- Email: [email protected]
The succession and development of insects on pig carcasses and their significances in estimating PMI in south China
Available online at www.sciencedirect.com
Forensic Science International 179 (2008) 11–18 www.elsevier.com/locate/forsciint
The succession and development of insects on pig carcasses and their significances in estimating PMI in south China Jiangfeng Wang a,*, Zhigang Li b, Yuchuan Chen a,**, Qiangsheng Chen b, Xiaohong Yin a a
Department of Forensic Science and Technology, Guangdong Police College, Guang Zhou, Guangdong 510230, China b Institute of Criminal Investigation, Bureau of Public Security of Guang Zhou, Guang Zhou 510080, China Received 18 January 2006; received in revised form 2 December 2007; accepted 12 April 2008
Abstract The succession of insect communities on carrion varies at local and global spatial scales. As such, ecological succession data obtained from corpses at one geographic location cannot necessarily be applied to other locations. Our study describes this succession in the far southern part of China to provide such data for forensic cases in this region. A total of 18 pig carcasses were placed in the field in four seasons, and the timing of the following events were recorded: appearance of larvae, onset of larval wandering, when most larvae had wandered, onset of pupariation, when most larvae had pupariated, onset of eclosion and end of eclosion. Our results indicated that all of the evaluated events could be used as accurate indicators of postmortem interval (PMI). The carcasses decayed fairly quickly in spring, summer and autumn, taking 225 75 h, 183 44 h, and 247 70 h, respectively, to decay from the fresh stage to skeletonisation. In winter, carcasses needed longer (1180 291) to decay as much. Carcasses attracted 47 species of insect, with flies predominating. The larvae were mainly Chrysomya megacephala (Fabricius), Chrysomya rufifacies (Macquart) and Hydrotaea (Ophyra) spinigera (Stein). Most necrophagous insects were found all year around, and there were no marked differences in species among the four seasons, except that Dermestes maculatus (De Geer) was absent in winter. Blowflies produced only one generation on a carcass before it became skeletonised, which simplified the estimation of PMIs. # 2008 Elsevier Ireland Ltd. All rights reserved. Keywords: Body decomposition; Forensic entomology; Insect succession; Postmortem interval
1. Introduction When a corpse appears, many insects may arrive, breed, develop and mature on it, producing an ecosystem. Studies of necrophage communities have been carried out in many places of the world, including China [1–3]. Those studies focused mainly on the insect taxa found on carcasses, the ecological succession patterns of those insects, the decomposition process of the carcasses and the effects of environment factors on both the decomposition and succession processes [4–12]. It has been shown that the ecological succession pattern of necrophagous insects can be useful in estimating postmortem intervals (PMIs) [13–16]. Diverse information about the process can be recorded that is relevant to such estimates [17,18], and internationally,
* Corresponding author. Tel.: +86 13503009425. ** Corresponding author. Tel.: +13922292800. E-mail addresses: [email protected] (J. Wang), [email protected] (Y. Chen). 0379-0738/$ – see front matter # 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2008.04.014
more and more cases have used entomological information to estimate PMIs [19]. The investigation of ecological succession and development of insects on carcasses in different regions is important because each region has its own ecological characteristics, and the succession and development of arthropods that colonise carcasses are influenced by these environment factors, so that succession data collected in one region cannot necessarily be used elsewhere [20,21]. Until now, no such research has been done in south China [1]. Since the climate in south China is very different from that in north China and other places of the world, we conducted this research to provide insects’ succession data for south China. 2. Materials and methods Two study sites were selected in downtown Zhongshan city (228310 N; 1138220 E), Guangdong province, in southern China, a region that experiences a subtropical monsoon climate. The sites were 1.8 km apart and each had woods and grassland. Since each experiment may enlarge the insect population around that study sites and thus affect subsequent experiments, the sites were used alternately.
12
J. Wang et al. / Forensic Science International 179 (2008) 11–18
Table 1 Dates of exposure of study pigs and weather conditions during the observation periods Date
Pigs
Mean air temperature (8C)
Mean relative humidity (%)
December 16, 2003 March 31, 2004 August 6, 2004 October 22, 2004
4 4 5 5
18.5 22.4 33.6 23.2
62 84 91 68
Eighteen pigs were used, ranging from 32 to 67 kg (mean = 50.83 kg, standard error = 2.69 kg), similar to the adult weight distribution of the Chinese population. They were killed by a blow to the head after anesthesia with syringe a method permitted by the society of animal protection. The anesthetic drug used on the pigs was Tertracine Hydrochloride. It was given through ear vein. The carcasses were placed in the shade of trees to avoid exposure to direct sunlight and covered with metal cages about 2 m 2 m 1.5 m to protect them from scavenging vertebrates. The carcasses were placed on site in different seasons (Table 1) and left to decompose naturally. Air temperature and humidity were automatically recorded once an hour by an electronic thermohygrometer (ZDR-20, Hangzhou Zeda instruments Co. Ltd., China). We observed and sampled at 09:00 and 15:00 at the first 2 weeks and at 15:00 thereafter until the carcasses decomposed completely, although we did not observe the dry remains stage. Representative samples of adult and immature necrophagous insects were collected using the appliance designed by Catts and Haskell [22]. Each time, 50 individual larvae were collected with fine forceps, killed with X.A. solution [17], and preserved in 75% ethanol. SPSS v.11.0 software was employed to analyse the data.
3. Results 3.1. The decomposition process of the carcasses We used the stage system defined by Tullis and Goff [23] to describe our observations. The whole process
was divided into five stages, fresh, bloated, decay, post-decay, and remains (Fig. 1). The carcasses took an average (standard deviation) of 225 75 h, 183 44 h, and 247 70 h, to reach the remains stage in spring, summer and autumn, respectively; in winter this took 1180 291 h. 3.2. The carcass community The carcasses yielded 47 species of insect, representing 6 orders and 20 families (Table 2). Most of the insects were found all year round, and there was no obviously difference in species between the four seasons, although dermestid beetles were absent in winter. The larvae on the carcasses were dominated by two calliphorids, C. megacephala and Chrysomya rufifacies. 3.3. Succession of necrophagous insects on carcasses The succession patterns for the four seasons were shown in Tables 3–6. Different species of fly arrived at the carcasses in different times, but most arrived in the first 2–3 d. The larvae of Hydrotaea (Ophyra) spinigera (Stein) appeared later, living in the mud around and beneath the carcasses and pupating there. In southern China flies generally produce only one generation on a carcass, and a second generation was never seen in our experiments. The first generation of maggots ate most of the carcass, while the hot weather dried the remains of the carcass to a point where it was unsuitable for maggot feeding and flies stopped laying on it.
Fig. 1. Pig carcasses decay duration in different seasons.
J. Wang et al. / Forensic Science International 179 (2008) 11–18 Table 2 Insect species found on pig carcasses exposed in the field in southern China Order
Family
Species
Diptera
Calliphoridae
Chrysomya megacephala Chrysomya rufifacies (Macquart) Ceylonomyia nigripes Aubertin Chrysomya pinguis (Walker) Lucilia sericata (Meigen) Lucilia cuprina (Wiedemann) Lucilia (Luciliella) bazini
Sarcophagidae
Parasarcophaga ruficornis (Fabricius) Parasarcophaga albiceps (Meigen) Parasarcophaga taenionota
Muscidae
Musca domestica Linnaeus Musca ventrosa Wiedemann Hydrotaea (Ophyra) spinigera (Stein) Opyra chalcogaster (Wiedemann)
Sepsidae
Unidentified
Phoridae
Unidentified
Coleoptera
Hymenoptera
Stratiomyidae
Hermetia illucens (L.)
