SCUTTLE FLY INFESTATION IN DETERIORATING FLUID-PRESERVED SPECIMENS (DIPTERA: PHORIDAE: MEGASELIA SCALARIS)
KATE POCKLINGTON
Lee Kong Chian Natural History Museum, National University of Singapore, 2 Conservatory Drive,
Singapore, 117377 email: [email protected] Downloaded from http://meridian.allenpress.com/collection-forum/article-pdf/29/1-2/67/1503634/0831-4985-29_1_67.pdf by guest on 27 September 2021
Abstract.—An infestation of scuttle flies, Megaselia scalaris (Loew, 1866), was found in deteriorating 19th century fluid-preserved specimens contained in a glass tank in the Vertebrate Spirit Store at Oxford University Museum of Natural History. A test showed ethanol levels were inadequate to maintain specimen preservation, and a vast amount of fluid had evaporated, leaving the specimens exposed and in a state of decomposition. The conditions provided a suitable habitat for the infestation and subsequent reproduction of M. scalaris. Here, I provide a method for the removal of M. scalaris from infested museum collections, as well as notes on their behavior and the conditions that promote fly infestation. Remedial salvage of the specimen that involves refixation, staging, and
final preservation in 75% industrial methylated spirits (IMS/H2O) is described. Key words.—fluid-preserved, wet, and alcohol collections, pest management, infestation, scuttle flies, Phoridae, Megaselia scalaris, conservation, treatment, natural history collections Associate Editor.—Christine Johnson
INTRODUCTION In 2008, the Oxford University Museum of Natural History carried out a conservation project in the Vertebrate Spirit Store to refurbish the storage facilities, improve the condition of the vertebrate wet collection, and resolve any preservation issues. The environmentally stable Vertebrate Spirit Store (,18uC 65uC per 24 hour period) holds scientifically important material as well as historic specimens dating back to the late 18th century. During a routine check of fluid levels, a 20-liter tank containing both whole and dissected specimens of fluid-preserved fish dating from the late 1890s was found with greatly reduced fluid level and infested with thousands of active small flies, eggs, larvae, and pupae (Fig. 1). Larvae were actively feeding, and pupae lined the sides and lid of the tank. The infested tank had been covered with a flat sheet of glass, which was sealed with soft white paraffin and had an overhang of approximately 1 cm on all edges. A sample of the remaining solution (approximately 5 liters) was strained and measured with an Anton Paar DMA 35N density meter and found to be 9.8% alcohol/water and pH 7.3. The specimens had been preserved previously in formalin, with an assumed standard 5–10% formalin dilution. The deteriorated and exposed specimens created an ideal habitat for infestation. An adult fly (Fig. 2) was caught and identified by dissection of the male genitalia (Disney 2008) by Darren Mann of the Hope Entomological Collection, Oxford University Museum of Natural History, as Megaselia scalaris (Loew, 1866). Staff in the Entomology Department noted an increased presence of M. scalaris throughout the museum, where the flies may have been attracted to warmer conditions and live specimen tanks in the area. Robinson (1975) described a successful method of eradicating flies from cockroach-rearing containers by limiting potential oviposition sites and vacuuming adult flies from heavily infested containers. Since this method of removal is not practical for removing flies from fluid-preserved specimens, I had to devise an alternative method of removal.
Collection Forum 2015; 29(1–2):67–72 E 2015 Society for the Preservation of Natural History Collections 68 COLLECTION FORUM Vol. 29(1–2) Downloaded from http://meridian.allenpress.com/collection-forum/article-pdf/29/1-2/67/1503634/0831-4985-29_1_67.pdf by guest on 27 September 2021
Figure 1. Tank containing two 19th century specimens of fish largely infested with Megaselia scalaris,the surfaces can be seen covered with pupae cases and larvae.
