Humidity affects oviposition behavior of Phormia regina (Diptera: Calliphoridae)

The application of blow flies in forensic entomology for postmortem interval estimation is limited in cases without entomological evidence, when assumptions about climate and time play a large role. The time it takes for an insect to locate an oviposition site, and oviposit, is typically referred to as a pre-appearance interval (PAI). While certain environmental variables are fairly well understood in terms of preventing oviposition (i.e. rain, wind, less so darkness), the effect of humidity on regulating oviposition behaviors has not been objectively studied. Here, we assessed the relationship between humidity and oviposition in the black blow fly, Phormia regina (Diptera: Calliphoridae), with the aim of understanding its role in assumptions made about the PAI. Under four different temperature and humidity conditions (a total of 16 different conditions ranging from 30 % rh to 85 % rh across 20 °C to 35 °C) over five days demonstrated a significant delay in oviposition at lower relative humidities, especially at the higher temperatures. We demonstrate how the interplay between temperature and relative humidity collectively influences the initiation of oviposition. At 30 % rh and 25 °C the delay in oviposition was 20.3 hours; 30 % rh and 30 °C the delay was 10 hours, and at 30 % rh and 35 °C the delay was 5.3 hours ( p ≤ 0.0001). These results directly address an important climatic factor in using temperatures alone to make assumptions about the barriers to blow fly oviposition, especially in geographic areas with sustained dry periods.