Environmental Factors Affecting Early Carcass Attendance by Four Species of Blow (Diptera: ) in Texas Author(s): Rachel M. Mohr and Jeffery K. Tomberlin Source: Journal of Medical Entomology, 51(3):702-708. 2014. Published By: Entomological Society of America URL: http://www.bioone.org/doi/full/10.1603/ME13149

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BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. DIRECT INJURY,,FORENSICS Environmental Factors Affecting Early Carcass Attendance by Four Species of Blow Flies (Diptera: Calliphoridae) in Texas

1,2 3 RACHEL M. MOHR AND JEFFERY K. TOMBERLIN

J. Med. Entomol. 51(3): 702Ð708 (2014); DOI: http://dx.doi.org/10.1603/ME13149 ABSTRACT As the most common primary colonizer of carrion, adult blow ßies (Diptera: Calli- phoridae) play an important role in initiating -mediated breakdown of soft tissue; however, their timing is highly variable. This variability complicates the estimation of precolonization intervals or periods of activity by forensic entomologists. In this study, the size of the adult blow ßy on swine carcasses was compared with various environmental conditions including time of day, tem- perature, wind speed, and light levels. Four trials were conducted: two in August and September 2008, one in January 2009, and one in FebruaryÐMarch 2010. Of the measured variables, time of day was the only consistent factor explaining the population size of blow ßy on a carcass, although precipitation and high winds affected winter-active Calliphora vicina Robineau-Desvoidy. Male ßies were also collected, suggesting that carcasses may play additional roles in adult blow ßy ecology beyond that of a simple oviposition site. For both sexes of ßies, a strong diel pattern of behavior emerged, which could be useful in estimating precolonization intervals by considering the environmental conditions at a scene, and thus forensic entomologists may be better able to estimate the likelihood of adult activity at a carcass.

KEY WORDS forensic entomology, precolonization interval, macellaria, rufifacies, Calliphora vicina

Under normal circumstances, after an dies, it particularly blow ßy larvae, collected from a corpse of becomes one of a “patchy” distribution of remote re- interest. The age of these immatures is then calculated sources for various necrophilous organisms (Hanski using the accumulated degreeÐday and accumulated 1987). As the resource ages, it passes through a con- degreeÐhour concepts of insect growth (Higley and tinuum of decay from fresh to dried bony remains Haskell 2010, Wells and LaMotte 2010). The exact (Haglund and Sorg 1996). This process of carcass mathematical methods for making such estimates can change is exploited and facilitated by a succession of be quite complex, ranging from simple summation to different arthropod taxa (Carter et al. 2007). This nonlinear general additive models encompassing faunal succession, and its relationship to the state of length, weight, developmental stage, and the strain or decomposition, has been studied in depth in a variety population membership (Tarone and Foran 2008). of systems, including humans (Motter 1898, Rodriguez None of these models explicitly considers the role of and Bass 1983), dogs (Reed 1958), and swine (Payne the adult ßies, although Amendt et al. (2007) recom- 1965). The successional waves of that arrive at mend the term “minimum PMI” to account for the fact each corpse are typically described based on the de- that (particularly immatures) are not gen- compositional phase they arrive and their overall or- erally present instantaneously following death. der. In these studies, blow ßies (Diptera: Calliphori- In contrast to the larvae-focused method, the dae) are most commonly cited as the Þrst insects to Tomberlin PMI model is a comprehensive interpre- arrive at fresh carrion. These early-arriving ßies ef- tation for PMI that divides the relationship between fectively “start the clock” for arthropod-facilitated de- the corpse and the associated arthropods in a precolo- composition