Sasha C. Voss

Annual and seasonal patterns of insect succession on decomposing remains at two locations in Western Australia

This study considered annual, seasonal and shorter term variation in patterns of insect succession onto decomposing remains at two contrasting locations in Western Australia, bushland and agricultural. The degree of consistency in insect succession patterns over spatial and temporal scales was evaluated through multivariate analysis of occurrence-based distance matrices. Insect assemblages were strongly correlated between locations, within corresponding time periods, indicating that patterns of insect succession were similar between localised sites within the same broad geographic area. This suggests that there is reasonable scope for the application of baseline succession data generated at a single study site to a range of decomposition sites within a given region. Differences were largely due to species absences at the agricultural site. Three species of Coleoptera were identified as possible representatives of bushland habitat, Ptomaphila lacrymosa (Silphidae), Omorgus tatei (Trogidae) and Helea castor (Tenebrionidae), and may be indicative of post mortem movement between habitat types. Within locations, variation in insect assemblages was not significant between years. Within years, insect assemblages varied significantly over time on a seasonal time scale and as decomposition progressed through defined decomposition stages. Forensically relevant data detailing the seasonal pattern of insect succession onto decomposing remains for Western Australia are reported. Additional focus has been directed towards hymenopteran parasitoids that frequent decomposing remains and parasitise Diptera colonisers. Parasitoids can be used to provide an extended PMI timeframe in cases where traditional forensic indicators have completed their development.

Decomposition and insect succession of clothed and unclothed carcasses in Western Australia

The effect of clothing on carcass decomposition and patterns of insect succession onto remains were investigated in two separate years during autumn in Western Australia. The progression of decomposition differed between clothed and unclothed carcasses in both years of the study. The presence of clothing markedly prolonged the wet decay stage in both years with larval feeding occurring across the moist skin surface underneath clothing, as well as within and under the carcasses. Ambient temperatures were higher in the second year of the study and corresponded to marginally faster rates of decay throughout decomposition. Within years, insect arrival and oviposition were largely consistent between clothed and unclothed carcasses with a few notable exceptions. The green blow fly, Lucilia sericata Meigen (Diptera: Calliphoridae) oviposited one day earlier on clothed than unclothed carcasses in both years of the study. The black carrion fly, Australophyra rostrata Robineau-Desvoidy, (Diptera: Muscidae) colonised clothed carcasses in two distinct waves of succession but only one wave of ovipoistion was observed on unclothed carcasses in either year. Correspondingly, clothed carcasses supported larval feeding by A. rostrata for a longer duration than unclothed carcasses. Finally, dipteran larval masses were more widely distributed across the carcass surface and were present for a longer period of time on clothed carcasses than on unclothed carcasses in both years. Forensically relevant data detailing the seasonal pattern of insect succession onto clothed and unclothed decomposing remains in Western Australia are reported.

Hymenopteran parasitoids of forensic importance: host associations, seasonality, and prevalence of parasitoids of carrion flies in Western Australia.

ABSTRACT A 2-yr survey of hymenopteran parasitoids associated with carrion-breeding flies was conducted to establish the parasitoid species of potential forensic significance in Western Australia. Host associations, seasonality, and rates of parasitism in the field were examined to assess the value of the identified parasitoids as forensic indicators of time since death. Four species of parasitoid emerged from dipteran specimens collected from carcasses: Tachinaephagus zealandicus Ashmead (Encryptidae), Nasonia vitripennis Walker (Pteromalidae), Spilomicrus sp. (Diapriidae), and Aphaereta sp. (Braconidae). Overall parasitism of carrion-breeding flies was 11.8%. T. zealandicus and N. vitripennis were the predominant species, accounting for 86.3 and 11.5% of parasitism observed, respectively. In contrast, Aphaereta sp. and Spilomicrus sp. were intermittently collected from carcasses throughout the study and the parasitism rates of both species were low (≤3.0%). Our findings provide forensically important biological and behavioral data of parasitoid—host interactions within carcass environments. The cosmopolitan parasitoids T. zealandicus and N. vitripennis have the greatest potential as indicators of time since death in forensic investigations based on their broad host ranges, rates of parasitism, and seasonal prevalence. In combination, these two species are present throughout the year and they parasitized nearly all of the dipteran species that colonize carcasses. Because both are cosmopolitan species, the data presented here are applicable to regions experiencing a similar Mediterranean climate. This work reports the first incidence of T. zealandicus and N. vitripennis parasitizing the dipteran species Calliphora albifrontalis Malloch (Calliphoridae), Calliphora dubia Macquart (Calliphoridae), and Hydrotaea rostrata Robineau-Desvoidy (Muscidae).

