Endosymbiotic bacteria are key factors that regulate the biological traits of Liposcelis bostrychophila. This study employed metagenomic methods to analyze the dominant species of symbiotic microorganisms associated with L. bostrychophila. By controlling the environmental temperature, we were able to manipulate the abundance of endosymbionts and establish populations with high, medium, and low levels of these bacteria. This allowed us to examine the fitness parameters of L. bostrychophila under different levels of endosymbiont abundance. The experimental results revealed that L. bostrychophila hosts 51 genera of symbiotic microorganisms, with Rickettsia being the dominant genus, accounting for 84.11% to 98.16% of the total share. Environmental temperature significantly affected the abundance of Rickettsia, with notable differences observed during the adult stage of L. bostrychophila. A temperature gradient of 28 °C, 35 °C, and 37 °C was established, allowing for the classification of populations based on Rickettsia abundance into three categories: high-abundance populations (LBhp), medium-abundance populations (LBmp), and low-abundance populations (LBlp). The abundance of Rickettsia had a significant impact on the fitness of L. bostrychophila. Specifically, a high abundance of Rickettsia contributed positively to population fitness by increasing egg production, prolonging egg hatching time, enhancing lifespan, and improving both survival and reproductive rates. Therefore, the endosymbiont Rickettsia plays a crucial role in the growth and development of L. bostrychophila. In the future, our research will help further uncover the interactions between Rickettsia and its host, providing new perspectives for pest control and offering a better understanding of insect biology and ecology.

Aphis spiraecola is a major pest of fruit trees worldwide, causing significant yield reductions and economic losses in apple production. Chemical control remains the primary and most effective method for managing A. spiraecola in the field. Imidacloprid, the first neonicotinoid insecticide, effectively targets piercing–sucking pests. However, the time-dependent response of A. spiraecola to imidacloprid exposure has not been well characterized. In this study, we assessed the susceptibility of an A. spiraecola population from Zhengzhou to imidacloprid. Enzymatic assays revealed that the activities of cytochrome P450s, glutathione S-transferases (GSTs), and carboxylesterases (CarEs) were significantly increased following imidacloprid treatment. A synergism assay further demonstrated that the P450 inhibitor PBO and the CarE inhibitor TPP significantly enhanced the imidacloprid toxicity against A. spiraecola. Transcriptome analysis revealed that LC₅₀ imidacloprid treatment induced time-dependent changes in gene expression at 12, 24, and 36 h. A total of 46 P450 genes, 42 esterase genes, and six GST genes were identified in the transcriptome of A. spiraecola. Five detoxification enzyme genes, CYP380C6, CYP6CY19, GSTS3, GSTL, and CarE6, were significantly overexpressed, as confirmed by both transcriptomic and qPCR analysis. Moreover, RNAi-mediated knockdown of CYP6CY19 and CarE6 substantially increased aphid sensitivity to imidacloprid compared with the dsGFP control group. These results demonstrate that CYP6CY19 and CarE6 play an important roles in determining A. spiraecola susceptibility to imidacloprid. Our findings provide a theoretical basis for the rational and scientific use of imidacloprid in aphid management.