Histeridae
Saprinus splendens Merohister jekeli (Marseul) Saprinus optabilis (Marseul) Altholus depister (Marseul)
Cleridae
Necrobia rufipes (De Geer) Necrobia ruficollis (Fabricius)
Staphylinidae
Creophilus maxillosus Platydraus sp. Aleocharinae
Silphidae
Diamesus osculand (Vigors)
Dermestidae
Dermestes maculatus (De Geer)
Scarabaeidae
Onthphagus taurinus (White) Onthophagus proletarius (Harold)
Carabidae
Unidentified
Elateridae
Chiagosnius obscuripes (Gyllenhal)
Nitidulidae
Unidentified
Vespidae
Vespa bicolor bicolor (F.) Vespa affinis affinis (L.) Vespa velutina nigrithorax Buysson Paravespula flavices flaviceps
Formicidae
Harpegnathos venator (F. Smith) Pheidologeton affinis (Jerdon) Camponotus variegates (F. Smith)
Orthoptera
Gryllidae
Unidentified
Acari
Unidentified
Unidentified
Dermaptera
Forficulidae
Unidentified
3.4. Developmental landmarks of flies in carrion When flies arrived, they laid eggs promptly in places that were not crowded with larvae. The first larvae to hatch would out-compete subsequent cohorts of larvae and even eat them. This led to the co-ordinated maturation of larvae. The key developmental events of maggots in the carrion are listed in Table 7.
13
3.5. The relationship between larvae length of flies and PMI Larval of C. megacephala reached a maximum body-length of 14.18 0.59 mm, 14.85 0.70 mm and 11.05 1.21 mm in 5 d in spring, summer and autumn, respectively, and 11.90 1.79 mm in 11 d in winter (Fig. 2). The body-length of C. rufifacies was difficult to measure because they shrank or curled into a ball when we treated them with X.A. fixative. The change of the body-length of C. megacephala with day could be simulated with logistic equation (Fig. 2). The larval body-length changes of C. megacephala with time in our research environment conditions appeared showed a rapid increase stage in feeding stage and a decrease stage in postfeeding stage. Before pupariation the body-length decreases rapidly to pupal size. The body-length of larval of C. megacephala will reached a maximum body-length of 14.18 0.59 mm, 14.85 0.70 mm and 11.05 1.21 mm in 5 d in spring, summer and autumn, respectively, and 11.90 1.79 mm in 11 d in winter (Fig. 2). The relationship between body-length (y) and time (x) under different temperatures has been modelled using the Logistic function. The body-length of C. rufifacies was difficult to measure because they shrank or curled into a ball when we treated them with X.A. fixative. The body-length of larval of flies has been well studied in different constant temperatures and controlled cyclic temperatures. But the true temperature that maggots experience was different from all that. Because the temperature of decay corpse could be raised by the activities of insects and microorganism. The reason why insects could bear with so high temperature still remains a puzzle. In this research we just exhibited the body-length of larval in our research conditions, the larval maybe did not come from the same individual or same group of gravid flies. The rigid relationship between the flies’ bodylength and the field natural temperature should be researched deeply. 4. Discussion The succession pattern of necrophagous insects can be used for the estimation of PMIs, but the pattern must first be quantified. Internationally, studies have been carried out on dogs [24], pigs [25], rabbits [26] and humans [27]. Corpses that have been exposed, buried [28], burnt [29], and waterimmersed [30] have been observed. Comparable studies have also been done by Zhou et al. [3] and Ma and Hu [1] in China. Most studies of the development of carrion-feeding insects were made under well-controlled laboratory conditions, but natural conditions are affected by many uncontrolled environment factors, such as fluctuating temperatures, rainfall, humidity, insolation, inter- and intraspecific competition and so on. This study presents the first observations of development of flies in carrion outdoors, the decay process of carrion and the patterns of ecological succession in different season in China. The results indicate that carrion decays very quickly in south China, which is consistent with results from
14
J. Wang et al. / Forensic Science International 179 (2008) 11–18
Table 3 Succession of necrophagous insects on carcasses in spring PMI (d) 1 2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19 20 22 24 26 28 30 34 38 42 46 50 54
+ +
++ +
+ +
+ +
+ +
+
+
+
+
+
A + ++ +++ +++ ++ ++ + + + + ++ + ++ ++ + + L ++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +
+ +
+
+
+
+
+
++ ++ ++ ++ ++ ++ +++ +++ +++ +++ +++ ++ + +++ +++ +++ +++ +++ +++ + + + + + + +
+ +
+ +
+
+
+
++
+
+
+
+
I A + ++ +++ +++ ++ ++ + + + + + + L ++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ + II
III A L
+
IV A L
+
+
++
++
+
++
+
++
+
+
+
+
+
+
+ +
+
+ +
+
+
+
+
+
+
+ +
+
+
+
+
+
+
+
V A L
+
+
+
+++ +
+
++
+
+
+
++
++ ++ ++ ++ ++ +
VI A L
+ +
VII A L
+
+
+
+
+
+
++
++
++
++
++
+
++
+
+
++
+
++ ++
+ +
+
+
+
+ +
+ +
+ +
++ ++ +
+
+ +
+
+ +
+ +
I: C. megacephala; II: C. rufifacies; III: Hydrotaea (Ophyra) spinigera; IV: Saprinus splendens; V: Necrobia ruficollis (Fabricius); VI: Dermeses maculates; VII: Creophilus maxillosus. A: adult insect; L: larvae; +: fewer than 10 individual flies or 2 individual beetles; ++: between 10 and 50 flies or 2–10 beetles; +++: more than 50 flies or 10 beetles. Blanks, no individuals.
Table 4 Succession of necrophagous insects on carcasses in summer PMI (d) 1
2
3
4
5
6
7
8
9
10
11
12
13
++
++
++
+
+
+++ ++ + +
14
15
16
17
18
19 20 22 24 26 28 30 34 38 42 46 50 54 58 62 66 70
I A +++ +++ ++ + L +++ +++ +++ ++
+ +
II A ++ L
+++ ++ ++ + +++ +++ +++ +++ +++ +
A L
+
+
++ ++ +++ +++ ++ ++ +++ +++ ++ + + + + +++ + +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ + +
+
+
+
+
+
+ +
III
IV A L
+
+
+
+
+
+
+
+
+
+ +
+ +
+
+
+
+
+ +
+ +
+ +
+ + + + + + + + + + + + + + +
+ + + + + + +
+
+
+
+ + + + ++ + + + + + + + + + + + + + + + + +
V A L
+
+
+
+
++
++
VI A L VII A L
+
+
+
+
+ +
+ +
++
++
++
++
++
++
++
++
++
++
++
++ ++ ++ ++ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ + + + + + + + + + + + + + + +
+ + + + + + + + + +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+
+
+
+
+
+
+
+
+ + + + + + + +
+ + + +
I: C. megacephala; II: C. rufifacies; III: Hydrotaea (Ophyra) spinigera; IV: Saprinus splendens; V: Necrobia ruficollis (Fabricius); VI: Dermeses maculates; VII: Creophilus maxillosus. A: adult insect; L: larvae; +: fewer than 10 individual flies or 2 individual beetles; ++: between 10 and 50 flies or 2–10 beetles; +++: more than 50 flies or 10 beetles. Blanks, no individuals.
