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

The smell of death. State-of-the-art and future research directions

The decomposition of a body is inseparably associated with the release of several types of odors. This phenomenon has been used in the training of sniffer dogs for decades. The odor profile associated with decomposition consists of a range of volatile organic compounds (VOCs), chemical composition of which varies over time, temperature, environmental conditions, and the type of microorganisms, and insects colonizing the carcass. Mercaptans are responsible for the bad smell associated with corpses; however, there are no unified recommendations for conducting forensic analysis based on the detectable odor of revealed corpses and previous research on VOCs shows differing results. The aim of this review is to systematize the current knowledge on the type of volatile organic compounds related to the decomposition process, depending on a few variables. This knowledge will improve the methods of VOCs detection and analysis to be used in modern forensic diagnostics and improve the methods of training dogs for forensic applications.

Linking bacteria, volatiles and insects on carrion: the role of temporal and spatial factors regulating inter-kingdom communication via volatiles

Multi-kingdom community complexity and the chemically mediated dynamics between bacteria and insects have recently received increased attention in carrion research. However, the strength of these inter-kingdom interactions and the factors that regulate them are poorly studied. We used 75 piglet cadavers across three forest regions to survey the relationship between three actors (epinecrotic bacteria, volatile organic compounds (VOCs) and flies) during the first 4 days of decomposition and the factors that regulate this interdependence. The results showed a dynamic bacterial change during decomposition (temperature-time index) and across the forest management gradient, but not between regions. Similarly, VOC emission was dynamic across a temperature-time index and the forest management gradient but did not differ between regions. However, fly occurrence was dynamic across both space and time. The strong interdependence between the three actors was mainly regulated by the temperature-time index and the study regions, thereby revealing regulation at temporal and spatial scales. Additionally, the actor interdependence was stable across a gradient of forest management intensity. By combining different actors of decomposition, we have expanded our knowledge of the holistic mechanisms regulating carrion community dynamics and inter-kingdom interactions, an important precondition for better describing food web dynamics and entire ecosystem functions.

Floral and Bird Excreta Semiochemicals Attract Western Carpenter Ants

Ant colonies have vast and diverse nutritional needs but forager ants have limited mobility to meet these needs. Forager ants would accrue significant energy savings if they were able to sense and orient toward odor plumes of both carbohydrate and protein food sources. Moreover, if worker ants, like other flightless insects, had reduced olfactory acuity, they would not recognize the specific odor signatures of diverse carbohydrate and protein sources, but they may be able to orient toward those odorants that are shared between (macronutrient) food sources. Using the Western carpenter ant, Camponotus modoc, as a model species, we tested the hypotheses that (1) food sources rich in carbohydrates (aphid honeydew, floral nectar) and rich in proteins (bird excreta, house mouse carrion, cow liver infested or not with fly maggots) all prompt long-distance, anemotactic attraction of worker ants, and (2) attraction of ants to plant inflorescences (fireweed, Chamaenerion angustifolium; thimbleberry, Rubus parviflorus; and hardhack, Spiraea douglasii) is mediated by shared floral odorants. In moving-air Y-tube olfactometer bioassays, ants were attracted to two of four carbohydrate sources (thimbleberry and fireweed), and one of four protein sources (bird excreta). Headspace volatiles of these three attractive sources were analyzed by gas chromatography-mass spectrometry, and synthetic odor blends of thimbleberry (7 components), fireweed (23 components), and bird excreta (38 components) were prepared. In Y-tube olfactometer bioassays, synthetic blends of thimbleberry and fireweed but not of bird excreta attracted ants, indicating that only the two floral blends contained all essential attractants. A blend of components shared between thimbleberry and fireweed was not attractive to ants. Our data support the conclusion that C. modoc worker ants can sense and orient toward both carbohydrate and protein food sources. As ants were selective in their responses to carbohydrate and protein resources, it seems that they can discern between specific food odor profiles and that they have good, rather than poor, olfactory acuity.

Is Resource Change a Useful Predictor of Carrion Insect Succession on Pigs and Humans?

