Molecular and Biochemical Mechanisms of Scutellum Color Variation in Bactrocera dorsalis Adults (Diptera: Tephritidae).

Bactrocera dorsalis (Hendel) is an invasive fruit and vegetable pest, infesting citrus, mango, carambola, etc. We observed that the posterior thoracic scutella of some B. dorsalis adults are yellow, some light yellow, and some white in China. Compared with the B. dorsalis races with a yellow scutellum (YS) and white scutellum (WS), the race with a light-yellow scutellum (LYS) is dominant in citrus and carambola orchards. To reveal genetic correlates among the three races, the genomes of 22 samples (8 with YS, 7 with LYS, and 7 with WS) were sequenced by high-throughput sequencing technology. Single-nucleotide polymorphism (SNP) annotation showed that there were 17,580 non-synonymous mutation sites located in the exonic region. Principal component analysis based on independent SNP data revealed that the SNPs with LYS were more similar to that with YS when compared with WS. Most genes associated with scutellum color variation were involved in three pathways: oxidative phosphorylation, porphyrin and chlorophyll metabolism, and terpenoid backbone biosynthesis. By comparing the sequences among the three races, we screened out 276 differential genes (DGs) in YS vs. WS, 185 DGs in LYS vs. WS, and 104 DGs in YS vs. LYS. Most genes determining color variation in B. dorsalis scutella were located on chromosomes 2-5. Biochemical analysis showed that β-carotene content in YS and LYS was significantly higher than that in WS at any stage of adult days 1, 10, and 20. No significant differences were observed in cytochrome P450 or melanin content in YS, LYS, or WS. Our study provides results on aspects of scutellum color variation in B. dorsalis adults, providing molecular and physiological information for revealing the adaptation and evolution of the B. dorsalis population.