Ent. Lab Practical 4 (combined)

Why must insects molt?

The exoskeleton is limiting, growth requires periodically replacing the old cuticle with a larger one.

What is molting?

Shedding of the old cuticle and the building of a new one.

When do most insects stop molting?

At the adult stage.

What are the three phases in the molt cycle?

Pre-ecdysis, ecdysis, and post-ecdysis.

What is apolysis?

When the epidermis separates from the old cuticle.

What happens during pre-ecdysis?

Apolysis (epidermis detaches), new cuticle begins forming.

What fills the gap left by apolysis during pre-ecdysis?

Molting fluid.

What is laid down first during pre-ecdysis?

The new epicuticle, it protects the new cuticle.

What digests the old endocuticle in pre-ecdysis?

Enzymes in the molting fluid.

During pre-ecdysis, what is the digested material recycled into?

The new cuticle.

What happens during ecdysis?

The old cuticle splits and is shed.

Why do insects swallow air or water during ecdysis?

To build up body pressure.

When and where does the old cuticle split during ecdysis?

During ecdysis, along the ecdysial lines (usually along the head and thorax).

What is the cast-off cuticle in ecdysis called?

An exuvium.

Which internal structures need to molt during ecdysis?

Tracheal linings and parts of the gut lining.

What happens during post-ecdysis?

New cuticle expands and hardens (tans).

When is soft new cuticle stretched to its larger size using blood pressure and swallowed air?

During post-ecdysis.

How are wings expanded during post-ecdysis?

By pumping hemolymph into the veins (in the final molt).

What is tanning (sclerotization)?

When the cuticle darkens and hardens over hours.

What does it mean to say an insect is teneral?

It is pale, soft, and vulnerable (unhardened).

Why is molting risky?

Predation risk (soft body, poor mobility), desiccation, unable to feed or defend, and incomplete ecdysis (stuck exuvial) can occur.

Why do insects undergo metamorphosis?

To separate life roles (larvae, adult), less competition between life stages as larvae and adults often use different good and different habitats.

Larvae specialize in:

Eating and growing.

Adults specialize in:

Dispersal and reproduction.

What are the different patterns of development?

Ametabolous (no metamorphosis), Hemimetabolous, and Holometabolous (complete metamorphosis).

Ametabolous:

Hatchlings look like small adults, growth is mostly by size, and continue to molt as adults.

Ametabolous Examples:

Silverfish, firebrats, and bristletails.

Hemimetabolous:

Stages (egg → nymph/naiad (several instars) → adults), wings develop externally as wings pads and enlarge each molt, no pupal stage.

Hemimetabolous Examples:

True bugs, grasshoppers, dragonflies, and more.

Holometabolous:

Stages (egg → larva → pupa → adult), wings develop internally.

Holometabolous Examples:

Beetles, flies, moths, butterflies, and more.

How can larvae be classified?

Oligopod, Polypod, and Apodous.

Oligopod:

Thoracic legs only, no abdominal prolegs.

Oligopod Classifications:

Campodeiform and Scarabaeiform.

Campodeiform:

Elongated, flattened, active, long legs and prominent mandibles, often predators or active foragers.

Campodeiform Examples:

Ground beetle larvae, lady beetle larvae, and lacewing larvae.

Scarabaeiform:

C-shaped, thick, whitish, short legs, sluggish, usually living in soil or decaying matter.

Scarabaeiform Examples:

June beetle and other scarab grubs.

Polypodous:

Thoracic legs plus abdominal prolegs (eruciform).

Polypod (Eruciform):

Caterpillar-like body, 3 pairs of true thoracic legs plus fleshy abdominal prolegs.

Polypodous Examples:

Butterfly and moth caterpillars, and sawfly larvae.

Apodous:

No legs at all, vermiform and others).

What is vermiform?

Maggot-like, often with reduced or no head.

Apodous Examples:

Fly maggots, many weevil and wood-boring beetle larvae, and bee and wasp larvae.

What are the different pupal types?

Exarate, Obtect, and Coarctate.

Exarate:

Pupal type; Legs, wings, and antennae free (not glued to the body).

Exarate Examples:

Many beetles, wasps, and bees.

Obtect:

Appendages held against the body by a hardened cuticle.

Obtect Examples:

Butterfly chrysalids, and moth pupae.

Coarctate:

Pupa encased in the hardened last larval skin (puparium).

Coarctate Examples:

Many flies, including house flies.

What are special cases of pupal types?

Hypermetamorphosis (first larval instar differs greatly from later instar) and Subimago (winged pre-adult stage.

Hypermetamorphosis:

The first larval instar differs greatly from later instars (blister beetles, some parasitoids).

Subimago:

A winged pre-adult stage (mayflies).

Reproduction Disadvantages:

Cost of meiosis (transmit only half of genes), must find mate, predation risk, and primary and secondary sexual characteristics.

Reproduction Advantages:

Muller’s ratchet (accumulation of deleterious mutation in asexuals), Red Queen hypothesis (coevolving parasites/pathogens), and genetic novelty and rapid adaptation.Mo

Types of mating systems:

Monogamy, Polygyny, Polyandry, Polygynandry, and Promiscuity.