Carrion is a dynamic and nutrient-rich resource that attracts numerous insect species that undergo succession due to the rapid change in the carrion resource. Despite this process being well-understood, few studies have examined resource change as a driver of carrion insect succession, and instead have focused on the effects of time per se, or on coarse, qualitative measures such as decay stage. Here we report on three field succession experiments using pig carcasses and human cadavers encompassing two winters and one summer. We quantified the effects of resource change (measured as total body score, TBS), carrion type, initial carrion mass, ambient temperature, and season on insect species richness and community composition. We found that all variables had an effect on different taxonomic or trophic components of the insect community composition, with the exception of initial carrion mass which had no effect. We found significant positive effects of TBS on beetle species richness and composition, while fly species richness was not significantly affected by TBS, but was by ambient temperature. TBS had a significant positive effect on all trophic groups, while ambient temperature also had a significant positive effect on the necrophages and predator/parasitoids. Our study indicates that resource change, as indicated by TBS, is an important driver of carrion insect species turnover and succession on carrion, and that TBS can provide information about insect ecological patterns on carrion that other temporal measures of change cannot.

A phylotranscriptomic framework for flesh fly evolution (Diptera, Calyptratae, Sarcophagidae)

The Sarcophagidae (flesh flies) comprise a large and widely distributed radiation within the Calyptratae (Diptera). Larval feeding habits are ecologically diverse and include sarcosaprophagy, coprophagy, herbivory, invertebrate and vertebrate predation, and kleptoparasitism. To elucidate the geographic origin and evolution of flesh fly life-history, we inferred a backbone phylogeny based on transcriptomic data from 26 sarcophagid species covering all three subfamilies plus 15 outgroups. The phylogeny was inferred using maximum parsimony and maximum likelihood methods based on a series of supermatrices, one set with overall information content improved by MARE (2290 loci), one set with 100% gene coverage for all included species (587 loci), and the last set including mitochondrial and nuclear genes (589 loci) and additional taxa. In order to obtain a more detailed hypothesis, we utilized the supertree approach to combine results from the present study with previously published hypotheses. This resulted supertree covers 84 of the one hundred currently recognized sarcophagid genera and formed the basis for the ancestral state reconstructions. The monophyletic Sarcophagidae is well-supported as sister to {Mystacinobiidae + Oestridae}, and relationships at the subfamily level are inferred as {Sarcophaginae, (Paramacronychiinae + Miltogramminae)}. The Sarcophagidae and each subfamily originated in the Americas, with Sarcophaginae diversifying mainly in the Neotropics, whereas the major radiation of both Miltogramminae and Paramacronychiinae occurred in the Palaearctic. Sarcosaprophagy is reconstructed as the ancestral larval feeding habit of the family Sarcophagidae and each subfamily. The ancestral sarcophagid larva probably utilized dead invertebrates as food, and the food spectrum expanded together with the diversification of breeding strategies. Particularly, kleptoparasitism in Miltogramminae is derived from sarcosaprophagy and may be seen as having derived from the breeding biology of 'lower' miltogrammines, the larvae of which feed on buried vertebrate carrion.

Field succession studies and casework can help to identify forensically useful Diptera

Fly development rates, and to a lesser extent succession data, can be used to provide an estimate of a minimum postmortem interval (mPMI). Yet, these data are most useful when a full account of species' ecology, seasonality, and distribution is known. We conducted succession experiments on human cadavers over different seasons near Sydney, Australia, to document forensically useful information, including the pre-appearance interval for carrion flies. We also compiled a detailed record of flies identified in casework collected in 156 cases distributed across New South Wales, Australia. We then compared the occurrence of fly species from both field and casework datasets to identify any consistencies or gaps to determine how useful species might be for forensic investigations. In the field experiments, we found differences in species diversity and abundance between seasons, as well as yearly variation between two winter seasons. Most fly species we recorded ovipositing showed a 2- or 3-day delay between adult arrival and oviposition in summer, with a longer delay in winter. Species that were previously encountered in casework, such as Calliphora augur (Fabricius, 1775) and Calliphora ochracea Schiner, 1868, were confirmed as forensically useful, with their colonization behavior and seasonal preferences documented here. Although not encountered in casework, we confirmed Hemipyrellia fergusoni Patton, 1925 as a primary colonizer of human cadavers. Our study emphasizes the need to link field and casework data for a complete understanding of all aspects of a carrion fly's ecology to assist forensic investigators in mPMI estimations.

