Habitat Preference of Forensically Important Diptera in Toco, Trinidad, WI

Rachel McNeal Texas A&M University

Abstract: Species of Diptera are studied across the world to help further understand patterns and habits so the behavior can be applied in forensics. In this study, habitat preference for various types of forensically important Callliphoridae, Muscidae, and Sarcophagidae were studied. A coastal habitat and an inland habitat were compared. Fly trap bags using putrescent egg solids and water were set up at inland and coastal habitats. The flies were analyzed and identified from the traps. There were 16 specimens of Calliphoridae, twelve Sarcophagidae specimen, and seven Muscidae specimen. Members of the Sarcophagidae were more prevalent at the coastal habitat, while members of Muscidae and Calliphoridae were significantly more prevalent at the inland habitat (p=0.004).

Keywords: forensics, entomology, investigation, habitats

Due to high species level diversity, people and knowledge of the local fauna (Bryd and have been studying forensically important Caster, 2010). Understanding how these insects on islands. Because of the isolation, behavioral patterns work for various islands have some of the most diverse families and species of forensically arthropod life that can be found (Gillespie important flies can help predict trends, and Roderick, 2002). Globally, the field of which would not only help solve for TOC forensic entomology is expanding as more and PMI, but it may also help show a scientists begin to learn about and discrepancy in behavior if those patterns are understand forensically important insects in not followed, which could lead forensic their area. Studying Calliphoridae, scientists to determine why those trends are Sarcophagidae, and Muscidae flies is slowly not occurring. Since a large factor of becoming more and more common. forensic entomology is the distribution, diversity, and abundance of various species Insects, such as flies or beetles, are a good of carrion flies in locations, many surveys way to determine the time of colonization have been done to map these species of flies. (TOC), which can equal the post mortem Klong-Klaew and associates used interval (PMI). Flieswill arrive on carrion geographic and climactic factors to map two almost immediately at the time of death as subfamilies of flies: Lucilinae and well as colonizing in a pattern that is Chrysomyinae (Klong-Klaew et al., 2018). predictable based on environmental factors Season, geographical location, altitude, and and different settings. Research conducted type of habitat have been identified as on Calliphoridae of the Columbian important factors that influence the type and Caribbean coast showed that there was an abundance of carrion flies found within an abundance of blow flies in the urban areas, area (Zabala et al., 2014). However, very including species known to prefer human little research has been done on how settlements (Santodomingo-M. et al., 2014). proximity to coastal (marine) environments However, this research did not compare affects the abundance and diversity of these urban sites to rural sites, nor was it carrion flies that appear, as most previous determined whether the coastal area had any research has focused on urban versus rural impact on the species that appeared. This areas (Brundage et al., 2011) Few studies research was designed to determine if there have investigated the habitat preference of is any preference for coastal habitats or forensically important species of Diptera on urban habitats. the Caribbean islands (Yusseff-Vanegas and Agnarsson, 2016), no research about habitat Materials and Methods: preference on the island of Trinidad. The research took place over three days at The Caribbean Islands and surrounding the end of May 2019. Two sites were tested, areas, such as South America, offer a unique one inland and one at the coastline, 2.68 km opportunity to investigate the diversity and apart. The traps used were the RESCUE! habitat preferences of forensically important Outdoor Non-Toxic Disposable Fly Traps insects. For instance, nine different species model number FTD, which contain sucrose, in four different genera of female flesh flies putrescent whole egg solids, yeast, have been identified in Southern Brazil by trimethylamine, and indole. The inland traps distinguishing their genital characteristics were placed at the Jammev Beach Resort, (Vairo et al., 2015). By studying insects Toco, Trinidad, WI. The coastal traps were inhabiting these islands, more can be placed at the Keshorn Walcott Galera Point understood about how these insects operate Lighthouse, Toco, Trinidad, WI. Each site and the importance of their behaviors in new is displayed in Figure 1.

Figure 1.

Fig 1. A satellite map of trap placement in Toco, Trinidad, with the two locations marked.

There were three trials for each test site, Results consisting of a maximum three traps per site. A list of the species and families of insects Traps were deployed for 24 hours. Both collected from each is provided in Table 1. inland and coastal traps were placed a A total of 20 specimens were collected at the minimum of 1 meter away from each other. inland site, and a total of 15 specimens were The coastal traps were placed a minimum of collected at the coastal site (Figure 2). The 10 km away from the coastline. Traps were inland traps had much more fly activity. reused for subsequent trials. All trapped There was a higher abundance for the insects were identified to the lowest Sarcophagidae to be drawn to the coastal taxonomic level using local keys traps, the Muscidae and Calliphoridae flies (Whitworth, 2010). The contents were had a higher abundance at the inland traps compared between the two traps. A Fisher’s (df=2, p = 0.004). exact test was calculated to determine statistical significance of the abundance at each test site. Table 1. List of forensically important species at each test site.

