Analysis of the 13C isotope ratios of amino acids in the larvae, pupae and adult stages of Calliphora vicina blow flies and their carrion food sources.

Adult blow flies are one of the first necrophagous insects to colonize fresh carcasses. The eggs they lay hatch into larvae, which then feed on the decomposing body. Like all organisms, blow flies "are what they eat," meaning that the isotopic composition of their body tissues reflects their diet. This manuscript combines ecology with a forensic application by using isotope ratio mass spectrometry (IRMS) to understand the relationship between the δ13C of amino acids in different carrion sources and the blow fly that feed on them. We also measure the amino acid-level fractionation that occurs at each major life stage of the blow flies. Adult blow flies from a commercial strain of Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae) oviposited on raw pork muscle, beef muscle, or chicken liver. Larvae, pupae, and adult blow flies from each carrion were selected for amino acid compound-specific isotope analysis. Canonical discriminant analysis showed that flies were correctly classified to specific carrion types in 100% (original rules) and 96.8% (leave-one-out cross-validation [LOOCV]) of cases. Regarding life stages, we obtained 100% and 71% of correct classification in original rules and LOOCV, respectively. The isotope ratios of most of the essential amino acids did not significantly change between life stages (at 95% CI). However, some non-essential amino acids (Ala, Ser, and Glu) and some conditionally essential amino acids (Gly and Pro) were isotopically depleted in the adult stage. Except for the essential amino acids, the amino acids in larvae and pupae were enriched in 13C, and adult blow flies were depleted in 13C relative to the carrion on which they fed. These results make it possible to exclude potential sources of carrion as larval food. Amino acid-specific IRMS could help inform entomologists whether a fly has just arrived from another location to feed on a corpse or has emerged from a pupa whose feedstock was the corpse. Such insight could enhance the significance of blow flies for post-mortem interval determinations. The analytical ability to link organisms from one trophic level to another through the use of compound-specific isotope analysis of amino acids could have wide-reaching consequences in a variety of disciplines. Graphical abstract ᅟ.

Development and validation of a new technique for estimating a minimum postmortem interval using adult blow fly (Diptera: Calliphoridae) carcass attendance.

Understanding the onset and duration of adult blow fly activity is critical to accurately estimating the period of insect activity or minimum postmortem interval (minPMI). Few, if any, reliable techniques have been developed and consequently validated for using adult fly activity to determine a minPMI. In this study, adult blow flies (Diptera: Calliphoridae) of Cochliomyia macellaria and Chrysomya rufifacies were collected from swine carcasses in rural central Texas, USA, during summer 2008 and Phormia regina and Calliphora vicina in the winter during 2009 and 2010. Carcass attendance patterns of blow flies were related to species, sex, and oocyte development. Summer-active flies were found to arrive 4-12 h after initial carcass exposure, with both C. macellaria and C. rufifacies arriving within 2 h of one another. Winter-active flies arrived within 48 h of one another. There was significant difference in degree of oocyte development on each of the first 3 days postmortem. These frequency differences allowed a minPMI to be calculated using a binomial analysis. When validated with seven tests using domestic and feral swine and human remains, the technique correctly estimated time of placement in six trials.

Environmental factors affecting early carcass attendance by four species of blow flies (Diptera: Calliphoridae) in Texas.

As the most common primary colonizer of carrion, adult blow flies (Diptera: Calliphoridae) play an important role in initiating arthropod-mediated breakdown of soft tissue; however, their timing is highly variable. This variability complicates the estimation of precolonization intervals or periods of insect activity by forensic entomologists. In this study, the size of the adult blow fly on swine carcasses was compared with various environmental conditions including time of day, temperature, wind speed, and light levels. Four trials were conducted: two in August and September 2008, one in January 2009, and one in February-March 2010. Of the measured variables, time of day was the only consistent factor explaining the population size of blow fly on a carcass, although precipitation and high winds affected winter-active Calliphora vicina Robineau-Desvoidy. Male flies were also collected, suggesting that carcasses may play additional roles in adult blow fly ecology beyond that of a simple oviposition site. For both sexes of flies, a strong diel pattern of behavior emerged, which could be useful in estimating precolonization intervals by considering the environmental conditions at a scene, and thus forensic entomologists may be better able to estimate the likelihood of adult activity at a carcass.

