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Occurrence of Poecilochirus austroasiaticus (Acari:
Parasitidae) in forensic autopsies and its application
on postmortem interval estimation
Alejandro Gonza
´lez Medina •Lucas Gonza
´lez Herrera •
M. Alejandra Perotti •Gilberto Jime
´nez Rı
´os
Received: 25 January 2012 / Accepted: 17 July 2012
!Springer Science+Business Media B.V. 2012
Abstract Despite the fact that mites were used at the dawn of forensic entomology to
elucidate the postmortem interval, their use in current cases remains quite low for pro-
cedural reasons such as inadequate taxonomic knowledge. A special interest is focused on
the phoretic stages of some mite species, because the phoront-host specificity allows us to
deduce in many occasions the presence of the carrier (usually Diptera or Coleoptera)
although it has not been seen in the sampling performed in situ or in the autopsy room. In
this article, we describe two cases where Poecilochirus austroasiaticus Vitzthum (Acari:
Parasitidae) was sampled in the autopsy room. In the first case, we could sample the host,
Thanatophilus ruficornis (Ku
¨ster) (Coleoptera: Silphidae), which was still carrying pho-
retic stages of the mite on the body. That attachment allowed, by observing starvation/
feeding periods as a function of the digestive tract filling, the establishment of chrono-
logical cycles of phoretic behavior, showing maximum peaks of phoronts during arrival
and departure from the corpse and the lowest values in the phase of host feeding. From the
sarcosaprophagous fauna, we were able to determine in this case a minimum postmortem
interval of 10 days. In the second case, we found no Silphidae at the place where the corpse
was found or at the autopsy, but a postmortem interval of 13 days could be established by
the high specificity of this interspecific relationship and the departure from the corpse of
this family of Coleoptera.
Keywords Forensic entomology !Silphidae !Parasitidae !Thanatophilus ruficornis !
Poecilochirus austroasiaticus !Postmortem interval
A. Gonza
´lez Medina (&)!G. Jime
´nez Rı
´os
Institute of Legal Medicine of Granada, Avenida de la Innovacio
´n 1, 18007 Granada, Spain
e-mail: agm@ugr.es
L. Gonza
´lez Herrera
Department of Forensic Medicine and Physical Anthropology, Faculty of Medicine,
Avenida de Madrid s/n, 18071 Granada, Spain
M. A. Perotti
School of Biological Sciences, University of Reading, Whiteknights,
Reading, Berkshire RG6 6AS, UK
123
Exp Appl Acarol
DOI 10.1007/s10493-012-9606-1
Author's personal copy
Introduction
Forensic entomology is the scientific discipline that uses knowledge about community
dynamics and the developmental biology of arthropods to clarify legal issues. The issues
addressed by this science are very diverse, from urban pests to contamination of food, but
perhaps the best known application is the investigation of criminal cases. Only a detailed
study of sarcosaprophagous fauna can give useful information. As examples, we cite the
location of the real place where a murder was committed (Hawley et al. 1989), the origin of
a consignment of drugs (Crosby et al. 1985) and diagnosis of abuse and neglect of the
elderly (Benecke et al. 2004). In everyday practice, a forensic entomologist is often
required to estimate the postmortem interval or the ammount of time that has passed since
death. To this end, the expert uses two resources: the study of the developmental stages of
indicator organisms and the composition of the sarcosaprophagous community in terms of
succession (Catts and Haskell 1990).
Commonly used entomological evidences involves the different instars of the life cycle
of Diptera and Coleoptera. Protocols for sampling and analysis used in forensic ento-
mology (Lord and Burger 1983; Amendt et al. 2007) are especially detailed in the treat-
ment of these orders of insects, but often ignore information that other groups can provide.
In some cases, Lepidoptera (Introna et al. 2011), Collembola (Merrit et al. 2007) or
Trichoptera (Wallace et al. 2008) have been used in such estimations. It may seem that the
study of mites in relation to the postmortem interval is something new, but this is hardly
the case (Braig and Perotti 2009; Perotti et al. 2009). One of the founders of forensic
entomology, Jean Pierre Me
´gnin, was an acarologist of recognised prestige and, in the first
case he attended as a forensic consultant, he used the life cycle of Tyrophagus longior
(Gervais) (Acari: Acaridae) to determine the time of the death of a mummified baby
(Me
´gnin 1894). Although it is now known that much of the information provided by
Me
´gnin was partially inaccurate (Perotti 2009), this does not diminish the importance of
this type of evidence, which might easily have been overlooked by untrained eyes.
