How do I look when I'm infected? Morphometric changes in heads associated with Trypanosoma cruzi infection in flightless Triatominae

Mepraia spinolai is a triatomine endemic to Chile vector of Trypanosoma cruzi (the causative agent of Chagas disease) that presents a marked wing polymorphism. This study investigates morphometric changes in the heads of flightless individuals of this vector. It is known that infection by T. cruzi produces physiological, morphological, and behavioral changes, among others, in triatomine vectors. This study aims to evaluate whether T. cruzi infection modifies head morphometry in micropterous M. spinolai, and to infer the behavioral and ecological implications of such changes. Results revealed that infected individuals had significantly smaller heads in both sexes. Shape analysis distinguished infected from uninfected groups, showing infected individuals with wider heads and smaller eyes in both sexes. Furthermore, in infected females, the heads were shorter. Fluctuating asymmetry of shape (FA), was higher in infected insects, suggesting T. cruzi imposes physiological costs. Reduced eye size and head width could impair vision-based behaviors like host-seeking or predator avoidance, while increased FA indicates infection-related stress. These findings highlight the phenotypic plasticity of triatomines under parasitic infection and suggest potential biomarkers for identifying infected vectors. This is the first experimental study to characterize morphological changes in the heads of triatomines infected with T. cruzi, and also the first to analyze them in micropteran insects. Identifying morphometric traits in heads associated with infection could optimize entomological surveillance strategies in endemic areas, particularly for M. spinolai where the use of wing morphology as a diagnostic tool is restricted, and for nymphal instars of other triatomine species.