大頭金蠅 (雙翅目：麗蠅科) 蛆團溫度及其在死後間隔時間估算上之應用

Abstract

麗蠅幼蟲的聚集，又稱蛆團 (maggot mass)，能產生豐沛的消化液及代謝熱 (metabolic heat)，使其中的蠅蛆發育速率產生顯著的改變。許多研究都曾提及蛆團內部的溫度會比起周遭環境明顯高出許多。因此，在有蛆團形成的情況之下，利用蠅蛆的發育速率估算屍體死後間隔時間 (postmortem interval, PMI) 時，蛆團熱則成為一大重要的影響因子。在本研究中，利用台灣地區最優勢的食腐性麗蠅之一，大頭金蠅 (Chrysomya megacephala (Fabricius))，觀察其蠅蛆的聚集及記錄其蛆團溫度的變化。實驗中所採用的蛆團中幼蟲數量為 1000、2000、4000、6000、8000 及 12000 隻，在此條件下記錄到的溫度比前人飼養較少蠅蛆的蛆團熱高出許多。在合適的範圍內，蛆團的溫度會隨著幼蟲的數量而增加。而在周圍環境溫度上升的情況下，相同數量幼蟲之蛆團其溫度上升的幅度會隨著周圍環境溫度而減少；當環境溫度達 40°C，接近前人研究中大頭金蠅幼蟲偏好溫度時，蛆團溫度幾乎與環境溫度一致。而此時即使增加幼蟲的數量，其蛆團內的溫度也不再上升。蛆團中的幼蟲可能會利用進出蛆團的行為形成較鬆散的蛆團散熱，以避免過熱致死，甚至更進一步調整其合適的生長環境。而由結果也顯示，蠅蛆的發育時間有一底限，自孵化至後食期最少約為64 小時。因此，當環境溫度達到 40°C 或是發育時間縮短到此底限時，以大頭金蠅的發育情形估算 PMI 時，可考慮忽略蛆團大小會造成的溫度變化及發育速率的改變。

Maggot mass, the aggregation of fly larvae, causes obvious changes on the developmental rate of maggots by producing abundant saliva and maggot mass heat. Many previous researches have also mentioned that the temperature in maggot mass is extremely higher than that of ambient surroundings. In these regards, when using the development of fly larvae on corpse to estimate the post-mortem interval (PMI), maggot mass heat is an important parameter which has to be considered. In our experiment, the larval aggregation of a dominant necrophagous blow fly species, Chrysomya megacephala (Fabricius), in Taiwan was examined, and the temperatures of maggot mass were also recorded. The number of larvae in maggot mass used in this study are 1000, 2000, 4000, 6000, 8000 and 12000. Temperatures recorded in this study in maggot mass were higher than that in the previous studies, which used fewer larvae to record the maggot mass heat. Within appropriate range, the temperatures increased with the numbers of larvae in mass. However, the temperature differences between maggot mass and surroundings decreased with the increasing of ambient temperature. When ambient temperature reaching to 40°C, the approximately favorite temperature of C. megacephala larvae in previous study, the temperature of maggot mass was almost equal to that of the surroundings; and there is no temperature raise in maggot mass even the number of larvae increased. The maggot in mass could move in and out the mass to form a looser mass to avoid overheating, or regulate their temperature. According to the results, there is a minimum maggot developmental duration, approximately 64 hours during larvae hatched to postfeeding. Thus, when ambient temperature reached to 40°C, or the minimum developmental duration arrived, the effects on temperature and developmental rate attributed to the size of maggot mass could probably be neglected when using in PMI estimation.