Objective Species and distribution of pest flies found in the major garlic-producing areas of China were identified, and endosymbiotic microbes in the dominant fly species compared for improved pest control.

Method At 8 typical garlic fields in 7 provinces in China including Jilin, Tianjin, Shandong, Henan, Jiangsu, Hubei, and Yunnan, adult flies were captured by sweep netting for the study. Species of the caught pests were determined by microscopic morphological observation and mitochondrial COI gene sequencing with dominant species identified. Morphological comparison was conducted to screen stable diagnostic traits for distinguishing the two dominant fly pests. The 16S rRNA and ITS high-throughput sequencing were used for microbial analysis; raw sequencing reads were quality-controlled and annotated, followed by calculation of Alpha and Beta diversity indices. LEfSe analysis was adopted to screen differential taxa among groups, to characterize the symbiotic microbial diversity of the two dominant fly species.

Result A total of eight fly pest species belonging to seven genera across six families were identified from major garlic production areas, including Anthomyiidae, Calliphoridae, Muscidae, Sarcophagidae, Drosophilidae, Ephydridae, and Delia, Adia, Lucilia, Sarcophaga, Coenosia, Drosophila, Paralimna. Fly communities exhibited significant geographical differentiation. Two congeneric species, Delia antiqua and Delia platura, were dominant across most surveyed regions. Four morphological characters, including compound eyes, thoracic pollinosity, subcostal vein of wings and setae on midtibia, could be used to separate these two closely related Delia species. The symbiotic bacterial communities differed markedly between the two dominant species, and bacterial community differentiation was driven by host species and sex. Fungal community structure was relatively conserved, with Cladosporium as the shared core fungal genus.

Conclusion D. antiqua and D. platura were identified as the primary pest fly species found in the garlic fields in the regions. Although closely related, they could be reliably distinguished by morphological characteristics. Depending upon the species and sex as well as the field condition where these flies inhibited, their symbiotic microbial communities varied significantly in composition but shared Cladosporium as the common fungal taxon.