of a carcass, a major concern for forensic nization (pre-CI) and postcolonization (post-CI) in- entomologists whose major service is to estimate the tervals (Tomberlin et al. 2011b). Beginning with postmortem interval (PMI) of the carcass or cadaver neurosensory detection and behavioral activation, fol- in question. lowed by searching and location of the carcass, the The traditional entomological means of estimating pre-CI accommodates all of the necessary neurosen- the PMI is based on determining the age of insects, sory and behavioral activities that must occur before blow ßy oviposition. In a complementary fashion, the 1 Forensic & Investigative Science Program, West Virginia Univer- post-CI then accounts for the rest of the period of sity. PO Box 6121, Morgantown, WV 2656-6121. insect use of the carcass, commonly the development 2 Corresponding author, e-mail: [email protected]. 3 Department of Entomology, Texas A&M University. 2475 TAMU, of immatures. In this respect, the post-CI is function- College Station, TX 77843-2475. ally equivalent to the minimum PMI. Unlike the post-

0022-2585/14/0702Ð0708$04.00/0 ᭧ 2014 Entomological Society of America May 2014 MOHR AND TOMBERLIN:ENVIRONMENTAL EFFECT ON BLOW FLIES 703

CI, factors affecting the pre-CI have been little stud- There were no obvious microenvironmental differ- ied. Blow ßy arrival times are not a constant. Although ences between the sites, although Site A was Ϸ20 m arrival times as low as 30 s have been reported (Gruner from a fence line, ditch, and low-trafÞc county road et al. 2007), location and colonization of a corpse can and Site B was Ϸ15 m from the solitary large tree in the be delayed by days owing to factors such as corpse pasture. For consistency, pigs were placed on their left wrapping or low temperature episode (Goff 1992, side with abdomens facing west. At the experimental Watson and Carlton 2005). Furthermore, blow ßies site, vegetation was typical for the upland Post Oak do not typically seek out carrion at night, although Savannah ecoregion of Texas (Correll and Johnston there have been at least two reports of nocturnal 1970), with this particular area dominated by oak oviposition under artiÞcial illumination (Greenberg (Quercus spp. L) and pecan (Carya illinoinensis 1990, Baldridge et al. 2006). (Wangenheim) K. Koch) trees, yaupon (Ilex vomito- Understanding the wide variation in adult arrival ria (Solander ex Aiton)) and American beautyberry times serves two purposes. From an ecological per- (Callicarpa americana L.) shrubs, and mixed grasses spective, it is useful to understand how adult blow ßies and forbs, predominantly bluestem (Andropogon spp. make use of a speciÞc carrion patch. As a highly mobile L) and buffalograss (Bouteloua dactyloides (Nutt)). group of insects, their choices about which patches to For the summer trials (7Ð9 August 2008 and 5Ð7 Sep- colonize affect diversity and species coexistence tember 2008), pigs were killed at 0745 hours and (Hanski 1987). Variation in adult ßy attendance at placed in the Þeld at 0845 hours. In winter Trial 1 (7Ð13 carcasses could also radically alter the critical ecosys- January 2009), pigs were killed at 0945 hours and tem service of carrion decomposition. Because many placed in the Þeld at 1045 hours; for winter Trial 2 (24 ßies involved in the carrion breakdown process are FebruaryϪ7 March 2010) pigs were killed at 0830 also human nuisance ßies, understanding the role that hours and placed in the Þeld at 1045 and 0945 hours, a carrion patch plays in mate-Þnding and adult nutri- respectively. Each trial period was selected for sea- tion could also play a role in developing control strat- sonally typical temperatures and predicted clear egies. However, the more direct value of understand- weather. To prevent nocturnal vertebrate scavenging, ing adult blow ßy behavior is its critical importance each carcass was placed beneath a wire cage each in creating accurate estimations of pre-CI lengths evening. The cage was removed each morning. (Tomberlin et al. 