Role of mitochondrial complex I genes in host plant expansion of Bactrocera tau (Tephritidae: Diptera) by CRISPR/Cas9 system.

Host expansion facilitates tephritid flies to expand their ranges. Unraveling the mechanisms of host expansion will help to efficiently control these pests. Our previous works showed mitochondrial complex I genes Ndufs1, Ndufs3, and Ndufa7 being upregulated during host expansion of Bactrocera tau (Walker), one of the highly hazardous species of tephritids. However, their roles in the host expansion of B. tau remain unknown. Here, using clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated nuclease 9 (Cas9) editing system for the first time, a stable homozygous Ndufa7 strain (Btndufa7^-/-), heterozygous Ndufs1 (Btndufs1^+/-), and Ndufs3 strains (Btndufs3^+/-) were obtained from F3 generation of B. tau, after gene knockout. Reduced sizes of larvae and pupae of the Ndufa7 knockout strain were first observed. Notably, the mean values of fitness estimation (pupal numbers, single-pupal weight and emergence rate) and Ndufa7 gene expression in the Ndufa7 knockout strain were slightly reduced on 2 native hosts (summer squash and cucumber), while it sharply decreased on the novel host banana and the potential host pitaya, compared with those of the wild-type strain. Furthermore, the Ndufa7 knockout strain did not survive on the novel host guava. These results suggested that Ndufa7 disturbs the survival on native hosts, expansion to novel hosts, and further expansion to potential hosts of B. tau. Homozygous lethality occurred after the knockout of Ndufs1 or Ndufs3, suggesting that these 2 genes play a role in the early development of B. tau. This study revealed that Ndufa7 is a target gene for the management of tephritids and opens a new avenue for pest control research.