Excretory system

• Excretion: Process of removal of nitrogenous waste to maintain ionic balance.
• Main excretory organ: Malpighian tubules (MT).
• Absent in: Collembola and Aphids.
• Primitive number of MT: 6.
• Number of MT varies: 2–200 depending on species (Orthoptera: 2–200, Isoptera: 2–8, Lepidoptera: 6).
• Excretory product (terrestrial insects): Uric acid (uricotelic).
• Excretory product (aquatic insects): Ammonia (ammonotelic).
• Main excretory product (mammals): Urea (ureotelic).
• MT origin: From junction of midgut and hindgut.
• MT connected to rectum: Cryptonephridial condition – found in Lepidopteran & Coleopteran larvae → conserves water.
• Other excretory organs: Nephrocytes, Fat bodies, Oenocytes, Integument, Tracheal system, Cephalic gland.
• Rectal pads: Help in reabsorption of water & salts.

Endocrine system

• Endocrine system = ductless glands secreting hormones directly into haemolymph.
• Neurosecretory cells (NSC): Produce Brain hormone / Activation hormone.
• Corpora cardiaca (CC): Paired neurohaemal organ; stores & releases brain hormone.
• Corpora allata (CA): Secretes Juvenile hormone (JH) / Neotenin.
• Prothoracic glands (PTG): Secretes Ecdysone (moulting hormone).
• Ecdysone: A steroid hormone → initiates moulting.
• Cholesterol acts as precursor of Ecdysone.
• Juvenile hormone (JH): Terpenoid in nature; maintains larval stage.
• High JH → larva → larva moult.
• Low JH → larva → pupa.
• No JH → pupa → adult.
• Brain hormone + Ecdysone + JH regulate growth and metamorphosis.

Insect growth regulators (igrs)

• Definition: Natural or synthetic chemicals that regulate insect growth.
• Term “Insect Growth Regulators” (IGR) – related to third generation pesticides.
• Concept by Prof. Williams (1956); term given in 1967.
• Types of IGRs:
  a. Insect hormones (JH analogues, anti-JH, moulting hormone analogues)
  b. Chitin synthesis inhibitors (CSI)

(A) Insect Hormones

• Brain hormone: Secreted by NSC; released via corpora cardiaca.
• Juvenile hormone (JH): Secreted by corpora allata; prevents metamorphosis.
• Anti-JH: Inhibit corpora allata or JH synthesis.
• Ecdysone: Produced by prothoracic glands; initiates moulting.
• Methoprene (Altosid): First JH analogue (biorational insecticide).
• Other JH analogues: Fenoxycarb (Logic), Pyriproxyfen (Admiral).

(B) Chitin Synthesis Inhibitors (CSI)

• Inhibit cuticle formation (chitin deposition).
• Buprofezin (Applaud): For homopteran pests.
• Teflubenzuron (Nomolt): For coleopteran & lepidopteran pests.
• Lufenuron (Match): For thrips and lepidopteran larvae.

Semiochemicals

• Definition: Chemical messengers affecting behavior of other organisms.
• Divided into:
  a. Pheromones – within same species (intraspecific).
  b. Allelochemicals – between different species (interspecific).

Pheromones

• Term “pheromone” coined by: Karlson & Lüscher (1959).
• First sex pheromone: Bombykol from female silkworm moth (By Butenandt, 1959).
• Used for: Monitoring, Mass trapping, Mating disruption.
• Usually secreted by: Female insects (more potent).
• Alarm pheromone: In aphids (from cornicles).
• Aggregation pheromone: In bark beetles.
• Trail pheromone: In ants (from cephalic glands).

Examples of Sex Pheromones

Allelochemicals (interspecific)

• Allomones: Benefit the emitter, neutral or harmful to receiver.
• Kairomones: Benefit the receiver, neutral/harmful to emitter.
• Synomones: Benefit both emitter and receiver.
• Example: Plant volatiles attracting parasitoids → Synomones.