entomology test

Directly Transmitted Parasites

• Passed from one host to another without intermediate host.

• Example: lice

• Lice (Psocodea) – live entire lifecycle on host; transmitted via contact

• Fleas (Siphonaptera) – jump between hosts, often carry diseases (e.g., plague)

move host-to-host

Trophically Transmitted Parasites

• Transferred when one host is eaten by another.

• Common in complex life cycles (e.g., tapeworms in prey-predator systems).

• Example (non-insect but relevant): A parasitized cricket infected by hairworms may jump into water so the parasite can complete its lifecycle in aquatic environments

Vector Transmitted Parasites

• Requires a vector (e.g., mosquito) to transmit from host to host.

• Example: malaria parasite via Anopheles mosquitoes.

• insect examples:

  • Mosquitoes (Diptera: Culicidae) transmit Plasmodium (malaria)

  • Tsetse flies transmit Trypanosoma (sleeping sickness)

  • Fleas (again) transmitted Yersinia pestis (Black Death)

Micropredation

• Feed briefly and move on (like leeches or mosquitoes).

• They don’t stay long enough to establish a true parasitic relationship

• Mosquitoes and biting midges – feed on blood then move on

• Blackflies (Simuliidae) – vectors for river blindness.

Parasitic Castration

• Parasite prevents host reproduction, diverting energy to itself.

• Often seen in marine invertebrates and snails.

• Parasite inhibits host’s reproductive capacity

• Not common in insects, but some wasps and trematodes do this to snail hosts

• Concept to understand: energy diverted to parasite growth instead of reproduction

Parasitoids

• Lay eggs inside a host; larvae kill the host after developing.

• Common in Hymenoptera (wasps).

• Hybrid between parasitism and predation

• Parasite kills the host eventually

• Most common insect orders:

  • Hymenoptera (e.g., parasitoid wasps like Ichneumonidae)

  • Diptera (e.g., Tachinidae flies)

• Idiobionts: Stop host development immediately after infection

• Koinobionts: Let host grow while feeding internally

Evolutionary Stable Strategy (ESS)

Parasites must balance damage and survival:

• Some evolve long-term relationships (low virulence).

• Others are "slash and burn" – exploit and leave (high virulence).

Insects as Parasites

Important insect orders that include parasites:

• Siphonaptera (fleas)

• Strepsiptera

• Psocodea (lice)

• Hymenoptera

• Diptera

What is Parasitism?

• form of antagonistic ecological interaction, where the parasite benefits at the host’s expense.

• Key distinction: Unlike predators, parasites do not immediately kill their host.

• Parasites can be:

  • Ectoparasites: Live on the surface (e.g., lice, fleas)

  • Endoparasites: Live inside the host’s body (e.g., parasitic nematodes)

Ectoparasites

live on the outside of the host's body.
They feed externally, often on blood or skin tissue, and may transmit diseases or cause irritation and secondary infections.

Why Ectoparasitism is Significant:

• Major interface between insects and vertebrates

• Ectoparasites often serve as vectors for pathogens

• Many have specialized adaptations for attachment, feeding, or host-finding

Common Ectoparasitic Insect Orders (with examples):

Phoresis

• Phoresis is a non-parasitic interaction where one organism (usually smaller) hitches a ride on another.

• Important distinction: not feeding on the host, just using it for transport.

• Found in some Diptera and Dermaptera.

• Example: Mites riding on flies (may later parasitize the same host)

Adaptations of Ectoparasitic Insects:

• Flattened bodies for moving through fur or feathers (lice = dorsoventral, fleas = lateral)

• Claw-like legs for clinging to host hair or feathers

• Piercing-sucking mouthparts for blood-feeding

• Reduced wings or winglessness in permanent ectoparasites

• Chemical detection of hosts: CO₂, heat, odor

What is a Parasitoid?

• A parasitoid is an insect whose larvae live in or on a host, ultimately killing it.

• Unlike parasites, parasitoids are lethal to their host and are closer to predators in outcome — but they only consume one host.

Idiobiont Parasitoids

• Immediately immobilize or kill host after laying egg.

• Host does not develop further.

