Effects of bait age, larval chemical cues and nutrient depletion on colonization by forensically important Calliphorid and Sarcophagid flies

A preliminary study of carrion insects in Greece and their attraction to three animal baits: a forensic entomology perspective

The current study provides data on the composition of the dipteran and coleopteran fauna attracted to three different animal baits (chicken stomach, beef liver, fish) in the urban ecosystem of Athens, Greece. An additional objective was to examine the effect of bait choice by the collected taxa. Three trap locations were established within the Agricultural University of Athens. At each location two different types of baited traps were used to capture and record the local dipteran and coleopteran biodiversity. During the sampling period, a total of 2416 dipteran and coleopteran specimens representing 43 species were collected and identified. The three most abundant dipteran taxa were Sarcophaga sp. (Diptera: Sarcophagidae), Calliphora vicina Robineau-Desvoidy, Lucilia sericata (Meigen) (Diptera: Calliphoridae). The results showed that the structure of the local insect community associated with the decomposition of animal baits depends on the bait used for sampling. This study reinforced the feasibility of using animal tissues as attractants to a wide diversity of medical, parasitological and forensically important taxa. Overall, beef liver attracted the most insects with Diptera preferring beef liver and Coleoptera preferring chicken stomach. Furthermore, this study revealed that baits of one animal tissue did not attract all species but in combination a much better understanding of this biodiversity was achieved. Finally, from a forensic entomology perspective this study highlights the lack of understanding of the value of entomological data related to case work in Greece.

Acquired Smell? Mature Females of the Common Green Bottle Fly Shift Semiochemical Preferences from Feces Feeding Sites to Carrion Oviposition Sites

We investigated foraging decisions by adult females of the common green bottle fly, Lucilia sericata, in accordance with their physiological state. When we gave female flies a choice between visually occluded, fresh canine feces (feeding site) and a CO2-euthanized rat (carrion oviposition site), 3-d-old "protein-starved" females responded equally well to feces and carrion, whereas protein-fed gravid females with mature oocytes responded only to carrion, indicating resource preferences based on a fly's physiological state. Dimethyl trisulfide (DMTS) is known to attract gravid L. sericata females to carrion. Therefore, we analyzed headspace from canine feces by gas chromatographic-electroantennographic detection (GC-EAD) and GC/mass spectrometry. In bioassays, of the 17 fecal odorants that elicited GC-EAD responses from fly antennae, a blend of indole and one or more of the alcohols phenol, m-/p-cresol and 1-octen-3-ol proved as attractive to flies as canine feces. Unlike young females, gravid females need to locate carrion for oviposition and distinguish between fresh and aging carrion, the latter possibly detrimental to offspring. Gravid female L. sericata accomplish this task, in part, by responding to trace amounts of DMTS emanating from fresh carrion and by discriminating against carrion as soon it begins to produce appreciable amounts of indole, which is also the second-most abundant semiochemical in fresh canine feces, and apparently serves as an indicator of food rather than oviposition resources. Our results emphasize the importance of studying foraging choices by flies in accordance with their physiological stage.

Chemosensory genes identified in the antennal transcriptome of the blowfly Calliphora stygia

BACKGROUND

Blowflies have relevance in areas of forensic science, agriculture, and medicine, primarily due to the ability of their larvae to develop on flesh. While it is widely accepted that blowflies rely heavily on olfaction for identifying and locating hosts, there is limited research regarding the underlying molecular mechanisms. Using next generation sequencing (Illumina), this research examined the antennal transcriptome of Calliphora stygia (Fabricius) (Diptera: Calliphoridae) to identify members of the major chemosensory gene families necessary for olfaction.

RESULTS

Representative proteins from all chemosensory gene families essential in insect olfaction were identified in the antennae of the blowfly C. stygia, including 50 odorant receptors, 22 ionotropic receptors, 21 gustatory receptors, 28 odorant binding proteins, 4 chemosensory proteins, and 3 sensory neuron membrane proteins. A total of 97 candidate cytochrome P450s and 39 esterases, some of which may act as odorant degrading enzymes, were also identified. Importantly, co-receptors necessary for the proper function of ligand-binding receptors were identified. Putative orthologues for the conserved antennal ionotropic receptors and candidate gustatory receptors for carbon dioxide detection were also amongst the identified proteins.

CONCLUSIONS

This research provides a comprehensive novel resource that will be fundamental for future studies regarding blowfly olfaction. Such information presents potential benefits to the forensic, pest control, and medical areas, and could assist in the understanding of insecticide resistance and targeted control through cross-species comparisons.

Correlation of molecular expression with diel rhythm of oviposition in Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae) and implications for forensic entomology

This study explored the molecular mechanisms potentially underlying blow fly nocturnal oviposition. A behavioral study revealed that Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae) possesses a diel rhythm of oviposition in light under 12:12 light/dark conditions. Reversal to 12:12 dark/light resulted in oviposition behavior changing to align with the adjusted regime in most females, but four of 59 experimental females lacked a diel rhythm of oviposition (were arrhythmic). Real-time PCR was used to monitor the molecular expression levels of known circadian genes per and tim in C. vicina to determine whether gene expression and behavior correlated. As with behavior, reversing light/dark conditions changed rhythmic gene expression to align with an adjusted light regime. This suggests that although it is unlikely that C. vicina will colonize dead bodies at night, arrhythmic females and oviposition in the dark was demonstrated.

Blow fly responses to semiochemicals produced by decaying carcasses

Volatiles from mouse carcasses in decay stages ranging from fresh to 33 days old were used to investigate oriented flight and landings in male and female blow flies of Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae). Oriented flight increased significantly from 36% towards fresh carcasses to 68%, 61% and 65% towards carcasses aged 3 days, 6 days and 9 days, respectively. Carcasses aged 20 days and 33 days were significantly less attractive, achieving 51% and 41% attraction, respectively. No differences emerged between the sexes in oriented flight, but a significant increase in female landings at the most attractive carcasses was observed. Headspace collections from the different stages of decay showed a succession in the volatile profile emitted from the carcasses and identified nine chemicals which peak in quantity in concurrence with the most attractive stages of decay. Three of these chemicals also showed dose-response effects as indicated by a significant correlation between the amount present and the proportion of flies responding. Blow flies are important pests and efficient traps are needed. The significant interaction between fly sex and carcass age highlights behavioural differences between male and female blow flies which can be exploited in blow fly trapping. Three new volatile chemicals, butylated hydroxyl toluene, 3-hydroxy-2-butanone and nonanal, emitted from dead mice are suggested as potential attractants.