The association between mites, the remaining sarcosaprophagous fauna and the decay
stage of a body reaches its maximum expression in the behaviour of certain phoretic mites.
During their ontogeny, certain groups of mites go through a phoretic stage that facilitates
dispersal. The developmental stage in which this behavior and accompanying morpho-
logical adaptations appear shows variability depending on the type of mite (Perotti and
Braig 2009). However, there are two facts that are of interest to forensic practice: the
coupling of the life cycles of phoront-host (Houck and OConnor 1991; Neuman 1943) and
high specificity that mites may show to their carrier (Brown and Wilson 1992; Costa 1969).
Provided that such specificity is demonstrable (Neuman 1943), we can use the presence of
a certain phoront in some cadaveric remains as strong evidence of the activity of its host,
which may be present or not in the remains.
Apart from these theoretical considerations, it is necessary to provide real-life cases in
which the application of these principles will allow a more accurate estimate of the
minimum postmortem interval from the period of activity of insects. To this end, in this
article we describe two cases in which the knowledge of the biology of Poecilochirus
austroasiaticus Vitzthum (Acari: Parasitidae) enabled a better understanding of the peri-
mortem circumstances. In the first of them, we could analyze the phoretic activity on the
corpse and its rhythms. In the second one, the discovery of the phoront and the absence of
the host allowed the most direct implementation to date of phoretic activity as evidence
with testimonial value (Perotti and Braig 2009). Finally, we include in our work an
Exp Appl Acarol
123
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experiment on the transport capacity of phoronts with respect to the stage in the host
feeding cycle.
Materials and methods
In the following cases, once the corpses were removed from the death scene, autopsies
were performed following the European normative (Council of Europe 1999). Before the
medical examiner made the exploratory incisions, the forensic entomologist was allowed to
collect samples and document with photographs the decay stage of the corpses. For evi-
dence sampling, we followed the Best Practice Manual of the European Association for
Forensic Entomology (EAFE) (Amendt et al. 2007). As such guidelines do not contain any
standard for the use of mites in the research, we captured free mites with a brush of
synthetic hair previously soaked in saline and transfer them to 70 % alcohol. For the
identification of mites, we used the keys of Krantz and Walter (2009), Wise et al. (1988),
Hyatt (1980) and Solarz (2011); for Coleoptera, Prieto Pilon
˜a et al. (2002), Audisio (1993),
Peacock (1993) and Outerelo and Gamarra (1985); for Diptera, Rognes (1991) and Szpila
(2010).
The study of phoretic activity as it relates to trophic behavior of the host was conducted
in two stages. Thanatophilus ruficornis were captured, and mites attached to their bodies at
the time of capture were counted. For this purpose, we designed a methacrylate cube of
5 cm side where we placed the host so it could be seen from all angles. After the surface
inspection, we put the sample in a killing jar with ethyl acetate and included individuals
that had remained hidden in places that simple inspection could not see clearly (under the
elytra, coxal area…). After all mites were counted, we dissected Thanatophilus digestive
tracts and measured the level of filling by weighing. We worked in a phosphate buffer
solution (PBS), composed by 7.5 g of NaCl, 2.38 g of Na
2
HPO
4
and 2.72 g of KH
2
PO
4
in
100 ml of bidistilled water. After the measurement of all Thanatophilus digestive tracts,
the one with the highest content in fresh weight was considered as 100 % replete and, from
there, we determined percentage repletion proportionately.
Results
Case 1
In October 2010 the corpse of a 73-years-old man was found in Baza (Granada, SE Iberian
Peninsula) in a forested area far away from any human settlement. The body was in an
advanced bloated stage (Anderson and VanLaerhoven 1996) with the exception of the
head, which showed a more advanced state of decomposition, close to skeletonization.
