Thermoregulation in Larval Aggregations of Carrion-Feeding Blow Flies (Diptera: Calliphoridae)

Abstract

The growth and development of carrion-feeding calliphorid (Diptera: Calliphoridae) larvae, or maggots, is of great interest to forensic sciences, especially for estimation of a postmortem interval (PMI). The development rate of calliphorid larvae is influenced by the temperature of their immediate environment. Heat generation in larval feeding aggregations (=maggot masses) is a well-known phenomenon, but it has not been quantitatively described. Calculated development rates that do not include internally generated temperatures will result in overestimation of PMI. Over a period of 2.5 yr, 80 pig, Sus scrofa L., carcasses were placed out at study sites in north central Florida and northwestern Indiana. Once larval aggregations started to form, multiple internal and external temperatures, and weather observations were taken daily or every few days between 1400 and 1800 hours until pupation of the larvae. Volume of each aggregation was determined by measuring surface area and average depth. Live and preserved samples of larvae were taken for species identification. The four most common species collected were Lucilia coeruleiviridis (=Phaenicia) (Macquart) (77%), Cochliomyia macellaria (F.) (8.3%), Chrysomya rufifaces (Macquart) (7.7%), and Phormnia regina (Meigen) (5.5%). Statistical analyses showed that 1) volume of a larval mass had a strong influence on its temperature, 2) internal temperatures of masses on the ground were influenced by soil temperature and mass volume, 3) internal temperatures of masses smaller than 20 cm3 were influenced by ambient air temperature and mass volume, and 4) masses larger than 20 cm3 on the carcass had strongly regulated internal temperatures determined only by the volume of the mass, with larger volumes associated with higher temperatures. Nonsignificant factors included presence of rain or clouds, shape of the aggregation, weight of the carcass, species composition of the aggregation, time since death, or season.

Variation in Developmental Time for Geographically Distinct Populations of the Common Green Bottle Fly, Lucilia sericata (Meigen)*

“…It may be that ambient temperature is insignificant when a large maggot mass is present. Maggot masses greater than 20 cm 3 exhibit internal temperatures independent of the ambient temperature (24). Thus, an investigation on developmental variation between populations under more natural conditions is necessary.…”

Thermal attributes of Chrysomya species

“…It has been shown that larval population density is related to the increase in heat generated relative to ambient tem-peratures (Marchenko, 2001;Slone & Gruner, 2007). In many studies, the ambient temperatures (e.g., the setpoints of temperature-controlled cabinets) are reported, but the temperatures actually experienced by the growing larvae are neglected (e.g., Byrd & Butler, 1997).…”

“…However, it is expected that larval development remains possible during the cooler months due to the maggot-mass effect in infested carrion in the field. This would maintain high temperatures, overcoming unfavourable weather conditions and extending the breeding season Slone & Gruner, 2007). Indeed, maggot-masses have been observed to still be active when air temperatures are as low as )4°C (Greenberg, 1991).…”

ForenSeek: un programme de simulation du développement des insectes nécrophages dédié à l’entomologie médico-légale

“…De plus, le dégagement de chaleur produit par chaque individu conduit à une augmentation de température au centre de la masse pouvant aller jusqu'à une quinzaine de degrés (Deonier 1940, Greenberg 1991, Joy et al 2006, Slone & Gruner 2007. Cette variation de la température entraîne des variations de vitesse de développement entre les individus se trouvant au centre et ceux en périphérie.…”