Recent African derivation of Chrysomya putoria from C. chloropyga and mitochondrial DNA paraphyly of cytochrome oxidase subunit one in blowflies of forensic importance

Chrysomya chloropyga (Wiedemann) and C. putoria (Wiedemann) (Diptera: Calliphoridae) are closely related Afrotropical blowflies that breed in carrion and latrines, reaching high density in association with humans and spreading to other continents. In some cases of human death, Chyrsomya specimens provide forensic clues. Because the immature stages of such flies are often difficult to identify taxonomically, it is useful to develop DNA-based tests for specimen identification. Therefore we attempted to distinguish between C. chloropyga and C. putoria using mitochondrial DNA (mtDNA) sequence data from a 593-bp region of the gene for cytochrome oxidase subunit one (COI). Twelve specimens from each species yielded a total of five haplotypes, none being unique to C. putoria. Therefore it was not possible to distinguish between the two species using this locus. Maximum parsimony analysis indicated paraphyletic C. chloropyga mtDNA with C. putoria nested therein. Based on these and previously published data, we infer that C. putoria diverged very recently from C. chloropyga.     

Records of Chrysomya albiceps in the Ukraine

First records of the presence of the blowfly, Chrysomya albiceps in the western and northern Ukraine are presented.     

Seasonality of Old World screwworm myiasis in the Mesopotamia valley in Iraq

Following the first recorded introduction of the Old World screwworm fly (OWS), Chrysomya bezziana Villeneuve (Diptera: Calliphoridae), into the Mesopotamia valley in Iraq in September 1996, cases of livestock myiasis caused by OWS developed a distinctly seasonal pattern. The annual cycle of clinical OWS cases is explained here on the basis of environmental variables that affect the different life-cycle stages of C. bezziana. This analysis suggests that low temperatures restricted pupal development during the winter, whereas the dispersal of adult flies was constrained by hot/dry summer conditions. A restricted number of OWS foci persisted throughout the year. In these foci, pupal development was fastest during the autumn months. In autumn, rapid multiplication, lasting several OWS generations, allowed subsequent adult fly dispersal across the valley floor during the winter. Hence, the monthly incidence of clinical OWS cases in livestock peaked during December-January and was lowest during July-August. In addition to temperature and humidity, vegetation cover played a role in OWS distribution. Hence the majority of OWS cases were clustered in the medium density type of vegetation [normalized difference vegetation index (NDVI) values of 0.2-0.4] along the main watercourses in the marshy Mesopotamia valley. Although sheep were the host most commonly infested by C. bezziana, local sheep density was not found to be a major factor in disease spread. Satellite imagery and the application of Geographical Information System (GIS) tools were found to be valuable in understanding the distribution of OWS in relation to vegetation and watercourses. The presence of screwworm in Iraq, at the perimeter of the intercontinental OWS distribution, may give rise to major seasonal flare-ups.     

Dynamics of handling time and functional response by larvae of Chrysomya albiceps (Dipt., Calliphoridae) on different prey species

Abstract:  One way to understand the behavioural patterns exhibited by a predator in response to prey density is to evaluate its functional response. Such evaluation yields information about basic mechanisms of prey–predator dynamics, and is an essential component of prey–predator models. In this paper we analysed experimentally the functional response and the handling time spent by Chrysomya albiceps on different prey species and larval instars of blowflies. The type II functional response was observed when second instar larvae of Chrysomya megacephala and Chrysomya macellaria were consumed. The handling time spent by the predator was significantly different between instars and species. The implications of the functional response and handling time for the interaction dynamics of Brazilian Chrysomyinae species are discussed.     