2011a). Fundamental information Each carcass was observed at hourly intervals fol- necessary to understand the pre-CI is documenting lowing placement in the Þeld, between sunrise and when, and under what conditions, adult blow ßies sunset as deÞned by the US Naval ObservatoryÐAs- appear at a carcass. Such factors play a role in the tronomical Applications Department ([USNOÐAAD] critical switch between the pre-CI and the post-CI: 2011). An observation consisted of a standardized col- acceptance of the carrion by the adult female ßies and lection of 10 directed sweeps of a 21-cm aerial net oviposition upon it. The purpose of this study, there- made over each carcass within 30 s. The ßies so col- fore, was to examine the role of season, species, and lected were preserved immediately in Ϸ80% ethanol. selected environmental and physiological factors on Ambient air temperature was recorded to 0.1ЊC, and the initiation and variation in population size at a wind speed was assessed on a 5-point scale using a carcass for locally dominant species of Calliphoridae. plastic portable anemometer (Dwyer Instruments, Environmental effects, such as temperature, time of Michigan City, IN): 0 was calm, 1 was Ͻ2.25 m/s, 2 was day, and wind level, affect blow ßy activity levels to 2.25Ð4.5 m/s, 3 was 4.5Ð9 m/s, and 4 was Ͼ9 m/s. the point that activity can be mathematically modeled Ambient light intensity was qualitatively assessed on a with some degree of success (Nicholson 1934, Digby 3-point scale with 0 equating to deep twilight, 1 for 1958, Crystal 1964, Vogt et al. 1983, Vogt 1988, Wall et 50Ð70% cloud cover, and 2 for normal daylight. Ob- al. 1993b). Within this context, the intent of this study servations were made until third-instar dipteran larvae was to characterize the species, sex, size, time of Þrst were observed on the carcass. arrival, and population size with respect to parameters Statistical Analysis. Only species with a total col- such as PMI, temperature, time of day, and season. lection of more than two individuals were used for statistical analysis using SPSS 15.0 (SPSS Inc, Chicago, IL). As there was a large difference in the total number Methods and Materials of ßies captured between trials, capture numbers were Field Site. For each trial, three white commercial transformed to proportionate catch per observation. swine (Sus scrofa domesticus L.) were obtained from One-way analysis of variance (ANOVA) was used to a commercial abattoir. The swine were mixed-sex, compare temperatures, wind speed, and light intensity with individuals weighing 60Ð80 kg (Catts and Goff between trials for each season. Full factorial ANOVA 1992). Each pig was killed by cranial trauma to avoid was run to compare number of ßies collected and time any tranquilizer effects (Patrican and Vaidyanathan of Þrst arrival by trial, species, and position for each 1995) and to better mimic traumatic human death season of collection. (Schoenly et al. 2007). Crepuscular time, the amount of time elapsed since Within1hofdeath, the swine were placed in a sunrise or time remaining until sunset was calculated fallow pasture near Snook, TX (30Њ 26Ј14Љ N/96Њ 25Ј12Љ for each observation (Mohr et al. 2011). Species-ap- W). Each pig was placed in full sun along a northÐ propriate accumulated degree hour values were also south line Ϸ40 m apart at sites labeled A, B, and C. calculated for each observation, using a lower biolog- 704 JOURNAL OF MEDICAL ENTOMOLOGY Vol. 51, no. 3

Table 1.Numeric capture of all collected Calliphoridae adults for each species, sex, trial, and season at each position during each of four trials (7–9 August 2008, 5–7 September 2008,7–13 January 2009, and 24 FebruaryϪ7 March 2010) in a rural pasture near Snook, TX

