Department of Entomology, National Taiwan University, Taipei, Taiwan.
J Med Entomol. 2012 Mar;49(2):424-35. doi: 10.1603/me11133.
Necrophagous blow fly species (Diptera: Calliphoridae) are the most important agents for estimating the postmortem interval (PMI) in forensic entomology. Nevertheless, the oviposition preferences of blow flies may cause a bias of PMI estimations because of a delay or acceleration of egg laying. Chrysomya megacephala (F.) and C. rufifacies (Macquart) are two predominant necrophagous blow fly species in Taiwan. Their larvae undergo rather intense competition, and the latter one can prey on the former under natural conditions. To understand the oviposition preferences of these two species, a dual-choice device was used to test the choice of oviposition sites by females. Results showed when pork liver with and without larvae of C. rufifacies was provided, C. megacephala preferred to lay eggs on the liver without larvae. However, C. megacephala showed no preference when pork liver with and without conspecific larvae or larvae of Hemipyrellia ligurriens (Wiedemann) was provided. These results indicate that females of C. megacephala try to avoid laying eggs around larvae of facultatively predaceous species of C. rufifacies. However, C. rufifacies showed significant oviposition preference for pork liver with larvae of C. megacephala or conspecific ones when compared with pork liver with no larvae. These results probably imply that conspecific larvae or larvae of C. megacephala may potentially be alternative food resources for C. rufifacies, so that its females prefer to lay eggs in their presence. When considering the size of the oviposition media, pork livers of a relatively small size were obviously unfavorable to both species. This may be because females need to find sufficient resources to meet the food demands of their larvae. In another experiment, neither blow fly species showed an oviposition preference for pork livers of different stages of decay. In addition, the oviposition preferences of both species to those media with larvae were greatly disturbed in a dark environment. If we removed the larvae that had previously fed on the pork liver and let the females choose, no oviposition preference was observed; but both species still showed a preference for the larger media in the dark. This suggests that female blow flies can use visual cues to recognize larvae on the media and decide on their oviposition site. Our studies point out the effects of some biotic and abiotic factors which were previously overlooked, and remind us to reevaluate these effects on oviposition, especially when using insect developmental data to estimate PMIs.
食尸性丽蝇（双翅目：丽蝇科）是法医昆虫学中估计死后时间（PMI）最重要的指标。然而，丽蝇的产卵偏好可能会导致 PMI 估计的偏差，因为这会导致产卵延迟或加速。巨尾阿丽蝇（F.）和红头丽蝇（Macquart）是台湾两种主要的食尸性丽蝇。它们的幼虫竞争非常激烈，在自然条件下，后者可以捕食前者。为了了解这两种物种的产卵偏好，使用双选择装置来测试雌性对产卵地点的选择。结果表明，当提供带有和不带有红头丽蝇幼虫的猪肝脏时，巨尾阿丽蝇更喜欢在没有幼虫的肝脏上产卵。然而，当提供带有和不带有同种幼虫或黄腹潜蝇幼虫的猪肝脏时，巨尾阿丽蝇没有表现出偏好。这些结果表明，巨尾阿丽蝇的雌性试图避免在红头丽蝇的幼虫周围产卵。然而，当与没有幼虫的猪肝脏相比，红头丽蝇对带有巨尾阿丽蝇幼虫或同种幼虫的猪肝脏表现出明显的产卵偏好。这些结果可能意味着同种幼虫或巨尾阿丽蝇的幼虫可能是红头丽蝇的替代食物来源，因此其雌性更喜欢在它们的存在下产卵。当考虑产卵媒介的大小时，相对较小的猪肝脏对两种物种都明显不利。这可能是因为雌性需要找到足够的资源来满足其幼虫的食物需求。在另一个实验中，两种丽蝇都没有对不同腐烂阶段的猪肝脏表现出产卵偏好。此外，在黑暗环境中，两种物种对带有幼虫的产卵媒介的产卵偏好大大受到干扰。如果我们去除之前吃过猪肝脏的幼虫，让雌性选择，就不会观察到产卵偏好；但在黑暗中，两种物种仍然更喜欢较大的媒介。这表明雌蝇可以使用视觉线索来识别媒介上的幼虫，并决定产卵地点。我们的研究指出了一些以前被忽视的生物和非生物因素的影响，并提醒我们重新评估这些因素对产卵的影响，特别是在使用昆虫发育数据来估计 PMI 时。