• Often found in ectoparasitoids (live on the host).

• Example: A wasp lays eggs on a paralyzed spider.

Koinobiont Parasitoids

• Allow host to continue development after parasitism.

• Larvae grow internally while host lives and functions.

• Common in endoparasitoids (live inside the host).

• Can manipulate host behavior (e.g., causing caterpillars to protect pupating parasitoids).

Host Behavior Manipulation

• Some parasitoids can alter the host’s behavior to enhance survival of their own offspring.

• Examples:

  • Wasp larvae cause host caterpillars to stop moving or defend them.

  • Hairworms (non-insects) force crickets to jump into water.

Hyperparasitoids

• Parasitoids of parasitoids (a second layer of parasitism!)

• Example: A wasp lays eggs inside a caterpillar already parasitized by another wasp

Central Dogma of Biology:

• DNA → RNA → Protein

• Genes are located on eukaryotic chromosomes, with most coding DNA organized into exons/introns.

Insect Ploidy and Reproduction

Term	Description
Diploid (2n)	Most insects have 2 sets of chromosomes (1 from each parent)
Haploid (n)	Gametes (eggs/sperm) have 1 set
Parthenogenesis	Development from unfertilized egg; can result in males, females, or both

Three Types of Parthenogenesis:

• Deuterotoky – Both sexes produced

• Arrhenotoky – Only males produced (e.g., honeybees)

• Thelytoky – Only females produced (e.g., aphids)

Genetic Model Organisms in Insect Research

Species	Why It's Important

Drosophila melanogaster

First eukaryotic genetic model; short lifecycle; many tools available

Mosquitoes

Vector research (malaria, dengue)

Honey bees

Behavioral & caste genetics

Nasonia

Parasitoid wasps; model for sex determination

Silk moth (Bombyx mori)

Silk protein production

Tribolium castaneum

Beetle model; functional genomics

🧪 The Dynamic Insect Genome: How It Changes

Polyteny – Giant chromosomes (e.g., in fly salivary glands) for studying transcription2. 

Polyploidy – Extra chromosome sets (uncommon but used for tissue growth)

3. Gene Amplification – Temporary increase in gene copies (e.g., for rapid protein production)

4. Transposable Elements – "Jumping genes" that rearrange genome structure

5. Horizontal Gene Transfer – Genes acquired from non-parental sources (often microbes)

Gene Duplication Outcomes

Outcome	Example
Redundancy	Histone genes, heat shock proteins
Neofunctionalization	Opsins (light-sensitive proteins in eyes)
Subfunctionalization	Hox genes – split roles in development
Pseudogenes	"Dead" genes; common in large genomes

Insect Genomes

• Over 1,200 insect genome projects have been completed.

• Genomics helps us understand insect evolution, function, behavior, and their role as pests or vectors.

Shotgun Sequencing

• DNA is randomly broken into fragments, sequenced, and reassembled by a computer.

• Benefits: fast and scalable

• Challenges: must reassemble correctly, especially in repetitive regions

Assembly

• Reconstructs the full genome using overlapping sequences (called contigs).

• Two methods:

  • Reference-based: aligns to a known genome

  • De novo: builds from scratch — needed for new or poorly studied insects

3. Annotation

• dentifying genes, regulatory elements, and functions.

• Critical for linking genotype to phenotype.

Drosophila melanogaster

• First sequenced insect genome

• Size: ~180 megabases (Mb)

• ~13,600 protein-coding genes

• Serves as the gold standard for insect genetics

Genome Size Variation

• Some insects have tiny genomes (e.g., fruit flies)

• Others (e.g., grasshoppers) have very large genomes due to repetitive DNA

Repetitive Elements

• Transposons and satellite DNA make assembly harder

• Can lead to genome inflation

Data Storage and Access

Specialized databases are required

• FlyBase (for Drosophila)

• VectorBase (for disease-vector insects like mosquitoes)

• BeeBase, i5k Workspace, etc.

Definition of Ecology:

• From Greek "oikos" (home) — the study of organisms' interactions with their environment

• Insects play key ecological roles in virtually all ecosystems

Why Are Insects So Biodiverse?