NATURAL HISTORY OF MEGASELIA SCALARIS Megaselia scalaris (Loew, 1866) is a species of phorid fly (Diptera: Phoridae), commonly known as scuttle flies or coffin flies. They are most abundant in areas of decomposition and liquefaction of animal and plant material. Megaselia scalaris is frequently found in tropical climates; its life-cycle ranges between 11.5 days and up to 2 months, depending on temperature (Mainx 1964; Disney 2008; Kamarudin and Khoo 2011). Megaselia scalaris tend to lay eggs on decomposing material that has become fluid, allowing larvae to feed as soon as they hatch. The optimum consistency is 50–80% fluid (Kamarudin and Khoo 2011); a higher fluid concentration results in increased larval drowning. The tank discovered in the Oxford collection contained a consistency in this range, where decomposing specimens were exposed and liquefaction presented an organic solution of material leached from the fish. Some areas were covered with fungal growth, which also serves as a suitable growth medium for M. scalaris (Disney 2008). As detritivores, M. scalaris larvae depend on moist decaying and relatively fluid plant or animal matter suitable for their sponging mouthparts. Although the adults do have tooth-like structures, these are used just for emergence from the pupa (Sukontason et al. 2003). Pupae cases were found in clusters lining most of the drier surfaces of the tank (Fig. 3), with larvae seen moving between them. This suggests the larvae pupate away from the moist conditions to be able to fasten themselves to the drier surface. I have also observed M. scalaris at the Raffles Museum of Biodiversity Research at the National University of Singapore (before moving and becoming the newly established Lee Kong Chian Natural History Museum). Adults of M. scalaris were particularly 2015 POCKLINGTON—SCUTTLE FLY INFESTATION 69 Downloaded from http://meridian.allenpress.com/collection-forum/article-pdf/29/1-2/67/1503634/0831-4985-29_1_67.pdf by guest on 27 September 2021
Figure 2. Male adult of Megaselia scalaris retrieved from infestation. attracted to discolored waste alcohol from a range of fluid-preserved vertebrates and invertebrates and appeared within half an hour of opening a container. Often M. scalaris are so attracted to this fluid that they ultimately drown trying to land on it. There is evidence that M. scalaris is resistant to chemicals and solvents such as emulsion paint, shoe polish, and alcohol (McCrae 1967). When adult M. scalaris were sprayed with
75% industrial methylated spirit (denatured ethanol)/water (IMS/H2O), this seemed to only knock them out temporarily. Once the alcohol evaporated, the adult flies revived within a few minutes. This ability to tolerate a variety of chemicals, solvents, and tissue (both living and decomposing) creates problems in trying to eliminate such a large infestation. Furthermore, it was unclear how to prevent further infestations in the fluid-preserved collections that were scientific, educational, and historic. Apart from the risk to the collections, M. scalaris also poses a health risk, having been found to cause myiasis (parasitic invasion) in living animals, including humans (Disney 2008). Preventing the spread of the infestation once the tank was removed was a key factor in deciding how to avoid disturbing the adult flies, since they can escape and enter minute spaces. They have been known to penetrate eight layers of gauze at 20 squares to the linear inch (Roberg 1915). Thus, the initial migration to and from the tank may have been relatively easy for this species.
MITIGATION Preparatory fumigation was conducted with a standard can of RaidH House and Garden Bug Killer, following the instructions on the label and safety data sheet (SDS). 70 COLLECTION FORUM Vol. 29(1–2) Downloaded from http://meridian.allenpress.com/collection-forum/article-pdf/29/1-2/67/1503634/0831-4985-29_1_67.pdf by guest on 27 September 2021
Figure 3. Clusters of pupae cases located on the drier areas of the tank.
The inside of the tank was sprayed and sealed with duct tape, followed by spraying of all three rooms of the store, and entry was barred from the rooms overnight for approximately 14 hours. The efficacy of Raid was a concern because of the species’ general resistance to chemicals and the fact that M. scalaris is not listed as a target pest. Raid House and Garden Bug Killer Formula 7 contains water, butane, propane, petroleum distillates, isobutane, allethrin, and D-Phenothrin (SC Johnson 2009). The store was examined the following day for flies. Many dead adult flies were found around the perimeter of the tank, although there seemed to be no effect on the larvae and pupae cases. The store was also examined for other specimens that had low levels of preservative but had not yet undergone conservation treatment. One container with Bos taurus was found to have a few M. scalaris specimens in the low level of preservative; this was easily remedied since the infestation was only in the fluid and not the specimen itself. The fluid was replaced with 75% IMS/H2O and monitored with no noted changes. The ensuing treatment of the badly infested tank was completed outdoors, in order to provide adequate ventilation for health and safety purposes, while also removing the infestation from inside the museum. This provided us the means to thoroughly survey the condition of the specimens without infecting other collection areas. After rinsing the tank and specimens with water, the decomposition was found to have left very little salvageable material, and none of the material was suitable for DNA analysis (Fig. 4). The specimens had begun to dehydrate in exposed areas from the low level of preservative. The remaining fluid was strained to remove any M. scalaris and was rebottled for disposal. An initial attempt to drown M. scalaris using 10% formalin as 2015 POCKLINGTON—SCUTTLE FLY INFESTATION 71 Downloaded from http://meridian.allenpress.com/collection-forum/article-pdf/29/1-2/67/1503634/0831-4985-29_1_67.pdf by guest on 27 September 2021
Figure 4. Cyprinus carpio Linneaus, 1891 removed from the infested tank and flushed with water. a fixative failed, larvae could be seen floating to the surface and crawling to the lid of a well-sealed jar. After 3 days the larvae were still alive. Harrison and Cooper (2003) report that M. scalaris larvae are able to swallow air into the gut allowing buoyancy to avoid drowning. The specimens were injected with 10% formalin to flush the larvae from within. The specimens were again placed in 10% formalin and monitored until most of the larvae had floated to the surface. These were removed, placed in a bowl, and covered in boiling water to destroy them. Boiling water, or freezing, should only be used to exterminate the flies once removed from the infested specimens or containers. Irretrievable areas of decomposition were cut away with a scalpel and disposed. The remaining specimens were stored in 10% formalin for 3 months in a suitable container with a ground glass lid and soft white paraffin sealant. The specimens were monitored for active infestation, and the fluid was strained and replaced every other week. Once the emergence of larvae had ceased, the specimens were rinsed in distilled water and staged at a20% IMS/H2O interval per week until reaching the required strength of 75% IMS/H2O.
