Immune defenses of Agriotes lineatus larvae against entomopathogenic nematodes

Abstract

The present work describes the immune response of wireworm larvae, Agriotes lineatus (L.) (Coleoptera: Elateridae) when challenged with two species of entomopathogenic nematodes, Steinernema feltiae (Filipjev) (Strongyloidea: Steinernematidae) and Heterorhabditis bacteriophora (Poinar) (Rhabiditoidea: Heterorhabditidae). Two main immunological processes including cellular and humoral reactions have been addressed. Total haemocyte counts after infection with H. bacteriophora increased quickly in initial times, but decreased over time post-injection (at 12 and 16 h). Instead, haemocyte numbers after infection with S. feltiae was unchanged in the early stage, but significantly decreased until 16 h post-injection. Plasmatocytes and granulocytes showed more significant changes compared to other haemocytes. The encapsulation response to parasites was significantly different against two nematode species. Particularly, S. feltiae was almost unrecognized by host haemocytes (5.85 % of encapsulated parasites). Assays with H. bacteriophora showed 23.5 % of encapsulated nematodes. From 8 to 12 h after H. bacteriophora infection, an increase in phenoloxidase activity was detected, while in the larvae injected with S. feltiae the enzymatic activity decreased gradually reaching the lowest level 16 h post-injection. This is the first report on the modulation of immune response of wireworm larvae after infection with entomopathogenic nematodes.