Analysis of volatiles from feces of released Przewalski's horse (Equus przewalskii) in Gasterophilus pecorum (Diptera: Gasterophilidae) spawning habitat

The absolute dominant species that infests wild population of Przewalski’s horse (Equus przewalskii) is Gasterophilus pecorum, and feces of released Przewalski’s horse, a habitat odor, plays an important role in mating and ovipositing locations of G. pecorum. To screen out unique volatiles for attracting G. pecorum, volatiles from fresh feces of released horses at stages of pre-oviposition (PREO), oviposition (OVIP), and post-oviposition (POSO) of G. pecorum, and feces with three different freshness states (i.e., Fresh, Semi-fresh, and Dry) at OVIP were collected by dynamic headspace adsorption and determined by automatic thermal desorption GC–MS. Results show that there were significant differences in fecal volatiles within both test conditions. Of the five most abundant volatiles from the five individual samples, the most important volatile was ammonium acetate at OVIP/Fresh, followed by acetophenone (Semi-fresh), toluene (PREO, OVIP and POSO), butanoic acid (OVIP and Semi-fresh), acetic acid (PREO, POSO and Semi-fresh), 1,6-octadiene,3,7-dimethyl-,(S)- (PREO, OVIP and POSO), 1,5,9-undecatriene,2,6,10-trimethyl-,(Z)- (PREO and Semi-fresh) and caprolactam (all conditions), which seem to be critical substances in oviposition process of G. pecorum. The findings may be beneficial to development of G. pecorum attractants, facilitating prevention and control of infection by G. pecorum to released Przewalski’s horse.

Diverse roles of microbial indole compounds in eukaryotic systems

Indole and its derivatives are widespread across different life forms, functioning as signalling molecules in prokaryotes and with more diverse roles in eukaryotes. A majority of indoles found in the environment are attributed to bacterial enzymes converting tryptophan into indole and its derivatives. The involvement of indoles among lower organisms as an interspecies and intraspecies signal is well known, with many reports showing that inter‐kingdom interactions involving microbial indole compounds are equally important as they influence defence systems and even the behaviour of higher organisms. This review summarizes recent advances in our understanding of the functional properties of indole and indole derivatives in diverse eukaryotes. Furthermore, we discuss current perspectives on the role of microbial indoles in human diseases such as diabetes, obesity, atherosclerosis, and cancers. Deciphering the function of indoles as biomarkers of metabolic state will facilitate the formulation of diet‐based treatments and open unique therapeutic opportunities.

Burying Beetle Parents Adaptively Manipulate Information Broadcast from a Microbial Community

AbstractMicrobial volatiles provide essential information for animals, which compete to detect, respond to, and perhaps control this information. Burying beetle parents have the opportunity to influence microbially derived semiochemicals, because they monopolize a small carcass for their family, repairing feeding holes and applying exudates that alter the microbial community. To study adaptive manipulation of microbial cues, we integrated mechanistic and functional approaches. We contrasted gas chromatography-mass spectrometry (GC-MS) volatile profiles from carcasses that were or were not prepared by a resident pair of Nicrophorus orbicollis. Methyl thiocyanate (MeSCN), the primary attractant for burying beetles seeking a fresh carcass, was reduced 20-fold by carcass preparation, while dimethyl trisulfide (DMTS), which deters breeding beetles, was increased 20-fold. These results suggest that parental care serves to make previously public information more private (crypsis, MeSCN) and to disinform rivals with a deterrent (DMTS). Functional tests in the field demonstrated that carcass preparation reduced discovery and use by congeners (threefold) as well as by dipteran rivals. Because microbes and their chemicals influence nearly every aspect of animal ecology, animal manipulation of microbial cues may be as widespread as manipulation of their own signals.

Scent chemistry and pollinators in the holoparasitic plant Cynomorium songaricum (Cynomoriaceae)

