Matthes Kai, Zehner Richard, Amendt Jens
Institute of Legal Medicine, University Hospital Frankfurt, Goethe-University, Kennedyallee 104, D-60596 Frankfurt am Main, Germany.
Institute of Legal Medicine, University Hospital Frankfurt, Goethe-University, Kennedyallee 104, D-60596 Frankfurt am Main, Germany.
Sci Justice. 2021 Sep;61(5):579-585. doi: 10.1016/j.scijus.2021.06.005. Epub 2021 Jun 16.
One of the main tasks in forensic entomology is the determination of the minimum post-mortem interval (PMI) based on the age of the juvenile insects feeding and developing on the dead body. An important task is to store the evidence appropriately so that the evaluation and expert report can be used in court. However, existing recommendations can be contradictory or lacking scientific validation, e.g. by proposing various preservation liquids without knowing whether and to what extent the period of storage in such a liquid has an effect on the length of the preserved larvae. Storage time can be an issue since, due to technical and procedural circumstances, killed larvae may be stored for hours, days, weeks or even longer prior length measurement. A changed body length would have consequences for the entomological report, as the age of the larvae is usually derived from their length. This study investigates the effect of four differently concentrated ethanol solutions (70%, 80%, 90% and 96%) during a storage period of up to 196 days on the body length of stored larvae of the forensically important blow fly species L. sericata (Diptera: Calliphoridae). Larvae of different ages (24 h, 48 h and 72 h after hatching) were killed by immersion in hot, non-boiling water (≥80 °C) for at least 30 s. Their lengths were measured immediately. Subsequently samples were stored in ethanol of appropriate concentration at room temperature (approx. 22 °C). Further length measurements were made at 16 different storage intervals between 1 and 196 days. Many specimens showed a length decrease for most storage conditions and all larval ages. However, there was a tendency for 48 h- and 72 h-old larvae to increase in length after the first days of storage of up to 1.1 mm which may lead to an erroneous overestimation of the PMI using this kind of specimens. All changes in length within each cohort over total time were in the range of +7% to -9.1%. Significant differences in length changes within the first days of storage were found mainly in larvae stored in 70%- and 80%-ethanol, but larvae stored in 90%- and 96%-ethanol showed first significant differences on day 56 at the earliest. Our results lead to the recommendation that the measurements of fly larvae samples should be taken immediately after killing and before storage to avoid any effects. Ethanol ≥90% should be used for storage.
法医昆虫学的主要任务之一是根据在尸体上取食和发育的幼虫的年龄来确定最短死后间隔时间（PMI）。一项重要任务是妥善保存证据，以便评估和专家报告能在法庭上使用。然而，现有建议可能相互矛盾或缺乏科学验证，例如提出各种保存液，但却不知道在这种液体中的保存时间是否以及在多大程度上会对保存幼虫的长度产生影响。由于技术和程序方面的情况，被杀死的幼虫在进行长度测量之前可能会被保存数小时、数天、数周甚至更长时间，因此保存时间可能成为一个问题。体长的变化会对昆虫学报告产生影响，因为幼虫的年龄通常是根据其体长推断出来的。本研究调查了四种不同浓度的乙醇溶液（70%、80%、90%和96%）在长达196天的保存期内对法医重要的丝光绿蝇（双翅目：丽蝇科）保存幼虫体长的影响。将不同年龄（孵化后24小时、48小时和72小时）的幼虫浸入热的、非沸腾的水中（≥80°C）至少30秒将其杀死。立即测量它们的长度。随后将样本在室温（约22°C）下保存在适当浓度的乙醇中。在1至196天之间的16个不同保存间隔进行进一步的长度测量。在大多数保存条件下以及所有幼虫年龄组中，许多样本都出现了体长下降。然而，48小时和72小时大的幼虫在保存的头几天之后有体长增加的趋势，最多增加1.1毫米，这可能会导致使用这类样本错误地高估PMI。每个队列在总时间内的所有体长变化范围在+7%至 -9.1%之间。在保存的头几天内，体长变化的显著差异主要出现在保存在70%和80%乙醇中的幼虫中，但保存在90%和96%乙醇中的幼虫最早在第56天才出现显著差异。我们的研究结果建议，蝇幼虫样本的测量应在杀死后、保存前立即进行，以避免任何影响。应使用≥90%的乙醇进行保存。
