Morphological description and morphometry of the nymphal instars of five species of Rhodnius Stål, 1859 (Hemiptera: Reduviidae: Triatominae)

Rhodnius is a genus with unresolved taxonomic questions. These insects are potential vectors of Trypanosoma spp., including the etiological agent of Chagas disease. Their presence in urban areas has become increasingly frequent, and in some cases, immature specimens are observed in the absence of adults, making identification on the species level difficult. Given their vector capacity and the scarcity of taxonomic studies on immatures, this study aims to describe morphologically, as well as through linear and geometric morphometry, the five nymphal instars of R. montenegrensis, R. nasutus, R. neglectus, R. neivai, and R. stali. The morphological description of the immature instars allows for differentiation among the studied species. In linear morphometry, at least one trait in all instars showed a statistically significant difference between groups (p < 0.05). Geometric morphometry of the head highlighted differences that segregated the species; however, the pronotum was not an informative structure. The techniques used in this study enabled the specific identification of the analyzed species. As with Rhodnius adults, the head is highly informative for nymphs and should continue to be explored in taxonomic studies.