Holoparasitic plants are interesting heterotrophic angiosperms. However, carrion- or faeces-mimicking is rarely described for such plants. There is no information on the pollination biology of Cynomoriaceae, despite the fact that these plants are rare and vulnerable. This is the first study to reveal pollination in a member of this family, Cynomorium songaricum, a root holoparasite with a distinctive and putrid floral odour. From 2016 to 2018, we studied the floral volatiles, floral visitors and pollinators, behavioural responses of visitors to floral volatiles, breeding system, flowering phenology and floral biology of two wild populations of C. songaricum in Alxa, Inner Mongolia, China. A total of 42 volatiles were identified in inflorescences of C. songaricum. Among these volatiles are compounds known as typical carrion scents, such as p-cresol, indole, dimethyl disulphide and 1-octen-3-ol. C. songaricum is pollinated by various Diptera, such as Musca domestica, M. stabulans (Muscidae), Delia setigera, D. platura (Anthomyiidae), Lucilia sericata, L. caesar (Calliphoridae), Wohlfahrtia indigens, Sarcophaga noverca, S. crassipalpis and Sarcophila meridionalis (Sarcophagidae). The inflorescence scent of C. songaricum attracted these pollinators. The plants significantly benefit from insect pollination, although wind can be a pollen vector in the absence of pollinators. C. songaricum is a cross-pollinated, self-incompatible plant. Our findings suggest that C. songaricum releases malodorous volatiles to attract Diptera to achieve pollination. This new example lays the foundation for further comparative studies in other members of this plant group and contributes to a better understanding of fly-pollinated, carrion mimicking plants.

Why wild giant pandas frequently roll in horse manure

Attraction to feces in wild mammalian species is extremely rare. Here we introduce the horse manure rolling (HMR) behavior of wild giant pandas (Ailuropoda melanoleuca). Pandas not only frequently sniffed and wallowed in fresh horse manure, but also actively rubbed the fecal matter all over their bodies. The frequency of HMR events was highly correlated with an ambient temperature lower than 15 °C. BCP/BCPO (beta-caryophyllene/caryophyllene oxide) in fresh horse manure was found to drive HMR behavior and attenuated the cold sensitivity of mice by directly targeting and inhibiting transient receptor potential melastatin 8 (TRPM8), an archetypical cold-activated ion channel of mammals. Therefore, horse manure containing BCP/BCPO likely bestows the wild giant pandas with cold tolerance at low ambient temperatures. Together, our study described an unusual behavior, identified BCP/BCPO as chemical inhibitors of TRPM8 ion channel, and provided a plausible chemistry-auxiliary mechanism, in which animals might actively seek and utilize potential chemical resources from their habitat for temperature acclimatization.

The Succession of Flies of Forensic Importance Is Influenced by Volatiles Organic Compounds Emitted During the First Hours of Decomposition of Chicken Remains

After death, a series of primary reactions occur that produce volatile organic compounds (VOCs) that are released into the environment. In this study, we investigated if the succession of flies of forensic importance in the first hours after death is mediated by VOCs in order to better understanding of the ecology of necrophagous insects. In total, 685 adult insects (Diptera and Hymenoptera) were collected by traps baited with chicken remains at different decomposition times (0, 6, 12, 24, 36, or 48 h). Of the total of insects caught, individuals from six families of Diptera can be cataloged of forensic importance. The most abundant dipteran family was Piophilidae with 213 individuals, followed by Calliphoridae with 178 specimens. Of the total flies caught, 90% were females and the rest were males. Most of the caught females were categorized as gravid, which visited more often the decaying tissues compared to nongravid females. The abundance of the flies increased in the remains with a longer time of decomposition. Six VOCs emitted in different relative quantities were identified according to the decomposition time of the remains. An apparent association was observed between the emission of ρ-cresol with Lucilia eximia (Wiedemann), between the emission of phenol, dimethyl disulfide, and dimethyl trisulfide with Chrysomya rufifacies (Macquart), and between the emissions of indole with Cochliomyia macellaria (Fabricius).

The evolution of sexually dimorphic cuticular hydrocarbons in blowflies (Diptera: Calliphoridae)

Cuticular hydrocarbons (CHCs) are organic compounds found on the cuticles of all insects which can act as close-contact pheromones, while also providing a hydrophobic barrier to water loss. Given their widespread importance in sexual behaviour and survival, CHCs have likely contributed heavily to the adaptation and speciation of insects. Despite this, the patterns and mechanisms of their diversification have been studied in very few taxa. Here, we perform the first study of CHC diversification in blowflies, focussing on wild populations of the ecologically diverse genus Chrysomya. We convert CHC profiles into qualitative and quantitative traits and assess their inter- and intra-specific variation across 10 species. We also construct a global phylogeny of Chrysomya, onto which CHCs were mapped to explore the patterns of their diversification. For the first time, we demonstrate that blowflies express an exceptional diversity of CHCs, which have diversified in a nonphylogenetic and punctuated manner, are species-specific and sexually dimorphic. It is likely that both ecological and sexual selection have shaped these patterns of CHC diversification, and our study now provides a comprehensive framework for testing such hypotheses.

