大頭金蠅與紅顏金蠅 (雙翅目：麗蠅科) 幼蟲競爭及其在法醫昆蟲學上之應用

Abstract

Chrysomy megacephala and C. rufifacies are the two dominant necrophagous species in Taiwan, Larvae of the latter can prey on other maggots including its own species as facultative foods. This habitat enhances competition strength to other maggots. In this study, we used these two species to investigate and try to understand the effect of competition on the development and growth of larvae. Intraspecific competition mostly occurred in competing for food; increasing the rearing density, larvae pupated earlier and resulted in lighter adult dry weight. The tendencies are similar in both species, but C. megacephala could develop smaller viable adults and with higher survivorship under hight density condition. Although C. rufifacies could use food resource by cannibalism, its survivorship is still lower. Under interspecific competition, first instar larvae of C. rufifacies invaded the maggot mass of C. megacephala to feed together. Third instar larvae of C. rufifacies will expel C. megacephala larvae from their foods by using their fleshy protrusion on body surface, and the C. megacephala will be forced to pupate earlier by decreasing their larval stages. Under mixed-species rearing of different ratio, the larval duration of C. rufifacies will increase as the ratio increases, but this result did not exhibit in C. megacephala . In general, under mixed-species rearing in different temperatures and densities, both species decreased the larval duration, adult dry weight and the survivorship; in a word, decreased their overall fitness. This result is opposite to the previous studies; and the different results are probably caused by different experimental designs. We allowed the maggots left from the food resource freely, won’t affect each other outside between species, as in the wild field. Interspecific competition affects the duration of third instar, feeding and postfeeding larvae of C. megacephala and the duration of second instar larvae of C. rufifacies. Duration of larval development of both species may decreased up to 54 hours when limited the food resource in single species rearing. The largest reducing amount of duration of larvae caused by interspecific competition is 11.9 hours in C. megacephala and 18.3 hours in C. rufifacies in density of 40 larvae (per 60g medium) at 23℃. At 28℃, the longest shorten larval duration of 24.8 hours in C. megacephala is happened under the density of 160 larvae; and 34.0 hours in C. rufifacies under the density of 320 larvae. Finally, larval competition decreased the larval duration of C. megacephala and C. rufifaies up to 0.5 ~ 2 days; this results could also be applied to justify the PMI estimation when competition effects existed.