DISCUSSION AND CONCLUSIONS Topping up of preservatives is an essential museum duty, but the concentration of the remaining preservative and the pH should be tested, and the fluid should be replaced entirely where possible as a standard to prevent M. scalaris infestation. Fluid replacement is often overlooked, and the ease of topping up often results in preservative dilution.
Preservative strength should ideally be at 75% IMS/H2O, but can suffice at 56% IMS/ H2O. Regular condition checks of fluid-preserved collections should include the level of fluid, sealants, composition of preserved material, leaching lipids found on the surface of the fluid, and any decomposing material. Any problems should be brought to attention and remedied immediately. 72 COLLECTION FORUM Vol. 29(1–2)
Owing to the presence of Megaselia scalaris almost worldwide, I propose including them into integrated pest management (IPM) programs to ensure recognition by museum staff. The behavior of M. scalaris is notable by their attraction to areas of museums keeping fruit, live specimens, or fresh collections from field work. They are distinguished by their “scuttling” movements and tend to run rather than fly when approached. Museums tend to focus integrated pest management (IPM) systems on dry organic material. Often fluid-preserved specimens are overlooked, since they attract fewer pests (e.g., silverfish on exterior labels). Megaselia scalaris should be recognized as seriously as Downloaded from http://meridian.allenpress.com/collection-forum/article-pdf/29/1-2/67/1503634/0831-4985-29_1_67.pdf by guest on 27 September 2021 other museum pests, since they can cause extensive damage. As found here, very little scientific, historic, or educational material was retrievable for analysis from the infected specimen. This infestation occurred in 9.8% alcohol/water. It would be interesting to determine the minimum preservative concentration at which Megaselia scalaris cease to exist and the maximum point they are attracted to decay in containers containing formalin and ethanol. Disney (2008) reared M. scalaris from a snake preserved in alcohol, yet there is still little insight into this problem. It is likely that other museums have had problems concerning Megaselia scalaris;I would therefore request those who may have had a similar experience to contact me, so that we can work together to further our understanding of the infestations of these flies in museum collections.
ACKNOWLEDGMENTS
Many thanks to Janet Waddington for her valuable review and constructive comments, Christine Johnson for patience and clear guidance, and to Darren Mann for his support, advice, and entomological excellence.
REFERENCES
Disney, R.H.L. 2008. Natural history of the scuttle fly, Megaselia scalaris. Annual Review of Entomology 53:39–60. Harrison, D.A. and R.L. Cooper. 2003. Characterization of development, behaviour and neuromuscular physiology in the phorid fly, Megaselia scalaris. Comparative Biochemistry and Physiology Pt A. 136:427–439. Kamarudin, M.I. and C.K. Khoo. 2011. Megaselia scalaris as food of domesticated Aerodramus fuciphagus swiftlet. International Conference and Training on Swiflet Ranching (ICOTOS). 2011. Terengganu: Malaysia. Mainx, F. 1964. The Genetics of Megaselia scalaris Loew (Phoridae): A new type of sex determination in Diptera. The American Naturalist 98 (203), 415–430. McCrae, A.W.R. 1967. Infestation of emulsion paint by the fly Megaselia scalaris (Loew) (Dipt., Phoridae). Entomologist’s Monthly Magazine 102:241–243. Roberg, D.N. 1915. I. The role played by the insects of the dipterous family Phoridae in relation to the spread of bacterial infections. II. Experiments on Aphiochaeta ferruginea Brunetti, with Cholera vibrio. The Philippine Journal of Science Section B Tropical Medicine 10:309–336. Robinson, W.H. 1975. Megaselia: M. scalaris. Diptera: Phoridae associated with laboratory cockroach colonies. Proceedings of the Entomological Society of Washington 77(3):384–390. SC Johnson. 2015. RaidH House & Garden Bug Killer Formula 7. http://enlight.consumercare.net/scripts/cgiip.exe/ WService5enlight/scj/kb/1607/19933745_1428578807 (9 October 2015). Sukontason, K., K.L. Sukontason, S. Piangjai., N. Boonchu, T. Chaiwong, and R.C. Vogtsberger. 2003. Mouthparts of Megaselia scalaris (Loew) (Diptera: Phoridae). Micron 34(8):345–350.