ENT201 - Exam 1 - Metamorphosi, Growth and Development

Insect Life Cycle Stages (General Progression)

Fertilized egg → embryo → newborn/immature → adult

Chorion

The protective outer shell of an insect egg.

Exceptions to External Egg-Laying (Examples)

• Cockroaches keep egg cases in/on their bodies; tsetse flies give birth to live larvae.

Immature Stage — Primary Mission

Eat, grow, and store resources for adulthood

Instar

The developmental stage of an insect between successive molts.

Adult Stage — Key Features & Mission

• Fully developed wings and functional reproductive organs; mission is to disperse and reproduce

Metamorphosis — Definition

A change in body form or shape as an insect develops from immature to adult (Meta = change, Morphosis = form).

Ametabolous Development — Characteristics

No metamorphosis (Egg → Young → Adult).

Wingless; young and adults look identical and share the same environment/diet.

Least common type.

Hemimetabolous Development — Characteristics

Simple/incomplete metamorphosis (Egg → Nymph → Adult).

Nymphs resemble adults in appearance and diet, but only adults have wings and active reproductive organs.

Holometabolous Development — Characteristics

Complete metamorphosis (Egg $\rightarrow$ Larva $\rightarrow$ Pupa $\rightarrow$ Adult). Immatures look completely different from adults.

Key Ecological Advantage of Holometabolous Development

Allows larvae and adults to exploit completely different environments and food sources, avoiding competition.

Definition of a Generation

The time required to complete a full life cycle from egg to egg.

Poikilothermic

Cold-blooded; an organism's internal body temperature fluctuates directly with environmental temperature.

Thermal Lethal Limits for Insects

• High Temp: Dies at 140–150 °F for 1 hour (or 125–135 °F for 4–5 hours) due to protein breakdown.

• Low Temp: Activity slows at ~40 °F; most die at 0 °F for 4–5 hours.

Insect Endocrine System — Function

Secretes hormones (chemical messengers) to regulate growth, molting, and metamorphosis.

Molting Hormone (MH) vs. Juvenile Hormone (JH) Roles

• MH + High JH: Produces a larval cuticle.

• MH + Low JH: Produces a pupal cuticle.

• MH + No JH: Produces an adult cuticle.

Zygentoma — Common Names

Silverfish and firebrats.

Zygentoma — Distinctive Morphology

Dorsally flattened, covered in silver scales, wingless, 2 cerci equal in length to the central caudal filament, chewing mouthparts, and small or absent compound eyes.

Development & Lifespan

Ametabolous (continues molting even as an adult); can live 3–8 years.

Firebrat Mating Requirements

Females must perform indirect copulation 4–5 days after each molt to fertilize their single clutch per cycle.

Archaeognatha — Common Name & Key Feature

Jumping bristletails; known for jumping ability (Family Machilidae).

Archaeognatha — Distinctive Morphology

Cylindrical, humped-back body covered in scales, wingless, large eyes that touch at the top of the head, and a central caudal filament longer than its 2 cerci.

Archaeognatha vs. Zygentoma Eye Comparison

Archaeognatha have large eyes that touch; Zygentoma have small or absent compound eyes.

Archaeognatha & Zygentoma — Common Life History Traits

• Both are nocturnal, ametabolous detritivores/scavengers found in dark, moist leaf litter, debris, or rocks.