Experimental studies in insect parasitism XIII. The haemocytic reaction of a caterpillar to eggs of its habitual parasite

Abstract

Caterpillars of Ephestia kuehniella promptly encapsulate alien parasites, living tissues from other species of insects, and filaments of such inert substances as Polythene and Polyfluorocarbon implanted in their haemocoele. They do not encapsulate eggs of their habitual parasite Nemeritis canescens, and the paper records an investigation of that failure. Eggs of Nemeritis do not repel the haemocytes or prevent them from forming capsule tissue; they escape encapsulation because they do not stimulate the blood cells to react. The property that enables them to avoid evoking a reaction is located on their surface: dead eggs that retained an unaltered surface were not encapsulated, living or dead eggs of which the surface was experimentally altered were encapsulated. Since eggs of Nemeritis possess this protective surface immediately after oviposition, its origin was sought in the adult parasite. The surface of eggs removed from the distal part of the ovarioles is formed by the chorion; eggs removed from the genital tract below the calyx were found to have a visible layer outside the chorion. When eggs bearing this visible layer were removed from several parts of the genital tract and injected into caterpillars of Ephestia, they were not encapsulated. When eggs not bearing the visible layer outside the chorion were removed from ovarioles, and were injected into caterpillars, they always evoked a haemocytic reaction and were usually completely encapsulated. The property of its surface that enables the egg of Nemeritis to avoid evoking a haemocytic reaction in Ephestia is therefore acquired in the region of the calyx, where also the visible layer appears on the outer surface of the chorion. A few by-products of the investigation are mentioned in the discussion.