Host location and behavioural response patterns of the parasitoid, Tachinaephagus zealandicus Ashmead (Hymenoptera: Encyrtidae), to host and host-habitat odours.

Abstract 1. To overcome the challenge of host location in patchy and complex environments, many parasitoids exploit host‐habitat derived odour cues. This study investigated the role of odour cues used during host location by the generalist parasitoid, Tachinaephagus zealandicus, a common parasitoid of Dipteran larvae found in association with decomposing carrion.

Temperature-dependent development of the parasitoid Tachinaephagus zealandicus on five forensically important carrion fly species.

The influences of temperature and host species on the development of the forensically important parasitoid Tachinaephagus zealandicus Ashmead (Hymenoptera: Encyrtidae) were studied at six constant temperatures in the range of 15–30°C. T. zealandicus completed development successfully between 15°C and 27°C on five species of Calliphoridae, Calliphora albifrontalis Malloch, Calliphora dubia Macquart, Lucilia sericata Meigen, Chrysomya rufifacies Macquart and Chrysomya megacephala Fabricius. No adult parasitoids emerged from any of the host species reared at 30°C. Temperature and host species significantly influenced development time, emergence success and progeny size. Development was significantly longer on Ch. megacephala and Ch. rufifacies at 18–24°C and significantly longer on Ch. rufifacies and C. albifrontalis at 15°C and 27°C. Parasitoid emergence success was greatest at 21°C, declined at the temperature extremes (15°C and 27°C) and was significantly lower on Ch. megacephala and Ch. rufifacies than on the three other host species. Progeny numbers per host pupa were highest at 21–24°C, declined on either side of this temperature range and were significantly lower on L. sericata, Ch. rufifacies and Ch. megacephala than on either C. dubia or C. albifrontalis. An effect of host species on sex ratio was only observed at 27°C, at which a higher proportion of T. zealandicus females emerged from Ch. megacephala and Ch. rufifacies than from the other host species. The thermal requirements for development (developmental thresholds, thermal constant, optimum temperature) of T. zealandicus in each host species were estimated using linear and non‐linear models. Upper and lower developmental thresholds ranged between 29.90°C and 31.73°C, and 9.73°C and 10.08°C, respectively. The optimum temperature for development was estimated at between 25.81°C and 27.05°C. Given the significant effect of host species on development time, the use of parasitoid–host‐specific developmental data in forensic application is recommended.

Temperature-dependant development of Nasonia vitripennis on five forensically important carrion fly species

The effects of temperature and host species on the development of Nasonia vitripennis Walker (Hymenoptera: Pteromalidae), a forensically important parasitoid of carrion flies, were studied under laboratory conditions. Development time of N. vitripennis on five species of Calliphoridae (Diptera), Calliphora albifrontalis Malloch, Calliphora dubia Macquart, Lucilia sericata Meigen, Chrysomya rufifacies Macquart, and Chrysomya megacephala Fabricius, were determined under eight constant temperatures (15, 18, 21, 24, 27, 30, 33, and 36 °C). Thermal requirements for development (developmental thresholds, thermal constant, and optimum temperature) of N. vitripennis in each host species were estimated using linear and nonlinear models. Upper and lower developmental thresholds ranged between 36.6–38.4 and 9.6–11.1 °C, respectively. The optimum temperature for development was estimated at between 30.6 and 31.8 °C. Statistical differences in the development time of N. vitripennis on the various calliphorid host species were evident within all temperature treatments, particularly at the upper and lower temperature range investigated. As such, it is recommended that insect‐based estimates of time since death in forensic investigations relying on parasitoid evidence should use host‐specific development data where available.

