Parasite-host relationships in the biological control of insects: strategies of immunoevasion/immunosuppression and interference of temperature on the lethality of entomoparasites.

In this PhD project were considered two aspects of the relationship between bio-insecticide and insect hosts: the first has been the study the mechanisms carried out by EPNs complexes (Steinernema carpocapsae - Xenorhabdus nematophila) to overcome or neutralize the immune system of the insect host. The success of the EPNs results mainly from immunological disabling induced by nematode and its symbionts by immunoevasion/immunosuppression process when released inside the host hemocoel. The functions of structures and molecular components of the surface of both nematodes and bacteria play a key role and we assessed the role of protein pools isolated against Galleria mellonella (Lepidoptera). The eluted compounds from live nematode possessed a slight cytotoxicity on the haemocytes, whereas those from live bacteria markedly affected the host cells’ viability. Bacterial proteins can inhibit the phagocytic activity, despite they strongly trigger the host prophenoloxidase-phenoloxidase system. The second part of the project is aimed to acquire useful information on host-parasite relations in the context of climate change and, we reconsidered the physical conditions (such as temperature) in which bioinsecticides are highly effective. We evaluated the effectiveness of different commercial bio-insecticides (Steinernema feltiae, Steinernema carpocapsae, Heterorhabditis bacteriophora and Bacillus thuringiensis) assessing the mortality rate induced in two insect models, Galleria mellonella (Lepidoptera) and Sarcophaga africa (Diptera) after conditioning at various temperatures (10, 20 and 30 °C); moreover, we investigated the effects of temperature on the basal humoral immunity (phenoloxidase and lysozyme activity).