Antibiotics are designed to treat bacterial infections in humans and animals; however, the overuse of various antibiotics and consequent contamination in the environment can have adverse effects on aquatic, soil, and saprophytic organisms. The house fly, an important decomposer in ecosystems, has been used for bioconversion of human and animal waste. Vermireactors have been used to remove antibiotics from waste for pollution control, but the effects of antibiotics on fly larvae are unclear. In the present work, we aimed to reveal the mechanism underlying the effects of antibiotics on larval growth in house flies at the transcriptome and microbiome levels and the relationships between genes and the microbiota. Observation of house flies after antibiotic exposure showed that gentamicin sulfate and levofloxacin hydrochloride inhibited larval development to a greater extent than amoxicillin. Transcriptome analysis revealed that biological pathways related to protein synthesis and the metabolism of fatty acids, pentose, and glucuronate were significantly enriched in flies exposed to gentamicin sulfate and levofloxacin hydrochloride. Crucial genes in these pathways were identified as candidates for future study. Microbiome analysis revealed three key bacteria that were closely correlated with gentamicin sulfate and levofloxacin hydrochloride exposure. The correlation network between the differentially expressed genes and bacteria identified an important microbic effector, Pseudomonas and its associated genes. This work will improve the knowledge about the mechanism underlying the effects of antibiotics on the larval development of house flies in the environment and provide guidance for improving the application of house fly bioconversion.

Introduction: Bacillus spp. are widely used as biological agents for managing diseases in crops, livestock, poultry, and aquatic animals. Bacillus velezensis, a novel species within the Bacillus genus, is extensively used in the biological control of animal and plant diseases. However, the association between B. velezensis and insect hosts remains a complex and poorly understood process.Methods: In this study, we utilized a housefly larvae model to investigate the relationship between B. velezensis and houseflies by examining the changes in intestinal microbiota, transcriptomics, and humoral immunity following symbiotic B. velezensis treatment.Results: The results revealed striking dynamic changes in the bacterial community composition of larvae in the treatment group at the genus level. Notably, Providencia and Morganella content increased, while Enterobacter content decreased, leading to inhibited larval growth. Moreover, the bacterial association with the larva significantly impacted the larval transcriptome, modulating the expression of genes involved in various biological pathways, including host growth and development, macronutrient metabolism, and energy production, which are essential for insect development and survival. Oral feeding of B. velezensis also caused significant morphological changes in the larval gut, resulting in notable larval mortality, cell degeneration, shrinkage, and the formation of various vacuoles. Additionally, we observed a significant decrease in immune response in housefly larvae, with a reduction in phenoloxidase activity and melanization ability in treated larvae compared to controls.Discussion: Therefore, B. velezensis can damage the vital functions of housefly larvae and may be utilized as a microecological regulator for the green prevention and control of housefly populations.

Chemical pesticides are widely used in prevention and control of pests. However, low insecticidal efficacy, high environmental risks and pesticidal resistance severely constrain further applications. In this study, a near-infrared (NIR) laser-activated pesticide-free Fe₃O₄@PDA nanoplatform with a low production cost was constructed for precise photothermal killing of housefly larvae. The polydopamine (PDA) surface-functionalized Fe₃O₄ nanoparticles (Fe₃O₄@PDA NPs) were synthesized by simply mixing dopamine with Fe₃O₄ NPs under aerobic alkaline conditions. These Fe₃O₄@PDA NPs exhibited superb photothermal performance with near-infrared (NIR) laser irradiation. Larval uptake results revealed greater in vivo uptake of Fe₃O₄@PDA NPs than bare Fe₃O₄ NPs when housefly larvae were fed a NP-treated diet. These NPs exhibited favorable biocompatibility and showed no obvious influence on larval development and intestinal microbial population. However, when irradiated with a NIR laser, the NPs efficiently induced death of housefly larvae with high temperature (T_max > 50 ℃) damage to the intestinal wall and subsequent leakage of intestinal bacteria into the hemocoel. Furthermore, uneaten NPs can be collected by magnetic absorption and show excellent thermal stability, which allowed recycling of these environmentally friendly nanoparticles. The Fe₃O₄-based nanoparticles described in the present study integrate the independence of pesticides, pronounced photothermal control of pests, and environmental friendliness, making this nanoplatform promising for controlling vector pests and diseases.