Chasing Flies: The Use of Wingbeat Frequency as a Communication Cue in Calyptrate Flies (Diptera: Calyptratae).

The incidental sound produced by the oscillation of insect wings during flight provides an opportunity for species identification. Calyptrate flies include some of the fastest and most agile flying insects, capable of rapid changes in direction and the fast pursuit of conspecifics. This flight pattern makes the continuous and close recording of their wingbeat frequency difficult and limited to confined specimens. Advances in sound editor and analysis software, however, have made it possible to isolate low amplitude sounds using noise reduction and pitch detection algorithms. To explore differences in wingbeat frequency between genera and sex, 40 specimens of three-day old Sarcophaga crassipalpis, Lucilia sericata, Calliphora dubia, and Musca vetustissima were individually recorded in free flight in a temperature-controlled room. Results showed significant differences in wingbeat frequency between the four species and intersexual differences for each species. Discriminant analysis classifying the three carrion flies resulted in 77.5% classified correctly overall, with the correct classification of 82.5% of S. crassipalpis, 60% of C. dubia, and 90% of L. sericata, when both mean wingbeat frequency and sex were included. Intersexual differences were further demonstrated by male flies showing significantly higher variability than females in three of the species. These observed intergeneric and intersexual differences in wingbeat frequency start the discussion on the use of the metric as a communication signal by this taxon. The success of the methodology demonstrated differences at the genus level and encourages the recording of additional species and the use of wingbeat frequency as an identification tool for these flies.

Domestic Filth Flies in New Haven, Connecticut: A Case Study on the Effects of Urbanization and Climate Change by Comparing Fly Populations after 78 Years.

Changes in common and widespread insect populations such as the domestic filth fly in urban cities are useful and relevant bioindicators for overall changes in the insect biomass. The current study surveyed necrophagous flies by placing a weekly trap from June-September over a two-year period in the city of New Haven, Connecticut, to compare data on fly abundance and diversity with data collected 78 years earlier. Climate and land cover changes were also assessed in combination with the fly population for each period. The survey results suggest the domestic filth fly population is now less diverse with decreased species richness and changes in the relative abundance of species. In both surveys, 95-96% of the population was composed of only three species. The current survey data indicate the numerical dominance of Lucilia sericata has decreased, the abundance of several species, notably Lucilia coeruleiviridis, has increased, and Lucilia illustris is absent. Species that showed a significant interaction with temperature in the 1940s survey have now increased in abundance, with several of the trapped species continuing to show an interaction with temperature and rainfall. Analysis of the land cover and climate data characterizes the trap site as a region exposed to a prolonged period of industrialization and urbanization, with only 7% of the land cover remaining undeveloped and over 50% impervious, coupled with an increase in temperature and rainfall. This study serves as a model for changes in domestic filth fly populations and other insects in similarly highly urbanized established cities.

Forensically relevant blow flies (Diptera: Calliphoridae) of Central Connecticut, USA.

Connecticut and the Northeastern United States in general, lacks forensically relevant entomological survey data. To determine which forensically relevant calliphorid (blow flies, Diptera: Calliphoridae) and non-calliphorid species dominate Connecticut, 5 traps using pork bait were set out 7 times over a 2-year period to collect adult and immature specimens. Insects collected from human corpses in this region were also tabulated to collaborate the forensic relevance of trapped specimens. The survey identified a total of 8 species of blow flies of the Lucilia and Calliphora genera, 6 of which colonized the baits, and 5 of which have been found to colonize human corpses in the area. Non-calliphorid genera Sarcophaga and Muscina were also found to be colonizers of the baited traps but in relatively lower numbers. Trap sites differed significantly in the degree of urbanization which was determined by using GIS mapping to classify a 1 kilometer (km) radius around each site using land use and the percent of urban impervious surfaces. The 1 km radius revealed the highly fragmented nature of the immediate habitats of the trap sites and no habitat or seasonal preference was demonstrated by blow flies under these trap conditions. Temperature was the one variable which significantly affected the number of flies trapped and the colonizing species. All trapped species have been described previously as widespread and common in the United States and as synanthropic. Further research in this region should trap at the constantly changing extreme ends of the urban-rural gradient and in the colder temperatures of winter to explore the limits of the flexibility of these blow fly species.