The Attraction of the Dung Beetle Anoplotrupes stercorosus (Coleoptera: Geotrupidae) to Volatiles from Vertebrate Cadavers

During decomposition, vertebrate carrion emits volatile organic compounds to which insects and other scavengers are attracted. We have previously found that the dung beetle, Anoplotrupes stercorosus, is the most common dung beetle found on vertebrate cadavers. Our aim in this study was to identify volatile key compounds emitted from carrion and used by A. stercorosus to locate this nutritive resource. By collecting cadaveric volatiles and performing electroantennographic detection, we tested which compounds A. stercorosus perceived in the post-bloating decomposition stage. Receptors in the antennae of A. stercorosus responded to 24 volatiles in odor bouquets from post-bloating decay. Subsequently, we produced a synthetic cadaver odor bouquet consisting of six compounds (benzaldehyde, DMTS, 3-octanone, 6-methyl-5-hepten-2-ol, nonanal, dodecane) perceived by the beetles and used various blends to attract A. stercorosus in German forests. In field assays, these beetles were attracted to a blend of DMTS, 3-octanone, and benzaldehyde. Generalist feeding behavior might lead to the super-dominant occurrence of A. stercorosus in temperate European forests and have a potentially large impact on the exploitation and rapid turnover of temporally limited resources such as vertebrate cadavers.

New Insights Into Culturable and Unculturable Bacteria Across the Life History of Medicinal Maggots Lucilia sericata (Meigen) (Diptera: Calliphoridae)

Because of the nutritional ecology of dung- and carrion-feeding, bacteria are the integral part of Lucilia sericata life cycle. Nevertheless, the disinfected larvae of the blowfly are applied to treat human chronic wounds in a biosurgery named maggot debridement therapy (MDT). To realize the effects of location/diet on the gut bacteria, to infer the role of bacteria in the blowfly ecology plus in the MDT process, and to disclose bacteria circulating horizontally in and vertically between generations, bacterial communities associated with L. sericata specimens from various sources were investigated using culture-based and culture-independent methods. In total, 265 bacteria, including 20 families, 28 genera, and 40 species, were identified in many sources of the L. sericata. Culture-dependent method identified a number of 144 bacterial isolates, including 21 species, in flies reared in an insectary; specimens were collected from the field, and third-instar larvae retrieved from chronic wounds of patients. Metagenetic approach exposed the occurrences of 121 operational taxonomic units comprising of 32 bacterial species from immature and adult stages of L. sericata. Gammaproteobacteria was distinguished as the dominant class of bacteria by both methods. Bacteria came into the life cycle of L. sericata over the foods and transovarially infected eggs. Enterococcus faecalis, Myroides phaeus, Proteus species, Providencia vermicola, and Serratia marcescens were exchanged among individuals via transstadial transmission. Factors, including diets, feeding status, identification tool, gut compartment, and life stage, governed the bacteria species. Herein, we reemphasized that L. sericata is thoroughly connected to the bacteria both in numerous gut compartments and in different life stages. Among all, transstadially transmitted bacteria are underlined, indicating the lack of antagonistic effect of the larval excretions/secretions on these resident bacteria. While the culture-dependent method generated useful data on the viable aerobic gut bacteria, metagenomic method enabled us to identify bacteria directly from the tissues without any need for cultivation and to facilitate the identification of anaerobic and unculturable bacteria. These findings are planned to pave the way for further research to determine the role of each bacterial species/strain in the insect ecology, as well as in antimicrobial, antibiofilm, anti-inflammatory, and wound healing activities.

The fly factor phenomenon is mediated by interkingdom signaling between bacterial symbionts and their blow fly hosts

