ENTOMOLOGY AND POST-MORTEM INTERVAL: A SYSTEMATIC APPROACH.

A Systematic Approach

V.K. KASII

YAP a),

V. V.

PILLA Y b)

a) Assistant Director, I3iology Division, Central Forensic Science Laboratory, Hyderabad 500 013, India

a) Assistant Professor, Forensic Medicinc, PSGLVlS., Coimbatore, Tamil Nadu, India

ENTOMOLOJi vc POST-MORTEM SURE Sistcmatik 13ir Yakla~lm Ozct

Adli entomoloji, ~ilriimcktc olan ccsetlerde Olumdcn bu yana ge\;en silrenin hcsaplanmasmda, boceklerin ve bunlarm larvalannm ge9irdigi a~amalardan yararlanma ilkesine dayanmaktadlr. I3u 9alt~malar slrasmda, ba~ltca iki onemli faktor soz konusudur; bir ceset i\,crisinde saptanan bocek tiirlerinin goriilme Slrasmm aynnttlan ve 0 slrada bulunan bocek Cirneklcrinin ya~L SCiz konusu yontemi sistematik bir yakla~lmla vc etkili bir ~ckilde kllllanabilmek i9in bu boceklerin IOplanmasl, korunmasl, ilretilmcsi, eri~kin ve larva ya da kiln diinemindcki iizclliklerinin saptanmasl, yapyabildiklcri smlr iklim ozelliklerinin tcsbit edilmcsi ile birbirlcrinin 90galmaSI ve geli~mesi ilzcrindeki ctkilerinin bilinmesi gereklidir. I311 9ah~mamlzda, bir adli cntomoloji 9all~masl slrasmda goz onilnde bulundurulmasl gereken onemli noktalan belirlemeyi ama9ladtk.

Summary

Forensic entomology is mainly concerned with estimation of timc since death and depends upon two faclors for correct application: details of faunal succession on a corpse and age of insect specimens located. To make thc method effective a systematic approach is to be followed in the collection, preservation, rearing and identification of immature and mature insect forms, collection of information about micro-climatic conditions and their influence on faunal succession and insect growth. This paper deals with some imponant aspects to be considered in an entomological study.

Key words: Forensic entomology - Postmortem interval - Cadaver maggots - Time of death - Maggot ident ificat ion

INTRODUCTION

In

the ecological balance of nature, the

decay

and decomposition of animals

is

dominated by the action of insects. This

specia

l

class

of

insects has been designated as

Sarcosaprophagous

insects. Conclusions

about

the time of death in a c

r

ime can

often

be

drawn from the character of insect fauna on the corpse, and from

t

he stage of

development of their offspring (1-7).

174 V.K. KASHYAP, V.V. PILLA Y

Various

methods exist

for elucidating

the

post-mortem interval, which

can

be

calculated fairly accurately by observing and recording certain post-mortem findings like

fall in body temperature, stage of rigor mortis, post-mortem

hypostasis, etc.; but their

main value is only in the early hours

following death (8-10). When a body has however,

regressed into

the stage of putrefaction

the

issue becomes complicated.

Average

estimates do

exist for the different stages of putrefaction

b

ut they

are subject to very

wide

variation.

It is during

this period that a

zoological

method based on

a faunistic

study

of the

corpse can

give

quite

accurate results.

In

the past two decades,

several

entomologists have been

able to provide

very close estimates of the

t

ime

of death by

using the

age of insect forms feeding on

the

corpse. However, it is

i

mperative that a

proper

procedure should

be adopted regarding collection, rearing and

preservation of

insect forms and recording of relevant data at the crime scene

i

ncluding macro and micro

climatic factors,

failing

which results may prove unsatisfactory (11

-l3

).

It

is

wit

h

this

objective

in mind that the authors

have undertaken the

present paper wherein

some

necessary information required for application

of

F

orensic Entomology

to deduce

the

post-mortem interval has been

outlined.

