From discovery to engineering

Angela Meccariello’s research background is rooted in the molecular genetics of sex determination. During her PhD, she helped uncover the primary male-determining signal in Tephritid fruit flies: the Y-linked gene Maleness-on-the-Y, or MoY. This discovery changed the way the field understood sex determination in major agricultural fruit fly pests. MoY is necessary and sufficient for male development in Ceratitis capitata, and its function is conserved in other Tephritidae, including the olive fruit fly and the oriental fruit fly.

This discovery did more than identify a gene. It revealed that Tephritid sex determination is unusually programmable. By disrupting or overexpressing key sex-determination signals, genetic males can be feminised, and genetic females can be masculinised. This biological plasticity provides a rare opportunity: to use the sex-determination pathway itself as an engineering platform for pest control.

Since then, the lab has built a research programme that moves from gene discovery to functional validation, from CRISPR tool development to population-control design, and from contained laboratory proof-of-principle to collaborative translational pipelines.

A major frontier for the lab is the discovery and functional characterisation of sex determination in Anastrepha ludens, the Mexican fruit fly. This species is a serious agricultural pest, particularly of citrus and mango, and remains a major target for area-wide control programmes.

Unlike Ceratitis capitata, where MoY and downstream sex-determination components have created a strong foundation for engineering, the sex-determination architecture of Anastrepha ludens remains an important open area for discovery. Our goal is to identify the molecular signals that initiate male development, map sex-linked genomic regions, characterise sex-specific splicing, and determine which components of the pathway can be used for genetic control.

This work is both fundamental and translational. Understanding sex determination in A. ludens will reveal how rapidly evolving master sex-determining systems diversify across Tephritid pests. At the same time, it will provide the biological knowledge needed to build new genetic sexing strains and precision-guided sterile insect technologies for Mexfly control.

We are developing precision-guided sterile insect technique approaches for Tephritid pests, including Ceratitis capitata and Anastrepha ludens. These systems aim to generate sterile or sex-converted insects through carefully designed CRISPR-based genetics, creating a new generation of SIT-compatible tools that are more precise than classical irradiation-only approaches.

In Ceratitis capitata, our recent work established a split CRISPR/Cas9 system called Sex Conversion Induced by CRISPR, or SCIC. By targeting the sex-determination gene transformer, this system induces female-to-male sex conversion and provides a foundation for self-limiting genetic pest-control strategies. Modelling suggests that SCIC and pgSIT-like approaches could outperform traditional SIT under some release scenarios, allowing faster population elimination with fewer released sterile males.

The next step is to transfer this logic into additional pest species, especially Anastrepha ludens, in collaboration with international and industrial partners including Akbari lab, Evan Braswell USDA-APHIS, and Agragene. This is where the lab’s strength lies: not simply applying CRISPR but combining species-specific developmental genetics with practical pest-control needs.

Genetic sexing strains, or GSSs, are a cornerstone of efficient SIT. They allow males and females to be separated during mass rearing so that only males are released. However, classical GSS development can be slow, species-specific and genetically unstable.

The Meccariello Lab is developing two complementary strategies to generate next-generation GSSs.

The first is a neoclassical Y-chromosome engineering approach. Here, we aim to engineer male-linked genetic features directly onto the Y chromosome or Y-linked regions, creating strains in which useful markers or conditional traits are inherited specifically through males. This strategy is being pursued in Ceratitis capitata and Bactrocera dorsalis to improve SIT pipelines for both established and emerging pest threats. The European REACT project (Coordinator: Prof. Dr. Marc F. Schetelig) specifically includes the development of genetic sexing strains and bioinformatic pipelines for invasive fruit fly control.

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The second is a cisgenic marker-switching strategy, inspired by sex determination itself. Instead of relying solely on large chromosomal rearrangements, we can use sex-specific splicing to confer a visible phenotype that is male- or female-specific. In our 2026 Communications Biology paper, we generated a cisgenic genetic sexing strain by inserting a sex-specifically spliced transformer intron into the endogenous white pupae gene. This created the IMPERIAL strain, in which female pupae are brown and male pupae are white, allowing sex sorting by eye while preserving a minimal, cisgenic genomic modification.

This work also underpins the patent application PCT/US2025/061221, Method for Sex-Sorting Insects, which protects a broader strategy for identifying phenotypic markers and converting them into sex-specific tools by exploiting the sex-determination pathway.

In Meccariello et al. 2024, we helped establish the Mediterranean fruit fly, Ceratitis capitata, as the first Tephritid agricultural pest in which homing-based gene drives were characterised. This study showed that medfly can support CRISPR-based homing and demonstrated that gene-drive activity can be linked to the sex-determination gene transformer, opening a new experimental route for genetic-control research in agricultural fruit flies.

Our lab is now building on these results to understand whether gene-drive technologies can be adapted and optimised for Tephritidae. Rather than treating gene drive as a ready-made solution, we are developing the medfly toolkit required to study this technology rigorously: from construct design and germline expression to target-gene choice, inheritance analysis and phenotypic evaluation.

This work addresses a key challenge in the field: gene-drive performance is highly species-dependent. A system that works efficiently in one insect does not automatically translate to another. The reproductive biology, genome structure and developmental genetics of Tephritid pests create their own opportunities and limitations. Our aim is to define these rules in medfly.

By improving the gene-drive toolkit in Ceratitis capitata, the Meccariello Lab is creating the foundation to assess how this technology could eventually be used in Tephritid agricultural pests. This research connects fundamental insect genetics with the long-term development of precise, species-adapted and sustainable genetic biocontrol strategies.

We are not simply applying gene drive to medfly; we are building the toolkit needed to understand, optimise and evaluate gene-drive engineering in Tephritid pests.