We tested the recent hypothesis that the "fly factor" phenomenon (food currently or previously fed on by flies attracts more flies than the same type of food kept inaccessible to flies) is mediated by bacterial symbionts deposited with feces or regurgitated by feeding flies. We allowed laboratory-reared black blow flies, Phormia regina (Meigen), to feed and defecate on bacterial Luria-Bertani medium solidified with agar, and isolated seven morphologically distinct bacterial colonies. We identified these using matrix-assisted laser desorption/ionization mass spectrometry and sequencing of the 16S rRNA gene. In two-choice laboratory experiments, traps baited with cultures of Proteus mirabilis Hauser, Morganella morganii subsp. sibonii Jensen, or Serratia marcescens Bizio, captured significantly more flies than corresponding control jars baited with tryptic soy agar only. A mixture of seven bacterial strains as a trap bait was more attractive to flies than a single bacterial isolate (M. m. sibonii). In a field experiment, traps baited with agar cultures of P. mirabilis and M. m. sibonii in combination captured significantly more flies than traps baited with either bacterial isolate alone or the agar control. As evident by gas chromatography-mass spectrometry, the odor profiles of bacterial isolates differ, which may explain the additive effect of bacteria to the attractiveness of bacterial trap baits. As "generalist bacteria," P. mirabilis and M. m. sibonii growing on animal protein (beef liver) or plant protein (tofu) are similarly effective in attracting flies. Bacteria-derived airborne semiochemicals appear to mediate foraging by flies and to inform their feeding and oviposition decisions.

Responses of the putative trachoma vector, Musca sorbens, to volatile semiochemicals from human faeces

The putative vector of trachoma, Musca sorbens, prefers to lay its eggs on human faeces on the ground. This study sought to determine whether M. sorbens females were attracted to volatile odours from human faeces in preference to odours from the faeces of other animals, and to determine whether specific volatile semiochemicals mediate selection of the faeces. Traps baited with the faeces of humans and local domestic animals were used to catch flies at two trachoma-endemic locations in The Gambia and one in Ethiopia. At all locations, traps baited with faeces caught more female M. sorbens than control traps baited with soil, and human faeces was the most successful bait compared with soil (mean rate ratios 44.40, 61.40, 10.50 [P<0.001]; 8.17 for child faeces [P = 0.004]). Odours from human faeces were sampled by air entrainment, then extracts of the volatiles were tested by coupled gas chromatography-electroantennography with laboratory-reared female M. sorbens. Twelve compounds were electrophysiologically active and tentatively identified by coupled mass spectrometry-gas chromatography, these included cresol, indole, 2-methylpropanoic acid, butanoic acid, pentanoic acid and hexanoic acid. It is possible that some of these volatiles govern the strong attraction of M. sorbens flies to human faeces. If so, a synthetic blend of these chemicals, at the correct ratios, may prove to be a highly attractive lure. This could be used in odour-baited traps for monitoring or control of this species in trachoma-endemic regions.

Volatiles from Merino fleece evoke antennal and behavioural responses in the Australian sheep blow fly Lucilia cuprina

To identify flystrike-related volatile compounds in wool from Merino sheep, the attractiveness of wool to Lucilia cuprina Wiedmann (Diptera: Calliphoridae) was examined. First, a selection of wool samples guided by previous knowledge of sheep lines, predicted to be more susceptible or more resistant to flystrike, was tested. The attractiveness of the 10 samples selected was not associated with field susceptibility: two samples from the more resistant line were identified as most attractive and two samples from the more susceptible line were identified as least attractive, based on the behavioural assays with gravid flies. Comparison of the headspace volatiles of these samples, using solid phase microextraction and gas chromatography-mass spectrometry-electroantennographic detection, revealed octanal and nonanal to be present in the attractive wool samples that elicited responses from the fly antenna. Furthermore, the two compounds were not present in wool that was least attractive to L. cuprina. In laboratory bioassays, octanal and nonanal evoked antennal and behavioural responses in gravid L. cuprina, thus confirming their potential role as semiochemicals responsible for attracting L. cuprina to Merino sheep.

Occurrence of Escherichia coli O157:H7 in Pest Flies Captured in Leafy Greens Plots Grown Near a Beef Cattle Feedlot

Leafy greens are leading vehicles for Escherichia coli O157:H7 foodborne illness. Pest flies can harbor this pathogen and may disseminate it to produce. We determined the occurrence of E. coli O157:H7-positive flies in leafy greens planted up to 180 m from a cattle feedlot and assessed their relative risk to transmit this pathogen to leafy greens. The primary fly groups captured on sticky traps at the feedlot and leafy greens plots included house flies (Musca domestica L.), face flies (Musca autumnalis L.), stable flies (Stomoxys calcitrans L.), flesh flies (family Sarcophagidae), and blow flies (family Calliphoridae). E. coli O157:H7 carriage rates of house, face, flesh, and blow flies were similar (P > 0.05), ranging from 22.3 to 29.0 flies per 1,000 flies. In contrast, the carriage rate of stable flies was lower at 1.1 flies per 1,000 flies (P < 0.05). Differences in carriage rates are likely due to the uses of fresh bovine feces and manure by these different pest fly groups. E. coli O157:H7 carriage rates of total flies did not differ (P > 0.05) by distance (ranging from 0 to 180 m) from the feedlot. Most fly isolates were the same predominant pulsed-field gel electrophoresis types found in feedlot surface manure and leafy greens, suggesting a possible role for flies in transmitting E. coli O157:H7 to the leafy greens. However, further research is needed to clarify this role and to determine set-back distances between cattle production facilities and produce crops that will reduce the risk for pathogen contamination by challenging mechanisms like flies.

