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Wing Buds

Developing wing outgrowths visible externally in immature insects, especially nymphs of insects with incomplete metamorphosis. They grow and develop into adult wings.

Imaginal cells

Cells in immature insects that contribute to adult structures. In insects with complete metamorphosis, groups of these cells form imaginal discs, which develop into structures such as wings, legs, and eyes.

What are wing buds compared to imaginal cells?

A wing bud describes a developing structure; imaginal cells describe the cells responsible for producing adult structures.

First event that occurs during typical insect reproduction

Mate location: Individuals locate potential mates using chemical, visual, auditory, or vibrational cues.

Second event that occurs during typical insect reproduction

Mate attraction: One individual produces a signal that attracts a potential mate. For example, a female moth releases a sex pheromone.

Third event that occurs during typical insect reproduction

Courtship: Individuals exchange signals or perform behaviors that help establish whether mating will proceed.

Fourth event that occurs during typical insect reproduction

Mate evaluation: One or both individuals assess potential mates using information such as size, movement, chemical cues, or courtship performance.

Fifth event that occurs during typical insect reproduction

Copulation: The insects physically mate, allowing sperm transfer.

Sixth event that occurs during typical insect reproduction

Sperm storage and fertilization: Sperm may be stored in a specialized organ called the spermatheca. Fertilization occurs when sperm and an egg unite.

Seventh event that occurs during typical insect reproduction

Oviposition: The female deposits eggs, often in a location that provides suitable resources for developing offspring.

Eighth event that occurs during typical insect reproduction

Embryonic development and hatching: The embryo develops inside the egg, and the offspring eventually hatch.

When and how does mate evaluation happen in insect sexual reproduction?

Mate evaluation can occur before, during, and sometimes after courtship, as insects use signals and physical characteristics to assess potential partners.

Mate evaluation may involve:

• Chemical signals: Pheromones can indicate species identity, reproductive status, or mate suitability.

• Visual signals: Coloration, body size, and displays may influence mate choice.

• Acoustic signals: Songs or calls can communicate species identity and provide information about a potential mate.

• Vibrational signals: Vibrations transmitted through plants or other surfaces can help insects locate and assess mates.

• Behavioral displays: Courtship movements and behaviors can affect whether a potential mate accepts or rejects the other individual.

• Physical assessment: In some species, contact or close-range interactions provide additional information.

Mate evaluation can help insects avoid mating with individuals of the wrong species and can influence reproductive success.

Example: A female may evaluate a male's courtship song before accepting him as a mate.

What is the electroantennogram (EAG)

An electroantennogram is a technique that measures the electrical response of an insect's antenna to chemical stimuli

EAG functions

• An insect antenna is connected to electrodes.

• Researchers expose the antenna to an odor or chemical stimulus.

• Chemical molecules activate odor-sensitive sensory neurons.

• The combined electrical activity produces a measurable voltage change.

• Researchers record the response to determine whether the antenna detects the chemical.

EAG applications

• Testing whether insects detect particular pheromones.

• Screening chemicals that may attract or repel insects.

• Identifying candidate compounds for pest monitoring and control.

• Investigating insect olfaction and chemical communication.

• Helping identify biologically active compounds for further behavioral testing.

Mating disruption

False trails, sensory confusion, sensory adaptation

• Targets insect communication system but doesn’t kill the insect

How can signals used within an insect species be exploited by predators, humans, or insect population-control methods?

Signals that evolved to communicate information can be intercepted or imitated by other organisms, including predators and humans.

ex: phernome trap

Neoptera

Insects characterized by the ability to fold their wings over the abdomen

Direct flight muscles

Muscles act directly on the wings or associated structures

Indirect flight muscles

Muscles deform the thorax to move the wings

Reynolds number

Compares inertial and viscous forces in fluid flow

Insect flight

Uses moving wings and unsteady aerodynamic mechanisms

Wing evolution

Investigated using fossils, comparative anatomy, developmental biology, and aerodynamics

Specialized chemical defense

Bombardier beetle - Chemical precursors react in a chamber to produce a hot, irritating discharge

Chemical sequestration and resistance

Monarch butterfly - Milkweed-derived cardenolides can be retained for defense

Evolution and epistatis

Monarch resistance mutations - The effects of mutations can depend on other mutations and their order

Aposematism + chemical defense

A defended insect's conspicuous coloration can warn predators of the costs of attacking it.

Basic insect signaling structure formula

Signal producer → signal → sensory organ → receiver response → biological outcome.