Position Trial Species Sex Total ABC Trial 1 Co. macellaria F 118 104 92 314 Co. macellaria M18101139 Ch. rufifacies F 121 208 105 434 Ch. rufifacies M2 4511 Trial 2 Co. macellaria F 209 381 324 914 Co. macellaria M 28 44 31 103 Ch. rufifacies F 247 325 267 839 Ch. rufifacies M15183568 Chrysomya megacephala (F.) F 0 2 0 2 Summer total 758 1096 870 2724 Trial 3 Co. macellaria F1001 C. vicina F581023 P. regina F 39 28 59 126 P. regina M2 5310 Trial 4 C. vicina F127726 P. regina F1326 P. regina M4 138 L. sericata F0101 Winter total 64 53 84 201 ical threshold of 10ЊC for Cochliomyia macellaria (F.) were caught in Trial 3 (January) than in Trial 4 (Feb- (Byrd and Butler 1996) and Chyrsomya rufifacies ruaryÐMarch; F ϭ 27.712; df ϭ 1; P ϭ 0.034). There (Macquart) (Byrd and Butler 1997), 8ЊC for Phormia were no signiÞcant differences in capture between regina Meigen (Nabity et al. 2006), and 1ЊC for Cal- positions (F ϭ 1.552; df ϭ 2; P ϭ 0.392), but there was liphora vicina Robineau-Desvoidy (Donovan et al. a signiÞcant interaction between trial and species (F ϭ 2006). Analysis of covariance (ANCOVA) was used to 21.62; df ϭ 1; P ϭ 0.002) such that signiÞcantly more regress proportionate capture data for each season, P. regina were captured than C. vicina in Trial 3; how- trial, species, and sex against objective time of day, ever, there was no signiÞcant difference in capture in wind speed, and light intensity. Accumulated degree Trial 4. hour, PMI, temperature, and crepuscular time were Environmental Conditions. The summer trials were tested as covariates. Lowest mean square error was characterized by high heat, up to 38.2ЊC. Trial 1 was an used to reÞne the regression equation. As part of this average of 4.2ЊC warmer than Trial 2, though temper- ANCOVA, TukeyÕs honest signiÞcant difference post atures for both trials were consistent with the normal hoc test was used to compare capture between factor temperature for the area for the time of year (National levels, generally time of day. Because the observations Environmental Satellite, Data, and Information Ser- generally did not meet the assumptions of normality or vice [NESDIS] 2011). Winds were generally light, and of equality of variances, the KruskallÐWallis (KW) test there was little cloud cover. In the Þrst3dofthe was used with DunnÕs posttest to compare on-carcass winter trials, Trial 3 averaged 10.2ЊC warmer than Trial population size across times of day, for species and 4 and was very close to the areaÕs record high of 27.8ЊC. sexes using GraphPad Instat 3.0 (GraphPad Software, On ensuing days, Trial 3 was Ϸ3.3ЊC cooler than Trial LA Jolla, CA). Size zero collections from early morn- 4, slightly cooler than the normal low of 5.0ЊC for ing hours before the Þrst capture of a ßy type were mid-January. Trial 4Õs temperatures were generally omitted to avoid artiÞcially inßating the test statistic. consistent with the local area normal of 9Ð20ЊC for late February to early March (NESDIS 2011). Wind speed was variable in the winter trials, although Trial 4 often Results had the strongest wind during mid-afternoon. Both of Over the course of this study, 2,925 calliphorid ßies the winter trials also exhibited at least 1 d each with were collected (Table 1). Although Ϸ10 species of heavy cloud cover. Trial 4 had two rain events: a short blow ßy occur in central Texas (Tenorio et al. 2003), shower at 0830 hours on 26 February and a sustained only four species were collected in great number: Co. light rain from 0830 to 1130 hours on 1 March 2010. No macellaria and Ch. rufifacies in the summer and C. ßies were collected during rain. vicina and P. regina in the winter. In terms of total For both male and female Co. macellaria, time of day collections, for summer trials, signiÞcantly more ßies was the only signiÞcant explanatory variable for pop- were captured in Trial 2 (September) than in Trial 1 ulation size, with an adjusted R2 of 0.146 for the males (August; F ϭ 35.451; df ϭ 1; P ϭ 0.027). There were no and 0.179 for the females (F Ͼ 2.038; df ϭ 1; P Ͻ 0.031). differences in overall capture between species (F ϭ For females, the relationship between time of day and 0.009; df ϭ 1; P ϭ 0.993) or position (F ϭ 2.455; df ϭ population size was borne out by the nonparametric 2; P ϭ 0.289); nor were there signiÞcant interactions test, with population sizes between 1845 and Ð1945 between species, trial, or position (F Ͻ 1.152; df ϭ 4; hours signiÞcantly higher than the 0645 Ð0845 (KW ϭ P Ͼ 0.05). For winter trials, signiÞcantly more ßies 31.502, df ϭ 13, P ϭ 0.0028; Fig. 1). For males, no May 2014 MOHR AND TOMBERLIN:ENVIRONMENTAL EFFECT ON BLOW FLIES 705

