Bioluminescence, morphology, biological aspects and molecular association of larvae and adults of Stenophrixothrix (Coleoptera: Phengodidae)

Railroad-worms (Phengodidae) occur in the Americas, Turkey and Middle East, but are especially diverse in the Neotropical region. In Brazil there are 63 described species, but except for Phrixothrix hirtus, larvae of described species could not be associated with their adults, due to the difficulty of rearing these beetles. In the campus of Sorocaba of the Universidade Federal de São Carlos, São Paulo, Brazil, we found a railroad-worm species inhabiting secondary growth forests, which was also found in other locations in the transition of Atlantic rainforest to Cerrado in São Paulo state. Here we describe the morphology of the larva of Stenophrixothrix sp., along with bioluminescence and ecological aspects of this species. The adult males were attracted to light traps and produce a yellow bioluminescence. The larva displays dark brown dorsal coloration, with yellow emitting lateral lanterns along the dorsal part of the body and a single small cephalic lantern which emits yellow to orange light. Analysis of the mitochondrial 16S marker shows that the larva and adults are indeed from the same species. Whereas the in vitro bioluminescence spectra for lateral and cephalic lanterns extracts overlap, suggesting the presence of a single luciferase isozyme, the in vivo bioluminescence color of the cephalic lantern changes from yellow to orange depending on the angle, probably due to the filtering effect caused by the highly sclerotized cuticle.