Using COI barcodes to identify forensically and medically important blowflies

Abstract.  The utility of cytochrome oxidase I (COI) DNA barcodes for the identification of nine species of forensically important blowflies of the genus Chrysomya (Diptera: Calliphoridae), from Australia, was tested. A 658-bp fragment of the COI gene was sequenced from 56 specimens, representing all nine Chrysomya species and three calliphorid outgroups. Nucleotide sequence divergences were calculated using the Kimura-two-parameter distance model and a neighbour-joining (NJ) analysis was performed to provide a graphic display of the patterns of divergence among the species. All species were resolved as reciprocally monophyletic on the NJ tree. Mean intraspecific and interspecific sequence divergences were 0.097% (range 0–0.612%, standard error [SE] = 0.119%) and 6.499% (range 0.458–9.254%, SE = 1.864%), respectively. In one case, a specimen that was identified morphologically was recovered with its sister species on the NJ tree. The hybrid status of this specimen was established by sequence analysis of the second ribosomal internal transcribed spacer (ITS2). In another instance, this nuclear region was used to verify four cases of specimen misidentification that had been highlighted by the COI analysis. The COI barcode sequence was found to be suitable for the identification of Chrysomya species from the east coast of Australia.     

Selective attractiveness of rodent-baited traps for female blowflies

Five species of Calliphoridae, mostly females, were collected using fly-traps baited with freshly killed rodent carcasses. Female blowflies were examined to determine the stages of ovarian development. The traps were selective for certain ovarian stages which varied according to the species. Phaenicia eximia (Wiedemann) was attracted to the traps mainly to oviposit, whereas females of Chrysomya albiceps (Wiedemann), C. putoria (Wiedemann) and C. megacephala (Fabricius) were captured in intermediate stages of oogenesis but seldom with eggs mature for oviposition. It is concluded that this kind of baited trap is unsuitable for the collection of male blowflies and that samples of female blowflies are specifically biased in favour of certain ovarian conditions.     

Ovarian development rates in the Old World screw-worm fly, Chrysomya bezziana

Rates of ovarian development in relation to temperature were determined for autogenous females of the screw-worm fly, Chrysomya bezziana. Percentage durations of the different ovarian stages (scaled 2–10) were estimated on the basis of observed lengths of the developing oocytes. Mean durations (h) of each ovarian stage was determined at 20, 25, 28 and 35°C. A model of ovarian development rate (%/d) in relation to temperature (T) is presented, the fitted curve being give by R(T)=EXP (–2.73+0.362T–0.0055T²).     

Temperature‐dependant development of Nasonia vitripennis on five forensically important carrion fly species

The effects of temperature and host species on the development of Nasonia vitripennis Walker (Hymenoptera: Pteromalidae), a forensically important parasitoid of carrion flies, were studied under laboratory conditions. Development time of N. vitripennis on five species of Calliphoridae (Diptera), Calliphora albifrontalis Malloch, Calliphora dubia Macquart, Lucilia sericata Meigen, Chrysomya rufifacies Macquart, and Chrysomya megacephala Fabricius, were determined under eight constant temperatures (15, 18, 21, 24, 27, 30, 33, and 36 °C). Thermal requirements for development (developmental thresholds, thermal constant, and optimum temperature) of N. vitripennis in each host species were estimated using linear and nonlinear models. Upper and lower developmental thresholds ranged between 36.6–38.4 and 9.6–11.1 °C, respectively. The optimum temperature for development was estimated at between 30.6 and 31.8 °C. Statistical differences in the development time of N. vitripennis on the various calliphorid host species were evident within all temperature treatments, particularly at the upper and lower temperature range investigated. As such, it is recommended that insect‐based estimates of time since death in forensic investigations relying on parasitoid evidence should use host‐specific development data where available.     

二种尸食性蝇类幼虫形态学变化及在法医学上的意义

为了满足实际工作中利用蝇类幼虫日龄推断尸体死后间隔时间的需求,采用形态观察与图像分析相结合的方法对巨尾阿丽蝇Aldrichina grahami(Aldrich)、大头金蝇Chrysomya megacephala(Fabricius)幼虫前气门、后气门、头咽骨进行了研究,筛选适合日龄推断的指标。结果显示:2种尸食性蝇类幼虫前气门、后气门、头咽骨均随着时间的延长发生规律性的变化。其中,咽骨的骨化面积、平均光密度,后气门的平均光密度是最理想的判断幼虫日龄的指标,为法医昆虫学精确推断死后间隔时间提供重要的指导意义。