Fig. 1. Mean Ϯ 1 SEM of the percentage capture of each sex and species of ßy collected from the carcasses for each time of day. Summer Trials 1 and 2 are pooled, as are winter Trials 3 and 4. For the summer trials, n ϭ 6 for each time of day between 0645 and 1945 hours. For the winter trials, n ϭ 51 for each time of day. signiÞcant variation in the medians was found (KW ϭ level, with an adjusted R2 of 0.178 (F ϭ 1.565; df ϭ 14; 20.315, df ϭ 13, P ϭ 0.0876; Fig. 1). Similarly, time of P ϭ 0.015). The presence of high wind or heavy cloud day was the only signiÞcant explanatory variable for cover signiÞcantly reduced capture during their active female Ch. rufifacies, with an adjusted R2 of 0.173 (F ϭ time of day (F ϭ 4.232; df ϭ 2; P Ͻ 0.001). For P. regina, 2.269; df ϭ 13; P ϭ 0.3098). They also had a signiÞ- PMI strongly interacted with time of day (F ϭ 2.907; cantly higher population size at 1845 versus 0645 hours df ϭ 10; P ϭ 0.002), with later PMI seeing higher (KW ϭ 27.198, df ϭ 13, P ϭ 0.0117; Fig. 1). population. Males of this species, however, were ex- Male Ch. rufifacies had a slightly more complex plained by the interaction of ambient temperature and ANCOVA result, with PMI being the most important time of day (F ϭ 2.319; df ϭ 10; P ϭ 0.011). For winter explanatory variable, but including a signiÞcant inter- ßies of both sexes, the KW test statistics showed a action between PMI and time of day, with an adjusted strong likelihood of median differences between R2 of 0.300 (F Ͼ 2.516; df ϭ 13; P Ͻ 0.007). This times of day (KW Ͼ 18.275; df ϭ 10; P Ͻ 0.032). interaction may help explain the high standard error Despite this low P-value, the DunnettÕs post hoc test of the mean for Ch. rufifacies males (Fig. 1). found no signiÞcant differences in capture, proba- Populations of C. vicina were explained by a com- bly because of the large number of zero-value col- plex interaction of time of day, light level, and wind lections and ties. 706 JOURNAL OF MEDICAL ENTOMOLOGY Vol. 51, no. 3

Discussion Deonier (1940). Heavy cloud cover was a deterrent to activity, as also documented by Payne (1965) and Environmental Factors on Population Size. In this Deonier (1940). Heliotaxis cannot be assumed in this study, summer ßies population size was unaffected by species; however, Isiche et al. (1992) found them to wind. We expected a positive response because wind strongly prefer shady to sunlit conditions. This com- spreads odor cues and allows anemotaxis, which are plex interaction may indicate an overall greater sen- important in resource location (Ashworth and Wall sitivity to environmental conditions for this species. 1994). However, wind speeds as low as 2.5 m/s inhibit For P. regina, activity during the middle of the day is ßight in Lucilia cuprina (Wiedemann) (Diptera: Cal- unsurprising, as this species is less cold tolerant than liphoridae) (Vogt et al. 1983). Although wind speeds C. vicinaÐit is considered a summer active species in up to 4.5 m/s were observed in the summer, no such South Carolina, not far north of the study site inhibitory effect was seen, consistent with two studies (Tomberlin and Adler 1998). of Ch. rufifacies (Vogt and Starick 1985, Vogt et al. Male Flies. The collection of male blow ßies (Table 1985). These conßicting results suggest that the ßy 1) was unexpected, as they neither oviposit nor do body size may play an important role. This idea is they require a protein meal to produce sperm (Mack- borne out by the results of the winter ßies. C. vicina, erras 1933). They do, however, need to locate females, a relatively large blow ßy compared with Co. macel- so they are probably attracted to carcasses for mating laria or Ch. rufifacies (Mohr 2012) is reportedly ca- opportunities (Archer and Elgar 2003). Therefore, it pable of coordinated ßight between 4.5Ð8.0 m/s is not surprising that in males the on-carcass popula- (Digby 1958). In the winter trials, wind speeds above tions generally tracked with the relative size of female 9.0 m/s were frequently observed. These high speeds populations across the day. Synchronizing their activ- may explain why wind speed was a signiÞcant com- ity to females increases malesÕ likelihood of mating ponent of the regression equation for female C. vicina. (Zeil 1986) and avoids substantial wasted energy Temperature is a signiÞcant predictor of activity (Hocking 1953). Female ßies typically arrive at a car- level for a variety of species, explaining 97.7% of vari- cass either fully gravid or nulliparous (Mohr 2012). In ation in tabanid (Diptera: Tabanidae) host-seeking laboratory colonies of Co. macellaria cogener Cochlio- (Cilek and Schreiber 1996) and up to 67% of variation myia hominivorax (Coquerel), peak mating occurs in Lucilia sericata (Meigen) trap counts (Wall et al. preoogenty at 3Ð4 d old (Crystal 1964). Likewise, Ch. 1993a). For L. cuprina, temperature explained 74.3% of rufifacies mate early in life, before oogeny is complete within-day variation in catch rates (Vogt 1988), al- (Baumgartner 1993). Even if mating occurs at preoog- though that study did not attempt to separate the eny, it may be successful for males, as females of L. effect of time of day from temperature. In this exper- cuprina have been found to be refractory to further iment, temperature was never an explanatory variable mating attempts for up to 7 d following a Þrst mating for population size, but time of day was a predictor for (Smith et al. 1990), likely a sufÞcient period to com- all four species and both sexes. The signiÞcant rela- plete oogeny and oviposition. Female blow ßies re- tionship between time of day and population size at quire a protein meal before oogenesis, one which can the carcass seems to indicate that carcass attendance be readily obtained from decomposing animal tissue may have a strong circadian rhythm component. Solar- (Rasso and Fraenkel 1954). As both mates and protein activated circadian control might also explain the diel meal can be found together, this suggests that car- behavioral patterns (Saunders 2009). Adult Co. ma- casses may play an important role in adult blow ßy cellaria and Ch. rufifacies assemble at the carcass after biology well before the carcasses are used as an ovi- dawn and stay at a relatively constant level until sig- position site. Using carcasses as an aggregation point niÞcantly increasing in the2horsobefore sunset avoids extensive energy use during mate searching, (Fig. 1). and may also serve to increase the chances of suc- NocturnalÐcrepuscular activity is not uncommon in cessful reproduction in otherwise widely distributed Diptera, typically in hematophagous species (Barrozo species. et al. 2004). However, there is an abrupt drop-off of In this experiment, during both winter and summer, blow ßy activity after sunset (Payne 1965) and lack of the size of the ßy population on the carcass was gov- nocturnal oviposition (Baldridge et al. 2006, Amendt erned by time of day and extreme weather conditions. et al. 2008). Only in cases of artiÞcial illumination have The species collected in each season had notably sim- there been documented Þndings of nocturnal activity ilar diel patterns of behavior. These two observations of blow ßies (Greenberg 1990), probably because light seem to indicate that carcass attendance for these four is an exogenous activity stimulant, particularly in the species of necrophilous ßies is governed by an endog- presence of an odor cue (Wooldridge et al. 2007). enous circadian mechanism (Saunders 2009). Under- Curiously, the overnight resting places of the summer- standing the circadian rhythm of blow ßies to a carcass active ßies could not be readily located, although the may make it possible to predict how likely adult blow surrounding vegetation and trees and the experimen- ßies