From a pathological point of view, significant external injuries were only located in the
frontal bone probably as the result of a fall to the ground. Myocardial infarction due to long
term congestive heart failure was established as the cause of death. Different arthropods
found on the body during the removal of the corpse and the autopsy stage are detailed in
Table 1. With respect to the spatial distribution of P. austroasiaticus, we noted a prefer-
ence by this species for the dry patches regions of the skin. We observed, moreover, an
interesting fact: where the skin was not covered by clothes, mites were mainly concen-
trated in areas where there were Phoridae eggs or Calliphoridae larvae I. Areas without
eggs or early instar larvae and covered by clothing were ignored by the Poecilochirus.
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In order to calculate the minimum postmortem interval, the degree of larval develop-
ment of Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) found on the
corpse was studied. Considering the larval stage, length of older individuals and the record
of ambient temperatures from the scene, it could be concluded that the minimum post-
mortem interval was 10 days (Anderson 2000; Reiter 1984). In this case, we did not
required the use of the remaining cadaveric fauna for estimating the period of activity of
insects, but enough T. ruficornis were captured to carry out the study that we explain
below.
Poecilochirus austroasiaticus was not the only mite found on the corpse. We also
recovered members of the family Acaridae, specifically Acarus siro L. and Tyrophagus
putrescentiae (Schrank). Their location in the body consisted of monospecific aggregations
that could be seen as tiny bands in areas where cuticular or skeletal tissue was exposed
(teeth, nails, and exposed regions of the cheek bone).
Case 2
The body of a 54-years-old female was discovered on September 2011 in a country house
located in Granada. Residents of nearby houses had complained about strong odors that
emanated from the door of the apartment, but authorities were only warned when notified
that the home owner had not been seen for 2 weeks. The corpse was in active decay stage
and the environment in which the deceased lived was compatible with typical Diogenes
Table 1 Arthropods sampled in case 1
Family and species Developmental stage Number of
individuals
Calliphoridae [100
Calliphora vicina Adult females 2
Larvae III [100
Larvae I and II 87
Muscidae 1
Muscina stabulans Adult females 1
Phoridae 74
Megaselia sp. Adult (males and females) 4
Species unknown Eggs 70
Staphylinidae 3
Aleochara villosa Adult male 1
Philonthus jurgans Adults males 2
Silphidae 21
Thanatophilus ruficornis Adults (males and females) 21
Parasitidae 352
Poecilochirus austroasiaticus Deuteronymphs 300
Adult males 22
Adult females 30
Acaridae 43
Acarus siro Adults (males and females) 33
Tyrophagus putrescentiae Adults (males and females) 10
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syndrome behavior. A detailed inspection of the place where the corpse was found allowed
us to afirm that, despite the unsanitary conditions indoors, the organic remains of garbage
and fecal material were in other rooms, and not in the bedroom in which the body was
found. In this way, we could eliminate a cross-contamination between garbage feeding
insects and insects that fed on the body, which could have resulted in an error in calculation
of the postmortem interval. Cause of death was an acetaminophen overdose.
The main drawback we found in this case was the fact that the cause of death had a clear
toxicological component. It has been observed experimentally that few xenobiotic agents
are repellent in the colonization of the corpse by insects, provided that they are not sprayed
on the surface of the carcass. However, it has been demonstrated that xenobiotics may alter
the rates of development and growth of the insects that feed on the carcass (Introna et al.
2001). Therefore, despite having one primary colonizer species to make the calculations of
larval development (C. vicina), we declined its use in favor of an analysis based on
succession (Table 2), a more robust technique with respect to the non-measurable varia-
tions that a toxicological entity might introduce in our calculations.
In accordance with previous successional studies in this biogeographical region
(Gonza
´lez Medina 2008), we noticed that the absence of Silphidae in our sampling was not
consistent with the calculation of the period of insect activity and created an uncertainty
window (Fig. 1). Moreover, calculation became considerably difficult because of the
apparent impossibility to establish which side of the presence period for Silphidae we
should include in the calculation. The presence of P. austroasiaticus and the lack of
evidence of phoretic saturation and loss of specificity due to simulation of captivity (Perotti
and Braig 2009) allowed us to reach the conclusion that the Silphidae had already finished
residency at the corpse and had left it. The logical conclusion that results from these
observations was a period of insect activity of 13 days.
The presence of adults of Poecilochirus in both case studies confirm that the arrival of
the beetles took place sometime (at least 1 day) before the discovery of the bodies (Perotti
and Braig 2009).
