Urban and Rural Spatial Delineations in Blow Fly Species (Diptera: Calliphoridae) Across Canada: Implications for Forensic Entomology.

Blow fly (Diptera: Calliphoridae) larvae are commonly used in forensic cases to determine postmortem intervals using development rates and successional changes in community composition. Studies are conducted from different regions to provide these data. We wanted to know how widely applicable these data are. We examined whether urbanized landscapes have distinct urban blow fly communities or whether the community composition in urbanized areas is simply a variation of that found in the surrounding habitat or ecozone. Using liver baited traps, we sampled 7,272 flies from 32 sites across Canada and used mapping analysis to assess urban and rural landcover classifications, and compared urban and rural species abundance and composition. Blow fly species communities from urban areas across Canada were made up of similar species and differed from the communities found in nearby rural sites. Trapping at rural sites caught more blow flies compared with urban sites (mean flies/site 59.5 and 12.4). Of the 14 species caught, 8 were caught at urban sites, 61% of these being Cynomya cadaverina Robineau-Desvoidy, 14% Phormia regina Meigen, and 11% Lucilia sericata (Meigen). In rural sites, all 14 species were caught, 41% of specimens caught were P. regina, 21% C. cadaverina, 10% Calliphora vomitoria (Linnaeus), with only 4% L. sericata. These data suggest that regional studies are appropriate for forensic entomology applications in urban landscapes, given the similar trends across Canada, less so for wilderness or rural landscapes.