Differential effects of photophase on the reproductive behaviour of two species of medico‐legal relevance, <i>Peckia</i> ( <i>Peckia</i> ) <i>chrysostoma</i> (Wiedemann, 1830) and <i>Peckia</i> ( <i>Sarcodexia</i> ) <i>lambens</i> (Wiedemann, 1830) (

The nocturnal behaviour and reproduction patterns of Sarcophagidae species during the scotophase are largely unexplored for species in the Neotropical region. The aim of this study was to assess the light regimes under which females of Peckia (Peckia) chrysostoma (Wiedemann, 1830) and Peckia (Sarcodexia) lambens (Wiedemann, 1830) would larviposit and understand how these variables influence intrauterine development in these flies. The experiments were conducted in an experimental room (lux = 100) in two independent experiments: I. Larviposition test: Females mated with males of over 8 days old. II. Intrauterine development test: females over 8 days old and mated were individually isolated. Both experiments were performed under photophases (L:D) of 0:24, 6:18; 12:12; 18:6 and 24:0 for a period of 96 h. Larviposition occurred in total darkness for P. (P.) chrysostoma and P. (S.) lambens in all treatments, without significant differences among photophase treatments (p > 0.05). Photophase influenced the timing of larviposition, occurring as early as 24 h in 12:12 L:D conditions, while no larviposition was observed in the first 24 h in the 0:24 treatment for either species. The light duration significantly affected the percentage of gravid females of both species (p < 0.05), with higher percentages of gravid females in treatments of longer light duration. Females at the initial and intermediate stages of egg development were more strongly associated with treatments of continuous darkness (0:24) or short photophase (6:18), whereas females with an advanced stage of egg development were more prevalent in the 12:12 treatment. The implications of these findings for forensic entomology are profound, challenging conventional knowledge by revealing that necrophagous insects are not limited to diurnal activity patterns.