INSECT REPRODUCTIVE SYSTEM

Vincent Wigglesworth

widely considered the father of insect physiology, and his text requires a focus on both historical experimental techniques and foundational biological mechanisms. 

 Parthenogenesis

 asexual reproduction where offspring develop from unfertilized eggs.

Hermaphroditism

insects utilize a rare reproductive strategy called androdioecy.

Internal genitalia

— serve the development of germ cells (sperm and egg).

 External genitalia

— accomplish the union of two sexes and enable the deposition of eggs by females.

Testes

• Primary, paired organs responsible for sperm production (spermatogenesis). They are usually suspended in the fat body of the abdomen.

• Produce and mature flagellated sperm cells

Vasa Deferentia

Store mature sperm until copulation

Accessory Glands

Produce seminal fluid, spermatophores, and behavior-altering peptides

Ejaculatory Duct

Forcefully expels sperm out of the male body

Aedeagus

Delivers sperm directly into the female tract

Testicular Follicles (Sperm Tubes)

Each testis is composed of one to many tubular follicles enclosed in a protective membrane. Sperm development happens along the length of these tubes.

Germarium

The topmost region of the follicle containing primary germ cells (spermatogonia) that undergo active cell division.

 Zone of Maturation

The middle region where spermatogonia transform into spermatocytes and undergo meiosis.

 Zone of Transformation

The lowest region where round spermatids transform into mature, motile, flagellated sperm cells (spermatozoa).

ducts

The _______ transport, store, and expel mature sperm from the body.

Vas Deferens

A pair of lateral tubes, one extending from each testis, lined with muscles that contract to move sperm downward.

Seminal Vesicles

Enlarged, dilated sections of the vasa deferentia. They store mature sperm temporarily until mating occurs.

Ejaculatory Duct

The single, muscular main tube formed where the two vasa deferentia join. It contracts forcefully to propel sperm into the female during copulation.

 Male accessory glands

• are typically paired structures that open into the vasa deferentia or the ejaculatory duct.

• classified into mesadenia (mesodermal origin) or ectadenia (ectodermal origin).

Seminal Fluid Secretion

They produce the liquid medium that activates, nourishes, and protects sperm during transfer.

Spermatophore Production

In many insects, these glands secrete proteins that form a gelatinous capsule (spermatophore) to enclose and protect the sperm packet.

Female Behavior Modification

The fluid contains chemical compounds (peptides) that, once transferred, stimulate egg-laying and temporarily suppress the female's desire to mate again.

bursa copulatrix

other term for female's vagina

Claspers (Parameres)

External grasping structures used to hold and secure the female firmly in place during mating.

Mushroom Gland (Utricular Gland)

A large, mushroom-shaped accessory gland located at the junction of the vasa deferentia and the ejaculatory duct (in the 6th and 7th abdominal segments). It consists of two types of tubules:

long tubules

The ______________ secrete the innermost layer of the spermatophore (the protective capsule around the sperm).

small tubules

The __________ provide nourishment to the stored sperm.

External Genitalia (Gonapophyses / Phallomeres)

 They open the female genital pouch, grasp the female securely, and ensure accurate delivery of the spermatophore.

Structure: Three asymmetrical, chitinous hooks and plates surrounding the male gonopore:

○    Right Phallomere: Possesses a hook for anchoring.

○    Left Phallomere: Features a long, curved hook called a titillator and a pseudopenis.

○    Ventral Phallomere: The simplest plate, which supports the ejaculatory duct.

Right Phallomere

Possesses a hook for anchoring.

 Left Phallomere

Features a long, curved hook called a titillator and a pseudopenis.

Ventral Phallomere

The simplest plate, which supports the ejaculatory duct.

Ovaries

Generate, nurture, and mature egg cells

Lateral Oviducts

Channel eggs from ovaries to the main tract

Common Oviduct

Directs eggs toward the vagina

Spermatheca

Collects, preserves, and nourishes live sperm

Accessory Glands in Female

Secretes protective glues, shells, or protective casings

Ovipositor

Places eggs into specific environments/substrates

ovaries

The __________ are the primary, paired organs responsible for egg production (oogenesis).

Ovarioles

Each ovary is composed of a cluster of functional units called _______. The number of _______ varies from one (in some dung beetles) to several thousand (in queen termites).

Terminal Filament

A thread-like cord at the tip of each ovariole that anchors the ovary to the insect's body wall or fat body.

Germarium

The topmost region of the ovariole where primary germ cells (oogonia) divide to produce eggs (oocytes) and nurse cells.

Vitellarium

The main body of the ovariole where oocytes grow, accumulate yolk (vitellogenesis), and fully mature into eggs.

Lateral Oviducts

Individual tubes exiting each ovary. They are lined with muscles that contract to push mature eggs downward.

Common Oviduct

The single main tube formed where the two lateral oviducts merge.

Vagina / Genital Chamber

The terminal portion of the duct system opening to the exterior via the vulva. It holds the egg during fertilization and receives the male genitalia during mating.

Spermatheca (Semen Bank)

  Because insects often mate only once but lay eggs over weeks or years, they require a specialized storage organ.

Spermathecal Pouch

A small, sac-like pouch branching off the common oviduct or vagina that stores viable sperm received during mating.

Spermathecal Gland

Produces a nutrient-rich fluid to feed and keep the stored sperm alive for extended periods.

Accessory Glands (Colleterial Glands)

These paired glands open into the vagina or common oviduct and secrete specialized non-reproductive substances.

Egg Protection

They produce adhesive substances to glue eggs to surfaces (like leaves or soil).

Ootheca Formation

In insects like cockroaches and praying mantises, these glands secrete a frothy liquid that hardens into a rigid, protective egg case

Venom Production

In social wasps, bees, and ants, these glands are evolutionarily modified into venom sacs used for defense or paralyzing prey.

Ovipositor

• is the external organ located at the tip of the abdomen, formed by modified abdominal segments.

• It is used to drill, pierce, or dig into substrates (such as wood, soil, or plant tissue) to safely deposit and bury eggs.

Oviparity

●    Egg is laid shortly after fertilization.

●    No retention of the egg inside the female.

●    No nutrients are supplied to the embryo after fertilization.

Ovoviviparity

●    Eggs are retained inside the female until embryogenesis is complete.

●    Embryo is fed by egg reserves (not by the mother directly).

●    Female deposits/gives birth to a nymph or larva.

●    Example: Aphids

Viviparity

●    Eggs are retained inside the female.

●    Embryo is fed directly by the mother.

●    Immatures may complete development before deposition.

●    Examples: Strepsipterans, Tsetse fly

Paedogenesis

Reproduction by larval insects (the larval/mother stage produces daughter larvae without reaching the adult stage).

Parthenogenesis

 Development without fertilization; unfertilized eggs produce offspring.

Arrhenotoky

Unfertilized eggs produce males — seen in Hymenoptera.

Thelytoky

Unfertilized eggs produce females — seen in aphids.

Deuterotoky

Unfertilized eggs produce both sexes — seen in some wasps.

Polyembryony

• One embryo divides mitotically, producing many genetically identical individuals which develop at the expense of one host.

•  Sequence: Parasitization → Egg → Morula → Polyembryo → Reproductive larva → (some develop into) Soldier larva.

  
  

Hermaphroditism

 A rare reproductive strategy in insects; associated with androdioecy (as noted in the Introduction).