The Effect Of Ketamine On The Development Of Chrysomya Megacephala (Diptera: Calliphoridae) For Forensic Appli Cations

Background and Objective Drugs are involved in a large number of overdose death in recent years. Since the presence of some drugs or toxicants can affect the development rate of the larvae of necrophagous flies feeding on the corpse, this inFLuence should be taken into consideration in estimation of the postmortem interval (PMI) of drug-related death. Deaths caused by ketamine are very common in new drugs. The application of development duration of Chrysomya Megacephala for the minimum PMI estimation is well documented and widely accepted. There is no previous study of the effect of ketamine on the development of Chrysomya megacephala at present. The objective of this study is to research the pattern of larvae and pupae development when exposed to ketamine and provide a basic data for forensic entomotoxicology. The achievement of this study can be used to guide the estimation of the PMI of death relevant to ketamine in judicatory practice.Methods Eggs oviposited by Chrysomya megacephala in natural environment were collected and reared in the laboratory for 3 generations at a constant temperature. The larvae used in this study were obtained from colonies established from eggs of the 3rd generation. The larvae were reared in artificial diets containing different ketamine hydrochloride concentrations (K₀, 0 mg/kg; K₁, 25 mg/kg; K₂, 50 mg/kg; K₃, 100 mg/kg). Egg batches from each adult were divided equally into 4 sections and were deposited on the above-mentioned artificial diets. The container of the diets were maintained in a controlled temperature room at 32℃, and a 12h:12h light cycle. Take the oviposition time as hour 0 of the developmental time of C. megacephala. Every 12h, 10 larvae samples were randomly collected from each group from hour 16 to prepupal period. The larvae samples were put to death with XA solution, and were preserved in Hood's solution. The larvae samples were individually measured and totally weighted, as an indicator of the development rate. The length data were recorded with the form of mean±SD, and the weights data were only recorded the mean. The growth curves were established with all of the above-mentioned data. Observed and recorded the time of most larvae (>95%) left food, most larvae (>95%) pupated and most pupae (>95%) emerged. The average length, the average weight, developmental time, the accumulated degree hour and the emergence rates were calculated and analyzed with Excel 2007. ANOVA was used to analyze if there were any differences of the above-mentioned data between the control group and the experimental groups. The experiments were repeated at 28℃and 24℃. ResultEffect of Different Ketamine Concentrations on Development RateLarvae of Chrysomya Megacephala exposed to ketamine showed a decrease of development rate, with higher drug concentrations further retarding the development. For the tested range, ketamine made the growth rate of larval length decrease by 20.0% at most, and the growth rate of larval length decrease by 23.1%. There was no significant difference of the maximum average length between the control group and the experimental groups. The maximum average weight between the control group and the experimental groups also showed no significant difference except 32℃. Effect of Different Ketamine Concentrations on Emergence RateThe emergence rates revealed that there was no difference in statistics among the various ketamine concentrations, while the emergence rates of any concentrations of ketamine were obvious lower than the control group only at 24℃. The emergence rate of experimental groups at 24℃decreased by 41.3% and 36.4% compared with those at 32℃and 28℃.Effect of Different Ketamine Concentrations on Developmental Time and Accumulated Degree Hour (ADH)Larvae of Chrysomya Megacephala exposed to ketamine showed an increase of developmental time and ADH, with higher ketamine concentrations further enhancing them at the tested range. The 1^st～3^rd instar period of larvae exposed to ketamine was the most significantly prolonged at 32℃and 24℃, whereas the pupal period was the most prolonged at 28℃.The results of this study indicated that it is more precise to estimate PMI in death cases without drugs with ADH, while development rate is better to be used in PMI determination in those drug-related deaths.ConclusionThis study obtained the data of the effect of ketamine on the development of C. Megacephala for the first time. The results indicated that the larvae of C. Megacephala exposed to ketamine of the tested range showed development rate of a decrease of development rate, with higher ketamine concentrations further retarding the development. The emergence rates of any concentrations of ketamine were obvious lower than the control group only at 32℃.The developmental time and ADH were also prolonged and further enhanced with higher ketamine concentrations. In general, the strong negative influence of C. Megacephala caused a 25h delay in the development. The difference between larvae and pupae stage duration together would prolong the estimation of PMI up to 44h.