University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications: Department of Entomology Entomology, Department of 2006 Effects of Temperature on Development of Phormia regina (Diptera: Calliphoridae) and Use of Developmental Data in Determining Time Intervals in Forensic Entomology P. D. Nabity University of Nebraska-Lincoln Leon G. Higley University of Nebraska-Lincoln, [email protected] Tiffany M. Heng-Moss University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/entomologyfacpub Part of the Entomology Commons Nabity, P. D.; Higley, Leon G.; and Heng-Moss, Tiffany M., "Effects of Temperature on Development of Phormia regina (Diptera: Calliphoridae) and Use of Developmental Data in Determining Time Intervals in Forensic Entomology" (2006). Faculty Publications: Department of Entomology. 277. https://digitalcommons.unl.edu/entomologyfacpub/277 This Article is brought to you for free and open access by the Entomology, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications: Department of Entomology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. DIRECT INJURY,MYIASIS,FORENSICS Effects of Temperature on Development of Phormia regina (Diptera: Calliphoridae) and Use of Developmental Data in Determining Time Intervals in Forensic Entomology 1 P. D. NABITY, L. G. HIGLEY, AND T. M. HENG-MOSS Department of Entomology, 202 Plant Industry, University of Nebraska, Lincoln, NE 68583Ð0816 J. Med. Entomol. 43(6): 1276Ð1286 (2006) ABSTRACT Precise developmental data for forensic indicator blow ßy species are essential for accuracy in the estimate of the post-mortem interval (PMI). Why, then, does the determination of the PMI result in conßicting time frames when published conspeciÞc developmental data are used? To answer this question, we conducted constant temperature trials between the developmental minimum temperature and upper threshold temperatures (8Ð32ЊC) on the forensically important blow ßy species Phormia regina (Meigen) (Diptera: Calliphoridae). Flies were reared using two designs to quantify sources of variation. We measured rearing container temperatures and internal growth chamber temperatures by using thermocouples to accurately record temperatures experi- enced by larvae and to construct a degree-day model. Differences in experimental design, as seen across temperature studies for this ßy species, did not signiÞcantly impact larval development. We also found that using set chamber temperatures rather than rearing container temperatures altered the Þnal degree-day model. Using any minimum threshold (including an empirically determined true mini- mum) other than that from linear interpolation (x-intercept) violated degree-day assumptions and invalidated estimates of the PMI. We observed the minimum developmental temperature to be higher (14ЊC) than that generated under the x-intercept method (5.46ЊC) by using data from oviposition to adult emergence. This difference along with the noted difference in accumulated degree-days (using different base temperatures) suggests a need for additional experimentation on other forensically important ßy species at low temperature thresholds to help with development of curvilinear models. Former and current estimates of the PMI may be inaccurate if the process to determine the time frame ignored degree-day model assumptions or was based upon questionable data sets. KEY WORDS blow ßies, degree-day analysis, temperature thresholds, post-mortem interval Forensic entomology is growing with the application Byrd and Allen 2001; Grassberger and Reiter 2001, of new technologies and the availability of new data on 2002a,b; Grassberger et al. 2003). forensically important species. Arguably, the key con- To use larval development in estimating PMI, ac- tribution of entomological information in criminal in- curate information on the development of individual vestigations is in the determination of the post-mor- species is essential. Currently, much of the available tem interval (PMI). Successional patterns of insect information comes from relatively few studies, often invasion may provide PMI indications over longer with limited data sets (Byrd and Allen 2001, Higley time intervals. For shorter periods, however, devel- and Haskell 2001). For example, data sets developed opmental rates of larvae are used. Decomposers such within limited temperature ranges (especially at low as blow ßies typically arrive and oviposit minutes after temperatures) (Nabity 2005) and data sets with only death. When correlated with environmental temper- single measures (no replication) exist for some tem- atures, development of these carrion ßies can provide peratures. Byrd and Butler (1996, 1997, 