• Small Size
  → Enables exploitation of microhabitats (e.g., soil, under bark, leaf surfaces)

• Wings
  → Mobility = colonization of new habitats = evolutionary success

• Complete Metamorphosis (Holometaboly)
  → Life stages occupy different niches (less competition between larvae and adults)

🧩 Ecological Interactions

• Predation: Praying mantis eating other insects

• Competition: Multiple insect species feeding on same host plant

• Mutualism: Ants protecting aphids in exchange for honeydew

• Parasitism: Parasitoid wasps, lice, or botflies

• Keystone Species: Insects whose absence would collapse ecosystems (e.g., pollinators like bees)

r-Selected vs. K-Selected Strategies:

Strategy	Traits	Insect Example
r-selected	Many offspring, short lifespan, low investment	Fruit flies
K-selected	Fewer offspring, longer development, higher investment	Some beetles, termites

Two Main Types of Eyes in Insects:

Type	Description
Ocelli (“simple eyes”)	Detect light intensity; help stabilize flight; usually 3 arranged in a triangle
Compound Eyes	Made up of many units called ommatidia; form images and detect movement, color, and polarized light

Each ommatidium contains:

• Cornea – outermost lens

• Crystalline cone – focuses light inward

• Rhabdom – photoreceptive part (where light is turned into a signal)

• Retinular cells – photoreceptor neurons

• Pigment cells – isolate ommatidia to sharpen image

• Basement membrane – structural support

Signal Transduction: How Insects “See”

• Light hits opsins (light-sensitive proteins)

• Opsins activate G-protein-coupled receptors (GPCRs)

• These initiate a signal cascade → electrical impulse → brain

Opsin Diversity in Insects

• Insects can have multiple opsin genes (more than humans)

• Some opsins are tuned to UV, blue, and green light

• Expression may vary by:

  • Life stage

  • Sex

  • Region of eye

  • Co-expression of multiple opsins in the same cell

Functional Specialization in Insect Vision

Feature	Example

Sexual dimorphism

Male butterflies with larger eyes or more opsins

Motion detection

Flies have fast flicker fusion rates for rapid visual updates

Polarized light vision

Used by bees and ants for navigation

Color vision

Often includes UV, helping insects detect nectar guides on flowers

Insect Ears

• Insects detect sound using tympanal organs and other mechanosensory structures.

• Unlike eyes, insect ears evolved independently multiple times → at least 19 times!

Key Structures of Insect Ears

Structure	Description
Tympanum	Thin membrane that vibrates with sound (like an eardrum)
Tympanal Organ	Sensory organ under tympanum, often composed of scolopidia (neural cells)
Tympanal Nerve	Sends sound information to brain

What Makes Insect Ears Unique?

• Some insects have no ears at all.

• Those that do may have ears in strange places:

  • Thorax (moths, cicadas)

  • Abdomen (grasshoppers, beetles)

  • Legs (katydids, crickets)

• Most ears are bilateral and tuned to specific frequencies (e.g., bat sonar)

Insect Orders with Ears (Examples):

Order	Example	Ear Location
Orthoptera	Crickets, katydids	Front legs
Lepidoptera	Moths	Thorax or abdomen
Mantodea	Praying mantis	Midline of abdomen
Hemiptera	Cicadas	Abdomen or thorax

Functions of Insect Hearing

• Predator detection: Moths detect echolocation from bats

• Communication: Crickets use chirps for mating; cicadas use tymbals

• Mate finding: Katydids listen for calls from others of their species

• Escape behavior: Hearing bat sonar = evasive flight

Insect Taste and Smell (Chemoreception)

Core Concept:

• Insects use chemoreceptors to detect odors, flavors, pheromones, and environmental cues.

• These receptors are located on antennae, mouthparts, feet, and other body parts.