Association between phoresis and trophic behavior of carriers
After the dorsal dissection of T. ruficornis collected in the case 1, we proceeded to the
separation of the crop from the rest of the digestive tract. The fresh weight of the isolated
crops showed a high heterogeneity (Pearson’s variation coefficient =73.3 %). The max-
imum fresh weight was 40.37 910
-5
g and the minimum 10.70 910
-5
g. If we assume
that the Silphidae begin to feed on the cadaveric remains as they arrive, we can suppose
that the variability in weights is a reflection of the continuous arrival of individuals of these
Coleoptera in this stage of decomposition.
Assuming the maximum fresh weight as 100 % repletion, we compared the different
percentages of repletion with the number of P. austroasiaticus deutonymphs found on the
body of the hosts under study (Fig. 2).
Discussion
Species in the genus Poecilochirus have always been closely related with phoresy over
Silphidae beetles. Except for the association between P. carabi G & R Canestrini with
Scarabeidae or Carabidae (Hyatt 1980; Schwarz and Koulianos 1998), the report of
Trogidae as an alternative host for P. necrophori Vitzthum (Perotti and Braig 2009) and
Exp Appl Acarol
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the occasional phenomenon of phoretic saturation, the great specificity of most species
selecting a silphid carrier makes Poecilochirus a genus of great forensic interest. Although
it’s possible that the second case above could raise doubts about the fact that the phoretic
saturation phenomenon could have been established, the finding of ‘‘classic’’ primary
colonizers (specifically C. vicina) rather than a high number of indicators of difficult access
to the corpse (like Phoridae), the absence of overcrowded hosts and the access to the
human remains by other Coleoptera allow us to rule out a microhabitat with limitation of
movements, even in an indoor environment.
As it can be confirmed from our experiment on the association between phoresy and
host breeding activity, phoretic activity peaks correspond to the beginning and the end of
T. ruficornis breeding on the corpse. However, there is a great difference in magnitude
between the two peaks, the first one being considerably larger than the second,
Table 2 Arthropods sampled in case 2
Family and species Developmental stage Number of individuals
Calliphoridae 30
Calliphora vicina Empty puparia 30
Sarcophagidae 25
Sarcophaga africa Adult males 1
Larvae III 10
Pupae 12
Sarcophaga sp. Adult females 2
Muscidae 4
Musca domestica Adult females 3
Hydrotaea aenescens Adult male 1
Phoridae 2
Megaselia sp. Adult (males and females) 2
Dermestidae 70
Dermestes frischii Adult (males and females) 20
Larvae 50
Histeridae 13
Saprinus subnitescens Adult males 7
Margarinotus brunneus Adult males 6
Parasitidae 87
Poecilochirus austroasiaticus Deuteronymphs 65
Adult males 10
Adult females 12
Acaridae 48
Acarus siro Adults (males and females) 18
Larvae 9
Tyrophagus putrescentiae Adults (males and females) 21
Macrochelidae 15
Macrocheles merdarius Adults (males and females) 13
Macrocheles spp. Larvae 2
Lardoglyphidae 3
Lardoglyphus zacheri Adults (males and females) 3
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corresponding to the distinction between feeding and post-feeding beetles. These results
coincide with those of Schwarz and Mu
¨ller (1992), who observed a smaller number of
P. carabi on Nicrophorus vespilloides Herbst in its feeding stage than on the post-feeding
carriers.
Future research lines should include sampling methods for mites in forensic settings and
protocols based on them, statistical validation of the acarological communities involved as
sarcosaprophagous fauna and successional studies focused on mites. The main objective of
these studies would be the transformation, from anecdotal to probative, of the sampling of
Acari during the evidence collection.
Acknowledgments We thank Krzysztof Solarz (Medical University of Silesia in Katowice, Poland) for
providing us with a valuable identification key of domestic mites and the assitance of an anonymous
reviewer for the confirmation of mites species and his suggestions for the improvement of the manuscript.
Fig. 1 Succesional occurrence matrix for autumn in Granada (SE Iberian Peninsula). We only included
those species found in case 2. Silphidae were not found in the autopsy, nor in the place where the corpse was
found
Fig. 2 Association between carrier breeding (given in percentage of crop filled with food, x-axis) and the
number of Poecilochirus mites found on the host body
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