MATERIALS and METHODS

Twelve cases were studied mainly during the period extending from May 1985 to September 1985 consisting of corpses infested with insects brought to the Mortuary of Gandhi Hospital, Secunderabad in Andhra Pradesh.

Collection and Preservation of Maggots: From each corpse, immature/mature insect fonns (depending on the presence of either from) were collected and subjected to detailed study. In each case, a minimum of 50-75 specimens were collected to ensure complcte representation of all insect species present. These werc then divided into two sub-samples. One consisting of killed specimens, and the other containing live fonns for rearing purpose. In the fonner case preservation was done in vials of isopropyl alcohol after first immersing the larvae in hot water (80"C) for 2 to 3 minutes. Fonnalin or salt solution or any other alcohol can also be used as a preservative for maggots.

Rearing of Larvae: Rearing to adult stage was done by placing the live maggots in chambers spccially fabricated for use in the present study. This is necessary because identification of insect species is rendered much easier in the adult stage than in immature stage. Each rearing chamber consisted of a liter glass beaker filled to one-fourth with dry, coarscgrained sand, the mouth being closed with a muslin cloth secured with a rubber band. In each beaker about 30-40 maggots were placed along with a small piece of flesh taken from the corpse during autopsy. The beaker was then placed in an incubator at 30 to 32"C, with relative humidity of 25 to 30 %, until adult flies emerged. Every 6 hours, larval size and other morphological details were recorded. 1be adult flies which emerged were used for further study of their life cycle under climatic conditions of the crime scene. A few flies were killed and preserved in glass tubes (after being sprayed with an antifungal agent), to aid in species identification. Other methods of rearing have been described by Easton and

with the help of a stage micrometer. The position of the posterior spiracles in each specimen was noted. The

maggots were then processed for microscopical study. Identification was done on the basis of morphological

and anatomical characteristics such as shape, colour, presence or absence of lateral processes, structure of cephalopharyngeal organ, position and other features of posterior spiracles, etc ..

Adult files were identified on the basis of colour, wing venation, notopleural bristles, propleuron,

squama, scutellum, etc .. Toxonomic keys available in literature (14-17) were consulted for correct identification. The characteristics considered for identification of the species in this study are laid out in

Table I.

Table I. Idcntification of mature I immature insect forms in the studied cases Morphological features

Immature insect (Larvae)

I. Naked eye appearance 1) Colour: Creamy white

2) Shape: Conical 3) Processes: Absent

fl. Microscopy

I) Cephalopharyngeal organ:

Accessory oral sclerite absent 2) Posterior spiracles:

Flush with posterior face of anal

segment with 2 to 3 spiracular slits parallel to each other I. Naked eye appearance 1) Colour: Greyish

2) Shape: Cylindrical

3) Processes: Lateral & dorsal processes present

fl. Microscopy

1) Cephalopharyngeal organ: Accessory oral sclerite present

2) Posterior Spiracles:

Located in a cleft on the posterior face of last segment with 2 or 3 spiracular slits. Peritreme sclero-tilcd and encloses bulton

Mature insect

I. Naked eye appearance

Greyish two winged fly

ll. Microscopy

Three notoplcural bristles, depression of propleuron bare,

base of radius before humeral cross vein bare posteriorly

I. Naked eye appearance

I31uish-green two winged fly

ll. Microscopy

Two notopleural bristles, depression of proplcuron hairy,

base of radius before humeral cross vein hairy posteriorly, lower squama hairy above, scutellum has 5 to 6 lateral

bristles on each side

Species Sarcophaga carnaria Calliphora erythrocepJUlla Case 2,5& 8 2,3,4,6,7, 9 & 10

Following identification in each case, careful note was made as to which wave of invasion the insects

belonged to. 1he infestation of a corpse by different species of insects is in the form of a number of successive waves (3). 'lhis is of help in deciding whether one or more life cycles have been completed on the corpse, a

point of vital importance in estimating time since death. Subsequently, the lengths of the largest larvae were