Three Families of Chemoreceptors:

Family	Function	Ligands Detected	Location
Olfactory Receptors (ORs)	Smell	Most diverse (pheromones, plant volatiles)	Primarily antennae
Ionotropic Receptors (IRs)	Smell	Acids, aldehydes, amines	Antennae, mouthparts
Gustatory Receptors (GRs)	Taste	Sugars, bitter compounds	Mouthparts, legs, wings, ovipositor

🔬 Chemoreception Signal Transduction

When a ligand binds to a receptor:

• Signal travels through a neuron (like a sensory hair)

• Converted into an electrical impulse

• Sent to insect brain for interpretation

Taste (Gustation)

• Gustatory receptors (GRs) respond to:

  • Sugars

  • Bitter/toxic compounds

  • Salts

• Often located on:

  • Mouthparts (for food evaluation)

  • Tarsi (feet) – e.g., flies "taste" with their feet

  • Ovipositor – females taste substrates before laying eggs

Smell (Olfaction)

• ORs and IRs detect:

  • Mates (sex pheromones)

  • Host plants

  • Enemies or predators

• Sensory hairs on antennae are often loaded with olfactory neurons

Notes on Diversity

• GRs are less understood than ORs

• Drosophila has:

  • ~60 OR genes

  • ~68 GR genes

• Insect ORs are seven-transmembrane proteins, like GPCRs, but evolved independently

What are the three main families of insect chemoreceptors and what do they detect?"

ORs (smell), IRs (small molecules like acids), GRs (taste)

"Where are gustatory receptors found in insects?"

Mouthparts, feet, wings, and ovipositor

What type of receptor allows flies to detect sugar with their feet?"

Gustatory Receptors (GRs)

"How does chemoreception differ from mechanoreception?"

1. Chemoreception involves chemical stimuli; mechanoreception responds to touch or vibration

What Is Chemical Defense?

• Insects produce or acquire toxic compounds to deter predators or protect themselves.

• Often paired with aposematism (warning coloration).

Aposematism

• Bright colors (e.g., red, orange, yellow, black) warn predators of toxicity

• Often seen in:

  • Monarch butterflies (toxic from milkweed)

  • Bombardier beetles

  • Wasps (yellow + black)

1. Poison

• Toxin is ingested by predator

• Examples:

  • Monarch butterfly larvae feed on milkweed → toxins stored in body

  • Grasshoppers with bitter-tasting compounds

Venom

• Toxin is injected or actively delivered

• Examples:

  • Wasps and bees with venomous stingers

  • Assassin bugs that inject toxic saliva

3. Sequestration

• Insects obtain chemicals from their diet and store them

• Examples:

  • Monarchs sequester cardiac glycosides from milkweed

  • Leaf beetles absorb plant alkaloids

Autogenous (Self-produced) Chemicals

• Synthesized by the insect itself

• Bombardier beetles: mix chemicals internally and eject hot, noxious spray

How Do Insects Avoid Poisoning Themselves?

1. Compartmentalization – toxins stored in special organs

2. Molecular resistance – their own enzymes neutralize effects

3. Behavioral control – only release toxins under stress

Unusual Delivery Systems

• Reflex bleeding – ladybugs release hemolymph (blood) laced with toxins from joints

• Explosive discharge – bombardier beetle releases boiling chemical spray

Insect Immune Systems

Insects lack adaptive immunity (no antibodies, no memory cells like mammals), but they have a powerful and highly effective innate immune system with:

• Physical barriers

• Cellular responses

• Humoral (chemical) responses

Cuticle:

First defense; protects against microbes and injury

Peritrophic membrane

gut): Protects from ingested pathogens

Cellular Responses

These involve hemocytes (insect blood cells) that circulate in the hemolymph and defend against invaders:

Response	Function

Phagocytosis

Hemocytes engulf small pathogens (like bacteria)

Melanization

Encapsulates pathogens and wounds in melanin → toxic to invaders

Encapsulation

Large invaders (like parasitoid eggs) are wrapped in layers of hemocytes

Nodulation

Clumping of hemocytes around many small invaders

Lysis

Direct rupture of invading cells

RNA interference

Destroys viral RNA → antiviral defense

Apoptosis

Programmed cell death to stop infection from spreading

Humoral Responses

• Antimicrobial peptides (AMPs): Small proteins that attack bacteria, fungi, or viruses

• Produced by fat body (like a liver) and released into hemolymph

• Examples: Defensins, cecropins, attacins