J. Wang et al. / Forensic Science International 179 (2008) 11–18
15
Table 5 Succession of necrophagous insects on carcasses in autumn PMI (d) 1 2 3
4
5
6
7
8
9 10 11
12
13
14
15
16 17
18
19 20
22
24 26
28
30
34 38
42
46
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+++ +
+
I A + + + + + + + L + +++ +++ +++ +++ ++
+
+
+
II A L
+ + + ++
+ ++
+ + + +++ +++ +++ +++ + +
+
+
+
++ ++ ++ +
++ +
III A L IV A L
+ +
++
++ +
++ ++ ++ ++ + +
+
+++ +++ + + + + +
+ +
++ + + +
++ + ++ +
++ ++ + ++ ++ +
+ +
+
+
+
+ +
+
++ ++ +++ ++ + + +
++ ++ + + ++ +
++ ++ + + +
+ +
+
+
+
+ +
+++ +
++ +
+
+ + + +
++ +
+ +
+ +
+ +
V A L VI A L
+
+
+
+
VII A L
+
+
+
+
++ +
+
+
+
+
+ + ++ +
+ ++ + + +++ +++ +++ +
+ + +++ +++
I: C. megacephala; II: C. rufifacies; III: Hydrotaea (Ophyra) spinigera; IV: Saprinus splendens; V: Necrobia ruficollis (Fabricius); VI: Dermeses maculates; VII: Creophilus maxillosus. A: adult insect; L: larvae; +: fewer than 10 individual flies or 2 individual beetles; ++: between 10 and 50 flies or 2–10 beetles; +++: more than 50 flies or 10 beetles. Blanks, no individuals.
Fig. 2. Change in the body-length of C. megacephala larvae with PMI in different seasons.
16
J. Wang et al. / Forensic Science International 179 (2008) 11–18
Table 6 Succession of necrophagous insects on carcasses in winter PMI (d) 0 13
1 a
2
19.5
a
3
21.5
a
16.5
4 a
14
5 a
6
14
a
7
20.0
a
8
22.0
a
9
23.5
a
10
23.0
a
20.5
11 a
14.5
12 a
17.0
13 a
14
22.3
a
15
24.0
a
23.5
16 a
24.0
17 a
24.3
18 a
25
19 a
20
23.5
a
25
22 a
22a
I A + L
+
A + L
+
+ +
+
+
+ +
+ +
+ ++
++ +++
++ +++
++ +++
++ +++
+++ +++
+++ +++
+++ +++
+++ +++
++ +++
+ + +++ +++
+ +++
+ +++
+ +
+ +
+ +
+ +
+ +
+ +++
++ +++
++ +++
++ +++
++ +++
++ +++
+++ +++
+++ +++
+++ +++
++ +++
+ + +++ +++
+ + ++++ +++
+
+
+
+
+
+
+
+
+
+
+
+ +
+ +
+
+
+
+
++
+++ +++
+++
+++
+
+
+
++
++
++
II +
III A L IV A L
+ +
V A L VII A L
+
++
PMI (d) 24 24
26 a
17
28 a
20
30 a
16.0
32 a
17
a
34
36
a
a
8
8
38 13.0
40 a
21.0
42 a
21.2
444 a
21.0
46 a
22.0
48 a
23.5
50 a
7
a
54 10
58 a
18
62 a
25
64 a
26.0
66 a
22.0
70 a
22.0
74 a
16.0
78 a
15.0a
I A + L +
+
+ ++
+ ++
+ ++
+
+
+
+
+
+
+
+ +
+
+
II A + + + ++ L +++ ++++ +++ +++
+ + +++ +++ +++ ++
+ +
+ +
+ +
+ +
+ +
+
A + L +
+ +++ +++ +++ +++
++ +++
++ +++
++ +++
+ +++
+ +++
+ + + +++ +++ +++ +++ ++
+++
+++
+++
+
+
+
+
+ +
+ +
+ +
+
+
+
+
+
+
+
+
+
+
III ++
+ ++ +++ +++
IV A +++ ++++ +++ +++ L +
++
+
+
+
+
V A + L VII A ++ L a
++
+++ ++
++
++
+++ +++ +
+++
+
+
+
+ +
+ +
+
+
Temperature (8C).
warm climates such as those of Hawaii [23], India [31] and Egypt [32]. Problems such as the diversity of necrophagous insects and the associated difficulty of identification, regional peculiarities of community composition, and cryptic behaviour of some species have made it hard for forensic entomologists to use ecological succession to estimate PMIs based on entomological evidence. On the other hand, oviposition, wandering, pupariation and eclosion are observed easily. The development of both fly and beetle larvae in corpses follows a reliable
pattern, thus providing the most important data for the estimation of a PMI. When estimating a PMI using insects, part of the problem is to know to which generation and cohort of colonisers the insect evidence belonged. Our results showed that necrophagous blowflies could produce only one generation on a carcass before it was desiccated or skeletonised. If rain moistened the carrion again, a second generation could colonise it, and this could be distinguished easily. Different species of blowflies appear at different stages in the succession.
a
1925 1.43 27.25 1.49 30.5 1.65 32.25 1.03
a
a
a
a
a
a a
2.83 0.24 15.25 1.43
2.6 0.21 15.03 1.11 a a 18 0.7 7.85 0.24 33.25 1.8 20 1.29 8.92 0.17 39 1.58 25.88 0.83 13.54 0.35 45 1.29 28.75 1.11 a 14.85 0.2 31.13 0.83 6.73 0.32
a a
a
0.83 0.08 4.29 0.12 a a 4.79 0.12 5.64 0.16 23.75 1.49 6.67 0.14 7.9 0.14 25.25 0.85 8.1 0.1 9.75 0.48 28.25 1.7 12 0.2 a 11.75 0.43 14.27 0.42 The phenomenon did not happen or was not easy to be observed. a
4.81 0.84
a a
a
0.88 0.05 4.13 0.13 a a 4.45 0.17 8.92 0.28 38 1.58 5.36 0.21 10.75 0.48 42.5 1.04 6.38 0.24 13.93 0.27 50.75 1.49 10.13 0.66 a 16.25 0.48 11.63 0.55 7.27 0.31
a a
a
Larvae appear 0.91 0.06 Start of wandering 5.5 0.28 Most larvae wandered 7.44 0.33 Start of pupariation 8.12 0.16 Most larvae pupated 9.06 0.16 Start of eclosion 13.5 0.65 End of eclosion 15.25 0.95
C. megacephala C. rufifacies H. spinigera C. megacephala C. rufifacies H. spinigera C. megacephala C. rufifacies H. spinigera C. megacephala C. rufifacies H. spinigera
Summer Spring Key events (d)
Table 7 The key events in the process of metamorphosis and development of larvae (mean S.E.)