Electrophysiological and Behavioral Responses of the Kudzu Bug, Megacopta cribraria (Hemiptera: Plataspidae), to Volatile Compounds from Kudzu and Soybean Plants

The kudzu bug, Megacopta cribraria, is a key pest of soybean in the United States. Electrophysiological and behavioral responses of adult M. cribraria to kudzu and soybean volatile compounds were examined to identify semiochemicals used for host location. Headspace volatiles collected from undamaged potted plants were analyzed by gas chromatography with electroantennographic detection (GC-EAD). Subsequently, six GC-EAD-active compounds were identified by gas chromatography-mass spectrometry (GC-MS). These six compounds, along with some previously reported insect attractants, were selected for electroantennogram (EAG) assays. The four chemicals that elicited the strongest EAG responses, 1-octen-3-ol, nonanal, benzaldehyde, and ocimene, were selected for evaluation in olfactometer bioassays. Both benzaldehyde and 1-octen-3-ol exhibited dose-dependent responses at higher concentration. Our results provide insight into host location compounds used by adult M. cribraria. These results may be evaluated in future field tests and ultimately useful to develop a semiochemical-based monitoring technique and integrated pest management program for M. cribraria.

The Effects of Diets and Long-term Laboratory Rearing on Reproduction, Behavior, and Morphology of Lucilia cuprina (Diptera: Calliphoridae)

The Australian sheep blow fly, Lucilia cuprina (Wiedemann), is commonly reared in the laboratory for many sequential generations on simple, fixed diets, so it can be used in veterinary, medical, and forensic studies. To investigate the effect of diet and long-term laboratory rearing on L. cuprina, flies were fed with two different diets (sugar and milk-sugar) over a year and F1, F6, and F11 generations were used for comparisons based on the number of eggs, attraction to wool and liver, and wing size. The results showed that the number of eggs of gravid flies, and the attractiveness of wool and liver did not differ significantly between diets and generations, but gravid flies were more attracted to wool and liver than non-gravid flies (P < 0.05). Moreover, in the F1 generation, thorax length and wing aspect ratio were significantly longer than in the F6 and F11 generations (P < 0.05), and the wing length was significantly longer than in the F11 generation (P < 0.05). It was concluded that neither diet nor long-term laboratory rearing affect potential fecundity or the behavioral responses of L. cuprina, but the gravidity of flies affects their behavioral response, and long-term laboratory rearing significantly affects fly morphology, apparently explaining a loss in flight performance.

Behavior and Electrophysiological Response of Gravid and Non-Gravid Lucilia cuprina (Diptera: Calliphoridae) to Carrion-Associated Compounds

The Australian blow fly, Lucilia cuprina Wiedmann (Diptera: Calliphoridae), is a major cause of myiasis (flystrike) in Merino sheep in Australia and New Zealand and, as a primary colonizer of fresh carrion, also an important species in forensic investigations. Olfaction is considered the most important cue for insects to rapidly locate carrion over long distances, so the first carrion visitors are predicted to be very sensitive to carrion-related volatile compounds. We studied the responses of the Australian blow fly, Lucilia cuprina, to the carrion-associated compounds dimethyl trisulfide (DMTS), butyric acid, 1-octen-3-ol and indole. We also tested 2-mercaptoethanol, a compound commonly used in fly traps in Australia. We investigated whether responses of the flies are affected by their ovarian status by comparing responses of gravid and non-gravid L. cuprina in electroantennography (EAG) and two-choice laboratory bioassays. All four compounds evoked an EAG response, while only DMTS evoked responses in gas chromatography-mass spectrometry electroantennographic detection (GCMS-EAD) analyses and two-choice bioassays. Gravid flies detected lower doses of the test compounds than non-gravid flies. Our results indicate that DMTS is an important semiochemical for L. cuprina to locate carrion resources, and has potential for use in fly traps for flystrike control. Our observations also suggest that the greater sensitivity of gravid L. cuprina allows them to find fresh carrion quickly to maximize reproductive success by avoiding unsuitable degraded carrion.

