Darkness as factor influencing the oviposition delay in Calliphora vicina (Diptera: Calliphoridae)

Many environmental and intrinsic factors (e.g. limited access to the body) can disrupt insect activity, causing a delay in the colonization of a corpse. These elements could hinder an accurate estimation of the minimum Post-mortem Interval (minPMI), raising questions about the limits of forensic entomology. Blow fly are considered mainly diurnal and relatively inactive at night, at extreme temperatures and in dark conditions. Data on their ability to lay eggs in darkness and in laboratory conditions are scarce. Oviposition by Calliphoridae during the day but in darkness has been documented in chimneys, cellars and cars. To investigate delays in oviposition in the dark we carried out laboratory experiments using plastic boxes containing Calliphora vicina Robineau-Desvoidy specimens placed in a climatic chambers at different temperatures. We found that C. vicina laid eggs in complete darkness inside the plastic boxes, but later than the specimens inside the boxes at light condition. We believe that oviposition can occur in dark indoor environments in conditions of optimal air temperature, gravid flies and an accessible corpse. However, when corpses are discovered in dark environments, entomologists should consider a significant delay in oviposition by blow fly in order to reduce errors in PMI estimation.