Autumn
Winter
J. Wang et al. / Forensic Science International 179 (2008) 11–18
17
Furthermore, if carrion appears at night or in the morning, the number of larvae in the cohort from the first day is large because adult flies have a whole day to oviposit, but if it appears in the afternoon or evening, the cohort of larvae is smaller because adult flies have less time to oviposit, and the cohort produced the following day is larger, sometimes even masking the previous one. In carrion dominated by the first cohort of maggots, those larvae will out-compete the subsequent cohorts, and so dominate the carcass until pupation. Thus most of the larvae are roughly the same size. When the first day’s cohort is small relatively to the next cohort, it cannot significantly influence its successor, so that the second cohort becomes dominant and may even conceal the first group. This phenomenon should be studied further. Average larval body-lengths are greater in spring and summer than in autumn and winter. The reason may be that there is much rain in spring and summer and little rain or snow in autumn and winter [33]. Decomposition is a natural process that is affected by many confounding factors that diminish the accuracy and precision of estimates of PMI. Rather than expecting unrealistic accuracy from entomological information, which would undermine confidence in such evidence, we sought predictable key developmental events during the decay process of the carcasses. These events can divide the decay process into several stages. When a corpse is found, the developmental stage of the insects should be obvious, and from it a PMI can be estimated accurately in conjunction with other evidence such as the larval body-length or the development of pupae. In our study, blowflies were the most significant species, arriving at carrion soon after death in the warm seasons and up to 7 d later in winter. These flies’ developmental landmarks will help greatly in estimating short-duration PMIs. H. spinigera (Stein) are also important because they appear very late in the succession process and persist in corpses for a long time, so that their developmental landmarks will help to estimate mediumduration PMIs. Hermetia illuscens arrives at highly decayed or skeletonised corpses [34–37], its development will help to estimate longer PMIs. Beetles also very important, but adults are often cryptic, elusive and difficult to sample, and so have less forensic value that their larvae. Our future research will focus on larvae, especially the population ecology of beetle larvae. 5. Conclusion In south China, we found 47 species of insect on carcasses. Most of the necrophagous insects could be found on carcasses year round, and there was no obviously difference in community composition between the four seasons, although dermestid beetles were absent in winter. The decay process and succession patterns are similar to those found in other studies. Necrophages produced only one generation on carcasses in most conditions, which was useful in estimating PMIs because the key events in the simple succession pattern are easier to observe. The dominant species were very obvious, being larvae of C. megacephala and C. rufifacies, and dermestid and histerid
18
J. Wang et al. / Forensic Science International 179 (2008) 11–18
beetles. With the above information and knowledge of the development process of the flies, we can get several key developmental events. Although this method cannot estimate PMI precisely, it may be more useful in practical work. Immature stages were more useful in estimating PMI than the adults. Acknowledgements We thank Mark Benecke (Germany) and Martin H. Villet (South Africa) for their help in revising this paper. This study was supported by the National Natural Science Foundation of China (Grant No. 30100216). References [1] Y.F. Ma, C. Hu, A preliminary study on the constitution and succession of insect community on pig carcass in Hangzhou, Acta Entomol. Sin. 23 (1997) 375–380. [2] Y. Wang, M. Liu, D.H. Sun, A study on sarcosaphagous insects species variety with seasons in Chengdu, Fa Yi Xue Za Zhi 19 (2003) 86–87, 91. [3] H. Zhou, Y. Yang, J. Ren, L. Lu, S. Wang, R. Yan, Y. Li, Studies on forensic entomology in Beijing district. I. Sarcosaprophagous beetles and their local specificity, Acta Entomol. Sin. 40 (1997) 62–70. [4] J.B. Davis, M.L. Goff, Decomposition patterns in terrestrial and intertidal habitats on Oahu Island and Coconut Island, Hawaii, J. Forensic Sci. 45 (2000) 836–842. [5] M. Wolff, A. Uribe, A. Ortiz, P. Duque, A preliminary study of forensic entomology in Medellin, Colombia, Forensic Sci. Int. 120 (2001) 53–59. [6] B. Bourel, G. Torunel, V. Hedouin, Entomofauna of buried bodies in northern France, Int. J. Legal Med. 118 (2004) 215–220. [7] L.M.L. Carvalho, A.X. Linhares, Seasonality of insect succession and pig carcass decomposition in a natural forest area in southeastern Brazil, J. Forensic Sci. 46 (2001) 604–608. [8] M.S. Archer, M.A. Elgar, Yearly activity patterns in southern Victoria (Australia) of seasonally active carrion insects, Forensic Sci. Int. 132 (2003) 173–176. [9] M.I. Arnaldos, E. Romera, J.J. Presa, A. Luna, Studies on seasonal arthropod succession on carrion in the southeastern Iberian Peninsula, Int. J. Legal Med. 118 (2004) 197–205. [10] M. Turchetto, S. Vanin, Forensic entomology and climatic change, Forensic Sci. Int. 146S (2004) S207–S209. [11] G.S. Anderson, Initial studies on insect succession on carion in southwestern British Columbia, J. Forensic Sci. 41 (1996) 617–625. [12] C.P. Campobasso, G. Di Vella, F. Introna, Factors affecting decomposition and Diptera colonization, Forensic Sci. Int. 120 (2001) 18–27. [13] G.S. Anderson, The use of insects in death investigations: an analysis of cases in British Columbia over a five year period, Can. Soc. Forensic Sci. 28 (1995) 277–292. [14] M. Benecke, Six forensic entomology cases: description and commentary, J. Forensic Sci. 43 (1998) 797–805. [15] M.L. Goff, Estimation of postmortem interval using arthropod development and successional patterns, Forensic Sci. Rev. 5 (1993) 81–94.
[16] L.R. Lamotte, J.D. Wells, p-Values for postmortem intervals from arthropod succession data, J. Agric. Biol. Environ. Statist. 5 (2000) 58–68. [17] E.P. Catts, M.L. Goff, Forensic entomology in criminal investigations, Annu. Rev. Entomol. 37 (1992) 253–272. [18] M. Benecke, Forensic entomology: arthropods and corpses. Forensic Path Rev, vol. II, Humana Press, Totowa, NJ, USA, 2004, pp. 207–240. [19] M. Benecke, A brief history of forensic entomology, Forensic Sci. Int. 120 (2001) 2–14. [20] J.H. Byrd, J.L. Castner, Forensic Entomology: The Utility of Arthropods in Legal Investigations, CRC Press, Boca Raton/London/New York/ Washington, DC, 2001. [21] J. Amendt, R. Krettek, R. Zehner, Forensic entomology, Naturwissenschaften 91 (2004) 51–65. [22] E.P. Catts, N.H. Haskell (Eds.), 1990. Entomology and death: a procedural guide. Joyce’s Print Shop, Clemson, SC. [23] K. Tullis, M.L. Goff, Arthropod succession in exposed carrion in a tropical rainforest on O’ahu Island, Hawai’I, J. Med. Entomol. 24 (1987) 332–339. [24] H.B. Reed, A study of dog carcass communities in Tennessee with special reference to the insects, Am. Midl. Nat. 59 (1958) 213. [25] L.M. Lopes de Carvalho, A.X. Linhares, Seasonality of insect succession and pig carcass decomposition in a natural forest area in southeastern Brazil, J. Forensic Sci. 46 (May (3)) (2001) 604–608. [26] M. Bharti, D. Singh, Insect faunal succession on decaying rabbit carcasses in Punjab, India, J. Forensic Sci. 48 (September (5)) (2003) 1133–1143. [27] W.C. Rodriguez, W.M. Bass, Insect activity and its relationship to decay rates of human cadavers in east Tennessee, J. Forensic Sci. 28 (1983) 423. [28] S.L. Van Laerhoven, G.S. Anderson, Insect succession on buried carrion in two biogeoclimatic zones of British Columbia, J. Forensic Sci. 44 ((1) Jan) (1999) 32–43. [29] F.W. Avila, M.L. Goff, Arthropod succession patterns onto burnt carrion in two contrasting habitats in the Hawaiian Islands, J. Forensic Sci. 43 ((3) May) (1998) 581–586. [30] G.S. Anderson, N.R. Hobischak, Decomposition of carrion in the marine environment in British Columbia, Canada, Int. J. Legal Med. 118 (August (4)) (2004) 206–209, Epub 2004 May 29. [31] M. Bharti, D. Singh, Insect faunal succession on decaying rabbit carcasses in Punjab, India, J. Forensic Sci. 48 ((5) Sep) (2003) 1133–1143. [32] T.I. Tantawi, B. Greenberg, The effect of killing and preservative solutions on estimates of maggot age in forensic cases, J. Forensic Sci. 38 (1993) 702–707. [33] Cai WanZhi, General Entomology, China Agricultural University Press, Beijing, 2001. [34] M. Turchetto, Implicazioni entomologica-forensi dell’introduzione in Italia della mosca neotropicale Hermetia illuscens L. (Diptera: Stratiomyidae), Rivista taliana di Medicina legale 22 (2000) 1279–1290. [35] J.K. Tomberlin, D.C. Sheppard, J.A. Joyce, A comparison of selected lifehistory traits of the black soldier fly (Diptera: Stratiomyidae) when reared on three diets, Ann. Entomol. Soc. Am. 95 (2002) 379–387. [36] J.K. Tomberlin, D.C. Sheppard, J.A. Joyce, Black soldier fly (Diptera: Stratiomyidae) colonization of pig carrion in south Georgia, J. Forensic Sci. 50 (2005) 152–153. [37] W.D. Lord, M.L. Goff, T.R. Adkins, N.H. Haskell, The black soldier fly Hermetia illucens (Diptera: Stratiomyidae) as a potential measure of human postmortem interval: observations and case histories, J. Forensic Sci. (1994) 215–222.
