Differentiation in bacterial symbiont growth between insecticide treated and untreated tropical bed bug.

Symbiotic bacteria are closely associated with insect adaptability and survival, particularly in species with nutritionally limited diets. In the tropical bed bug Cimex hemipterus, these microbial partners synthesize essential nutrients such as B vitamins and amino acids that are absent from blood meals. The global resurgence of bed bug infestations, fueled by increased international travel and insecticide resistance, has challenged conventional control methods. Microbial symbionts are increasingly suspected to contribute to resistance mechanisms, but their role remains poorly defined. This study investigated the impact of four insecticides-chlorfluazuron, tebufenozide, pyriproxyfen, and a combination of β-cyfluthrin and imidacloprid-on the culturable bacterial symbionts of C. hemipterus using surface contact bioassays at concentrations of 100, 500, 1000, and 10,000 parts per million (ppm). Results showed a statistically significant reduction in colony-forming units (CFUs) in treated groups (p = 0.01), with the greatest suppression observed at 10,000 ppm. A significant negative correlation was observed between CFU abundance and mortality in pyriproxyfen-treated groups (p = 0.005), suggesting a potential link between bacterial suppression and sublethal physiological effects. DNA sequencing identified Bacillus species-particularly B. cereus and B. thuringiensis-as predominant symbionts across all treatments, indicating core microbiota stability despite insecticidal stress. These findings highlight that while bacterial abundance can be reduced by insecticides, core symbionts persist, which may contribute to host resilience. This study provides foundational evidence for integrating symbiont-targeted strategies with existing chemical controls to improve bed bug management.