Content area
Full text
Hemolymph distributes nutrients throughout the bee and the immune components contained within it form one of the primary lines of defense against invading microorganisms.
Hemolymph of the honey bee is analogous to blood in higher animals that have a closed circulatory system (blood travels through blood vessels). Hemolymph fills the bee's entire body cavity (hemocoele), in an "open circulatory system." The various organs and tissues are surrounded by it and get all their requirements except oxygen from the hemolymph by direct diffusion. The hemolymph does not contain hemoglobin and is not involved in the distribution of oxygen. Hemolymph is colorless or a pale straw color, which is composed of a fluid (plasma) in which float many nucleated cells called hemocytes. Hemolymph is about 90% water (Morse and Hooper 1985).
The circulation of hemolymph is achieved by a four-chambered heart and a single tube, the aorta that carries hemolymph forward to the head. The heart, positioned dorsally in the abdomen, has a series of muscular chambers, each with a pair of openings (one-way valves called ostia). When the heart muscle is relaxed, hemolymph enters the four chambers from the abdominal cavity. These openings close when the heart muscle contracts and the hemolymph is forced forward through the aorta to the head. Once in the head, the hemolymph spills out into the body cavity near the brain. It sloshes around percolating backward to the abdomen where it again is sucked into the heart to repeat its circuit (Caron 1999). Muscles attached to a dorsal and ventral diaphragm are used to pump the hemolymph throughout the body and back to the heart (Winston 1987).
The main functions of the circulatory system are transporting nutrients from the midgut to the body cells, removing waste material from cells and returning it to excretory organs (Malpighian tubules), lubricating body movements and providing defense against pathogens by means of hemolymph cells that attack invading organisms (hemocytes). The hemolymph also provides turgor support to the body through hydrostatic pressure. This is demonstrated in the pressure required to evert the endophallus of the drone during mating and is also used to expand the wings as the bee emerges from its brood cell and to cast off the old exocuticle during molting. The hemolymph...