Experiments to Demonstrate the Function of Internal Excretory System of Insects

Abstract

Experimental methods to demonstrate the excretory function of an insect internal organ, the Malpighian tubules, were developed. Larvae of three lepidopteran species, Papilio bianor, Pseudaletia separata and Bombyx mori, were dissected in a tray for laparotomy showing their internal organs. Sodium chloride (NaCl) solution (150mM) containing O. 0005% methyl green dye was poured into the tray resulting in an immer­ sion of the insect body in the solution. In about 20 minutes, Malpighian tubules were observed to absorb the dye and to concentrate it in their internal cavity. A similar experiment was performed using a mixed solution of two different dyes. When the NaCl solution containing 0.0005% methyl green dye and 0.001% orange G dye was used, Malpighian tubules selectively concentrated the former one. A mixture of methyl green and amaranth dye could also have shown the selective excretion of methyl green dye by the tubules. These experiments clearly showed an ability of Malpighian tubules to excrete methyl green dye selectively. Educational application of these experiments to upper secondary school biology is discussed.