Postmortem scavenging by the Virginia opossum (Didelphis virginiana): Impact on taphonomic assemblages and progression.

The Virginia opossum (Didelphis virginiana) is a highly active scavenger whose behavior has significant impacts on rates of decomposition and skeletonization, which have previously not been addressed. In this study, scavenging by the opossum led to the skeletonization of carcasses in half of the accumulated degree days (ADD) of a comparable non-scavenged control carcass. Opossums used body orifices, as well as natural tears caused by the decomposition process, to access internal tissues and consume them. This activity resulted in little movement of the carcass and the retained appearance of natural undisturbed decomposition. This concealed activity has the potential to cause drastically incorrect estimates of time since deposition and post-mortem interval. Scavenging by opossums was also found to leave distinct tooth mark and other defects on bone, which have not been previously distinguished in the literature. This research suggests, beyond effects on PMI, that scavenging by opossums has been historically overlooked and misattributed to canid scavengers.

Forensically significant scavenging guilds in the southwest of Western Australia.

Estimation of time since death is an important factor in forensic investigations and the state of decomposition of a body is a prime basis for such estimations. The rate of decomposition is, however, affected by many environmental factors such as temperature, rainfall, and solar radiation as well as by indoor or outdoor location, covering and the type of surface the body is resting upon. Scavenging has the potential for major impact upon the rate of decomposition of a body, but there is little direct research upon its effect. The information that is available relates almost exclusively to North American and European contexts. The Australian faunal assemblage is unique in that it includes no native large predators or large detrivorous avians. This research investigates the animals that scavenge carcasses in natural outdoor settings in southern Western Australia and the factors which can affect each scavenger's activity. The research was conducted at four locations around Perth, Western Australia with different environmental conditions. Pig carcasses, acting as models for the human body, were positioned in an outdoor environment with no protection from scavengers or other environmental conditions. Twenty-four hour continuous time-lapse video capture was used to observe the pattern of visits of all animals to the carcasses. The time of day, length of feeding, material fed upon, area of feeding, and any movement of the carcass were recorded for each feeding event. Some species were observed to scavenge almost continually throughout the day and night. Insectivores visited the carcasses mostly during bloat and putrefaction; omnivores fed during all stages of decomposition and scavenging by carnivores, rare at any time, was most likely to occur during the early stages of decomposition. Avian species, which were the most prolific visitors to the carcasses in all locations, like reptiles, fed only during daylight hours. Only mammals and amphibians, which were seldom seen during diurnal hours, were nocturnal feeders. The combined effects of the whole guild of scavengers significantly accelerated the later stages of decomposition, especially in the cooler months of the year when natural decomposition was slowest.

A preliminary investigation into the scavenging activity on pig carcasses in Western Australia.

Human remains exposed to an outdoor environment are subject not only to the process of decomposition, but also to the activity of scavenging fauna. The scavenging behavior of fauna can vary considerably with region and season, affecting the rate of decomposition, and more importantly, the accuracy of postmortem interval estimations. A thorough knowledge of the scavenging behavior of fauna present in the local environment is imperative for law enforcement and forensic investigators dealing with decomposed remains located outdoors. This study was conducted to identify the major scavengers of decomposing remains in the southwest region of Western Australia. Avian species were identified as the dominant scavengers amongst a range of birds, reptiles, mammals, and amphibians feeding on cadaveric tissues and associated insects. The scavenging behavior of the fauna varied with seasonal factors, including temperature and rainfall. The preliminary results are useful for forensic investigations involving decomposed remains in the southwest region of Western Australia.