Larval instar estimation and ultra-structural analysis of Aphaenogaster cristata (Forel, 1902) and Aphaenogaster pachei (Forel, 1906) (Hymenoptera: Formicidae) from the Himalayas

The ontogeny of an organism provides fundamental insights into its life history and evolutionary background. Among insects, especially ants, relatively few observations have been formalized about the morphology of immature stages. Using light and scanning electron microscopy, this study presents the first description of the different larval instars of Aphaenogaster cristata (Forel, 1902) and Aphaenogaster pachei (Forel, 1906), species endemic to the Himalayas that predominate in areas where cold temperature stress and disturbances limit the presence of other ants. The existence of four larval instars was estimated based on the frequency distribution of their measured maximum head widths. We observed discrete alterations in the body constitution and parts among the different instars, suggesting they must follow similar habits until pupation. The two species, however, present noticeable particularities in their mandibles and hair types, suggesting intrinsic life adaptations. Observed traits complementary with previous descriptions with larvae of the genus and related taxa are suggestive of considerable evolutionary distance from Messor, considered the sister clade, which merits further taxonomic investigation in future studies.