are to react to and locate a carcass at a given time tal carcasses themselves were searched thoroughly. of day. When paired with basic ecological information, There was a marked difference in diel behavior such as relative species abundance, understating the pattern in the winter species. Adult C. vicina were only diel pattern of activity would make the estimation of active on the carcass at midday, regardless of morning the pre-CI and the PIA much more accurate and re- temperatures (Fig. 1), consistent with the Þndings of liable, something that has long been a challenge for May 2014 MOHR AND TOMBERLIN:ENVIRONMENTAL EFFECT ON BLOW FLIES 707 forensic scientists (Tomberlin et al. 2011b). These Byrd, J. H., and J. F. Butler. 1997. Effects of temperature on Þndings also represent an important increase in the Chrysomya rufifacies (Diptera: Calliphoridae) develop- usefulness of the adult ßies themselves in forensic ment. J. Med. Entomol. 34: 353Ð358. investigations. Although these results were unable to Carter, D. O., D. Yellowlees, and M. Tibbett. 2007. Cadaver successfully model adult carcass attendance in terms decomposition in terrestrial . Naturwissen- of environmental factors, some inferences can be schaften 94: 12Ð24. Catts, E. P., and M. L. Goff. 1992. Forensic entomology in made. The strong diel pattern of ßy behavior allows, criminal investigations. Annu. Rev. Entomol. 37: 253Ð272. in a qualitative sense, an assessment of the likelihood Cilek, J. E., and E. T. Schreiber. 1996. Diel host-seeking that adults will respond to a carcass, and may explain activity of Chrysops celatus (Diptera: Tabanidae) in some of the variation in arrival times documented northwest Florida. Fla. Entomol. 79: 520Ð525. throughout the forensic entomological literature, an Correll, D. S., and M. C. Johnston. 1970. Manual of the important goal in meeting the legal challenges to fo- vascular plants of Texas. Texas Research Foundation, rensic evidence (National Academy of ScienceÐNa- Richardson, TX. tional Research Council [NASÐNRC] 2009). Crystal, M. M. 1964. Observations on role of light temper- Obviously, further research is necessary to eluci- ature age and sex in response of screw-worm ßies to date the complex relationship between adult blow ßy attractants. J. Econ. Entomol. 57: 324Ð325. Deonier, C. C. 1940. Carcass temperatures and their rela- behavior and decaying carrion, which might allow the tion to winter blowßy populations and activity in the development of mathematical models similar to those 2 Southwest. J. Econ. Entomol. 33: 166Ð170. already applied to blow ßy larvae. Although the R Digby, P.S.B. 1958. Flight activity in the blowßy, Calliphora values in this study were too low to merit serious erythrocephala, in relation to wind speed, with special calculation, the emergence of some environmental reference to adaptation. J. Exp. Biol. 35: 776Ð795. factors as signiÞcant begins to explain why adult ßies Donovan, S. E., M.J.R. Hall, B. D. Turner, and C. B. Mon- show such extreme variability in their response to a crieff. 2006. Larval growth rates of the blowßy, Calli- carcass. phora vicina, over a range of temperatures. Med. Vet. Entomol. 20: 106Ð114. Goff, M. L. 1992. Problems in estimation of postmortem interval resulting from wrapping of the corpse - a case Acknowledgments study from Hawaii. J. Agric. Entomol. 9: 237Ð243. The Texas A&M University Institutional Animal Care and Greenberg, B. 1990. Nocturnal oviposition behavior of blow Use Committee required no animal use protocol for the swine ßies (Diptera: Calliphoridae). J. Med. Entomol. 27: 807Ð used in this experiment, as the were deceased at the 810. time of acquisition from a commercial supplier. We thank Gruner, S. V., D. H. Slone, and J. L. Capinera. 2007. Fo- Roy W. Vajdak for access to the pasture land. This publication rensically important Calliphoridae (Diptera) associated represents part of R.M.M.Õs dissertation. Partial Þnancial sup- with Pig Carrion in Rural North-Central Florida. J. 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