Heat shock proteins (HSPs) play a key role in enhancing insect resilience to abiotic and biotic stresses by preserving cellular integrity and modulating immune responses. This review summarizes the main functions of HSPs in insects, including protein stabilization, interaction with antioxidant systems, and involvement in the innate immune response. The expression of HSPs under environmental conditions reflects their evolutionary adaptation to various stressors, including thermal changes, chemical exposure, and pathogens. Future research should focus on the interaction between HSPs and other stress response systems to improve our understanding of insect adaptation. Furthermore, in the context of global climate change, HSPs emerge as a crucial resilience factor and potential biomarkers for environmental monitoring.

The aim of this work was to develop an experimental protocol for the infection of Galleria mellonella with Gram-positive bacteria. Some physiological characteristics of these insects are comparable to those of vertebrates, therefore allowing the replacement of mammals in the preclinical phases of drug development. G. mellonella Linnaeus 1758 (Lepidoptera: Pyralidae) is accepted as an alternative model for the study of infectious diseases. Since data on infection procedures with different bacterial strains are scarce and sometimes conflicting, also due to different and non-uniform protocols, we developed an experimental protocol that would allow for controlled and repeatable infections, using the Gram-positive bacterium GRAS (Generally Regarded As Safe) Micrococcus luteus. After analyzing the morphology and defining the growth rate of M. luteus, doses of between 10¹ and 10⁶ CFU/larvae were administered to late-stage larvae. The survival rate of the larvae was monitored up to 7 days and the LD₅₀ determined. The bacterial clearance capacity of the larvae after injection with 10³ and 10⁵ CFU/larvae was assessed by hemolymph bacterial load analysis. The results made it possible to define the growth curve of M. luteus correlated with the CFU count; based on the LD₅₀ (10^3.8 CFU/larvae) calculated on the survival of G. mellonella, infections were carried out to evaluate the immune efficiency of the larvae in bacterial clearance. This protocol, standardized on G. mellonella larvae, could provide a functional tool to study the course of bacterial infections.

Heat shock proteins (HSPs), particularly HSP90, play a vital role in insect responses to environmental and biotic stresses by maintaining protein stability and supporting immune defenses. This study explores HSP90 regulation in Galleria mellonella larvae following exposure to the nematode Steinernema carpocapsae and its symbiotic bacterium Xenorhabdus nematophila. Exposure to live nematodes caused slight changes in HSP90 expression, while non-viable nematodes had no effect, suggesting that nematode secretions or symbiotic bacteria do not directly influence HSP90 levels. However, nematodes with altered surface properties significantly increased HSP90 expression. X. nematophila also moderately elevated HSP90 levels but this effect disappeared when weakly bound surface proteins were removed. Interestingly, under thermal stress, live nematodes reduced heat-induced HSP90 expression, whereas surface-treated nematodes enhanced it. These findings suggest that HSP90 modulation is influenced by biological control agents, highlighting a potential link between HSP90 and immune detection of invaders. This interaction may be crucial in adapting biological control strategies in response to climate change. Further research is needed to clarify HSP activation pathways, host immune interactions, and mechanisms of entomopathogen immune evasion, particularly under varying environmental temperatures, to enhance bioinsecticide efficacy.

Insects represent powerful experimental systems for investigating host–microorganism interactions, providing valuable insights into bacterial pathogenicity, immune regulation, symbiosis, and antimicrobial discovery. This review examines the complex relationships between insects and bacteria, focusing on the mechanisms that control infection, immune activation, and microbial adaptation. Particular attention is given to the routes of pathogen entry and to the conserved innate immune pathways that coordinate host defenses, including the Toll, Imd, Duox, and Jak/Stat signaling cascades. The review illustrates how bacterial pathogens exploit toxins, immune evasion strategies, and metabolic adaptation to overcome host defenses, while insects rely on tightly regulated cellular and humoral responses, antimicrobial peptides, melanization, and microbiota-mediated homeostasis. Interactions between pathogenic and commensal bacteria in the insect gut are discussed in the context of immune tolerance, dysbiosis, and ecological adaptation. The dual role of bacterial virulence factors in both pathogenesis and symbiosis is highlighted through examples involving entomopathogenic bacteria such as Photorhabdus spp., Xenorhabdus spp., and Bacillus thuringiensis. In addition, the review summarizes the use of insect models, including Drosophila melanogaster, Galleria mellonella, Bombyx mori, and Apis mellifera, in experimental infections aimed at studying virulence mechanisms, host immune responses, and antimicrobial efficacy. Finally, multi-omic approaches, including transcriptomics, metabolomics, epigenomics, and single-cell technologies are discussed as transformative tools for dissecting host–microbe interactions at molecular and systems levels. Overall, insect–bacteria interactions emerge as dynamic and evolutionarily shaped systems in which immunity, metabolism, microbiota composition, and environmental factors are closely interconnected, offering important perspectives for both basic research and the development of sustainable biocontrol and antimicrobial strategies.