The Oviposition Preference of Chrysomya megacephala (Fabricius) and Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae)

In forensic entomology, the age of necrophagous blow fly maggots that feed on the carcass are often used to estimate the post-mortem interval (PMI). The oviposition behavior of adults may influence the inter- or intraspecific interactions between larvae, such as competition or predation, may change the growth and survial rate of larvae, and then cause the bias of PMI estimation. Chrysomya megacephala and Chrysomya rufifacies are two most dominant necrophagous blow fly species in Taiwan. To understand the oviposition preference of these two species, the dual-choice device was used to test the females of the two species to choose their oviposition site. Results showed that when pork liver with or without larvae of C. rufifacies were provided, C. megacephala significantly preferred to lay eggs on the livers without larvae. Yet C. megacephala showed no preference when provided pork livers with or without conspecific larvae, or the larvae of Hemipyrellia ligurriens. These results probably indicated the C. megacephala has tried to escape from the facultatively predaceous larvae of C. rufifacies. At the same time, C. rufifacies showed significant oviposition preference on the pork liver with the larvae of C. megacephala or their conspecific ones when compared to those pork livers of no larva. This result implied the conspecific larvae or the larvae of C. megacephala could be a potentially alternative food resource of C. rufifacies which made the female prefer to lay eggs around. When considering about the size of oviposition media, both species significantly disliked the pork livers of relatively small size. This may because the females need to find enough food sources to meet the growth of their larvae. According to our results, both blow flies species showed no preference between the pork livers of differently decayed stage. In addition, there is one thing that deserved to be mentioned: the oviposition preferences of both species to those media with larvae were greatly disturbed under the dark environment. And if we removed the larvae which previously fed on the pork liver and let the females to choose, no oviposition preference was observed. But both species still showed preference to the larger media in the dark. This probably suggests the blow flies could use vision to recognize the larvae on the oviposition media. By knowing the factors that may influence the oviposition preference of blow flies, we can gather more useful information to contribute to the forensic entomology especially to the more accurate PMI estimation.