Forensic Science International 179 (2008) 11–18 www.elsevier.com/locate/forsciint
The succession and development of insects on pig carcasses and their significances in estimating PMI in south China Jiangfeng Wang a,*, Zhigang Li b, Yuchuan Chen a,**, Qiangsheng Chen b, Xiaohong Yin a a
Department of Forensic Science and Technology, Guangdong Police College, Guang Zhou, Guangdong 510230, China b Institute of Criminal Investigation, Bureau of Public Security of Guang Zhou, Guang Zhou 510080, China Received 18 January 2006; received in revised form 2 December 2007; accepted 12 April 2008
Abstract The succession of insect communities on carrion varies at local and global spatial scales. As such, ecological succession data obtained from corpses at one geographic location cannot necessarily be applied to other locations. Our study describes this succession in the far southern part of China to provide such data for forensic cases in this region. A total of 18 pig carcasses were placed in the field in four seasons, and the timing of the following events were recorded: appearance of larvae, onset of larval wandering, when most larvae had wandered, onset of pupariation, when most larvae had pupariated, onset of eclosion and end of eclosion. Our results indicated that all of the evaluated events could be used as accurate indicators of postmortem interval (PMI). The carcasses decayed fairly quickly in spring, summer and autumn, taking 225 75 h, 183 44 h, and 247 70 h, respectively, to decay from the fresh stage to skeletonisation. In winter, carcasses needed longer (1180 291) to decay as much. Carcasses attracted 47 species of insect, with flies predominating. The larvae were mainly Chrysomya megacephala (Fabricius), Chrysomya rufifacies (Macquart) and Hydrotaea (Ophyra) spinigera (Stein). Most necrophagous insects were found all year around, and there were no marked differences in species among the four seasons, except that Dermestes maculatus (De Geer) was absent in winter. Blowflies produced only one generation on a carcass before it became skeletonised, which simplified the estimation of PMIs. # 2008 Elsevier Ireland Ltd. All rights reserved. Keywords: Body decomposition; Forensic entomology; Insect succession; Postmortem interval
1. Introduction When a corpse appears, many insects may arrive, breed, develop and mature on it, producing an ecosystem. Studies of necrophage communities have been carried out in many places of the world, including China [1–3]. Those studies focused mainly on the insect taxa found on carcasses, the ecological succession patterns of those insects, the decomposition process of the carcasses and the effects of environment factors on both the decomposition and succession processes [4–12]. It has been shown that the ecological succession pattern of necrophagous insects can be useful in estimating postmortem intervals (PMIs) [13–16]. Diverse information about the process can be recorded that is relevant to such estimates [17,18], and internationally,
* Corresponding author. Tel.: +86 13503009425. ** Corresponding author. Tel.: +13922292800. E-mail addresses: [email protected] (J. Wang), [email protected] (Y. Chen). 0379-0738/$ – see front matter # 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2008.04.014
more and more cases have used entomological information to estimate PMIs [19]. The investigation of ecological succession and development of insects on carcasses in different regions is important because each region has its own ecological characteristics, and the succession and development of arthropods that colonise carcasses are influenced by these environment factors, so that succession data collected in one region cannot necessarily be used elsewhere [20,21]. Until now, no such research has been done in south China [1]. Since the climate in south China is very different from that in north China and other places of the world, we conducted this research to provide insects’ succession data for south China. 2. Materials and methods Two study sites were selected in downtown Zhongshan city (228310 N; 1138220 E), Guangdong province, in southern China, a region that experiences a subtropical monsoon climate. The sites were 1.8 km apart and each had woods and grassland. Since each experiment may enlarge the insect population around that study sites and thus affect subsequent experiments, the sites were used alternately.
12
J. Wang et al. / Forensic Science International 179 (2008) 11–18
Table 1 Dates of exposure of study pigs and weather conditions during the observation periods Date
Pigs
Mean air temperature (8C)
Mean relative humidity (%)
December 16, 2003 March 31, 2004 August 6, 2004 October 22, 2004
4 4 5 5
18.5 22.4 33.6 23.2
62 84 91 68
Eighteen pigs were used, ranging from 32 to 67 kg (mean = 50.83 kg, standard error = 2.69 kg), similar to the adult weight distribution of the Chinese population. They were killed by a blow to the head after anesthesia with syringe a method permitted by the society of animal protection. The anesthetic drug used on the pigs was Tertracine Hydrochloride. It was given through ear vein. The carcasses were placed in the shade of trees to avoid exposure to direct sunlight and covered with metal cages about 2 m 2 m 1.5 m to protect them from scavenging vertebrates. The carcasses were placed on site in different seasons (Table 1) and left to decompose naturally. Air temperature and humidity were automatically recorded once an hour by an electronic thermohygrometer (ZDR-20, Hangzhou Zeda instruments Co. Ltd., China). We observed and sampled at 09:00 and 15:00 at the first 2 weeks and at 15:00 thereafter until the carcasses decomposed completely, although we did not observe the dry remains stage. Representative samples of adult and immature necrophagous insects were collected using the appliance designed by Catts and Haskell [22]. Each time, 50 individual larvae were collected with fine forceps, killed with X.A. solution [17], and preserved in 75% ethanol. SPSS v.11.0 software was employed to analyse the data.
3. Results 3.1. The decomposition process of the carcasses We used the stage system defined by Tullis and Goff [23] to describe our observations. The whole process
was divided into five stages, fresh, bloated, decay, post-decay, and remains (Fig. 1). The carcasses took an average (standard deviation) of 225 75 h, 183 44 h, and 247 70 h, to reach the remains stage in spring, summer and autumn, respectively; in winter this took 1180 291 h. 3.2. The carcass community The carcasses yielded 47 species of insect, representing 6 orders and 20 families (Table 2). Most of the insects were found all year round, and there was no obviously difference in species between the four seasons, although dermestid beetles were absent in winter. The larvae on the carcasses were dominated by two calliphorids, C. megacephala and Chrysomya rufifacies. 3.3. Succession of necrophagous insects on carcasses The succession patterns for the four seasons were shown in Tables 3–6. Different species of fly arrived at the carcasses in different times, but most arrived in the first 2–3 d. The larvae of Hydrotaea (Ophyra) spinigera (Stein) appeared later, living in the mud around and beneath the carcasses and pupating there. In southern China flies generally produce only one generation on a carcass, and a second generation was never seen in our experiments. The first generation of maggots ate most of the carcass, while the hot weather dried the remains of the carcass to a point where it was unsuitable for maggot feeding and flies stopped laying on it.
Fig. 1. Pig carcasses decay duration in different seasons.
J. Wang et al. / Forensic Science International 179 (2008) 11–18 Table 2 Insect species found on pig carcasses exposed in the field in southern China Order
Family
Species
Diptera
Calliphoridae
Chrysomya megacephala Chrysomya rufifacies (Macquart) Ceylonomyia nigripes Aubertin Chrysomya pinguis (Walker) Lucilia sericata (Meigen) Lucilia cuprina (Wiedemann) Lucilia (Luciliella) bazini
Sarcophagidae
Parasarcophaga ruficornis (Fabricius) Parasarcophaga albiceps (Meigen) Parasarcophaga taenionota
Muscidae
Musca domestica Linnaeus Musca ventrosa Wiedemann Hydrotaea (Ophyra) spinigera (Stein) Opyra chalcogaster (Wiedemann)
Sepsidae
Unidentified
Phoridae
Unidentified
Coleoptera
Hymenoptera
Stratiomyidae
Hermetia illucens (L.)
