The role of Apanteles glomeratus venom in the defensive response of its host, Pieris rapae crucivora

Abstract

It is my purpose in this paper to re-examine the experimental data on Apanteles glomeratus venom as means of resistance to the haemocytic encapsulation of the host, Pieris rapae crucivora and to postulate a hypothesis concerning the means by which A. glomeratus eggs evade the host's encapsulation reaction. Most of the eggs deposited in 2nd-instar host larvae by the parasitoid from which the venom apparatus was removed were encapsulated in 3rd-instar larvae within 2 days after oviposition. Although mature eggs injected with calyx fluid obtained from lateral oviducts of the parasitoid were encapsulated, the eggs injected with the calyx fluid plus venom of A. glomeratus were able to avoid the encapsulation. These and other additional results present evidence that the venom apparatus material of A. glomeratus is an important factor in suppressing the encapsulation of 1- or 2-day old eggs of the parasitoid in the host. Since the eggs of A. glomeratus are coated with a fibrous outer layer, probably mucopolysaccharides, the venom of the parasitoid may readily combine with the layer. The venom and egg-surface material may synergistically act as an encapsulation-inhibiting factor at the egg surface and may in some way suppress the ability of haemocytes to react against Apanteles eggs. The venom had no influence on the elongation or spreading as well as of retraction of the filopodia or lamellipodia of host's haemocytes (granular cells or plasmatocytes) and on the haemolymph melanization of the host.