The microbial community in arthropods often modulate host fecundity, yet processes driving their assembly remain poorly understood. In this study, we investigated bacterial community assembly and host fecundity in Tetranychus truncatus that were exposed to antibiotics and varying temperatures. Antibiotic exposure dominates over temperature in shaping spider mite bacterial composition and network properties. Specifically, complexity of microbiota networks tend to decrease with antibiotic treatment while increasing along a temperature gradient from 20°C to 35°C. Analysis using neutral and null models revealed that bacterial community assembly in mites was chiefly driven by stochastic processes such as drift, with relative contribution > 85%. Relative contributions of each ecological process was rather weakly correlated with antibiotic and temperature conditions. Finally, fecundity tended to be lower in mites with microbiota variation following antibiotic treatment. This study reveals mechanisms underlying bacterial community assembly in spider mites and establishes microbiota as a potential mediator of host fecundity. Our results provide new insights into immediate adaptive processes between mites and microbiome in the context of environmental change.