Investigation of the factors affecting adult fly production in biosolid cake

ABSTRACT The seasonal pattern of adult fly production in both fresh and aged biosolid cake was established by the exposure of biosolid cake to natural conditions in the central coastal region of Perth, Western Australia, over the course of a year. Relationships between fly emergence and six factors (weeks exposed, pH, NH4, rainfall, temperature, and moisture) suspected of facilitating the attraction of adult flies to biosolid cake were measured. The aim was to study the production of adult flies with regard to weeks exposed in different seasons to establish a “best practice” storage procedure for aged biosolid cake. Four fly species were collected during the study; Musca domestica L. (house fly), Stomoxys calcitrans L. (stable fly), Fannia canicularis L. (lesser house fly), and Muscina stabulans (Fallén) (false stable fly). Of the 5,303 flies identified, >97% of these were either M. domestica or S. calcitrans. Adult flies emerged from biosolid cake all year round with a sharp decline in winter. The number of emerged flies peaked in summer (3,163 flies) and declined during autumn (1,545 flies) and spring (532 flies). Significant positive relationships were observed between the number of adult flies emerging from biosolid cake and ambient temperature, NH4 content, and weeks exposed. Higher ambient temperatures and a higher NH4 content of the biosolid cake were associated with increased number of adult flies emerging from the biosolid cake. Similarly, the majority of flies emerged from biosolid cake in the first 10 wk of exposure to fly activity.

A Biological and Procedural Review of Forensically Significant Dermestes Species (Coleoptera: Dermestidae)

ABSTRACT The analyses of the insect species found on decomposing remains may provide useful information for the estimation of the minimum time elapsed since death and other parameters, such as causes and circumstances of death. The majority of research has focused on the early colonizing species, typically blowflies, while research concerning late colonizing insects is currently sparse. Dermestid beetles of the genus Dermestes L. (Coleoptera: Dermestidae) are one of the predominant insect species associated with decomposing remains during dry decay and skeletal stages of decomposition. In some dry environments, Dermestes species are likely to be the only necrophagous insects feeding on the decomposing remains. Furthermore, Dermestes species (immature and adults), their remains (cast skins and fecal material), and their artifacts (pupal chambers) are frequently found associated with ancient remains (e.g., mummies, fossils). Dermestes species have a worldwide distribution and are considered important in decomposition processes, forensic investigations, and economically as a known pest of stored products. Despite their recognized forensic importance, there is limited data documenting the ecology, biology, and the growth rates of the forensically relevant species. The aim of this review is to provide a comprehensive synopsis on the available literature concerning Dermestes species associated with forensic cases. In particular, aspects of colonization behavior, growth rates for forensic taxa and potential best practice guidelines for forensic casework encompassing late colonizing Dermestes species are discussed.

Management of stable fly and other nuisance flies breeding in rotting vegetable matter associated with horticultural crop production

Stable-fly (Stomoxys calcitrans L., Diptera: Muscidae) and other nuisance flies breeding in horticultural substrates around the Perth metropolitan area of Western Australia were investigated with regard to their larval habitats and relative abundances. Substrates were found to comprise either crop residue (i.e. stalks, leaves and fruit) left in or on the ground after harvesting, or harvested crop waste (i.e. reject produce or processing scraps dumped into open pits or fed to livestock). Stable-flies were the predominant species (>85%) developing from a wide variety of trashed vegetable crop residues. Other flies developing from these materials included house-fly, lesser house-fly, false stable-fly, blue-bodied blow-fly, black carrion-fly and flesh-flies. Stable-fly development was reduced by >90% when crop residues were sprayed with diazinon or chlorpyrifos, either prior to or immediately after incorporation of the residue into soil. Untreated crop residues yielded several hundred to >1,000 stable flies/m2 of production. Insecticides applied several weeks after crop residue incorporation into soil did not significantly reduce stable-fly emergence.

The laying of live larvae by the blowfly Calliphora varifrons (Diptera: Calliphoridae)

This study examined larviposition in Calliphora varifrons Malloch (Diptera: Calliphoridae), an ovoviviparous blowfly of forensic importance in Western Australia. Females took 1.5 min (mean 89±10.0s, n=42) to deposit their live, first instar larvae (average body length 2.5 mm) on fresh liver in the laboratory. Females laid an average of 30 live larvae (mean of 29.9±1.2, n=50) at a rate of 1 larva every 2 s (mean of 0.46±0.05 larvae/s, n=42). Most females (66%) laid live larvae only, but 18% laid fully developed eggs (half of the egg masses laid by individual females were viable) and 16% laid live larvae and some eggs at the same time. Females laying only eggs laid a mean of 24.1±3.0, n=10 eggs on each occasion. Field females carried between 20 and 44 live larvae (mean of 33.4±1.0, n=49) with a strong linear relationship between female size and number of live larvae. In the laboratory, females typically laid larvae in multiple locations. Very few females (<8%) retained some larvae in their ovisacs, retaining on average, half of their complement of developed larvae. Those larvae retained had begun to be resorbed by the female with necrosis evident on the posterior segments.