Habitat Species Coastal Calliphora vicina (1)

Lucilia cuprina (3)

Sarcophagidae (9)

Lucilia sericata (1)

Fanniidae (1)

Coleoptera – Scarabaeidae (6) Inland Lucilia cuprina (9)

Sarcophagidae (3)

Muscidae (5)

Musca domestica (2)

Fanniidae (1)

12

10 9 9

8

6 5

4 3 3 2 2 1 1 1 1 Number Specimen Number of 0 0 0 0 0

-2

Species Found

Inland Coastal

Figure 2. Number of each species found at the two test sites.

25

20 20

15 15

10 Diptera Collected Diptera Collected

5 NumberForensically of Important

0

Inland Coastal

Figure 3. Comparative graph of total number of forensically important Diptera collected at each site.

Discussion 2017). This study also did not find a habitat preference of Sarcophagidae, but rather they Sarcophagidae, the flesh flies, were studied were evenly distributed throughout the in Columbia in terms of habitat and diet habitats investigated. Therefore, the preference, and it was found that they have a preference for the coastline may be due to dietary preference of decomposing fish over diet preferences, rather than just habitat feces or rotting fruit (Valverde-Castro et al., preference. Muscidae, the house fly, was in higher habitats and seasons this species prefers. abundance at the inland traps. These traps Researchers in Thailand are using various were closer to civilization and had human climactic factors and geographic distribution activity at a higher rate than the ocean traps to construct a predicted distribution map of did. It has been hypothesized that the four forensically important species of lifespan of Musca domestica is affected by Chrysomyinae (Klong-klaew et al., 2018). the amount of sugar in the diet, and that The same team conducted a similar study in larger amounts of sugar in the diet may the same area with the subfamily Luciliinae cause longer lifespans (Lysyk, 1991). (Klong-klaew et al., 2018). Similar research Additional research has shown that female was conducted in South Africa with seven M. domestica lay the highest number of eggs species of Calliphoridae (Richards et al., when they are feed a diet of milk and yeast, 2009). Geographic distribution prediction but lay the heaviest eggs when fed a diet mapping could be a very useful tool for rich in protein (Pastor et al 2011). All eggs forensic scientists to help understand what had a 90% successful hatching rate, except species are in high populations in that area the eggs where the adult female had a diet of based on the climate and habitat. just sugar (Pastor et al., 2011). Another study has shown that the best diet for egg Further research into diet analysis and production of M. domestica was a 3:1 ratio habitat preference of Sarcophagidae, of Kraylift yeast and icing sugar (Shipp and Muscidae, and Calliphoridae flies could help Osborn, 1967). Muscid fly populations near understand how these flies behave and how urban areas, like the area that the inland the patterns that are exhibited can be applied traps were placed, may have longer lifespans to forensics and maybe even predict how the due to the garbage and disposed of food flies would behave based on habitat and from humans. Since there is an abundance climate. Understanding what flies are of food with a variety in diet, these flies can attracted to various areas may help have nutrients leading to a successful egg determine what species would show up in hatching diet, perhaps leading to larger higher proportions and predict what flies populations in total. This may be the cause may inhabit a body first. of an increase in M. domestica, as well as other Muscidae, in the inland traps. The Coleoptera (beetles) collected in the traps belong to the Scarabaeidae which can Calliphoridae, the blow flies, preferred the have forensic importance based on species. inland traps near urban areas. Several Beetles tend to be found later in the studies have investigated how season and decomposition process of a cadaver and habitat effect the behaviors and abundance another time of colonization (TOC) can be of calliphorid flies (Hwang and Turner, determined to help determine an accurate 2005). L. cuprina was found in high post mortem interval (PMI). By using the abundance at the inland sites. In Santa Clara predictable developmental stages of each County, California, it was found that L. species present, scientists can calculate a cuprina exhibited higher populations during TOC (Bala and Singh, 2015). However, the spring and summer months and thrived since species could not be determined, more in urban settings (Brundage et al., 2011). research would need to be done to see if Due to the timing and setting being similar these beetles were known to be forensically to the research conducted here, it is possible important and why they only appeared on for there to be a trend on the types of the coastal traps. Further research on the Coleoptera that were only found at the preference. However, due to small sampling coastal site should be performed, as all the size, limited time for trials, and weather, Coleoptera found were closely related, if not further research should be performed to help the same species. support or disprove this trend.

Conclusion Acknowledgments

Mapping forensically important flies can be Thank you to Dr. Adrienne Brundage, Dr. important into determining why some Kevin Conway, Kiara Dietze, Cody Murph, species would show up in higher proportions Madison Karsteter, Luke Pemberton, and at a scene. Sarcophagidae appeared in higher Texas A&M University for assistance with abundance at the coastal traps while this research. Muscidae and Calliphoridae appeared in higher abundance at the inland traps. This trend may possibly be due to habitat

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