For a very long time now, it has been common knowledge that blowflies do not oviposit in the dark. Owing to the great role played by the oviposition of blowflies in forensic science and the determination of the Postmortem Interval (PMI), understanding the nocturnal oviposition behaviour of blowflies has proved to be very important. In the recent past, however, contradictory studies have been conducted to challenge the long-held knowledge creating a lot of uncertainty and oblivion in forensic entomology.
This essay is geared towards bringing into limelight the nitty gritty about the oviposition of blowflies and creating an in-depth understanding of nocturnal oviposition conduct of blowflies and the impact it has in the determination of the Postmortem Interlude within forensic science.
Blow Flies Do Not Oviposit During the Night Time
According to a study done by Baldridge, diurnally lively flies dont oviposit through the
night (Baldridge et al., 2006, 125-126). With the night time being defined as the period between 2100hrs 0600hrs, he demonstrated that blowflies were to a large extent inactive at this time and did not oviposit on the baits of freshly killed mice, beef, and pigs.
His sentiments were further echoed by Stamper who also performed a study research in Ohio, on the nocturnal behaviour of blowflies on dead rats, and he was of the opinion that the ideological line of Greenberg (1990, 807-810) was not correct and that blowflies do not oviposit in the night time. (Stamper et al., 2009, 1450-1482)
Whilst environmental conditions are purported to play an influential role in the oviposition of blowflies, optimal ranges of air temperature, relative humidity and windspeed provided in the night time did not warrant the oviposition of blowflies (Baldridge et al., 2006, 125-126). In another study that sought to determine the nocturnal oviposition and flight of flies on carcasses of pigs and freshly cut liver in Michigan, findings showed that nocturnal oviposition is highly improbable even under the favourable weather, temperature, and light conditions (Zurawski, Benbow, Miller and Merritt 2009, 671 - 678). The four scientists also brought into light another aspect that affected nocturnal oviposition and this is flight. They shared the ideology that nocturnal flight activity was very minimal and in any case, the flies would crawl to the carcass. Thus, minimal flight activity would actually mean negligible nocturnal oviposition. (Zurawski, Benbow, Miller and Merritt 2009, 671 - 678). This challenged the findings presented by (Greenberg, 1990, 808 - 810)Blow Flies Do Oviposit During the Night Time
As years went by, the long-held fact that blowflies do not oviposit at night came to be challenged.
Greenberg, a well-renowned fly biologist, performed studies with 3 forensically important blowflies and showed that they would oviposit in the darkest hour of the night in the presence of a dim light. He made use of the artificial light to simulate a daylight condition for the blowflies. In line with this, he suggested that nocturnal oviposition of blowflies would take place more in urban areas than in rural areas, where the presence of streetlights would simulate daylight conditions. Greenberg (1990, 807-810).
The analogy was later backed up by Singh and Bharti (2001), who showed that Calliphoridae does lay eggs at night using the thawed mutton as bait for the blowflies. With an aim to deal with the shortcomings of Greenbergs experiment that had made it easy for the flies to crawl to the bait, the two now ensured that the flies were attracted to the mutton by flight and recorded 33% success rate as that of Greenberg thus confirming that blowflies would oviposit at night.
A laboratory test conducted by Wall and Fisher, which sought to determine the relationship between olfactory and visual cues in the landing responses of the blowfly Lucilia sericata (Diptera: Calliphoridae) in a wind tunnel, showed that the odour of liver and sodium sulphide solution released at 1 L/min, resulted in a greater number of landings which was more or less near the central odour release point, than when odour was absent. (Wall & Fisher 2001, 212 218) This study further supported the fact that blow flies do not oviposit during the night due to their landing responses.
The oviposition of Blow Flies in determining the Postmortem Interval (PMI)
The oviposition of blowflies plays a significant role in the determination of the PMI and this is why it makes it so important to understand their oviposition behaviours.
In forensic entomology, when the age of insect larvae is used to estimate the minimum Postmortem Interval (PMI), knowledge of the factors that are likely to delay the time between death and oviposition will clearly be of critical importance. (Wooldridge, Scrase & Wall 2007, 94 97). Taking into account that there has been an unending debate on the nocturnal activity of blowflies, it raises a lot of speculation on what happens in the periods of darkness.
Supposing we say that blowflies do not oviposit during the night, a body left exposed at night would not attract flies until the next morning. This, therefore, creates a pre-existing gap while determining the PMI of the body. It would be difficult to establish the exact PMI. (Wooldridge, Scrase & Wall 2007, 94 97)
On the other hand, if studies supporting the presence nocturnal oviposition are anything to go by, it would be difficult to mimic the favourable conditions for the same in a real-life case scenario. As a matter of fact, these studies revealed relatively low possibilities of nocturnal oviposition. (Zurawski, Benbow, Miller and Merritt 2009, 671 - 678).
In conclusion, A more thorough knowledge of oviposition behaviour by blowflies should allow for a more precise characterization of the postmortem interval (PMI) in forensic investigations. (Baldridge et al., 2006, 125-126). If the arising knowledge of nocturnal knowledge was to be adopted, this would greatly affect the accurate estimation of PMI. It is a question of whether the new knowledge is feasible or not. However, as it stands, the determination of the Postmortem Interval should be solely based on the knowledge that active blow flies do oviposit during the day and not at night.
Baldridge, R.S., Wallace, S.G, & Kirkpatrick, R. 2006. Investigation of nocturnal oviposition by necrophilous flies in central Texas. Journal Forensic Sciences 51(1): 125126.
Faucherre, J., Cherix, D. and Wyss, C. (1999) Behavior of Calliphora vicina (Diptera, Calliphoridae) under extreme conditions. Journal of Insect Behavior 12(5): 687-690.
Greenberg, B. 1990. Nocturnal Oviposition Behaviour of Blow Flies (Diptera: Calliphoridae). Journal of Medical Entomology 27(5), pp. 807810.
Singh, D. and Bharti, M. (2001) Further observations on the nocturnal oviposition behaviour of blow flies (Diptera: Calliphoridae). Forensic Science International 120(1-2): 124-126.
Stamper, T., Davis, P., & DeBry, R. (2009) The nocturnal ovipositing behaviour of carrion flies in Cincinnati, Ohio. Journal of Forensic Sciences 54(6): 1450-1452.
Wall, R. and P. Fisher (2001) "Visual and olfactory cue interaction in resource-location by the blowfly, Lucilia Sericata." Physiological Entomology, vol. 26, pp. 212-218.
Wooldridge, J., Scrase, L. and Wall, R. (2007) Flight activity of the blowflies, Calliphora vomitoria and Lucilia Sericata, in the dark. Forensic Science International 172(2007) pp. 9497.
Zurawski K.N., Benbow M.E., Miller J.R. & Merritt R.W. (2009) Examination of nocturnal blow fly (Diptera: Calliphoridae) oviposition on pig carcasses in Mid-Michigan. Journal of Medical Entomology 46(3), pp. 671-679.
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