Study of Life Cycle of Blowfly as an Indicator of Postmortem Interval: A Longitudinal Prospective Study

The main objective of a medicolegal autopsy is determination of the postmortem interval. In fresh bodies and in early stages of decomposition, it does not pose a major problem and can be easily calculated from various postmortem changes. However, sometimes it becomes very difficult to calculate postmortem interval in late stages of decomposition. Bodies after death are attracted by various arthropods mainly of Order Diptera, commonly called as blow flies. These flies lay eggs on the body, which transform into adult flies after a fixed period of time. Study of the life cycle of these insects can help in accurate determination of postmortem interval in putrefied bodies.

The objective of this study was to establish a relationship between the different stages of life cycle of blow fly and the time since death.

Eggs/larvae/pupae/adult insect of blow fly specimens flying or crawling over dead bodies were collected from 40 postmortem cases and were reared by transferring to 500 ml transparent glass beaker partially filled with sterilised sand. The glass beakers were observed daily for emergence of adults and development period was noted. The emerged adults were preserved by dry mounting for identification.

Time taken for development from eggs to first instar larvae varied from 10 hours to 24 hours; from 1^st instar larvae to 2^nd instar larvae in 12 hours to 48 hours; from 2^nd instar larvae to 3^rd instar larvae in 18 hours to 48 hours; from 3^rd instar larvae to pupa in 62 hours to 140 hours; and from pupa to adult in 60 hours to 120 hours. Conclusion: By ascertaining the stage of development of blow fly, the time since death can be calculated in expert hands.