The nocturnal oviposition behavior of blow flies (Diptera: Calliphoridae) and its applications on forensic entomology
Date Issued
2010
Date
2010
Author(s)
Tai-You, Chen
Abstract
One of the most common applications of forensic entomology is estimating the time since death (post-mortem interval). There are two basic ways to estimate the PMI. One is based on the degree of development of fly maggots and another is on the succession of arthropod species. Blow flies discover the corpse and lay eggs soon after death or corpse exposure. Thus the time of oviposition is only an approximation. The time of death estimated by the degree of development of fly maggots, in other words, is the earliest time the fly oviposit on the corpse. It is widely held that blow flies are not active at night and do not lay eggs during that time. However, some researches presented evidences of nocturnal oviposition by many forensically important blow fly species, including the dominant necrophagous blow flies in Taiwan, such as Chrysomya megacephala and Chrysomya rufifacies. Nocturnal oviposition can alter the usual estimate of the PMI in homicide cases by as much as 12 hours. Our field experiments showed that the blow flies oviposited eggs during the diurnal hours and did not ovposit during the nocturnal period between 21:00-05:00 in the October, January, April/May and July studies, and different dominant blow fly species appeared in different seasons. During our field experiments, the temperature and light intensity in the diurnal periods were significantly higher than that in the nocturnal periods. Even the temperatures recorded in night are optimal for oviposition, the oviposition didn’t occur. In diurnally active flies, locomotor activity shows a robust circadian rhythm, so that blow flies wouldn’t active and oviposit at night under natural conditions. The blow flies we used for indoor experiments were Chrysomya megacephala, the dominant species in Taiwan. The nocturnal oviposition occurred under lab conditions with switched photoperiods (12L/12D, 24D). The percentages of samples and the numbers of eggs were reduced when compared to the daytime. The indoor results reveal that density of flies, artificial light, rising temperature are the parameters that stimulate female Chrysomya megacephala to lay eggs at night.
Subjects
forensic entomology
Chrysomya megacephala
post-mortem interval
nocturnal oviposition
SDGs
Type
thesis
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