早期腐敗對麗蠅產卵之影響

Abstract

當麗蠅停在屍體上決定要產卵並拓殖 (colonize) 到屍體上時，同時也啟動了麗蠅的生命週期，生命週期的開始與結束也將會在屍體上完成。人們可以將這些重要的資訊應用在刑事調查的死後間隔時間 (Post-mortem interval, PMI) 之估算。從死亡發生到麗蠅完成其生命週期的屍體腐敗過程可以分為五個階段，屬於前拓值期 (pre-colonization stage) 的暴露期 (exposure phase)、偵測期 (detection phase) 和接受期 (acceptance phase); 屬於後拓值期 (post-colonization stage) 的消耗期 (consumption phase)以及散佈期 (dispersal phase)。先前大部分的研究主要都致力於後拓值期，不同因子對幼蟲和成蟲生長發育的影響 (如溫度、濕度等等…)。然而前拓值期的研究也是很重要，卻十分的缺乏。此研究主要針對大頭金蠅 (Chrysomya megacephala) 的接受期進行研究。接受期的定義為麗蠅找到屍體到決定產卵的這段時期，產卵延遲會導致接受期的延長，進而導致PMI估計的偏差。在此研究中，我們假設不同腐敗程度的豬肝可能會影響大頭金蠅對產卵的決定。在野外試驗中，當我們使用不同腐敗程度的豬肝當做產卵基質時，結果顯示在不同處理間的卵數具有顯著差異 (新鮮~腐敗8天)。而在偏好實驗中，不同的處理間的卵數也具有顯著差異(新鮮、腐敗2天、腐敗4天、腐敗6天、腐敗8天)。我們的結果指出不同腐敗程度確實會影響麗蠅的產卵；而當我們提供單一腐敗程度的產卵基質來測試不同腐敗程度的產卵率差異時，結果顯示不同腐敗程度間的產卵率確實是有顯著差異的，然而在測試不同腐敗程度的接受期長短時，卻沒有顯著差異。總結來說：不同的腐敗程度確實會影響大頭金蠅的產卵行為，但並不會影響到決定產卵的時間長短，然而在此研究中產卵延遲至9.83 1.92小時後的現象值得更進一步的研究與調查，希望這些研究資料能在未來對PMI估算上的校正有所幫助。

When blow flies land on the corpse and decide to lay eggs and colonize, it also starts their biological life cycle which will begin and finish on the corpse. People could use those vital information to estimate the post-mortem interval (PMI) in criminal investigations. The process of decomposition can be divided into five phases, from the death occurs to the finish of life cycle of blow flies. Those phases of exposure phase, detection phase and acceptance phase, belong to the pre-colonization stage; consumption phase and dispersal phase belong to the post-colonization stage. Most previous studies focused on the post-colonization stage, which are the study of effects from different factors (e.g. temperature, humidity…etc.) on the development of larvae or adults. However, the pre-colonization stage is also important, but related research is scarce. In this study we focus on the acceptance phase of Chrysomya megacephala, which was defined as the period between the corpse finding and the decision making of oviposition of blow flies. Longer time period caused by the delay of oviposition will further increase the bias in PMI estimation. In this study, we assumed that different degrees of decay of pork liver may affect the oviposition decision of the blow flies C. megacephala. In field experiment, our results showed significant differences on egg number among groups of using different decay-aged liver as oviposition media (fresh to 8-day-old). In preference test, the results showed significant differences on egg number among groups of using different decay-aged liver (fresh, 2-d old, 4-d old, 6-d old, 8-d old). Our results indicated different decomposition levels do affect the blow fly oviposition; and when we provide media of different decomposition level individually to test the incidence of oviposition, the results also show significant difference among different treatment. However, in the test of duration of acceptance phase, the results show the durations from media discovery to oviposition have no significant different for different decay-aged media. In conclusion, different decay-aged media have significant effects on the oviposition of blow fly C. megacephala, but no effect on the duration of acceptance phase. However, the delay of egg laying could be up to 9.83 1.92 hours due to media of different decomposition level and should be considered in the future study. Hopefully, these data could be helpful to the adjustment of PMI estimation in the near future.