Decomposition and insect succession in hanging and prone carcasses, with special reference to Chrysomya chloropyga (Diptera: Calliphoridae)

[摘要] Persons who commit suicide sometimes hang themselves. The body is frequently onlyfound after a few days have elapsed. In establishing the postmortem interval, it isimportant to know whether there are differences in the decomposition process of, and theinsect succession on hanging bodies compared to bodies lying on the ground.All field experiments were conducted at the experimental site on the western campus ofthe University of the Free State (29°08'S 26°10'E), Bloemfontein, South Africa. Thisregion is a summer rainfall region with an average rainfall of 450-500 mm per annum.Hot summers and cold winters prevail, with severe frost occurring regularly duringwinter.The field study was carried out by exposing prone pig carcasses to full sunlight andhanging pig carcasses to full sunlight and full shade during various seasons. Five stagesof decay were identified, viz. fresh, bloated, active decay, advanced decay and remains.Based on mass loss, the prone carcasses decomposed further and insects removed moretissue than was the case in the hanging carcasses. The hanging carcasses probably driedout more rapidly, slowing down the decomposition process.During this study, only the numbers of adult insects visiting the carcasses were recordedas it was impossible to make an accurate estimate of larval numbers. Significantdifferences were observed in the insects visiting the carcasses. On the hanging carcasses,Coleoptera were most abundant, and on the prone carcasses Diptera were most abundant.This was consistent with the hanging carcasses desiccating more quickly than the pronecarcasses. Larger maggot masses formed on the prone carcasses than on the hangingcarcasses. At the hanging carcasses, a drip zone was identified below the carcasses inwhich the fallen maggots developed. This area is extremely important for insect evidenceanalysis and is frequently overlooked in investigations by non-entomologists.The patterns of succession of insects on the carcasses revealed that Sarcophagacruentata, Chrysomya albiceps, C. marginalis and Musca domestica were the initialinvaders of the carcasses during decomposition. Larger numbers of Calliphoridae wererecorded continually on the prone carcasses, while fewer Calliphoridae were recorded onthe hanging carcasses. Larger numbers of Coleoptera were recorded on the hangingcarcasses while lower numbers of Coleoptera were recorded on the prone carcasses.Internal carcass temperatures measured in the thorax and upper abdomen were higherthan the ambient temperature owing to metabolic heat generated by large larval masses.At the hanging carcasses, the internal temperatures approximated the ambienttemperature. After post-feeding larvae had migrated from the carcasses to pupate, highinternal carcass temperatures were the result of sun insolation.The high incidence of C. chloropyga observed on the carcasses during spring and duringseveral case studies identified this species as an extremely important forensic indicatorspecies in the Free State Province. Laboratory studies on C. chloropyga at 25°C revealedthat chicken liver yielded the shortest mean development time (10.4 ± 0.71 days) with thehighest mean percentage (67.11 ± 11.09) of survival of larvae to adulthood occurringwith beef liver as rearing medium. Morphometric data revealed that the largest adultswere produced with beef liver as feeding medium (dry mass: 0.00878 ± 0.00122 g andwing length: 8.44 ± 0.32 mm).Temperature studies using chicken liver as feeding medium for C. chloropyga larvaerevealed that the shortest mean development time (9.4 ± 0.66 days) occurred at 30°C. Thehighest mean percentage (58.22 ± 9.4) survival of larvae to adulthood occurred at 35°C.Morphometric data revealed that the heaviest adults were produced at 10°C (dry mass:0.01123 ± 0.00015 g; percentage survival: 1.33 ± 2.0) and the longest wing lengths at20°C (8.67 ± 0.28 mm).

[发布机构] University of the Free State