1998) pro- a method for estimating the PMI. Consequently, pre- duced data sets by using cyclic temperatures spanning cise developmental data for forensic indicator species the median temperatures of the developmental spec- are essential for accuracy in the PMI estimate. Many trum (15.6Ð32.2ЊCin5.5ЊC intervals); and, Byrd and calliphorid and sarcophagid species have been studied Allen (2001) evaluated a greater temperature range because of their proliÞc occurrence on cadavers, eco- (10Ð40ЊC). However, neither study evaluated growth nomic importance, or role in decomposition succes- rates near the developmental threshold. Similarly, sion (Byrd and Butler 1996, 1997, 1998; Anderson 2000; Greenberg (1991) evaluated broad temperature ranges but produced data sets without regard for the minimum threshold and published data based upon 1 Corresponding author, e-mail: [email protected]. single measures. Developmental minima and maxima 0022-2585/06/1276Ð1286$04.00/0 ᭧ 2006 Entomological Society of America November 2006 NABITY ET AL.: P. regina DEVELOPMENT USED IN FORENSIC ENTOMOLOGY 1277 are not established for many forensic species, and Designs by Byrd and Butler (1996, 1997) also rep- developmental requirements, such as degree-days, licated larval containers within a chamber, rather than usually are not explicitly determined. More compre- between chambers. Grouping all rearing cups under hensive data are emerging for some species (e.g., the same environmental temperature, whether con- Byrd and Allen 2001, Grassberger et al. 2003), but stant or cyclic, may obscure the actual thermal envi- there remains a clear need for additional in-depth data ronment insects experience because of within cham- on development of forensically important insect spe- ber temperature variation. Additionally, there is little cies, such as Phormia regina (Meigen) (Diptera: Cal- if any mention of variability occurring in temperature liphoridae). studies, and only recently have investigators placed A further need is estimation of variation for con- electronic checks (thermocouples and data loggers) structing the PMI. One important issue is the assump- within experiments to monitor temperatures (Ander- tion that oviposition occurs shortly after death; yet, son 2000, Clarkson et al. 2004). Chamber effects may various circumstances (such as diurnal versus noctur- create the variation observed in data sets within and nal oviposition patterns, access to a body, or cold between studies on the same species (Kamal 1958, temperatures) may delay oviposition. Another major Greenberg 1991, Byrd and Allen 2001), and this vari- source of variation comes in determination of devel- ation needs to be investigated. opmental periods. Greenberg (1991), Byrd and Allen Traditionally, the experimental unit is deÞned as the (2001), and Clarkson et al. (2004) found ßuctuating entity to which a treatment is applied. However, in temperatures delayed larval development compared growth chamber studies involving temperature, the with constant temperature rearing. Thus, studies using treatment is not evenly applied (all locations within only cyclic temperatures to test development for some the chamber do not experience the same tempera- ßy species are incomplete. For example, Byrd and ture), and the presumed temperature (the set-cham- Butler (1996, 1997, 1998) tested development only ber temperature) may not match internal chamber under cycling temperatures with a period of 5.5ЊC, and temperatures. Thus, some investigators and statisti- one constant temperature (25ЊC). They argued for the cians have argued that within-chamber replications ßuctuating temperatures because specimens in nature are permissible if the treatments are recorded for each are subject to ßuctuating, not constant, temperatures. within chamber “replicate.” This argument assumes that temperature is the only signiÞcant factor affecting These studies also evaluated ßy development under replicates; otherwise, between-chamber replications various photoperiod settings; a concept that has not (to account for example, variability in light and rela- been directly tested in the literature. Although there tive humidity) would be necessary. The opposite in- are data to suggest photoperiod may inßuence devel- terpretation is that within chamber replicates, where opment (unpublished data) and investigators have temperature is the treatment, represent a lack of, or shown dipteran behavior to be augmented by light pseudoreplication (Hurlbert 1984). (e.g., Grassberger and Reiter 2001, 2002a,b), there are A less appreciated issue in the design of tempera- no conclusive studies testing the inßuence of light on ture studies is randomization.