Anoxia Tolerance in Four Forensically Important Calliphorid Species

Forensically important blow flies, Diptera: Calliphoridae, are among the first organisms to colonize carrion. After eggs hatch, the larvae of most blow fly species feed in an aggregation or “mass”. While in this mass larvae may experience periods of hypoxia/anoxia, but the tolerance of blow fly larvae to anoxic conditions is poorly studied. We tested the anoxia tolerance of four species of calliphorids (Calliphora vicina, Cochliomyia macellaria, Lucilia sericata, and Phormia regina), by examining actively feeding third-stage larvae across five temperatures. Experiments were conducted by exposing larvae to pure nitrogen environments and determining mortality at set time intervals. All species show significant linear relationships between survival time and temperature under anoxic conditions. Of species tested, C. macellaria had the greatest tolerance to anoxia (LT50 of 9 h at 20 °C). In contrast, C. vicina was the least tolerant (LT50 of 2.2 h at 40 °C). With all species, survivorship decreased with increasing temperature. Unlike many other insects tested in severe hypoxia, the larvae of the calliphorids tested, which included members of three subfamilies, were not tolerant of anoxic conditions. From these findings, it seems likely that hypoxia is a significant limitation for maggots in a maggot mass, particularly when the mass temperature is high (>40 °C). Forensically, these data provide a limit on potential maggot survival on bodies that have been submerged or otherwise experience severe hypoxia before discovery.