The forensically important blow fly, Chrysomya megacephala (Diptera: Calliphoridae), is more likely to walk than fly to carrion at low light levels

Chronobiological Effect on the Reproductive Behavior of Chrysomya megacephala (Diptera: Calliphoridae)

The most widely used entomological method of determining the time since death (minimum postmortem interval, mPMI) has been calculating the developmental time of blow flies (Diptera: Calliphoridae) on the deceased body. However, because blow flies are known to be diurnal, nocturnal oviposition has been excluded from standard mPMI calculations. This has been challenged by recent studies demonstrating nocturnal oviposition due to an unknown reason. Therefore, this study investigated the role of chronobiology. We recorded the locomotion amount and pattern of Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae) under different chronobiological conditions and examined whether Ch. megacephala can oviposit under nighttime conditions in field and laboratory settings. Subjects were found to have a daily activity pattern under normal darkness conditions (12:12 L:D) and under continuous darkness (DD), but they exhibited no pattern under continuous light (LL). Free-running period was approximately 1,341 min/d (22.35 h/d). In the field, no flies were observed during nighttime. Oviposition occurred in the laboratory setting during daytime with no lights and during nighttime with artificial lights. Free-running subjects oviposited in both active and resting periods, with more eggs laid during active than resting periods. The result of this study indicates it is possible to induce oviposition behavior during evening hours on Ch. megacephala. However, this was only observed in the laboratory setting and could only happen during the flies' subjective day.

The Nocturnal Ovipositon Behavior of Chrysomya megacephala (Diptera: Calliphoridae) in Brazil and Its Forensic Implications

Chrysomya megacephala (Fab. 1794) (Diptera: Calliphoridae) is a very important species for forensic entomology, mainly contributing estimations of the postmortem interval (PMI) in judicial investigations. There are some doubts about the nocturnal oviposition of these flies, which could lead to errors in the PMI calculation. This study aimed to monitor the nocturnal oviposition behavior of this species through four experimental conditions carried out in laboratory. Ten cages, each containing five males and females (n = 100), were kept in a fume hood and subjected to total darkness or to artificial light for 11 consecutive hours. Two verifications were performed to determine whether the females deposited eggs on the substrate of ~20 g of chicken gizzards per cage. The first verification occurred at 9:00 pm in nocturnal experiments and at 09:00 am in diurnal experiments. The second verification occurred at 05:00 am in nocturnal experiments and at 05:00 pm in diurnal experiments. Each experiment lasted 5 d. Chrysomya megacephala deposited eggs at night under artificial light and in total darkness, but the amount of eggs was significantly lower when compared with the daytime experiments in dark conditions and under natural light. Oviposition occurred when the average temperature was around 25°C (± 2°C) and relative humidity around 73% (± 6%). Night oviposition is a possibility which should not be ruled out. Thus, future experiments are recommended.

Environmental factors influencing flight activity of forensically important female blow flies in Central Europe

In forensic entomology, evaluation of a possible delay between a person's death and insect colonization is crucial. We monitored the seasonal flight activities of the most abundant blow flies in an urban habitat in Frankfurt/Germany based on 152 sampling days between April and October 2017. Thirty-six thousand female specimens of 12 necrophagous taxa were sampled as a possible groundwork for establishing a prediction tool for the activity of certain forensically relevant taxa. The most abundant taxon was Lucilia sericata (n = 19,544), followed by Lucilia caesar (n = 8025), Calliphora vicina (n = 5224), and Lucilia ampullacea (n = 1834). Up to six environmental parameters were statistically significant predictors of fly presence, leading to unique patterns of seasonal and daily activity for all four species. In detail, our analysis proved that L. sericata is a sun-loving, high-summer species that dominates the warmer months and is mostly influenced by mean day temperature. In contrast, L. caesar seems to be a shade-loving species that dominates in autumn resp. late-season and is mainly influenced by mean day temperature and wind speed. The activity of L. ampullacea was highly related to mean day temperature and relative humidity. In contrast to all other species, C. vicina behaved differently, particularly due to its occurrence throughout the entire sampling interval and the higher tolerance limits for the measured abiotic parameters, especially temperature. The present study is groundwork for establishing a prediction tool for the flight and oviposition activity of forensically relevant taxa.

The uses of Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae) in forensic entomology

Chrysomya megacephala (Fabricius, 1794) occurs on every continent and is closely associated with carrion and decaying material in human environments. Its abilities to find dead bodies and carry pathogens give it a prominence in human affairs that may involve prosecution or litigation, and therefore forensic entomologists. The identification, geographical distribution and biology of the species are reviewed to provide a background for approaches that four branches of forensic entomology (urban, stored-product, medico-criminal and environmental) might take to investigations involving this fly.