Dual application of entomopathogenic nematodes and fungi on immune and antioxidant enzymes of the greater wax moth, Galleria mellonella L.

Abstract

Abstract Pathogenicity and immunity effects of both the entomopathogenic nematode, (Heterorhabditis zealandica) and the entomopathogenic fungus (Beauveria bassiana) on the last larval instar of the greater wax moth, Galleria mellonella L. (Lepidoptera: Pyralidae), were investigated. Both pathogens were either applied separately or in a combination. The fungus was inoculated first, followed by the nematode on time manner 0, 2, 4, and 6 days. LC50 values for both pathogens were calculated and then used for determination of the changes in immune response-mediated phenoloxidase (PO) and detoxifying enzymes glutathione S-transferase (GST) and non-specific esterase (EST) activities. The results indicated that a positive correlation was found between pathogen concentration and host mortality percentage. LC50 values were 6.49 IJs/larva for H. zealandica and 3.1 × 102 conidia/ml for B. bassiana. Synergistic interactions were found in all combined applications. The degree of synergism increased (reaching 100% mortality), when the nematode was applied 2 days post-fungal infection. PO activity increased significantly (p < 0.05) in a time-dependent manner post-B. bassiana infection. In contrary, the combination of H. zealandica + B. bassiana or H. zealandica alone produced a significant suppressive effect on PO activity over time. GST activity increased significantly (p < 0.05) in 36 h, then decreased at 48 h post-combined application, while the fungal infection enhanced significantly GST activity in time-dependent manner than the control and other treatments. EST activity increased significantly (p < 0.05) in both combined application and the single nematode infection than the single fungal infection, which increased during the initial period only. The increased mortality rates and suppression of phenoloxidase and glutathione S-transferase enzymes, following the combined application suggests a strong synergistic effect between both pathogens. It could be concluded that the tested combined pathogens are compatible element for integrated pest management.

Keywords

• Galleria mellonella
• Entomopathogenic nematodes
• Entomopathogenic fungi
• Interaction effects