Unraveling the mysteries of egg development in Stomoxys calcitrans

In hematophagous dipterans, vitellogenesis is tightly linked to blood feeding, as the blood meal serves as the catalyst for the succession of egg development. While numerous reports have characterized this process in mosquitoes, there are limited studies in vectors of veterinary importance, such as Stomoxys calcitrans stable flies. In contrast to mosquitoes, stable flies require multiple blood meals in order to complete egg development, indicating unique regulatory mechanisms for this process. To further understand the dynamics of vitellogenesis in stable flies, we used immunohistochemistry and molecular biology to morphologically characterize follicular development and determine yolk protein gene expression in S. calcitrans females throughout this process. We were able to successfully identify five major stages of follicular development. Based on observed morphological and molecular changes in the primary follicle, we were able to identify the trophic stage of egg development in stable flies to occur throughout the third and fourth blood meal. Indeed, the primary follicle underwent major changes in size and lipid distribution and all monitored yolk protein genes were upregulated at these time points, emphasizing the importance of this blood meal for egg development completion. To confirm the location of yolk protein gene expression, midgut, ovary, fat body abdominal walls and remaining tissues were dissected after the third blood meal, revealing the ovary as the major tissue responsible for expression. Together these data illustrate the complexity of egg development and serve as a foundation for future work to understand the underlying molecular mechanisms of vitellogenesis in these understudied vectors.