Chrysomya megacephala, more commonly known as the oriental latrine fly or oriental blue fly, is a member of the family Calliphoridae (blowflies). It is a warm-weather fly with a greenish-blue metallic box-like body. The fly infests corpses soon after death, making it important to forensic science. This fly is implicated in some public health issues; it can be the cause of myiasis, and also infects fish and livestock.
Description
Chrysomya megacephala'''s eggs are "oval with one flat face and another convex". Adult flies reflect a metallic blue-green color on their thorax and abdomen and have yellow gena, or cheeks. Larvae vary in size according to instar and are shaped more thickly towards the rear. C. megacephala have large red eyes, those of males being close together, and those of females farther apart. The cercus of the male is longer than that of the female.
Distribution and habitatChrysomya megacephala has a wide geographical distribution. It is most common in the Oriental and Australasian realms. It is also found in Japan and the Palearctic realm. The range of C. megacephala has grown since the 1970s, with the species expanding into New Zealand and Africa, along with South, Central, and North America. C. megacephala entered the United States through harbors and airports. The fly has been found in California, as well as Texas, Louisiana, and Hawaii. C. megacephala exists in two forms, the normal and the derived. Tropical forests on the Pacific Islands, such as Samoa, are home to the normal form; the normal is considered to be the plesiomorphic form of C. megacephala. The derived form is thought to have emerged from Papua New Guinea and is said to be synanthropic, or ecologically associated with humans.
Behavior and ecology
Climatic variationChrysomya megacephala prefer warm climates, and display a correlation between warmer temperatures and higher fecundity. In tropical populations, such as in Brazil, fertility is also lower in areas with high densities of larvae, where many in one small area compete for the same food source. A correlation between wing size and temperature as well as tibia size and temperature has also been found in this species. There was a similar relationship between wing and tibia size and fecundity. All three of these values variables, fecundity, wing size and tibia size, stay within the same range throughout the year, showing seasonal variation to be absent. This has been of interest to researchers, since this fly is present in high numbers in warm weather and low numbers in cold weather. The majority of Dipteran species that have had a life table constructed have demonstrated a tendency for smaller bodies in the warmer months. C. megacephala has a relatively long lifespan as an adult which has helped the species become successful at invading new geographical areas. The long adult lifespan means that the parents are present to rear the offspring, ensuring their survival.
Reproduction
The developmental stages of C. megacephala include egg, larva and pupa. A female fly may lay as many as 200 to 300 eggs, often in human feces, meat or fish. Larval stages include first, second and third instals or growth periods. The eggs take approximately one day to develop, while the larvae take 5.4 days and the pupae 5.3 days. Population numbers as well as body size are greatly influenced by temperature. The adult lifespan of the fly is approximately seven days. The development of C. megacephala is linked to the length of time spent feeding in the larval stage, as well as to temperature; the lower the temperature, the more slowly the larvae develop. In laboratory studies conducted at 27 °C., eggs hatch in 18 hours; the first molt occurs in 30 hours; the second molt in 72 hours; pupation after 144 hours; and the adult emerges after approximately 234 hours. These intervals vary depending on geographical location; other environmental factors also can determine how long flies will stay in the larval stage. Males tend to emerge two or three hours ahead of the females.
The reproduction and survival rates of C. megacephala are closely related to developmental factors, including the amount of available food, and competition from larvae of other species, such as C. rufifacies. In the presence of competing larvae, those of C. megacephala spend less time feeding, leading to early pupation, smaller adults, and early reproduction. The second and third instar larvae of C. rufifacies are known predator that feeds on the larvae of C. megacephala when feeding substrate is less or larval density is high. In such cases C. megacephala tend to disperse early, thus remains malnourished.