Volume 48(6):41‑47, 2008 Rearing five species of Diptera (Calliphoridae) of forensic importance in Colombia in semicontrolled field conditions María C. Vélez1 Marta Wolff1,2 ABSTracT The family Calliphoridae is widely known to lead the colonization of corpses and their development rates are frequently used to estimate the postmortem interval. This study presents the larval growth of five forensically important species of Calliphoridae in Colombia. Rearing took place in semicontrolled field conditions where the egg masses were collected. We show curves of larval growth, larval length and time intervals to reach all immature stages for Lucilia eximia and Cochliomyia macellaria at two sites with different climatic conditions and for Chrysomya albiceps, Chrysomya megacephala and Calliphora nigribasis at one site. Overall, high temperatures speeded up the development of the species reared at two different sites, whereas low temperatures for C. nigribasis, lengthened the total development time. Differences between this study and others can be explained by the experimental conditions in the field without the possibility of strict laboratory rearing controls. Keywords: Lucilia eximia, Cochliomyia macellaria, Chrysomya spp., Calliphora nigribasis, larval growth. INTRODUCTION mologist to make more positive species identifica‑ tions, particularly with fly larvae as definitive species The estimation of postmortem interval is the determination cannot be made given the lack of dis‑ main application of forensic entomology. Therefore, tinct morphological differences. It also allows a clear‑ major knowledge requirements are the species associ‑ er determination of the postmortem interval (PMI) ated with decomposing corpses in different biogeocli‑ since rearing of subsequent life stages provides a better matic zones, their development rates with emphasis approximation of the development stage of the insects on development times of each immature stage (Tur‑ at the time of collection (Byrd, 2001). chetto et al., 2001) as well as lengths and weights of Larval lengths or weights can be used to estimate the different larval stages (Wells & Lamotte, 2001). PMI under two approaches. The first is to measure The laboratory rearing of insects collected from the accumulated amount of days or hours needed a death scene is an integral component of the analysis to reach a particular stage of development (Ames & of entomological evidence. Rearing allows the ento‑ Turner, 2003) and the second is the use of an iso‑ 1. Grupo de Entomología, Universidad de Antioquia. A.A. 1226, Medellín, Colombia. 2. Corresponding author: Marta Wolff, Dr.Sc., Instituto de Biología, Universidad de Antioquia, A.A. 1226, Medellín, Colombia, Tel. (576)2105662. E‑mail: [email protected] 42 Vélez, M.C. & Wolff, M.: Rearing Calliphoridae in semicontrolled conditions megalen diagram, i.e. matching the size of the larvae Chingaza National Park (paramo zone) is at found on the corpse with the development rates for 3035 m above sea level, it has an average temperature the same blowfly larvae experimentally reared at the of 10°C and relative humidity superior to 80% (IN‑ seasonal average temperature in which the body was DERENA, 1986). found (Introna et al., 1989). However, field tempera‑ The egg masses of approximately 100 to 130 in‑ tures are rarely constant and it has been shown that dividuals were placed in plastic jars with 150 g of beef fluctuating temperature has a great effect on larval liver. The jars were placed in containers of polystyrene development (Introna et al., 1989). to avoid contamination with other insects, to mini‑ The family Calliphoridae is known as the initial mize drastic changes in temperature and to eliminate colonizer in the faunal succession on human cadavers the effects of sun exposure. The larvae did not have a (Smith, 1986). Therefore, they are the primary and light source within the containers. most accurate forensic indicators of time of death Each plastic jar was sampled as follows: the time and their development rates are needed to allow more was noted at the moment of egg collection (we as‑ precise PMI estimates (Grassberger & Reiter, 2001). sumed this moment to be oviposition). During the Thus, it is necessary that the development rates for first 36 hours, we observed the moment of eclosion the species involved in decomposition be known for and removed samples every three hours between 7 am the same conditions of temperature at the possible and 7 pm in order to get sufficient larvae at the first crime scene (Introna et al., 1989). stage of development. These larvae growth faster and The main purpose of this study was the rearing observations need to be made at shorter intervals in situ of the first species to colonize pig corpses in (Krüger et al., 2003). After the first 36 hours, sam‑ decomposition in four different bioclimatic zones