Use of the CO I Gene as a Species Indicator for Forensically Important Flies - A Forensic Entomology Laboratory Exercise

Oct 15, 2026

Uploaded by Blitz

Forensic entomologists use insects—especially flies—to estimate the postmortem interval between death and body discovery, but this depends critically on correctly identifying the fly species. The exercise contrasts traditional morphological identification with faster, more reliable molecular approaches using mitochondrial DNA. Students apply CO I gene–based methods to generate DNA sequence data that supports building a molecular database for California forensic fly species while strengthening core molecular biotechnology skills.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages4

Reading Time10 min

AccessFree to download

Abstract

Introduction

Postmortem interval and fly development

Species identification challenges and molecular alternatives

Materials and Methods

Field collection and trap design

Specimen preservation and data recording

Use of the CO I Gene as a Species Indicator for Forensically Important Flies: A Forensic Entomology Laboratory Exercise Jeffrey Y. Honda Dept. of Biological Sciences, San Jose State University, One Washington Square San Jose, CA 95192-0100 Email: [Jhonda@email.sjsu.edu](Jhonda@email.sjsu.edu) Abstract: Forensic entomologists utilize insects (particularly flies) to establish the time interval between death and body discovery. This important piece of information may answer questions as to the circumstances of the individual’s death and insects are now routinely utilized and recognized as being important forensic indicators. Of extreme importance is the correct identification of the fly species associated with the body, as misidentifications will cause inaccurate time of death estimates. Traditional fly identification methods rely on recognizing distinct physical traits each fly species may possess; however, this has given way to molecular techniques (i.e. DNA sequences) that are quicker and more reliable. Unfortunately no DNA sequence information exists on the forensically important fly species in the western U.S. although a molecular database has been advocated by a number of forensic entomologists. This laboratory experience allows students to develop general molecular based skills they will need later in their careers while simultaneously contributing data that will be used to create a molecular database containing DNA sequences for forensically important California flies. Keywords: forensic entomology, undergraduate biotechnology laboratory, molecular techniques Introduction Medicocriminal entomology examines the utility of insect evidence in solving crimes, most often violent crimes including homicides. One of the most crucial pieces of information is determining the time elapsed since death, or postmortem interval (PMI) . Under most circumstances, this can be determined by a medical examiner as bodies generally are found within 48 hrs and indicators such as rigor mortis, algor mortis, or livor mortis can be used to determine PMI. However, bodies may often lie undiscovered for many days or months and those methods become less reliable. It has long been known that insects associated with remains display PMI-dependent processes, which includes the development of insect species whose larvae consume dead tissue. Thus, a PMI estimate can be based on the oldest developmental stage of an immature insect found on a body. Due to their size, numbers, and ubiquity, flies (i.e. Muscidae, Sarcophagidae, and Calliphoridae) are most noticeable and commonly found insects when a body is discovered. The most limiting factor in using flies as a PMI indicator is proper species identification as different fly species differ in terms of growth rate and arrival time on a body. Typically, identification is done through morphological examination of important setae (hairs) found on the body. This is a tedious, and often impossible prospect as many of these setae break off. More recently, forensic entomologists have advocated using DNA sequences and it appears that the cytochrome oxidase (CO) I gene in the mitochondria is excellent in discriminating species and would allow non-entomologists to easily identify flies based on their DNA sequences (Malgorn and Coquoz 1999; Sperling et al. 1994; Wells and Sperling 1999) . Although some work has been performed on a few common species found in the eastern U. S., no work has been attempted on flies found in the western U.S. The Department of Biological Sciences at SJSU now offers a course in forensic entomology (Entomology 106) that serves undergraduate biology majors and criminal justice administration majors with a concentration in biology forensics. This course examines the science and methodology used to collect, analyze, and present information regarding insects and other arthropods that are important in legal investigations. The majority of the laboratory component is devoted to the c

FAQs

Why is fly species identification crucial in forensic entomology?

Because different fly species differ in growth rate and arrival time on a body, misidentification leads to inaccurate estimates of the postmortem interval.

What gene and molecular approach does the laboratory exercise emphasize?

The exercise focuses on using the mitochondrial cytochrome oxidase (CO) I gene and molecular techniques to discriminate fly species using DNA sequences.

How do students collect and preserve flies for the exercise?

Students construct bottle-based fly traps, bait them with raw meat, record date and location, and preserve collected flies in 95% ethanol for downstream molecular analysis.

Oct 15, 2026

Uploaded by Blitz