Insemination

depositing of sperm into female

female control

• spermatheca receives, maintains, and releases sperm to fertilize eggs

Mate Location

• microclimates/swarms/leks (gatherings of male, no resources for females, male aggression)

  • visual marker/food source

  • species-specific

  • promotes outbreeding

  • aerial or on ground

• Smell: Pheromones (same species)

  • chemical signaling - female produces pheromones that male can detect from afar using antennae

Copulation

Female and male engage in activites that can stimulate mating readiness

nuptial gifts

Given to female to stimulate mating or acceptance (food/resources)

Indirect insemination

• Springtails: spermatophore - packet of sperm placed for females to pick up

• Silverfish: make silk basket with a spermatophore and guide female to pick it up, lock them inside

Direct insemination

• endophallus/organ of intromission (folding penis): genetic transfer

• bedbugs (hemiptera): traumatic insemination - stabbing female abdomen to reproduce

Fertilization

• Spermatheca

  • insemination does not ensure fertilization

  • females can store sperm

  • any male may actually fertilize the most eggs

• Chorion - eggshell, protective outer shell

• Serosa - covering of embryo

When and how does mate evaluation happen in insect sexual reproduction?

during courtship: through fitness, auditory cues, visual display, pheromones, and nuptial gifts

Historically, what important events occurred in going from a hypothesis of pheromone communication in insects to an applied product using pheromones for insect control?

I. John Henry Fabre (1870): Peacock Moth

• noticed female moth is able to attract many male moths from long distances

II. Electroantennogram (1957): method of using antenna of a moth to detect pheromones electrically

III. Adolf Butenandt (1959): Silk worm moth - isolates and characterizes the first pheromone

IV. David Wood (1966): pheromones used for forest pest management (synergism)

V. 1980 - Pheromones used commonly, more than a million traps to capture billions of beetles, curbing an epidemic of bark beetles in forests

What is the relationship between semiochemicals and aposematic signals?

• Semiochemicals often serve as the chemical component of aposematic signals (aposematic chemicals are under semiochemicals): signals between different species

  • Danger signals (allemones)

    • Color change

    • Smell warning

    • Aggression

Why are aposematic signals typically contrasting colors or bold patterns?

• Contrasting colors/bold patterns are thought to be:

  • a signal that works with the predator’s sensory capabilities

  • Easy to learn

  • More difficult to forget

  • As different as possible to edible prey

What is chemical ecology?

The production and reception of chemical signals and sending them between insects, between insects and plants, and the environment and the insects

What are the different categories of semiochemicals and how are they different?

• Pheromones (intraspecific interactions): chemical message that induce a behavioral reaction among individuals of the same species

  • species-specific

  • sex

  • trail

  • aggregation

  • host-marking

• Allelochemicals (interspecific interactions): chemical message that induce a behavioral reaction among individuals of different species

  • Allomones ( benefits +emitter)

  • Kairomones (benefits +receptor)

  • Synomones (benefits +emitter and receptor)

Allelochemicals

• Allomones (emitter benefit)

• Kairomones (receptor/receiver benefit)

• Synomones (emitter and receptor/receiver benefit)

Pheromones

• Sex: attract mates

• Aggregation: cause individuals of both sexes to gather in one spot for feeding, mating, or protection from the environment.

• Alarm: warns nearby members of same species about danger

• Trail: single ant finds food and lets a pheromones that gives a guide to other ants

• Host Marking: marking food source, plant, or host insect with eggs

What kinds of mimicry can insects have that are related to their chemical ecology? What is different between these types of mimicry?

• Batesian: nontoxic, cheaters

• Mullerian: toxic, shared signals, similar looking

What are the broad steps in evolving defensive allomones?

1. tolerance

2. safe storage of compounds

3. effective and efficient deployment

From what structures of the insect are the exocrine glands thought to have evolved?

Epidermis living cells, secrete cuticle that underlies the exoskeleton

What are the details of how the bombardier beetle delivering its explosive defensive discharge?

• Secretory cells produce chemicals

• Collecting duct: move fluids to reservoir

• Reservoir: stores admix

• Reaction chamber: mixes enzymes for explosive reaction

• Explosion is 100 degrees C

How do insects acquire cardiac glycosides and how does this class of chemicals affect most insects and other animals when ingested?

• Insects consume host plants (e.g., milkweed) and sequester the toxins within their bodies.

  • Effect: Toxic to most organisms because they disrupt the essential sodium-potassium pump.