in pling continued every six hours. The samples consist‑ Colombia. This is the first approach to the applica‑ ed of ten larvae per plastic jar at all of the evaluated tion of larval growth as a tool in PMI estimates. sites, except Medellín, where each sample consisted of four larvae. When the larvae reached the postfeed‑ ing stage, we placed sawdust in the jars (Dale & Pru‑ MATEriaL AND METHODS dot, 1986) and made observations every 12 hours to verify the presence of pupae and the emergence of All of the eggs were collected on pigs (by per‑ adults. During the postfeeding stage we stopped the mission of the Ethical Committee of Universidad de sampling to prevent handling just before pupation at Antioquia, Medellín) in the early stages of decompo‑ which time development can be delayed or blocked sition and larvae were reared at the same site as the (Anderson, 2000). The container and environmental corpses. temperatures were measured at each sampling time The study was carried out at four sites: Tintipán and the average temperature of rearing was calculated Island, municipality of Gomez Plata, city of Medellín from these data. and Chingaza National Park. All of the samples were fixed in 80% ethanol Tintipán Island (beach environment) is located and examined under a binocular stereoscope to iden‑ off the Caribbean coast within the San Bernardo ar‑ tify the species with the use of different keys (Shewell, chipelago. The area is designated as tropical very dry 1981; Dear, 1985; Smith, 1986; Wells et al., 1999). forest (bms‑T) (Holdridge, 1987), with mangroves as All larvae were measured (total body lengths) and the predominant flora, it has an altitude of 2 m above the accumulated time of development was calculated sea level, an average rainfall of 1000 mm and an aver‑ for all the instars for all the sample jars. Line graphs age temperature of 27°C. of larval growth, with intervals for the ages (in hours) Gomez Plata (rural environment) is located at and the lengths of each immature stage were plotted 75 km from Medellín. It is designated as tropical pre‑ using JMP 3.2.2 (SAS Institute Inc., 1997). All insect montane wet forest (bmh‑P) (Espinal, 1985). The site material was deposited in the Entomological Collec‑ is open pasture used by cattle, at 1080 m above sea tion of the Universidad de Antioquia in Medellín. level with an average temperature of 25°C, relative hu‑ midity of 80% and an average rainfall of 1800 mm. The city of Medellín (urban environment) is RESULTS designated tropical premontane moist forest (bh‑P) (Holdridge, 1987). It is located at 1450 m above sea During this study, five species belonging to Cal‑ level with an average temperature of 24°C and an av‑ liphoridae were reared: Lucilia eximia (Wiedemann, erage rainfall of 1409 mm. 1819), Cochliomyia macellaria (Fabricius, 1775), Papéis Avulsos de Zoologia, 48(6), 2008 43 Chrysomya albiceps (Wiedemann, 1819), Chrysomya (Fig. 2), whereas the lengths of third instar larvae of megacephala (Fabricius, 1794) and Calliphora nigriba- C. macellaria showed overlapped intervals between sis Macquart, 1851. L. eximia and C. macellaria were beach environment at 30.74°C and rural environ‑ reared at two different sites with different temperature ment at 25.30°C (Fig. 3, 4 and Table 2). Instead, the regimes (L. eximia at 23.13 ± 2.45°C, in Medellín postfeeding larvae characterized by a decrease in size and 25.30 ± 3.26°C, in Gómez Plata; C. macellaria at (Greenberg & Kunich, 2002) (Figs. 3 and 4), showed 25.30 ± 3.26°C, in Gómez Plata and 30.74 ± 0.71°C, narrower and not overlapped intervals for the length in Tintipán). C. albiceps, C. megacephala and C. nigri- (Table 2). basis, were reared at 25.30 ± 3.26°C, in Gomez Plata, With regard to the accumulated time of devel‑ 23.13 ± 2.45°C, in Medellín and 10.62 ± 2.51°C, in opment for immature individuals to reach all instars Chingaza, respectively. (Table 3), we observed that L. eximia exhibited suc‑ In all cases, development time for the eggs and cessful growth for all larval instars in both rearings, the moment of eclosion was obtained (Table 1). For according to the larval growth curves (Figs. 1 and L. eximia, C. macellaria, C. albiceps and C. megaceph- 2). However, we did not obtain pupae or adults. At ala, the eclosion was near to 15 hours subsequent to the oviposition, whereas C. nigribasis needed 64 TaBLE 1: Time of eclosion (in hours) of the species at all hours. development temperatures. The larval growth represented by the progressive Species Temperature (°C) Egg duration (h) increase in length is showed in larval growth curves Lucilia eximia 23.13±2.45 15.16±0.77 (Figs. 1‑7). The average and standard deviations of the Lucilia eximia 25.30±3.26 16.42±2.31 lengths and the development times guarantee the fact Cochliomyia macellaria 30.74±0.71 15.80±2.91 of find a larva in a particular stage (Table 2 and 3).