A non-destructive image-based approach to quantify blood meal size in Lutzomyia longipalpis (Diptera: Psychodidae)

BACKGROUND Phlebotomine sand flies are hematophagous vectors of major human pathogens, including Leishmania spp., with blood ingestion essential for reproduction and vector competence. Accurate quantification of blood meal volume is crucial for understanding physiological processes and transmission dynamics. OBJECTIVES Here, we introduce a novel, non-destructive image-based method to estimate blood intake in Lutzomyia longipalpis, the principal vector of Leishmania infantum in the Americas. METHODS High-resolution images of unfed and blood-fed females were analysed using Fiji ImageJ (open-source software) when several morphometric parameters were measured and validated against biochemical haemoglobin (Hb) quantification. FINDINGS Blood-fed females exhibited a 56.6% increase in abdominal width and a shift toward a rounded body shape, which was strongly correlated with a visible transilluminated abdominal area (R² = 0.92). Some parameters, such as mean grey value and abdominal length, showed a low to moderate correlation with Hb content (R 0.60). However, the correlation with abdominal area and width was R ≈ 0.90, indicating those are reliable parameters that can be used to estimate blood intake by Lu. longipalpis females. MAIN CONCLUSIONS Unlike spectrophotometric methods, this approach preserves specimen integrity, which, in theory, enables longitudinal studies on physiology and host-parasite interactions. This methodology offers a reliable, scalable, and cost-effective alternative for estimating blood meal.