Development, ecology and molecular species identification of corpse-associated calliphoridae (Diptera) - consequences for estimating the post-mortem interval [Elektronische Ressource] / vorgelegt von Saskia Reibe

Reibe Saskia

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• Publié par: rheinische_friedrich-wilhelms-universitat_bonn
• Publié le: 01 janvier 2010
• Nombre de lectures: 36
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Development, Ecology and Molecular
Species Identification of Corpse-Associated
Calliphoridae (Diptera) - Consequences for
Estimating the Post-Mortem Interval
Dissertation
zur
Erlangung des Doktorgrades (Dr. rer. nat.)
der
Mathematisch-Naturwissenschaftlichen Fakultät der
Rheinischen Friedrich-Wilhems-Universität Bonn
vorgelegt
von
Frau Dipl.-Biol. Saskia Reibe
aus
Köln
Bonn, 2010Angefertigt mit Genehmigung der
Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen
Friedrich-Wilhelms-Universität Bonn
1. Gutachter: Prof. Madea
2. Gutachter: Prof. Wägele
Tag der Promotion: 1. Juni 2010Abstract
Forensic entomology is the application of entomological knowledge in processing
forensic cases involving arthropod infested corpses. The question arising most fre-
quently concerns the estimation of a post-mortem interval (PMI). This endeavour
can be approached in two different ways. Firstly, the succession of insect colo-
nization can give reasonable evidence about the time interval of a decomposition
period, as different species prefer different decomposition stages, which are related
to temperature and time. Secondly, the age of the most developed blow fly larvae
(Diptera: Calliphoridae) can indicate a minimum post-mortem interval since blow
flies are usually the first colonizers on carcass. To calculate the age of blow fly larvae
developing on a corpse, their developmental progress has to be determined as accu-
rately as possible. Development is strictly temperature dependent as blow fly larvae
are poikilothermic animals. Thus, combining the developmental progress and the
temperature influencing it, the developmental time of the larvae can be calculated.
The commonly used methods for calculating larval age are isomegalen diagrams and
the concept of accumulated degree hours (ADH). These ADHs are the product of
a certain time interval and the corresponding temperature. The ADH method as-
sumes a linear relationship between the developmental rate (1/development time)
and the temperature. However, the relationship is only linear in certain temperature
thresholds. Using the method in temperature ranges beyond these thresholds leads
to miscalculations. A second problem in estimating the PMI based on the age of
the most developed blow fly larvae is the estimation of the time interval between
time of death and first colonization by blow flies. For corpses exposed outdoors and
in an easily accessible environment, this time interval can be neglected as the blow
flies will start depositing their immediately after death. However, when corpses are
found inside a room or were wrapped in plastic bags and stored in some kind of
container it is difficult to estimate the time interval between exposure of the corpse
and access of the flies. An experimental setup was designed to compare the time
interval between exposure of carcass and the first deposition of egg batches by blow
flies indoors and outdoors. The indoor carcasses were colonized on average up to 24
hours later than the outdoor carcass. In all nine experimental runs, indoors signifi-
cantly less egg batches were counted compared to outdoors at all time points (2, 8,
24, 48 hours after exposure). Furthermore, less egg batches resulted in less feeding
larvae which lead to no formation of larval masses. Inside such larval masses heat isproduced which accelerates larval growth. For the post-mortem interval estimation
of indoor corpses it has to be taken into account that the corpse was infested with
a delay. Moreover, the growth of the larvae might have been slower as indicated by
literature values for the corresponding mean air temperature as the missing larval
mass formation decelerated the developmental rate.
As mentioned above, the method of choice for calculating a PMI is based on the
assumption of a linear relation between temperature and developmental rate. For
this thesis a new model was designed using the curvilinear devt behavior of
blow fly larvae. To build the model, published data for the development of Lucilia
sericata were used. For each developmental stage an individual exponential function
was fitted and for the PMI determination an ambient time-temperature profile is
followed backwards using in each step the appropriate function. To validate the
model, two blow fly species (Lucilia sericata and Calliphora vicina) originating
from Bonn were bred to monitor their development under different constant and
fluctuating temperatures. These data were implemented in the new model. To test
the applicability of the new method, 3 piglets were exposed in the open with larvae
of Calliphora vicina developing under different temperature regimes and collected
at different stages of their development. Larval age was calculated using the new
method as well as existing methods and the results were compared. The new model
yielded the best results except for one trial when the temperature was constantly
below 10 C. As no developmental data was collected for such low temperatures,
the model extrapolated the values for the calculation which lead to results not as
accurate as for the other trials. However, the model appeared to be a reasonable
alternative to the other methods and has one big advantage: it can include possible
sources of error and calculates a standard deviation. No other method used for
PMI estimation in forensic entomology was designed to produce a value judging the
goodness of the results. The possible sources of error are the progress of the larval
stage and the precision of the implemented temperature regime.
In this thesis, several real cases were evaluated and the PMI was calculated. It
wasshownthatinsomeindoorscenarios, PMIestimationrevealsbetterresultswhen
the calculation is based on developmental data of Phoridae (Diptera), when they
are present on the corpse. They are much smaller and can gain access even to sealed
environments. Furthermore, they are also active during winter time in contrast to
most blow fly species. Moreover, two cases of corpses disposed in a compost binwere evaluated.
At last, most important in working with entomological evidence is the correct
identification of the collected specimens. The standard method is identification
based on morphological features of the animals. Nevertheless, it is possible to iden-
tify arthropods analyzing a small fragment of the mitochondrial DNA (mtDNA)
COI gene. The method was validated for blow flies originating from other parts
of the world but never for Germany. In this thesis it was shown that the primers
published for the usage of this method are applicable for blow flies originating from
Germany and that it is not possible by reference to the analyzed fragment to decide
where the specimen originated from.
Keywords: Forensic Entomology, Estimation of ost-mortem interval, Blow fly,
mtDNA, COI, Growth model, Curvilinear model, Arthropods, Corpse, Enclosed
environment, Forensic case reportsContents
I Introduction 1
1 Introduction 3
1.1 Forensic science - a survey . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Forensic entomology 25 years ago and today - any improvements? . . 5
1.2.1 Trends in forensic entomology . . . . . . . . . . . . . . . . . . 8
1.3 Basics of forensic entomology . . . . . . . . . . . . . . . . . . . . . . 9
1.3.1 Succession . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3.2 Blow flies and their behavior towards carcass . . . . . . . . . . 12
1.3.3 Identification of insects . . . . . . . . . . . . . . . . . . . . . . 14
1.4 Physiology of larval development . . . . . . . . . . . . . . . . . . . . 15
1.4.1 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.4.2 Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.4.3 Hormones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.4.4 Diapause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.5 Estimation of post-mortem interval (PMI) . . . . . . . . . . . . . . . 21
1.6 Aims and questions of the thesis . . . . . . . . . . . . . . . . . . . . . 25
II Impact of the location of a corpse for the estimation of
a post-mortem interval 27
2 Dumping of corpses in trash barrels - two forensic entomological
case reports 29
2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.3 Casuistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3.1 Place of discovery . . . . . . . . . . . . . . . . . . . . . . . . . 30
12.3.2 Entomological findings . . . . . . . . . . . . . . . . . . . . . . 31
2.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Use of Megaselia scalaris (Diptera: Phoridae) for post-mortem
interval estimation indoors 37
3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.1 Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4 How promptly do blow flies colonise fresh carcasses? A study com-
paring indoor vs. outdoor locations 45
4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45