Histeridae
Saprinus splendens Merohister jekeli (Marseul) Saprinus optabilis (Marseul) Altholus depister (Marseul)
Cleridae
Necrobia rufipes (De Geer) Necrobia ruficollis (Fabricius)
Staphylinidae
Creophilus maxillosus Platydraus sp. Aleocharinae
Silphidae
Diamesus osculand (Vigors)
Dermestidae
Dermestes maculatus (De Geer)
Scarabaeidae
Onthphagus taurinus (White) Onthophagus proletarius (Harold)
Carabidae
Unidentified
Elateridae
Chiagosnius obscuripes (Gyllenhal)
Nitidulidae
Unidentified
Vespidae
Vespa bicolor bicolor (F.) Vespa affinis affinis (L.) Vespa velutina nigrithorax Buysson Paravespula flavices flaviceps
Formicidae
Harpegnathos venator (F. Smith) Pheidologeton affinis (Jerdon) Camponotus variegates (F. Smith)
Orthoptera
Gryllidae
Unidentified
Acari
Unidentified
Unidentified
Dermaptera
Forficulidae
Unidentified
3.4. Developmental landmarks of flies in carrion When flies arrived, they laid eggs promptly in places that were not crowded with larvae. The first larvae to hatch would out-compete subsequent cohorts of larvae and even eat them. This led to the co-ordinated maturation of larvae. The key developmental events of maggots in the carrion are listed in Table 7.
13
3.5. The relationship between larvae length of flies and PMI Larval of C. megacephala reached a maximum body-length of 14.18 0.59 mm, 14.85 0.70 mm and 11.05 1.21 mm in 5 d in spring, summer and autumn, respectively, and 11.90 1.79 mm in 11 d in winter (Fig. 2). The body-length of C. rufifacies was difficult to measure because they shrank or curled into a ball when we treated them with X.A. fixative. The change of the body-length of C. megacephala with day could be simulated with logistic equation (Fig. 2). The larval body-length changes of C. megacephala with time in our research environment conditions appeared showed a rapid increase stage in feeding stage and a decrease stage in postfeeding stage. Before pupariation the body-length decreases rapidly to pupal size. The body-length of larval of C. megacephala will reached a maximum body-length of 14.18 0.59 mm, 14.85 0.70 mm and 11.05 1.21 mm in 5 d in spring, summer and autumn, respectively, and 11.90 1.79 mm in 11 d in winter (Fig. 2). The relationship between body-length (y) and time (x) under different temperatures has been modelled using the Logistic function. The body-length of C. rufifacies was difficult to measure because they shrank or curled into a ball when we treated them with X.A. fixative. The body-length of larval of flies has been well studied in different constant temperatures and controlled cyclic temperatures. But the true temperature that maggots experience was different from all that. Because the temperature of decay corpse could be raised by the activities of insects and microorganism. The reason why insects could bear with so high temperature still remains a puzzle. In this research we just exhibited the body-length of larval in our research conditions, the larval maybe did not come from the same individual or same group of gravid flies. The rigid relationship between the flies’ bodylength and the field natural temperature should be researched deeply. 4. Discussion The succession pattern of necrophagous insects can be used for the estimation of PMIs, but the pattern must first be quantified. Internationally, studies have been carried out on dogs [24], pigs [25], rabbits [26] and humans [27]. Corpses that have been exposed, buried [28], burnt [29], and waterimmersed [30] have been observed. Comparable studies have also been done by Zhou et al. [3] and Ma and Hu [1] in China. Most studies of the development of carrion-feeding insects were made under well-controlled laboratory conditions, but natural conditions are affected by many uncontrolled environment factors, such as fluctuating temperatures, rainfall, humidity, insolation, inter- and intraspecific competition and so on. This study presents the first observations of development of flies in carrion outdoors, the decay process of carrion and the patterns of ecological succession in different season in China. The results indicate that carrion decays very quickly in south China, which is consistent with results from
14
J. Wang et al. / Forensic Science International 179 (2008) 11–18
Table 3 Succession of necrophagous insects on carcasses in spring PMI (d) 1 2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19 20 22 24 26 28 30 34 38 42 46 50 54
+ +
++ +
+ +
+ +
+ +
+
+
+
+
+
A + ++ +++ +++ ++ ++ + + + + ++ + ++ ++ + + L ++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +
+ +
+
+
+
+
+
++ ++ ++ ++ ++ ++ +++ +++ +++ +++ +++ ++ + +++ +++ +++ +++ +++ +++ + + + + + + +
+ +
+ +
+
+
+
++
+
+
+
+
I A + ++ +++ +++ ++ ++ + + + + + + L ++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ + II
III A L
+
IV A L
+
+
++
++
+
++
+
++
+
+
+
+
+
+
+ +
+
+ +
+
+
+
+
+
+
+ +
+
+
+
+
+
+
+
V A L
+
+
+
+++ +
+
++
+
+
+
++
++ ++ ++ ++ ++ +
VI A L
+ +
VII A L
+
+
+
+
+
+
++
++
++
++
++
+
++
+
+
++
+
++ ++
+ +
+
+
+
+ +
+ +
+ +
++ ++ +
+
+ +
+
+ +
+ +
I: C. megacephala; II: C. rufifacies; III: Hydrotaea (Ophyra) spinigera; IV: Saprinus splendens; V: Necrobia ruficollis (Fabricius); VI: Dermeses maculates; VII: Creophilus maxillosus. A: adult insect; L: larvae; +: fewer than 10 individual flies or 2 individual beetles; ++: between 10 and 50 flies or 2–10 beetles; +++: more than 50 flies or 10 beetles. Blanks, no individuals.
Table 4 Succession of necrophagous insects on carcasses in summer PMI (d) 1
2
3
4
5
6
7
8
9
10
11
12
13
++
++
++
+
+
+++ ++ + +
14
15
16
17
18
19 20 22 24 26 28 30 34 38 42 46 50 54 58 62 66 70
I A +++ +++ ++ + L +++ +++ +++ ++
+ +
II A ++ L
+++ ++ ++ + +++ +++ +++ +++ +++ +
A L
+
+
++ ++ +++ +++ ++ ++ +++ +++ ++ + + + + +++ + +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ +++ + +
+
+
+
+
+
+ +
III
IV A L
+
+
+
+
+
+
+
+
+
+ +
+ +
+
+
+
+
+ +
+ +
+ +
+ + + + + + + + + + + + + + +
+ + + + + + +
+
+
+
+ + + + ++ + + + + + + + + + + + + + + + + +
V A L
+
+
+
+
++
++
VI A L VII A L
+
+
+
+
+ +
+ +
++
++
++
++
++
++
++
++
++
++
++
++ ++ ++ ++ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ + + + + + + + + + + + + + + +
+ + + + + + + + + +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+
+
+
+
+
+
+
+
+ + + + + + + +
+ + + +
I: C. megacephala; II: C. rufifacies; III: Hydrotaea (Ophyra) spinigera; IV: Saprinus splendens; V: Necrobia ruficollis (Fabricius); VI: Dermeses maculates; VII: Creophilus maxillosus. A: adult insect; L: larvae; +: fewer than 10 individual flies or 2 individual beetles; ++: between 10 and 50 flies or 2–10 beetles; +++: more than 50 flies or 10 beetles. Blanks, no individuals.
J. Wang et al. / Forensic Science International 179 (2008) 11–18
15
Table 5 Succession of necrophagous insects on carcasses in autumn PMI (d) 1 2 3
4
5
6
7
8
9 10 11
12
13
14
15
16 17
18
19 20
22
24 26
28
30
34 38
42
46
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+++ +
+
I A + + + + + + + L + +++ +++ +++ +++ ++
+
+
+
II A L
+ + + ++
+ ++
+ + + +++ +++ +++ +++ + +
+
+
+
++ ++ ++ +
++ +
III A L IV A L
+ +
++
++ +
++ ++ ++ ++ + +
+
+++ +++ + + + + +
+ +
++ + + +
++ + ++ +
++ ++ + ++ ++ +
+ +
+
+
+
+ +
+
++ ++ +++ ++ + + +
++ ++ + + ++ +
++ ++ + + +
+ +
+
+
+
+ +
+++ +
++ +
+
+ + + +
++ +
+ +
+ +
+ +
V A L VI A L
+
+
+
+
VII A L
+
+
+
+
++ +
+
+
+
+
+ + ++ +
+ ++ + + +++ +++ +++ +
+ + +++ +++
I: C. megacephala; II: C. rufifacies; III: Hydrotaea (Ophyra) spinigera; IV: Saprinus splendens; V: Necrobia ruficollis (Fabricius); VI: Dermeses maculates; VII: Creophilus maxillosus. A: adult insect; L: larvae; +: fewer than 10 individual flies or 2 individual beetles; ++: between 10 and 50 flies or 2–10 beetles; +++: more than 50 flies or 10 beetles. Blanks, no individuals.
