A forensic entomologist finds third-instar larvae of Calliphora vicina on a body. The known development time from egg to third instar at an average temperature of 20°C is 96 hours. However, the accumulated degree days (ADD) method is preferred. If the developmental threshold for Calliphora is 3°C and the average daily temperature has been 18°C, the ADD for third instar completion (96 hours at 20°C) expressed in degree days is approximately:
- A 80 ADD
- B 34 ADD
- C 68 ADD ✓
- D 96 ADD
Correct answer: C. 68 ADD
Explanation
ADD = (mean temperature − base threshold) × days. At 20°C with a threshold of 3°C: (20 − 3) × 4 days = 68 ADD. The ADD method standardises development time across varying temperatures, allowing accurate PMI estimation regardless of daily temperature fluctuations. Option A incorrectly uses 20 as the base without subtracting the threshold; option D confuses hours with degree-days.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.