Potential use of Braconidae (Hymenoptera) in forensic cases

Parasitic and predatory behavior of Alysia manducator (Hymenoptera: Braconidae) on blow fly larvae feeding on an adult pig carcass in the Western Cape Province of South Africa: preliminary observations and forensic implications

Wasps are part of the entomofauna associated with vertebrate carrion. They are known to parasitize and prey on specific life stages of insect hosts such as eggs, larvae, pupae, and/or adults associated with vertebrate carrion. However, reports of parasitic behavior of wasps on carrion-associated insect life stages and their possible forensic implications are non-existent in the Western Cape Province of South Africa. This study is part of ongoing research investigating the entomofauna and their pattern of succession on an adult pig carcass in Cape Town, South Africa. During this study, the parasitic wasp Alysia manducator was noted parasitizing and preying on blow fly larvae associated with the decomposing carcass. The arrival of A. manducator coincides with the occurrence of blow fly eggs and/or larvae on the carcass. These wasps were seen in close association with the eggs and larvae of blow flies on various parts of the carcass and some wasps were seen dragging fly larvae attached to their ovipositors away from one part of the carcass to another. Some A. manducator were also observed walking over several larvae on the carcass while exhibiting a stabbing behavior presumably in search of a host for oviposition. We suggest that the observations recorded in this study are of considerable forensic importance as the dragging effect and predatory and stabbing behavior exhibited by A. manducator could potentially disrupt the feeding and development of the fly larvae on the carcass. This could subsequently alter the process of carcass decomposition and/or affect minimum post-mortem interval estimations.

The community of Hymenoptera parasitizing necrophagous Diptera in an urban biotope

Most reports published in the field of forensic entomology are focused on Diptera and neglect the Hymenoptera community. However, Hymenoptera are part of the entomofaunal colonization of a dead body. The use of Hymenoptera parasitoids in forensic entomology can be relevant to evaluate the time of death. Hymenoptera parasitoids of the larvae and pupae of flies may play an important role in the estimation of the post-mortem period because their time of attack is often restricted to a small, well-defined window of time in the development of the host insect. However, these parasitoids can interfere with the developmental times of colonizing Diptera, and therefore a better understanding of their ecology is needed. The work reported here monitored the presence of adult Hymenoptera parasitoids on decaying pig carcasses in an urban biotope during the summer season (from May to September). Six families and six species of parasitoids were recorded in the field: Aspilota fuscicornis Haliday (Braconidae), Alysia manducator Panzer, Nasonia vitripennis Walker (Pteromalidae), Tachinaephagus zealandicus Ashmead (Encyrtidae), Trichopria sp. (Diapriidae), and Figites sp. (Figitidae). In the laboratory, five species emerged from pupae collected in the field: Trichopria sp., Figites sp., A. manducator, N. vitripennis, and T. zealandicus. These five species colonize a broad spectrum of Diptera hosts, including those species associated with decomposing carcasses, namely those from the families Calliphoridae, Muscidae, Fanniidae, and Sarcophagidae.

Oviposition restraint and developmental alterations in the ectoparasitic wasp, Nasonia vitripennis, when utilizing puparia resulting from different size maggot masses of Lucilia illustris, Protophormia terraenovae, and Sarcophaga bullata

Adult females of the ectoparasitoid Nasonia vitripennis (Walker) are capable of distinguishing between hosts of different quality, and then correspondingly adjust clutch sizes and sex ratios of the offspring. In this study, we examined whether the size of the maggot mass, and presumably the developmental temperature, influenced the suitability of the resulting fly pupal and pharate adult stages as hosts for N. vitripennis. Three sizes of maggot masses (100; 500; and 1,000 individuals per mass) were selected for use to generate hosts based on previous studies characterizing developmental and heat shock response differences for the flies. For all host species tested (Lucilia illustris, Protophormia terraenovae, and Sarcophaga bullata), the rate of parasitism by N. vitripennis decreased with increasing maggot mass size. When successful parasitism did occur, parasitoid development increased in duration, clutch sizes decreased, mortality from egg hatch to adult emergence elevated, male biased sex ratios were produced, and adult wasp body sizes were truncated with increasing fly larval density. These wasp life history features are consistent with reductions in host quality. Host quality reductions corresponded to production of heat shock proteins 23, 60, and 70. Heat shock protein synthesis appeared to occur at the expense of normal protein production because total hemolymph protein concentrations decreased with increased larval density in maggot masses. These observations argue that use of N. vitripennis in criminal investigations to estimate periods of insect activity or a minimum post mortem interval must take into account the maggot mass history of the hosts used by the wasp.

Physiological trade-offs of forming maggot masses by necrophagous flies on vertebrate carrion

Necrophagous flies that colonize human and animal corpses are extremely efficient at locating and utilizing carrion. Adult flies deposit eggs or larvae on the ephemeral food resource, which signals the beginning of intense inter- and intra-species competition. Within a short period of time after egg hatch, large larval aggregations or maggot masses form. A period of intense larval feeding ensues that will culminate with consumption/decomposition of all soft tissues associated with the corpse. Perhaps the most distinctive feature of these feeding aggregations is heat production; that is, the capacity to generate internal heat that can exceed ambient temperatures by 30°C or more. While observations of maggot mass formation and heat generation have been described in the research literature for more than 50 years, our understanding of maggot masses, particularly the physiological ecology of the aggregations as a whole, is rudimentary. In this review, an examination of what is known about the formation of maggot masses is presented, as well as arguments for the physiological benefits and limitations of developing in feeding aggregations that, at times, can represent regions of intense competition, overcrowded conditions, or a microclimate with elevated temperatures approaching or exceeding proteotoxic stress levels.

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

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 (< or = 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).

Duration of development of two species of carrion-breeding scuttle flies and forensic implications

A procedure for rearing carrion-breeding scuttle flies (Diptera: Phoridae) under naturally fluctuating temperatures is described. Data on the duration of development of the egg stage, egg plus feeding larval stages, postfeeding larvae and total development from egg to adult, at different temperature regimes (means of daily means) are tabulated for Megaselia giraudii (Egger) and M. rufipes (Meigen). The variation is greater than previously supposed and involves larvae derived from the same egg batch leaving the bait in successive waves. Despite this variation the tables allow the provision of percentage probabilities of estimations of the earliest oviposition dates for specimens collected from a forensic case.