Evaluation of ammonia, human sweat, and bovine blood as attractants for the female canyon fly, Fannia conspicua (Diptera: Muscidae), in southern California.

Human sweat, liquid ammonia, and bovine blood are known to be attractive to some hematophagous flies. These materials were evaluated with and without carbon dioxide (CO(2)) for their ability to increase capture of female "canyon flies" (Fannia conspicua Malloch) using CDC-type suction traps (without light). Ammonia acted synergistically with CO(2) to increase trap catch 89.9% over CO(2) alone. There was no synergistic effect of human sweat or bovine blood with CO(2). In the absence of CO(2), none of the three materials increased trap catch of female canyon flies relative to non-baited traps. Implications for canyon fly control and further trap improvement are discussed.

Diel patterns of female host seeking, male swarming, and sugar feeding in Fannia conspicua (Diptera: Muscidae) in southern California.

Adult Fannia conspicua Malloch were captured by sweep net at a southern California coastal mountain community to determine diel flight activity and crop/gut sugar (gut sugar) concentration. Male swarming activity was monitored by visual estimation of swarm numbers. Gut sugar content of captured flies was determined by cold anthrone assay. Peak host seeking by female flies generally occurred in early morning (0700-0800) and early evening (1900-2000). Variation in female host-seeking activity was significantly explained by the time elapsed since sunrise or time remaining until sunset, with temperature, humidity, and wind speed having small, but significant effects on activity. Male swarming activity occurred more generally throughout the day, with peaks in mid-morning and mid-afternoon and reduced swarming during periods of highest female host-seeking activity. Male swarming behaviors were only minimally explained by environmental variables. Flies of both sexes commonly fed on fructose sugars with 99.94% of host-seeking female flies (n = 1,647), and 98.93% of swarming male flies (n = 1,398) with gut sugar levels exceeding those of starved flies. Host-seeking female flies had significantly higher overall sugar content than swarming male flies. Male flies had peak gut sugar levels at 0800-0900 and 2000. Female flies had broad peaks in gut sugar level from 0700 to 1200 and 1600 to 1900. Stepwise regression showed that variation in gut sugar level was poorly explained by environmental variables for both sexes.

Basic research in evolution and ecology enhances forensics.

In 2009, the National Research Council recommended that the forensic sciences strengthen their grounding in basic empirical research to mitigate against criticism and improve accuracy and reliability. For DNA-based identification, this goal was achieved under the guidance of the population genetics community. This effort resulted in DNA analysis becoming the 'gold standard' of the forensic sciences. Elsewhere, we proposed a framework for streamlining research in decomposition ecology, which promotes quantitative approaches to collecting and applying data to forensic investigations involving decomposing human remains. To extend the ecological aspects of this approach, this review focuses on forensic entomology, although the framework can be extended to other areas of decomposition.

Ferruginous pygmy-owl (Glaucidium brasilianum) and eastern screech-owl (Megascopes asio): new hosts for Philornis mimicola (Diptera: Muscidae) and Ornithodoros concanensis (Acari: Argasidae).

While banding ferruginous pygmy-owls (Glaucidium brasilianum) and Eastern screech-owls (Megascops asio) in south Texas during 2004, we recorded Philornis mimicola (Diptera: Muscidae) and Ornithodoros concanensis (Acari: Argasidae) parasitizing nestlings. Inspection of nestlings revealed 54 P. mimicola and one O. concanensis. Inspection of nest material revealed 111 P. mimicola, including 57 puparia. The effect (e.g., blood loss, anemia) of these hematophagous parasites might have contributed to the demise of at least one Eastern screech-owl nestling. This is the first record of P. mimicola and O. concanensis parasitizing ferruginous pygmy-owls and Eastern screech-owls.