Biotechnology-enhanced genetic controls of the global pest Drosophila suzukii

Insect Pest Control from Chemical to Biotechnological Approach: Constrains and Challenges

The large growth in the global population requires new solutions for the control of harmful insects that compete for our food. Changing regulatory requirements and public perception, together with the continuous evolution of resistance to conventional insecticides, also require, in addition to innovative molecules with different modes of action, new non-chemical control strategies that can help maintain efficient integrated pest management programs. The last 30 years have inaugurated a new era characterised by the discovery of new mechanisms of action and new chemical families. Although European programs also promote a green deal in the crop protection sector, the existing thorough regulations slow down its spread and the adoption of new products. In light of these changes, this review will describe in more detail the dynamics of discovery and registration of new conventional insecticides and the difficulties that the agrochemical industries encounter. Subsequently, the different innovative control strategies alternative to conventional insecticides based on natural substances of different origin, entomopathogenic microorganisms, semiochemical and semiophysical compounds, and classical and augmentative biological control will be described. The advantages of these green strategies will be illustrated and also the constrains to their diffusion and commercialisation. Finally, the main biotechnological discoveries will be described, from transgenic plants to symbiotic control, classical genetic control, and, more recently, control based on insect genomic transformation or on RNAi. These new biotechnologies can revolutionise the sector despite some constrains related to the regulatory restrictions present in different countries.

Functional validation of a white pupae minimal gene construct in Ceratitis capitata (Diptera: Tephritidae)

Genetic sexing strains (GSS) are important tools for the sterile insect technique (SIT), an environmentally friendly and species-specific insect pest control method. GSS feature sex-specific phenotypes, enabling sex sorting in mass-rearing facilities and male-only releases, which significantly improve the cost-effectiveness and efficiency of SIT programs. In classical GSS, sex linkage of marker gene(s), such as white pupae (wp), is achieved through an irradiation-induced translocation between the marker-carrying autosome and the Y chromosome. However, this approach may render GSS males semisterile. The recently proposed neo-classical GSS concept suggests using genome editing to achieve sex linkage by directly inserting the wild-type marker allele onto the Y chromosome, potentially yielding GSS males with higher fertility. In this study, we examined the Ceratitis capitata wp gene as a genetic marker for the neo-classical GSS concept and developed a minimal, intronless version of this gene, termed mini-wp. We demonstrate that a single copy of mini-wp is sufficient to restore the wild-type brown puparium phenotype and is functional when integrated at various positions within the C. capitata genome, including the X chromosome. Due to its smaller size (4689 bp, including 2000 bp of putative promoter region) relative to the full wild-type wp allele (20868 bp), mini-wp may facilitate its precise insertion into the Y chromosome, representing an important step toward realizing neo-classical GSS. Furthermore, the methodology developed for designing and testing mini-wp in medfly may be adapted to other Tephritid species with an identified wp gene.

The transformer gene controls sexual development in Drosophila suzukii

The genetic network of sex determination in the model organism Drosophila melanogaster was investigated in great detail. Such knowledge not only advances our understanding of the evolution and regulation of sexual dimorphism in insects, but also serves as a basis for developing genetic control strategies for pest species. In this study, we isolated the sex determination gene transformer (Dstra) from a global fruit pest, the spotted-wing Drosophila (Drosophila suzukii), and characterized its gene organization. By comparing the deduced protein sequence of Dstra with its orthologs from 22 species, we found that tra genes from Dipteran species are divergent. Our research demonstrated that Dstra undergoes sex-specific splicing, and we validated its developmental expression profile. We engineered a piggyBac-based transformation vector expressing the complete Dstra coding sequence under the control of the Tetracycline-Off system. Through germ-line transformation, we generated 4 independent transgenic lines, producing pseudo-females from chromosomal males in the absence of tetracycline. This observation indicated ectopic expression of Dstra, confirmed by the detection of female Dstra transcripts in transgenic males. The pseudo-females exhibited altered wing patterns, feminized abdomen, abnormal reproductive organs, and disrupted sexual behavior. Ectopic expression of Dstra affected the sex-specific splicing pattern of the downstream gene fruitless, but not doublesex. In conclusion, our study provides comprehensive genetic, morphological, and behavioral evidence that Dstra controls sexual development in D. suzukii. We discuss the potential applications of this research for genetic control strategies targeting Dstra or using its gene elements.