The ultrastructure of the larval malpighian tubules of a saline-water mosquito

Abstract

The larval Malpighian tubules of the saline-water mosquito Aedes taeniorhynchus were examined using light and electron microscopy. The tubules contain two cell types; primary cells and stellate cells. Primary cells are characterized by their size (70 microns x 70 microns x 10 microns) and an abundance of intracellular membrane-bound crystals. Two types of microvilli are found on the luminal surface of the primary cells: (1) small microvilli containing core microfilaments and extensions of endoplasmic reticulum, and (2) larger microvilli (approximately equal to 3 microns in length) which in addition to the above components contain a mitochondrion along their entire length. Both microvillar types have abundant knobs lining the cytoplasmic surface of the microvillar membrane. These knobs, which are often found in insect ion transporting tissues, have been termed 'portasomes' by Harvey (1980). The possible role of these structures in ion transport and mitochondrial positioning is discussed. The stellate cells are much smaller than the primary cells, and lack intracellular crystals. Their microvilli are smaller as well (approximately equal to 0 x 6 microns in length) and contain no endoplasmic reticulum, mitochondria or knobs. The cells types found in the saline-water mosquito larva, Aedes taeniorhynchus, are identical to those found in Aedes aegypti, indicating that the unique capacity of saline-water mosquito larvae to transport Mg2+ and SO42 is not associated with the presence of an additional cell type.