The production of amylose in the faeces of psyllid larvae with special reference to the lerps of Cardiaspina densitexta

Abstract

The faeces of the larvae of many species of psyllids which feed on the phloem sap of the host plant solidify on contact with the air, and are built by the larvae into characteristic coverings known as lerps. Analysis of the lerps of Cardiaspina densitexta (and a number of other species) by spot testing with iodine, potentiometric iodine titration, precipitation with butanol, the production of spherocrystals of amylose, hydrolysis with sulphuric acid, and paper electrophoresis of the hydrolysis products of lerps, all point to starch—apparently identical to plant starch—being the major constituent of these structures. The relative proportions of amylose in the starch of the lerps of different species varies quite widely. The lerps of C. densitexta contain nothing other than amylose and amylopectin; nitrogen, phosphates, and even ash being absent. In some species other substances may be present in the lerp, and in still others liquid honey-dew containing various soluble sugars is produced as well. The possible selective advantage and evolutionary development of the construction of lerps is discussed.