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Table 1 Differences observed by optical microscopy between three species of Rhodnius in the five nymphal instars

From: Immature instars of three species of Rhodnius Stål, 1859 (Hemiptera, Reduviidae, Triatominae): morphology, morphometry, and taxonomic implications

Instars Species Characters
   Head Thorax Abdomen
  R. marabaensis Segments IV and V are the broadest. Segment I same length as the metanotum
First R. prolixus Larger, particularly between segments III and VI. Segment I same length as the metanotum
  R. robustus Widens gradually from segment I to IV. Segment I longer than the metanotum
  R. marabaensis Pronotum form of a trapezium. Mesonotum-metanotum dividing line straight Straight external limits between segments III and VI
Second R. prolixus Longest pronotum. Mesonotum-metanotum dividing line concave Maximum width in segment V
  R. robustus Shortest pronotum. Mesonotum-metanotum dividing line straight Widens gradually from segment I to IV
  R. marabaensis Prominent white stripe from the antennal tubercle to the neck Concavity is not seen Stripe that has straw-colored marks elongated in each segment
Third R. prolixus The stripe is not so evident Concavity near the metanotum Such marks are neither so elongated nor clear
  R. robustus Between the clypeus and the antennal tubercles; between the posterior region of the eye and the neck Concavity is not seen The marks are not elongated, yet clear
  R. marabaensis White stripe is very clear Pronotum-mesonotum line has a slight sinuosity overlapping a tiny part of the mesonotum
Fourth R. prolixus Stripe present, but narrower Same as R. marabaensis
  R. robustus Less clear in the intermediate portion Pronotum-mesonotum line has a concave aspect, the same for the metanotum-abdomen line
  R. marabaensis Maxillary plate reaches the clypeus (straight), the anteclypeus is curved Side limit of the anterior wing pads is diffuse and broad
Fifth R. prolixus Maxillary plate surpasses the clypeus (curve), anteclypeus has a trapezoidal shape Side limit of the anterior wing pads is a clear line
  R. robustus Maxillary plate reaches the clypeus (concave), anteclypeus has a semicircular shape Side limit of the anterior wing pads is a clear line