Fig. 2. Change in the body-length of C. megacephala larvae with PMI in different seasons.
16
J. Wang et al. / Forensic Science International 179 (2008) 11–18
Table 6 Succession of necrophagous insects on carcasses in winter PMI (d) 0 13
1 a
2
19.5
a
3
21.5
a
16.5
4 a
14
5 a
6
14
a
7
20.0
a
8
22.0
a
9
23.5
a
10
23.0
a
20.5
11 a
14.5
12 a
17.0
13 a
14
22.3
a
15
24.0
a
23.5
16 a
24.0
17 a
24.3
18 a
25
19 a
20
23.5
a
25
22 a
22a
I A + L
+
A + L
+
+ +
+
+
+ +
+ +
+ ++
++ +++
++ +++
++ +++
++ +++
+++ +++
+++ +++
+++ +++
+++ +++
++ +++
+ + +++ +++
+ +++
+ +++
+ +
+ +
+ +
+ +
+ +
+ +++
++ +++
++ +++
++ +++
++ +++
++ +++
+++ +++
+++ +++
+++ +++
++ +++
+ + +++ +++
+ + ++++ +++
+
+
+
+
+
+
+
+
+
+
+
+ +
+ +
+
+
+
+
++
+++ +++
+++
+++
+
+
+
++
++
++
II +
III A L IV A L
+ +
V A L VII A L
+
++
PMI (d) 24 24
26 a
17
28 a
20
30 a
16.0
32 a
17
a
34
36
a
a
8
8
38 13.0
40 a
21.0
42 a
21.2
444 a
21.0
46 a
22.0
48 a
23.5
50 a
7
a
54 10
58 a
18
62 a
25
64 a
26.0
66 a
22.0
70 a
22.0
74 a
16.0
78 a
15.0a
I A + L +
+
+ ++
+ ++
+ ++
+
+
+
+
+
+
+
+ +
+
+
II A + + + ++ L +++ ++++ +++ +++
+ + +++ +++ +++ ++
+ +
+ +
+ +
+ +
+ +
+
A + L +
+ +++ +++ +++ +++
++ +++
++ +++
++ +++
+ +++
+ +++
+ + + +++ +++ +++ +++ ++
+++
+++
+++
+
+
+
+
+ +
+ +
+ +
+
+
+
+
+
+
+
+
+
+
III ++
+ ++ +++ +++
IV A +++ ++++ +++ +++ L +
++
+
+
+
+
V A + L VII A ++ L a
++
+++ ++
++
++
+++ +++ +
+++
+
+
+
+ +
+ +
+
+
Temperature (8C).
warm climates such as those of Hawaii [23], India [31] and Egypt [32]. Problems such as the diversity of necrophagous insects and the associated difficulty of identification, regional peculiarities of community composition, and cryptic behaviour of some species have made it hard for forensic entomologists to use ecological succession to estimate PMIs based on entomological evidence. On the other hand, oviposition, wandering, pupariation and eclosion are observed easily. The development of both fly and beetle larvae in corpses follows a reliable
pattern, thus providing the most important data for the estimation of a PMI. When estimating a PMI using insects, part of the problem is to know to which generation and cohort of colonisers the insect evidence belonged. Our results showed that necrophagous blowflies could produce only one generation on a carcass before it was desiccated or skeletonised. If rain moistened the carrion again, a second generation could colonise it, and this could be distinguished easily. Different species of blowflies appear at different stages in the succession.
a
1925 1.43 27.25 1.49 30.5 1.65 32.25 1.03
a
a
a
a
a
a a
2.83 0.24 15.25 1.43
2.6 0.21 15.03 1.11 a a 18 0.7 7.85 0.24 33.25 1.8 20 1.29 8.92 0.17 39 1.58 25.88 0.83 13.54 0.35 45 1.29 28.75 1.11 a 14.85 0.2 31.13 0.83 6.73 0.32
a a
a
0.83 0.08 4.29 0.12 a a 4.79 0.12 5.64 0.16 23.75 1.49 6.67 0.14 7.9 0.14 25.25 0.85 8.1 0.1 9.75 0.48 28.25 1.7 12 0.2 a 11.75 0.43 14.27 0.42 The phenomenon did not happen or was not easy to be observed. a
4.81 0.84
a a
a
0.88 0.05 4.13 0.13 a a 4.45 0.17 8.92 0.28 38 1.58 5.36 0.21 10.75 0.48 42.5 1.04 6.38 0.24 13.93 0.27 50.75 1.49 10.13 0.66 a 16.25 0.48 11.63 0.55 7.27 0.31
a a
a
Larvae appear 0.91 0.06 Start of wandering 5.5 0.28 Most larvae wandered 7.44 0.33 Start of pupariation 8.12 0.16 Most larvae pupated 9.06 0.16 Start of eclosion 13.5 0.65 End of eclosion 15.25 0.95
C. megacephala C. rufifacies H. spinigera C. megacephala C. rufifacies H. spinigera C. megacephala C. rufifacies H. spinigera C. megacephala C. rufifacies H. spinigera
Summer Spring Key events (d)
Table 7 The key events in the process of metamorphosis and development of larvae (mean S.E.)
