Medical and Veterinary Entomology (2005) 19, 379–391 Spatial and temporal variability of necrophagous Diptera from urban to rural areas C. HWANG1,3 andB. D. TURNER1,2 1Department of Life Sciences and 2Department of Forensic Science and Drug Monitoring, King’s College London, U.K. 3Department of Bioresources, Da-Yeh University, Da-Tsen, Chang-Hua County, Taiwan (current address). Abstract. The spatio-temporal variability of necrophagous fly assemblages in a linear series of habitats from central London to the rural surroundings in the south-west was studied using bottle traps between June 2001 and September 2002. A total of 3314 individuals in 20 dipteran families were identified from 127 sampling occasions. Calliphoridae accounted for 78.6% of all the dipteran speci- mens, with Calliphora vicina Robineau-Desvoidy, being the most abundant spe- cies (2603 individuals, 46.9%). Using canonical correspondence analyses (CCA) on 72 fly taxa, six sampled sites and 36 environmental variables, three habitat types corresponding to three groups of flies were identified. These were an urban habitat characterized by C. vicina, Lucilia illustris (Meigen) and L. sericata (Meigen), a rural grassland habitat, characterized by L. caesar (Linnaeus) and a rural woodland habitat characterized by Calliphora vomitoria (Linnaeus), Phaonia subventa (Harris), Neuroctena anilis (Falle´n) and Tephrochlamys flavipes (Zetterstedt). Intermediate species (L. ampullacea Villeneuve and P. pallida (Fabricius), located between the three habitats, were also found. Temporal abun- dance of the 10 most abundant species showed fluctuations between seasons, having low numbers of captured individuals during winter. Correspondence analysis showed clearly seasonal patterns at Box Hill site. The species–habitat associations suggest habitat differentiation between necrophagous guilds in this area and may be of ecological value. Key words. canonical correspondence analysis, forensic entomology, habitat association, necrophagous Diptera, urban ecology, U.K. Introduction C. stelviana (Brauer & Bergenstamm) lives in both environ- ments (Nuorteva, 1963). Blow fly species–habitat associations and the characteristics Species sometimes show inconsistencies with such habitat of local fly communities vary both geographically and with association patterns. Lucilia sericata (Meigen) has been habitat. Calliphora vomitoria (Linnaeus) and Lucilia ampul- recorded commonly in open pasture in England (Smith & lacea Villeneuve are abundant in dense-covered vegetation, Wall, 1997b; Davies, 1999) and New Zealand (Dymock & whereas Lucilia illustris (Meigen) is more common in open Forgie, 1993), whereas the findings of Nuorteva (1963, conditions (heliophilic) (MacLeod & Donnelly, 1957). 1966) and Isiche et al. (1992) in Finland and southern Calliphora vicina Robineau-Desvoidy is synanthropic, England indicated that it was most common in urban habi- whereas C. vomitoria and C. loewi Enderlein are more tats. Lucilia caesar (Meigen), a dominant blow fly species in rural species (Nuorteva, 1963; Smith, 1986) and a wooded area in west Spain (Martı´nez-Sa´nchez et al., 2000) and agricultural sites in north-east England (Davies, 1999), was considered somewhat synanthropic and mainly distributed in urban sites by Nuorteva (1963, 1966) and Correspondence: Dr B. D. Turner, Life Sciences, King’s College Isiche et al. (1992). Nuorteva (1963) has suggested that London, Franklin-Wilkins Building, 150 Stamford St., London SE1 L. caesar is less synanthropic towards southern Europe. 9NH, U.K. Tel.: þ 44 (0)207 8484292; fax: þ 44 (0)207 848 4500; Lucilia illustris also showed a wide range of habitats in e-mail: [email protected] different studies (Nuorteva, 1963, 1966; Davies, 1999). # 2005 The Royal Entomological Society 379 380 C. Hwang and B. D. Turner These published findings are at variance with each other, indicating that associations with habitat vary locally. The distribution of a species results from the complicated eco- logical interactions between organisms and their physical environments, such as competition (Kouki & Hanski, 1995) and niche differentiation (Price, 1997). Some comparative studies on blow flies have been carried out in varied habitats, such as urban, suburban, pasturages and woodlands in the U.K. (MacLeod, 1956; MacLeod & Donnelly, 1957, 1958, 1962; Isiche et al., 1992; Smith & Wall, 1997a, b; Davies, 1999). No such studies have been done previously to associate the major habitat types and necrophagous flies in the London area, though incomplete surveys and unintentional records have been found (Parmenter, 1953; Owen & Owen, 1975; Owen, 1978; Smith, 1986; and references therein). Besides these spatial variations, the temporal activities of flies vary due to the interactions between intrinsic rhythms (e.g. life history, reproductive cycle, etc.) and extrinsic sea- sonal effects (e.g. temperature, photoperiod and availability of resources). The clear seasonal variations in temperature offer a good opportunity to evaluate the temporal variabil- ity of fly faunas. Some studies on temporal variations of corpse