Sequence of Filters:

Encounter → Species Recognition → Courtship → Acceptance or Rejection → Copulation → Sperm Storage → Oviposition

Encounter (Who Meets Who):

Habitat structure, population density, resource distribution, temporal synchrony, and mobility and signaling range.

Encounter (Leks):

Communal area where male animals gather during mating season to perform competitive displays to attract females.

Encounter (Long Range Detection):

Plumose antennae for long-distance detection of mates.

Species Recognition (Finding the Right Mate):

Pheromonal attraction, acoustic signaling, visual display and motion, and resource-based mate location.

Courtship (Nuptial Gifts):

May signal mating effort, paternal investment, sensory distraction, and signal of male condition.

Courtship (Communicating Information):

Signal species identity, advertise condition or resources, reduce female aggression or resistance, coordinate timing of mating, and stimulate acceptance.

Acceptance or Rejection (Female Choice):

Females may choose based on signal quality or intensity, male persistence or performance, resource possession, nuptial gifts, and compatibility or pervious mating status.

Acceptance or Rejection (Exaggerated Male Traits):

Females prefer males with longest eye spans, drives runaway sexual selection, genes for the exaggerated trait and genes for the female preference co-evolve.

Acceptance or Rejection (Male-Male Competition):

Direct contests, territoriality, scramble competition (indirect, race to find mate), interference with signals, and guarding of females or oviposition sites.

Acceptance or Rejection (Direct Contest):

Male rhinoceros beetles use their large horns to push, lift, and flip opponents in trials of strength and dominance.

Copulation (The Process of Mating):

Coupling (physical association), Insemination (sperm transfer), and Fertilization (subsequent union of sperm and egg).

Copulation (Copulatory Courtship):

Courtship often continues during copulation, encourage continued female cooperation, increase transfer time, stimulate oviposition or storage, reduce immediate remating, and bias paternity in favor of the current male.

Sperm Storage (Process of Fertilization):

Sperm is frequently stored and used later for fertilization, storage determines which ejaculates are available, how long sperm persists, and whether further mating occurs (generally a queen has one mating flight then uses sperm for rest of life cycle (3-5 years).

Sperm Storage (Sperm Competition):

Competition between ejaculates from different males for fertilization, numerical advantage, displacement of rival sperm, guarding against remating, and manipulating female remating or oviposition.

Sperm Storage (Damselfly Sperm Removal):

Some damselfly males can remove stored sperm from previous males before transferring their own ejaculate.

Sperm Storage (Cryptic Female Choice):

Female bias in paternity after mating has occurred, permitting or terminating copulation, transporting or discarding sperm, differential sperm storage, differential remating, and timing oviposition.

Oviposition (Laying Eggs):

Females decide when, where, and sometimes whether to lat eggs after mating.

Oviposition (Site Selection):

Chosen based on host availability, pathogen exposure, microclimate, predation risk, and competition.

What is life history?

The timing of development, survival, dormancy, dispersal, and reproduction across the life cycle.

What is the central problem?

Limited energy and time must be allocated among competing functions.

Where must resources be allocated?

Growth and development, survival through adverse periods, dispersal, mating, and egg production.

What are major tradeoffs?

Rapid development versus adult size and fecundity, current reproduction versus survival, immunity, and future reproduction, dispersal versus reproduction, and overwintering investment versus immediate reproductive output.

R-selected species:

Maximize their intrinsic growth rate (r) to reproduce quickly.

K-selected species:

Maintain population sizes near environmental carrying capacity.

R-leaning species Fecundity:

Very high (hundreds to thousands of eggs).

R-leaning species Parental Investment:

None, eggs scattered.

R-leaning species Generation Time:

Short, multivoltine.

R-leaning species Dispersal:

High (winged morphs, wind-borne).

K-leaning species Fecundity:

Low (few eggs or offspring).

K-leaning species Parental Investment:

Guarding, provisioning, nest building.

K-leaning species Generation Time:

Long, univoltine, or semivoltine.

K-leaning species Dispersal:

Often low.

What does stage structure influence?

Feeding roles, habitat shifts, exposure to enemies, and where reproduction is placed in the life cycle.

Hemimetaboly:

Egg → nymph → adult

Holometaboly:

Egg → larva → pupa → adult

What rules development?

Temperature, ectothermy ties development tightly to temperature, rate tracks body temperature.

Growing degree-days (GDD):

Amount of heat energy accumulated over time to track physiological development.

What does voltinism refer to?

Completed generations per year.

Univoltine:

One generation per year, common where season length is limited, western tent caterpillar.

Bivoltine:

Two generations per year, possible where favorable conditions are long enough, luna moth in S USA.

Multivoltine:

Multiple generations per year, typical of fast developing species in favorable environments, aphids or flies.

Semivoltine:

One generation takes more than one year, seen when development is slow, dormancy prolonged, or environment limits completion, periodical cicadas: 13 or 17 yr.