Autumn
Winter
J. Wang et al. / Forensic Science International 179 (2008) 11–18
17
Furthermore, if carrion appears at night or in the morning, the number of larvae in the cohort from the first day is large because adult flies have a whole day to oviposit, but if it appears in the afternoon or evening, the cohort of larvae is smaller because adult flies have less time to oviposit, and the cohort produced the following day is larger, sometimes even masking the previous one. In carrion dominated by the first cohort of maggots, those larvae will out-compete the subsequent cohorts, and so dominate the carcass until pupation. Thus most of the larvae are roughly the same size. When the first day’s cohort is small relatively to the next cohort, it cannot significantly influence its successor, so that the second cohort becomes dominant and may even conceal the first group. This phenomenon should be studied further. Average larval body-lengths are greater in spring and summer than in autumn and winter. The reason may be that there is much rain in spring and summer and little rain or snow in autumn and winter [33]. Decomposition is a natural process that is affected by many confounding factors that diminish the accuracy and precision of estimates of PMI. Rather than expecting unrealistic accuracy from entomological information, which would undermine confidence in such evidence, we sought predictable key developmental events during the decay process of the carcasses. These events can divide the decay process into several stages. When a corpse is found, the developmental stage of the insects should be obvious, and from it a PMI can be estimated accurately in conjunction with other evidence such as the larval body-length or the development of pupae. In our study, blowflies were the most significant species, arriving at carrion soon after death in the warm seasons and up to 7 d later in winter. These flies’ developmental landmarks will help greatly in estimating short-duration PMIs. H. spinigera (Stein) are also important because they appear very late in the succession process and persist in corpses for a long time, so that their developmental landmarks will help to estimate mediumduration PMIs. Hermetia illuscens arrives at highly decayed or skeletonised corpses [34–37], its development will help to estimate longer PMIs. Beetles also very important, but adults are often cryptic, elusive and difficult to sample, and so have less forensic value that their larvae. Our future research will focus on larvae, especially the population ecology of beetle larvae. 5. Conclusion In south China, we found 47 species of insect on carcasses. Most of the necrophagous insects could be found on carcasses year round, and there was no obviously difference in community composition between the four seasons, although dermestid beetles were absent in winter. The decay process and succession patterns are similar to those found in other studies. Necrophages produced only one generation on carcasses in most conditions, which was useful in estimating PMIs because the key events in the simple succession pattern are easier to observe. The dominant species were very obvious, being larvae of C. megacephala and C. rufifacies, and dermestid and histerid
18
J. Wang et al. / Forensic Science International 179 (2008) 11–18
beetles. With the above information and knowledge of the development process of the flies, we can get several key developmental events. Although this method cannot estimate PMI precisely, it may be more useful in practical work. Immature stages were more useful in estimating PMI than the adults. Acknowledgements We thank Mark Benecke (Germany) and Martin H. Villet (South Africa) for their help in revising this paper. This study was supported by the National Natural Science Foundation of China (Grant No. 30100216). References [1] Y.F. Ma, C. Hu, A preliminary study on the constitution and succession of insect community on pig carcass in Hangzhou, Acta Entomol. Sin. 23 (1997) 375–380. [2] Y. Wang, M. Liu, D.H. Sun, A study on sarcosaphagous insects species variety with seasons in Chengdu, Fa Yi Xue Za Zhi 19 (2003) 86–87, 91. [3] H. Zhou, Y. Yang, J. Ren, L. Lu, S. Wang, R. Yan, Y. Li, Studies on forensic entomology in Beijing district. I. Sarcosaprophagous beetles and their local specificity, Acta Entomol. Sin. 40 (1997) 62–70. [4] J.B. Davis, M.L. Goff, Decomposition patterns in terrestrial and intertidal habitats on Oahu Island and Coconut Island, Hawaii, J. Forensic Sci. 45 (2000) 836–842. [5] M. Wolff, A. Uribe, A. Ortiz, P. Duque, A preliminary study of forensic entomology in Medellin, Colombia, Forensic Sci. Int. 120 (2001) 53–59. [6] B. Bourel, G. Torunel, V. Hedouin, Entomofauna of buried bodies in northern France, Int. J. Legal Med. 118 (2004) 215–220. [7] L.M.L. Carvalho, A.X. Linhares, Seasonality of insect succession and pig carcass decomposition in a natural forest area in southeastern Brazil, J. Forensic Sci. 46 (2001) 604–608. [8] M.S. Archer, M.A. Elgar, Yearly activity patterns in southern Victoria (Australia) of seasonally active carrion insects, Forensic Sci. Int. 132 (2003) 173–176. [9] M.I. Arnaldos, E. Romera, J.J. Presa, A. Luna, Studies on seasonal arthropod succession on carrion in the southeastern Iberian Peninsula, Int. J. Legal Med. 118 (2004) 197–205. [10] M. Turchetto, S. Vanin, Forensic entomology and climatic change, Forensic Sci. Int. 146S (2004) S207–S209. [11] G.S. Anderson, Initial studies on insect succession on carion in southwestern British Columbia, J. Forensic Sci. 41 (1996) 617–625. [12] C.P. Campobasso, G. Di Vella, F. Introna, Factors affecting decomposition and Diptera colonization, Forensic Sci. Int. 120 (2001) 18–27. [13] G.S. Anderson, The use of insects in death investigations: an analysis of cases in British Columbia over a five year period, Can. Soc. Forensic Sci. 28 (1995) 277–292. [14] M. Benecke, Six forensic entomology cases: description and commentary, J. Forensic Sci. 43 (1998) 797–805. [15] M.L. Goff, Estimation of postmortem interval using arthropod development and successional patterns, Forensic Sci. Rev. 5 (1993) 81–94.
[16] L.R. Lamotte, J.D. Wells, p-Values for postmortem intervals from arthropod succession data, J. Agric. Biol. Environ. Statist. 5 (2000) 58–68. [17] E.P. Catts, M.L. Goff, Forensic entomology in criminal investigations, Annu. Rev. Entomol. 37 (1992) 253–272. [18] M. Benecke, Forensic entomology: arthropods and corpses. Forensic Path Rev, vol. II, Humana Press, Totowa, NJ, USA, 2004, pp. 207–240. [19] M. Benecke, A brief history of forensic entomology, Forensic Sci. Int. 120 (2001) 2–14. [20] J.H. Byrd, J.L. Castner, Forensic Entomology: The Utility of Arthropods in Legal Investigations, CRC Press, Boca Raton/London/New York/ Washington, DC, 2001. [21] J. Amendt, R. Krettek, R. Zehner, Forensic entomology, Naturwissenschaften 91 (2004) 51–65. [22] E.P. Catts, N.H. Haskell (Eds.), 1990. Entomology and death: a procedural guide. Joyce’s Print Shop, Clemson, SC. [23] K. Tullis, M.L. Goff, Arthropod succession in exposed carrion in a tropical rainforest on O’ahu Island, Hawai’I, J. Med. Entomol. 24 (1987) 332–339. [24] H.B. Reed, A study of dog carcass communities in Tennessee with special reference to the insects, Am. Midl. Nat. 59 (1958) 213. [25] L.M. Lopes de Carvalho, A.X. Linhares, Seasonality of insect succession and pig carcass decomposition in a natural forest area in southeastern Brazil, J. Forensic Sci. 46 (May (3)) (2001) 604–608. [26] M. Bharti, D. Singh, Insect faunal succession on decaying rabbit carcasses in Punjab, India, J. Forensic Sci. 48 (September (5)) (2003) 1133–1143. [27] W.C. Rodriguez, W.M. Bass, Insect activity and its relationship to decay rates of human cadavers in east Tennessee, J. Forensic Sci. 28 (1983) 423. [28] S.L. Van Laerhoven, G.S. Anderson, Insect succession on buried carrion in two biogeoclimatic zones of British Columbia, J. Forensic Sci. 44 ((1) Jan) (1999) 32–43. [29] F.W. Avila, M.L. Goff, Arthropod succession patterns onto burnt carrion in two contrasting habitats in the Hawaiian Islands, J. Forensic Sci. 43 ((3) May) (1998) 581–586. [30] G.S. Anderson, N.R. Hobischak, Decomposition of carrion in the marine environment in British Columbia, Canada, Int. J. Legal Med. 118 (August (4)) (2004) 206–209, Epub 2004 May 29. [31] M. Bharti, D. Singh, Insect faunal succession on decaying rabbit carcasses in Punjab, India, J. Forensic Sci. 48 ((5) Sep) (2003) 1133–1143. [32] T.I. Tantawi, B. Greenberg, The effect of killing and preservative solutions on estimates of maggot age in forensic cases, J. Forensic Sci. 38 (1993) 702–707. [33] Cai WanZhi, General Entomology, China Agricultural University Press, Beijing, 2001. [34] M. Turchetto, Implicazioni entomologica-forensi dell’introduzione in Italia della mosca neotropicale Hermetia illuscens L. (Diptera: Stratiomyidae), Rivista taliana di Medicina legale 22 (2000) 1279–1290. [35] J.K. Tomberlin, D.C. Sheppard, J.A. Joyce, A comparison of selected lifehistory traits of the black soldier fly (Diptera: Stratiomyidae) when reared on three diets, Ann. Entomol. Soc. Am. 95 (2002) 379–387. [36] J.K. Tomberlin, D.C. Sheppard, J.A. Joyce, Black soldier fly (Diptera: Stratiomyidae) colonization of pig carrion in south Georgia, J. Forensic Sci. 50 (2005) 152–153. [37] W.D. Lord, M.L. Goff, T.R. Adkins, N.H. Haskell, The black soldier fly Hermetia illucens (Diptera: Stratiomyidae) as a potential measure of human postmortem interval: observations and case histories, J. Forensic Sci. (1994) 215–222.