faunas have been done in England (Davies, 1990, 1999; Isiche et al., 1992; Smith & Wall, 1997a), but these pig liver were done only during the warmer months of April to Na2S + September. No systematic information is available on the pig liver seasonal variability of the fly fauna in England. This study compares the necrophagous fly fauna in a linear series of habitats of differing levels of urbanization Fig. 1. Design of the bottle trap. Details in text. in Greater London and surroundings, focusing particularly on temporal and habitat associations. liver is anchored to the inner bottom of the chamber using tape. A 15 ml glass vial, fixed on the inner wall by a wire support, contains 10 ml of a 30% sodium sulphide (Na2S) Materials and methods solution and a piece of liver (about 5 g) as chemical attrac- tant. The two halves of the trap are push-fitted together Design of the bottle trap and are secured by strips of waterproof adhesive tape. To avoid disturbance by ground dwelling animals and strong Many trapping methods using olfactory stimuli have winds, the traps are fixed above ground to tree trunks or been developed for sampling blow flies (Hall, 1995). To pillars using wire. This design is cheap, easy to make, obtain specimens in good condition for identification convenient to transport to the field, quick to set in position (Norris, 1965), a modified cone trap, based on a soft and convenient to bring live flies back to the laboratory. drink bottle with a baited target (Fig. 1), was developed for this study. The bottle trap, made from two 1.5-L clear plastic soft drink bottles with a diameter of 8 cm, consists Study area of two parts, the upper collection chamber and the lower bait chamber. The collection chamber is formed from the Six sites, subjectively categorized into levels of four urba- top parts of two bottles, one pushed inside the other. Two nization (urban, suburban, rural and semi-natural; defined centimetres of the inner bottle protrudes and is used to in Table 1), were sampled in this study. Basic geographical connect to the bait chamber. The walls of the outer bottle information on the sites is given in Table 1. are punctured with many small holes (about 1 mm in dia- meter) for ventilation. The height of the upper chamber is 30 cm and the height of the cone part (inner bottle) is 8 cm. Trapping, preservation and identification The bait chamber is the bottom part of a bottle with a height of 8 cm. Entry holes are made by cutting the plastic One bottle trap was fixed, about 1.5 m above ground, at with an X shape and folding back the triangular portions to each of the six sites. With the exception of the Waterloo form a square hole with four inner vanes restricting escape. roof level site, shaded positions were selected for the traps A disposable plastic weighing boat containing 30 g of pig to avoid thermal stress for the captured flies. Traps were set # 2005 The Royal Entomological Society, Medical and Veterinary Entomology, 19, 379–391 Spatio-temporal variability of necrophagous Diptera 381 Table 1. Descriptions of the sampled sites, abbreviations (Abbr.), grid references (OS grid ref., Ordnance Survey, 1989, 1 : 50 000), distance (Dist.) to centre of London (defined as St Paul’s Cathedral) in kilometres and altitudes (Alt.) in metres. Dist. Alt. Site Abbr. OS grid ref. (km) (m) Description and definition Finsbury Park FP TQ866319 6 25 An urban habitat with dense housing and private gardens, with commercial activities limited to a few streets only Waterloo ground WG TQ803311 2 5 This area is highly urbanized chiefly level for commercial purposes with very limited housing and gardens Waterloo roof WR TQ803311 2 23 The same area as WG, the south-western level corner of the roof of the east-wing of Franklin-Wilkins Building, Waterloo campus of King’s College London. The distance above ground is about 18 m (almost directly above site WG) Stoneleigh SL TQ644229 20 45 A suburban habitat with less dense housing, larger gardens and very few commercial activities Juniper Hall JH TQ524173 33 55 A rural habitat chiefly of pasturelands and agricultural activities. This area has some patchy housing and woodlands Box Hill, BH TQ517178 34 135 A semi-natural habitat chiefly of woodlands National Trust with little human interference. Used for leisure and occasional pasturage out every 2–4 weeks, depending on weather conditions, and were trapped more than 10 times in the 127 sampling occasions, normally left for a 2-day period, from June 2001 to were plotted. The Anthomyiidae taxon was omitted from this September 2002. The sampling period was extended by up definition. Shannon’s diversity index was calculated using to 6 days during the winter. Air temperatures were natural logarithms of the number of individuals caught daily. recorded every 30 min using data loggers (TinyTag Plus, Gemini Data Loggers, Chichester, U.K.) attached beside Canonical correspondence analysis. To understand the each trap. Flies were killed by putting the trap collection factors that affect the distribution of flies, two data matrices, chamber in a À70C freezer for 10 min.