176 V.K. KASHYAP, V.V. PILLAY different species at various times of their development. This gave the approximate age of the oldest larva in each case (Table IT) (Plate I). Duration of different stages of life cycle of various insects was then studied from the available literature. The time since death was then calculated after taking into consideration the influence of micro-climatic factors outlined in earlier work by the authors (18,19) as follows:

T=A+ B (cd)

where T is the time elapsed since death, A is the time of invasion of the insect species, B is the age of the most advanced insect form on the corpse and cd is correction for climatic variation wherever applicable.

Table II. Maggot species and their age in the present study

Case Species Length (Largest maggot) Age

Sarcophaga camaria 9mm 4-5 days

2 Calliphora erythrocephala 5mm 2-3 days

3 C. erythrocephala 9mm 4-5 days 4 C. erythrocephala 6mm 3-4 days 5 S. camaria 12mm 4-5 days 6 C. erythrocephala 3mm 1-2 days 7 C. erythrocephala 4mm 1-2 days 8 S. carnaria 6mm 2-3 days

9 C. erythrocephala 2mm Less than 1 day

10 C. erythrocephala (Egg) Less than 6 to 8 hours

RESULTS

and

DISCUSSION

From

a perusal of Tables

I and

II,

it

is evident that Calliphora erythrocephala and

Sarcophaga carnaria

arc the two common

insect species

infesting cadavers

in

the early

s

ta

ges

of decomposition

in this

geography

r

egion. T

his,

however,

does no

t

exclude the

possibility of encountering

other

cadaver

insect

species in Andhra

Pradesh

be

cause

fi

rstl

y, t

h

e number of cases

considered in

t

he study

is

limited in numbe

r and

secondly,

the

period of investigation

extended only

t

o one

year.

Insect species commonly

found

on

corpses

in

India are

listed

below:

A. DJPTERA (True Dics )

i) Calliphoridae ii) Muscidae iii) Phoridae iv) Piophilidae v) Sarcophagidae vi) Sepsidae vii) SplUleroceridae B. COLEOPTERA (Beetles) viii) Dermistidae ix) lIisteridae x) NitiduIidae xi) Silphidae xii) Staphylinidae xiii) Trogidae

o

'T "'" 'l Plate 1 CAS[ No

9.

CA5ENO.

~

,

mrn

CASE No· § CASE NO·

1

ll

~~

:[

i

~

~

3 If

mm

tntn

CASE No.9

, _ _ _ ___ ~ __ _ _ _ _ J O~'---~i---~2 trim 3 tnm 6

17& V.K. KASHYAP, V.V. PILLA Y Enviroıımental faeıors

have

signific311t

influence

on

the rate of

putrefactioIl

of a dead

badyas

weıı

as on the presenee

of

various fly species and their rate

of

growth.

Therdare, consideratian of temperature, humidity, vegetation and other micro-climatic

conditions prevailing at the site of corpsc recovery is important. A profarma devised by

the author (19) eould be hclpfuI

İn COllectiOll

of micro-climatie information.

if

data on

the latter are inadequate at a partieular place, a second life cycle of the recovered inseet

species may be

studıed

DIl

an

aııimal

earcass with simulated environmental conditions. It

is the experience of the authors that post-mortem interval estimated with the help of

cadaver inseets is mu ch closer to the exaet time of death than the time redueed on the

basis of other factors

(20-21). It

is hoped that the systematic approach outlined

İn

this

paper will be hclpful to forensic experts when applying the entomologica! method for

estimation of time of death.

Acknowledgemcnt

The authors are thankful lo Dr. D. Govindiah, Professor and Head of the Department of Forensic

i\kd:cine, Gandhi Medical College, Hydcrabad and to the Director of Central Forensic Scitncc Laboratof)',

Hydcrahad, [or their kecn mterest m ıhis study.

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r:.

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