Models of development for blowfly sister species Chrysomya chloropyga and Chrysomya putoria

Abstract

Developmental curves for the sister species Chrysomya chloropyga (Wiedemann, 1818) and Chrysomya putoria (Wiedemann, 1830) (Diptera: Calliphoridae) were established at eight and 10 different constant temperatures, respectively, using developmental landmarks and body length as measures of age. The thermal summation constants (K) and developmental threshold (D(0)) were calculated for five developmental landmarks using a previously described method. Isomorphen and isomegalen diagrams were also constructed for the purpose of estimating postmortem intervals (PMIs). Chrysomya chloropyga had an average developmental threshold value (D(0)) of 10.91 degrees C (standard error [SE] = 0.94 degrees C, n = 5), significantly lower than that of C. putoria (13.42 degrees C, SE = 0.45 degrees C, n = 5) (paired t-test: t = - 4.63, d.f. = 8, P < 0.00). Similarly, K values for C. chloropyga were larger than those for C. putoria for all developmental events except onset of the wandering phase. These are the first data that can be used to calculate minimum PMIs and predict population growth of C. chloropyga and C. putoria in Africa; the data indicate that developmental data for one of these species cannot be used as surrogate data for the sister species.

Forensic entomology: applications and limitations

“…Lastly, it is labor intensive to collect the experimental data for an isomegalen diagram and the model is not as simple to build as the isomorphen diagram. This is evident by the dearth of published studies reporting isomegalen diagrams of forensically important blowfly species [6,11,12,15].…”

“…Because these values are the end points of the regression, and are thus heavily weighted values, they significantly influence the confidence of the regression coefficients, which compromises the precision of a PMI min estimate. Recently, a revised regression model [21] has been used to model blowfly development [6]. It identifies the points nearest the extremes of the linear approximation that deviate significantly from it, which results in the calculation of more precise thermal summation parameters.…”

“…The rate of development of an insect is mainly governed by temperature and can differ between even closely related species [6]. Hence, a three-step process of, (1) accurately identifying the species found on a corpse, (2) reconstructing crime scene temperatures, and (3) modelling the rate of development of the immature insects found on a corpse, is absolutely essential to enable a forensic entomologist to calculate the age of a sampled insect.…”

Effect of temperature on development of the blowfly, Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae)

“…Median development times for L. sericata were 53.9 days at 19°C, 13.5 days at 27°C, and 11.3 days at 3°C; for L. cuprina, the median development times were 30.3 days at 19°C, 12.8 days at 27°C, and 10.4 days at 35°C. These differences in development show that even though the two species are closely related when both are present on carrion, it is not satisfactory to use the developmental constants for one species as proxies for those of the other, a conclusion also noted for other pairs of closely related species [30,31]. As discussed above, variation in the direction of differences in development rate between the two species also illustrates the need to more fully explore phenotypic variation [7,32].…”

Molecular identification of forensically important blowfly species (Diptera: Calliphoridae) from Germany

“…In particular, the calculation of larval age allows the determination of a minimum post-mortem interval (PMI min ) (Easton and Smith 1970;Marchenko 1982;Erzinclioglu 1983;Leclercq 1983;Goff et al 1986), which is often an important detail for the police investigations. Larval development is dependent on temperature (Bowler and Terblanche 2008), and every species has a slightly different growth rate (Erzinclioglu 1990; Davies and Ratcliffe 1994;Richards et al 2009). It is, thus, crucial to correctly identify the larval species feeding from a corpse to calculate the PMI min properly.…”