Use of low‐temperature field emission scanning electron microscopy to examine mites

Abstract

Summary:Partly because mites are microscopic in size and fragile in nature, acarologists estimate that less than five percent of extant species have been taxonomically described. Recently, data from conventional scanning electron microscopy (SEM) have been used to facilitate the descriptions and complement the information that has been historically obtained with the light microscope. However, the conventional preparation techniques associated with SEM frequently prevent or compromise the results. This study evaluated the use of low-temperature field emission SEM to image mites and their hosts. Results indicated that a modified cryofixation procedure, which was associated with this technique, retained the mites at their living/feeding sites in natural behavioral positions. Furthermore, the turgor of the specimens, even eggs and soft-bodied species, was also maintained. The structure and orientation of delicate structures such as setae, which would be subjected to mechanical damage during conventional chemical fixation, dehydration, and drying, were also preserved after cryofixation. Field emission SEM, which provided useful magnification beyond that attainable with a conventional SEM, also enabled resolution of ultrastructural features, such as tenent hairs on the empodium and pores on the dorsal surface that had not previously been observed. These advantages indicate that the low-temperature field emission SEM can provide important structural data that can be used to study the anatomy, morphology, and bioecology of mites.

Use of different SEM techniques in the study of Tyrophagus putrescentiae (Acari: Acaridae) in Costa Rica

“…Specimen preparation by conventional techniques of fixation and drying frequently damage or reorient delicate structures such as setae or segments that are slightly sclerotized (Wergin et al, 2000). Major differences were observed in the ability of each of the treatments to preserve the various body structures of the specimens that were prepared for observation with the SEM.…”

“…Wergin et al (2000) considered that the drying techniques commonly used (sublimation and critical point drying) are associated with distortion or collapsing of the biological samples.…”

“…Different SEM techniques have been used for the observation and analysis of surface structures, providing important information about the relief, texture, size and shape, both on biological and mineral samples (Postek, Howard, Johnson & McMichael, 1980). The electron microscope has been used during the last 30 years, as a tool to facilitate morphological descriptions of mites and as a complement of information obtained under the light microscope (Keirans, Clifford & Corwin, 1976;Wergin, Ochoa, Erbe, Craemer & Raina, 2000;Achor et al, 2001;Ochoa, Erbe, Wergin, Frye & Lydon, 2001;Mariana, Santana, Ho, Tan & Zuhaizam, 2008;Kucerova & Stejskal, 2009). Thus, it is possible to better observe the shape and position of the various morphological features of the species.…”

“…Thus, it is possible to better observe the shape and position of the various morphological features of the species. This leads to a better understanding of their functionality and how they relate to the biology and ecology of the species (ARS-USDA, 2000; Wergin et al, 2000).…”

“…Low temperature -SEM (LT-SEM) methods have been used in other studies, which have demonstrated excellent results on soft-bodied arthropods including mites (Achor et al, 2001;ARS-USDA, 2007;Erbe, Wergin, Ochoa, Dickens & Moser, 2001;Ochoa et al, 2001;Wergin et al, 2000;Dowling, Bauchan, Ochoa & Beard, 2010;Beard et al, 2012). Unfortunately, these methods require very specialized equipment attached to the SEM unit that is not available in Central America, which is why we only evaluated and discussed some techniques used for a standard SEM.…”