Description and phylogenetic interpretation of chromatophore migration from larval air sacs to adult structures in some Chaoboridae (Diptera)

During development, many chromatophores on the air sacs of larvae of Chaoborus Lichtenstein disperse to the tracheal trunks and throughout the body of the Pupae. In male pupae, chromatophores on the posterior air sacs move to the developing testes and vasa deferentia and some become the adventitious spotting previously reported for adults of Chaoborus. In larvae of Mochlonyx Loew, chromatophores have a similar development pattern, but in female pupae some also surround the spermathecae. Larvae of Eucorethra Underwood have chromatophores scattered throughout much of the body but it is uncertain whether these are homologous to those of Chaoborus and Mochlonyx. Outgroup comparisons show that the migration of chromatophores from the larval air sacs to the adult male testes and vasa deferentia is a synapomorphy of Chaoborinae. The presence of pigmented fat body on the larval testes in many Culicidae, Eucorethra, and Mochlonyx is plesiomorphic, and the transparent larval testes in Chaoborus are a synapomorphy of the genus. The dark adult testes in Mochlonyx are derived from pigmented larval fat body and chromatophores from the larval air sacs, and this is proposed as an intermediate evolutionary state. It is likely that the chromatophores surrounding the testes of pupae of Chaoborinae provide protection against ultraviolet radiation, but further study is needed.