Curvilinear development modeling of the blow fly Lucilia sericata (Meigen)

The blow fly Lucilia sericata (Diptera: Calliphoridae) is part of a necrophagous group of insects that requires decomposing tissue to complete its life cycle. When found on decomposing remains, L. sericata can be used in postmortem interval (PMI) estimations, which can be an integral part of crime scene/event reconstruction. To estimate PMI, oviposition time is established by determining the age of the insect and counting backwards. Larval development is temperature dependent and follows a curvilinear pattern; however, most development models currently used in PMI estimations are linear approximations.  

A series of experiments were conducted to create a curvilinear development model for L. sericata. Experiments were comprised of twelve temperatures (7.5 ^°C, 10 ^°C, 12.5 ^°C, 15 ^°C, 17.5 ^°C, 20 ^°C, 22.5 ^°C, 25 ^°C, 27.5 ^°C, 30 ^°C, 32.5 ^°C, and 35 ^°C). Twenty eggs (collected within 30 minutes of oviposition) were placed on 10 g of beef liver that was on a 5 cm strip of moist paper towel in a 29.5 mL plastic cup. The cup was placed in a 7 cm x 7 cm x 10 cm plastic container that had 2.5 cm of wood shavings in the bottom. Measurements were taken at intervals calculated from accumulated degree hours (ADH). Each life stage had five measurement points: at the beginning, one-quarter mark, one-half mark, three-quarter mark, and the end. Each point was replicated four times, for a total of 20 measurements per life stage. During each measurement, the cups were pulled from the chamber and the stage of each maggot documented morphologically using the posterior spiracular slits and cephalopharyngeal skeleton.

The L. sericata data illustrate the advantages of curvilinear models over linear approximations in describing development over a range of temperatures, especially near the biological minima and maxima. Results here represent the first in a series of larger studies modeling development of key forensically important blow flies of North America.