Studying the "fly factor" phenomenon and its underlying mechanisms in house flies Musca domestica

The "fly factor" was first discovered >60 years ago and describes the phenomenon that food currently or previously fed on by flies attracts more foraging flies than the same type and amount of food kept inaccessible to flies. Since then, there has been little progress made to understanding this phenomenon. Our objectives were (i) to demonstrate the existence of the fly factor in house flies, Musca domestica and (ii) to study underlying mechanisms that may cause or contribute to the fly factor. In 2-choice laboratory bioassays, we obtained unambiguous evidence for a fly factor phenomenon in house flies, in that we demonstrated that feeding flies are more attractive to foraging flies than are nonfeeding flies, and that fed-on food is more attractive to foraging flies than is "clean" food. Of the potential mechanisms (fly excreta, metabolic output parameters [elevated temperature, relative humidity, carbon dioxide]), causing the fly factor, fly feces, and regurgitate do attract foraging flies but none of the metabolic output parameters of feeding flies does. Even though feeding flies produce significantly more CO₂ than nonfeeding flies, elevated levels of CO₂ have no behavior-modifying effect on flies. Preferential attraction of house flies to fly feces and regurgitate indicates that the flies sense airborne semiochemicals emanating from these sources. Hypothesizing that these semiochemicals are microbe-produced, future studies will aim at isolating and mass producing these microbes to accumulate semiochemicals for identification.

Physical and Physiological Factors Influence Behavioral Responses of Cochliomyia macellaria (Diptera: Calliphoridae) to Synthetic Attractants

Volatile chemicals from waste artificial larval media as well as from bovine blood inoculated with bacteria isolated from screwworm-infested wounds attract gravid females of Cochliomyia hominivorax Coquerel and Cochliomyia macellaria (F.). Chemicals identified from volatiles are dimethyl disulfide, dimethyl trisulfide, phenol, p-cresol, and indole; a blend of these attracted females to oviposit. Present studies investigated the effectiveness of these compounds, either in a blend or individually as potential oviposition attractants. Tests were conducted to determine the effects of gender, ovarian age, and the color and type of substrates on attraction response and oviposition of C. macellaria adults. Results showed that substrates treated with dimethyl trisulfide (DMTS) alone or the five-compound blend alone attracted significantly more gravid females than other chemicals. Black substrates treated with DMTS attracted more gravid flies than did the yellow substrates. Yellow substrates treated with indole attracted more males and nongravid females. In oviposition tests, females deposited significantly more eggs on meat-based substrates than those without meat. These findings suggest that several factors have to be considered for developing an effective oviposition attractant that should include effectiveness of individual chemicals used, the ratio of the chemicals in a blend, and their concentrations. Also, an effective trap design will need to consider using suitable color which will selectively attract gravid females.

Volatile Organic Compounds of Decaying Piglet Cadavers Perceived by Nicrophorus vespilloides

In the necrophagous burying beetle Nicrophorus vespilloides (Coleoptera: Silphidae), cadaver preference appears to depend on cadaver size and on the maturity of the beetle. We previously showed that newly emerged females with immature ovaries prefer later stages of decomposition of large cadavers. Our present aim is the determination of specific chemical compounds involved in the discrimination of cadaveric odor bouquets and the recognition of specific stages of decomposition. We used headspace samples of maggot-infested piglet cadavers at various decomposition stages and performed gas chromatography coupled with electroantennography (GC-EAD) to record 45 EAD-active compounds. Using GC coupled with mass spectrometry, we identified 13 of the EAD-active compounds. The headspace of the fresh decomposition stage was characterized mainly by high relative amounts of trimethylpyrazine. High relative amounts of dimethyl trisulfide were characteristic of bloated, post-bloating, and advanced decay stages. The advanced decay and dry remains stages were dominated by high relative amounts of phenol. Statistically, this compound had the highest impact on discrimination between the fresh decomposition stage, which is important for mature burying beetles for reproduction, and the advanced decay stage, which is nutritionally more attractive for newly emerged beetles. Phenol might, therefore, function as a key substance for newly emerged female burying beetles, so that they can locate suitable cadavers for feeding to maturation.