Landscape genetics of Cochliomyia hominivorax (Diptera: Calliphoridae): predicting dispersal pathways and expansion potential after reintroduction.

The New World screwworm fly, Cochliomyia hominivorax (Coquerel, 1858) (Diptera: Calliphoridae), is an obligate parasitic blowfly that causes traumatic myiasis and represents a major threat to livestock production in the Neotropics. Although eradication programs based on the Sterile Insect Technique (SIT) successfully eliminated the species from North and Central America, the risk of reinvasion remains a persistent concern. Understanding how landscape structure influences dispersal and connectivity is therefore essential for improving surveillance and control strategies. We evaluated the influence of landscape configuration on gene flow using microsatellite data from 24 populations across South America. Resistance surfaces were generated from land-use maps by assigning resistance values (0 to 100) to landscape classes, producing 10,000 alternative resistance scenarios. Resistance distances were correlated with genetic differentiation (FST), and model selection was performed using Akaike's Information Criterion (AIC). Among all scenarios, only 13 showed significant associations (r = 0.271 to 0.513). The best-supported model explained 26.3% of the variation in genetic differentiation and identified lower resistance in pasture-dominated and agricultural mosaic landscapes, whereas preserved vegetation and water bodies imposed higher resistance. Sensitivity analyses demonstrated that model performance improved with increasing sample size and stabilized at approximately 10 to 14 populations, indicating that robust inference depends on adequate sampling. These results highlight the role of landscape structure in shaping connectivity and provide a spatial framework for identifying dispersal corridors and regions vulnerable to reinvasion.