Morphology and biochemical composition of mineralized granules from the malpighian tubules of Musca autumnalis de geer larvae (Diptera: Muscidae)

Abstract

Musca autumnalis De Geer (face fly) larvae form numerous small mineralized granules in the lumen of the anterior Malpighian tubules. The granules are spherical, ranging in diameter from 0.2 to > 10 μm and are composed of many concentric thin layers. The layers appear to be covered by an organic-rich material that may help to bind adjacent layers together. Individual layers appear to be heterogeneous with some composed of small rounded particles of inorganic-rich material imbedded in a loose fibrous mat while other layers appear more solid. The granules are primarily inorganic in composition (>85% ash) with calcium, phosphorus, and magnesium contributing more than 98% of the inorganic elements. Water content is approx. 10%. Carbonate carbon and hydrogen account for 2 to 3% of the granule weight. Nitrogen and organic carbon are only minor elements primarily present in the form of amino acids which contribute only 0.4% of the total granule weight. Aspartic acid and glutamic acid comprise more than 30% of the total amino acids detected after acid hydrolysis. The properties of face fly granules and puparial cuticle are compared, together with those of mineralized granules from other species of invertebrates.