Mosquito Blood Feeding as an Indicator for Estimating the Time of a Crime Using PCR Analysis
Abstract
Blood-fed female mosquitoes can carry human DNA away from a crime scene, but that DNA does not last. This study measured how long human DNA stays amplifiable inside the blood meal of Culex sp. Eighteen fully engorged females were fed on a human host under controlled laboratory conditions and were held in three post-feeding groups of six (24, 48 and 72 h). A further 20 extracts were prepared, 10 from human-fed and 10 from rat-fed mosquitoes. Each abdomen was dissected, homogenised in phosphate-buffered saline and processed on a silica-membrane spin column. DNA yield and purity were measured by UV spectrophotometry, and the first hypervariable region (HVR1) of the human mitochondrial control region was amplified by PCR. Products were resolved on ethidium bromide-stained agarose gels. Mean DNA yield was 86.00 ± 22.71 ng µL⁻¹ with a mean A260/A280 ratio of 1.90 ± 0.04 for the time-course extracts, and 47.60 ± 12.38 ng µL⁻¹ with a ratio of 1.90 ± 0.10 for the human- and rat-fed set. A clear 343 bp HVR1 product was obtained from every sample at 24 h. At 48 h the product was faint and was seen in only part of the samples. At 72 h no product was obtained. Human DNA in a mosquito blood meal is therefore recoverable within a short and definable window, and the chance of a result falls sharply after 48 h. The finding sets a practical collection deadline for investigators who plan to use blood-fed mosquitoes as biological evidence, and it supports the use of forensic entomology as a complement to conventional trace evidence in death-scene and identification casework.
Keywords:
Culex sp., forensic entomology, blood meal, human mitochondrial DNA, HVR1, post-feeding interval, PCR, DNA degradationDOI
https://doi.org/10.70604/jmtbas.v3i2.227References
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