A new diagnostic resource for Ceratitis capitata strain identification based on QTL mapping

Authors: Sim, Sheina; RUIZ, RAUL - Animal And Plant Health Inspection Service (APHIS); BARR, NORMAN - Animal And Plant Health Inspection Service (APHIS); Geib, Scott

Submitted to: G3, Genes/Genomes/Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2017
Publication Date: 11/6/2017
Citation: Sim, S.B., Ruiz, R.A., Barr, N.B., Geib, S.M. 2017. A new diagnostic resource for Ceratitis capitata strain identification based on QTL mapping. G3, Genes/Genomes/Genetics. 11:3637-3647. https://doi.org/10.1534/g3.117.300169.

Interpretive Summary: Sterile male Mediterranean fruit fly are reared and released by the billions in many parts of the world for the purpose of pest control through the sterile insect technique(SIT). Simultaneous to the release of flies for SIT are extensive trapping programs to promote the early detection of new incursions. The current method for distinguishing intentionally released SIT flies from wild incursions is the use of a fluorescent powdered dye. Unfortunately, this method can be unreliable due to imprecise application of the dye, removal of the dye through fly grooming, and the recovery of only partial and undyed flies. For this reason, it is necessary to develop a robust molecular assay for differentiating wild from SIT released flies. A molecular assay (the Medfly tool) that is capable of designating that a fly is of wild origin currently exists, but it is incapable of designating a fly as SIT. Through the integration of classical genetic and modern genomic techniques, we have developed a new assay that can supplement the existing Medfly tool and enables the designation of a fly as SIT. Additionally, the development of this assay resulted in the identification of loci tightly linked to a genetic sexing trait maintained in SIT released lines (white pupae) that will enable future identification of the gene and mutation conferring the white pupa trait. This information will be critical in future studies as it can be used to identify genes in other species which will lead to the development of genetic sexing strains for emerging tephritid pests.

Technical Abstract: The Mediterranean fruit fly Ceratitis capitata(Wiedemann), or medfly, is a destructive agricultural pest and the subject of exclusion efforts in many countries. Suppression and eradication of invasive populations to prevent establishment is facilitated by the release of sterile males using the sterile insect technique(SIT). In active SIT release areas, it is critical to accurately discriminate between released sterile males and wild-caught individuals to be able to detect extremely rare invasive individuals in areas inundated with millions of sterile male flies. Current methods for discrimination exist, but are not always definitive, and a more reliable method is necessary. To address this, we took a novel approach and developed a genotyping assay that is linked to traits that facilitate genetic sexing and are maintained in the SIT colonies, white pupae(wp) and temperature sensitive lethal(tsl). The development of this assay was achieved through linkage mapping and QTL mapping of wp in a mapping population derived from SIT colony flies and wild-type colony flies. This new method to discriminate released SIT flies from wild individuals was demonstrated across SIT colonies and wild individuals from across the geographic range of this species. In addition, linkage mapping and QTL mapping of wp in C.capitata has larger impacts as it can serve as a foundational tool to identify the genetic basis of genetic sexing traits which can be used to develop SIT programs in related species.