Insect Physiology - Endocrine System

Endocrine System

Hormones are the chemical substances that are transported in the insect’s body fluids (haemolymph) that carry messages away from their point of synthesis to sites that where physiological processes are influenced. These hormones are produced by glandular, neuroglandular and neuronal centres (Gullan & Cranston, 2005). Insects have several organs that produce hormones, controlling reproduction, metamorphosis and moulting (Triplehorn & Johnson, 2005). It has been suggested that a brain hormone is responsible for caste dermination in termites and diapause interruption in some insects (Triplehorn & Johnson, 2005).

Four endocrine centers have been identified:

1. Neurosecretory cells in the brain can produce one or more hormones that affect growth, reproduction, homeostasis and metamorphosis (Gullan & Cranston, 2005; Triplehorn & Johnson, 2005).
2. Corpora cardiaca are a pair of neuroglandular bodies that are found behind the brain and on either sides of the aorta. These not only produce their own neurohormones but they store and release other neurohormones including PTTH prothoracicotropic hormone (brain hormone), which stimulates the secretory activity of the prothoracic glands, playing an integral role in moulting.
3. Prothoracic glands are diffuse, paired glands located at the back of the head or in the thorax. These glands secrete an ecdysteroid called ecdysone, or the moulting hormone, which initiates the epidermal moulting process (Gullan & Cranston, 2005). Additionally it plays a role in accessory reproductive glands in the female, differentiation of ovarioles and in the process of egg production.
4. Corpora allata are small, paired glandular bodies originating from the epithelium located on either side of the foregut. They secrete the juvenile hormone, which regulate reproduction and metamorphosis (Gullan & Cranston, 2005; Triplehorn & Johnson, 2005).