labium, and hypopharynx

Labrum

• The top lip/front section of the mouth

• Prevents food from falling out while eating

Mandibles

• The hardest part of the exoskeleton

• Located behind the labrum

• Wearing it out causes starvation

Hypopharynx

The tongue-like structure tucked inside the insect’s mouth

Maxillae

• Paired structures behind the hypopharynx

• Recognized as the most ‘leg-like’ of mouthparts

Labium

The bottom lip/floor of the insect’s mouth

Piercing-sucking mouthparts

• Mouthparts that puncture tissues

• Extract liquids

• Common in mosquitoes

Sponging mouthparts

• Mouthparts that soak up liquids

• Common in house flies

Chewing-lapping mouthparts

• Mouthparts suited for both liquid nectar and solid pollen

• Common in bees

Siphoning mouthparts

• Tube-like mouthparts used to draw up uncontained liquids

• Common in butterflies and moths

Vestigial mouthparts

• Non-functional or absent mouthparts

• Certain moths and mayflies

Xanthopan morganii flower pollinator

• A specialized moth species with a long proboscis adapted for this specific flower

Main Functional Role of the Insect Thorax

• Center for locomotion (housing legs and wings)

Number of segments in the insect thorax

Exactly 3 segments

Three thoracic segments in order

Prothorax —> mesothorax —> metathorax

Structural shape of each thoracic segment

A four-sided box

Reason the prothorax can be elaborate

Wings are never attached to the prothorax segment

Number and placement of audit insect legs

Six legs total; one pair per thoracic segment

Advantage of having six legs

Forms an alternating tripod stance for highly stable locomotion

Saltatorial legs

Legs modified for jumping

Fossorial legs

Legs modified for digging

Raptorial legs

Legs modified for capturing and grasping prey

Natatorial legs

Legs modified for swimming

Cursorial legs

Legs modified for running

Thoracic segments where wings attach

Mesothorax and metathorax (never on the prothorax)

Hemelytra

• Forewings that are leathery at the base

• Clear membranous at the tip

Elytra

Hard protective forewings found in beetles