Death eaters respond to the dark mark of decomposition day and night: observations of initial insect activity on piglet carcasses.

Some insect taxa can be of critical importance for criminal investigations because they can be used to assist with a time since death determination. Blow flies (Diptera: Calliphoridae) often are the initial colonizers of a carcass, usually arriving within minutes to hours after carcass exposure during the day. Other insects, such as coleopterans and hymenopterans, can arrive to a carcass during early colonization and affect blow fly development. However, the extent of these interactions remains unclear. This study analyzed the initial 6 h after a piglet carcass was placed out in two locations (rural and urban) in diurnal and nocturnal conditions with continuous video recording and hourly observations. Four piglets were placed out every 2 weeks over the summer of 2014. Initial blow fly arrivals to the carcasses were only recorded during diurnal conditions, and a checklist of orders associated with each environment (time and location) was created. During diurnal conditions, initial blow fly arrival times in rural environments were significantly faster than those in urban, arriving as quickly as 23 s after exposure. These observations also included a novel interaction with Vespidae, which to the best of our knowledge has not been seen in the literature before. This experiment provides baseline data on early insect colonization in two environments in New Jersey, and lends insight into insect interactions that could affect initial colonization.

High Temperature Limits of Survival and Oviposition of Phormia regina (Meigen) and Lucilia sericata (Meigen).

The temperature dependent development rates of blow flies allow blow flies to be used as biological clocks in forensic death investigations. However, the upper thermal limits of adult survival and oviposition, both required for producing larvae, remains largely unknown. Therefore, in this study we examined the impact of a range of temperatures between 37 °C and 44 °C on the likelihood of survival and egg-laying behavior of two species of medicolegal forensic importance, Lucilia sericata (Meigen) and Phormia regina (Meigen) (Diptera: Calliphoridae). To quantify the upper temperature limits of survival, adult fly colonies were exposed to 37 °C, 41 °C, 42 °C, 43 °C, and 44 °C for 24 h. Similarly for oviposition trials, adults of both species were exposed to 40 °C, 42 °C, and 43 °C with P. regina oviposition also observed at 41 °C. Trials lasted for 24 h with oviposition substrate replenished at the 12 h mark. A yes/no determination on egg deposition was made, eggs were counted, and a yes/no determination was made on egg hatch. Survival did not differ by species (p = 0.096). Overall, survival decreased with increasing temperatures, with ~100% at 37 °C, ~50% at 41 °C, ~37% at 42 °C, ~15% at 43 °C and 0% at 44 °C. Lucilia sericata laid eggs capable of hatch up to 43 °C, while Phormia regina egg-hatch was observed up to 41 °C. These results indicate a greater thermal tolerance of adult survival than for egg deposition and successful egg hatch, which supports previous experiments indicating blow flies stop laying eggs at sub-lethal temperatures. Furthermore, these data indicate that adult blow flies may find remains at or near time of death but may delay egg deposition until temperatures drop below an acceptable threshold.