Surface ultrastructure of third-instar Megaselia scalaris (Diptera: Phoridae)

Abstract

We describe some ultrastructure of the third-instar Megaselia scalaris (Diptera: Phoridae) using scanning electron microscopy, with the cephalic segment, anterior spiracle and posterior spiracle being emphasized. This study provides the taxonomic information of this larval species, which may be useful to differentiate from other closelyrelated species.Key words: Megaselia scalaris -ultrastructure -third-instar -scanning electron microscopy -forensic entomology Megaselia scalaris (Loew), humpbacked fly, is an insect of medical importance worldwide. In addition to causing myiasis in humans (Trape et al. 1982, Singh et al. 1988, Singh & Rana 1989, it has also been reported as a forensically-important fly (e.g. Barnes 1990, Disney 1994. Larvae of this species have more recently been reported from both exposed human corpses and within a tightly sealed corpse (Greenberg & Wells 1998). Thus, the identification of this fly larva to species is mandatory to improve the accuracy of a forensic investigation, if this larva is present in a corpse and could be used as entomological evidence.The immature and adult stages of M. scalaris have been previously described based on light microscopy (Zumpt 1965, Tumrasvin et al. 1977, Kaneko et al. 1978, Liu & Greenberg 1989, and scanning electron microscopy (SEM) has been used to describe the egg (Greenberg & Wells 1998). We report, herein, some details of the surface ultrastructure of the third-instar M. scalaris with the aid of SEM. Particular attention was given to the morphology of the cephalic segment, anterior and posterior spiracles, in order to point out some taxonomic significance from the other Megaselia species.The third-instar M. scalaris, which was obtained from wild-caught females that came to lay eggs in a tray baited with fresh pork liver, was set up in the Department of Parasitology, Faculty of Medicine, Chiang Mai University, Thailand. The eggs were identified as M. scalaris according to the morphological features demonstrated by Greenberg and Wells (1998 from the egg, it was reared with fresh pork liver until reaching the third-instar. Some larvae were collected from the colony and washed several times with normal saline solution. They were killed by placing in hot water (≈70°C) for a few min and then fixed in a fixative agent consisting of 2.5% glutaraldehyde at 4°C for 24 h. The fixed larvae were then subjected to postfixation in 1% osmium tetroxide and dehydration in a graded alcohol series that was followed by treatment in acetone and critical-point drying. They were then mounted on stubs, sputter-coated with gold, and viewed with a JEOL-JSM840A scanning electron microscope. Photomicrographs were made using Kodak® Verichrome Panchromatic film VP 200.The third-instar M. scalaris is creamy white and ≈4 mm in length.

Megaselia scalaris(Diptera: Phoridae): an opportunistic endoparasitoid of the endangered Mexican redrump tarantula,Brachypelma vagans(Araneae: Theraphosidae)

“…1). Following Sukontason et al (2002) and Boonchu et al (2004), the binomial distribution of size frequencies (Fig. 1) and the larvae ultrastructures ( Fig.…”

Comparing Species Composition of Passive Trapping of Adult Flies with Larval Collections from the Body during Scene-Based Medicolegal Death Investigations

“…Preservation of a portion of the specimens was accomplished by hot water kill and placement in 70% ethanol [12,17] and the remainder of the specimens were reared to confirm identification. Identification of the larvae was accomplished with the use of taxon and life stage appropriate keys (e.g., [18,19,20,21,22]).…”

Simple clearing technique as species determination tool in blowfly larvae

“…In larvae however, species specific morphological features are considerably smaller and often internal organs or structures need to be consulted. The analysis of external features such as spiracles and spine bands can be performed by the use of a stereomicroscope [6][7][8] or scanning electron microscopy [9][10][11][12]. Analysis of internal organs however asks for challenging dissections and elaborate histological treatments [13].…”