Scanning Electron Microscope of Genus Leichenum Dejean, 1834 (Coleoptera: Tenebrionidae: Tenebrioninae: Pedinini) in Egypt

Citation: Egypt. Acad. J. Biolog. Sci. (A. Entomology) Vol. 10(3)pp: 5363(2017) Egyptian Academic Journal of Biological Sciences is the official English language journal of the Egyptian Society for Biological Sciences, Department of Entomology, Faculty of Sciences Ain Shams University. Entomology Journal publishes original research papers and reviews from any entomological discipline or from directly allied fields in ecology, behavioral biology, physiology, biochemistry, development, genetics, systematics, morphology, evolution, control of insects, arachnids, and general entomology. www.eajbs.eg.net Provided for non-commercial research and education use. Not for reproduction, distribution or commercial use.


INTRODUCTION
and El-Torkey et al. (2009) classified genus Leichenum within subfamily Opatrinae, tribe Leichenmini.Iawn and Löbl (2008) recorded the genus as belongs to subfamily Tenebrioninae, tribe Pedinini.The opatrine native to Ethiopian and Palearctic faunal regions (James and Warren, 2007).Spilman (1959) stated that species of Leichenum have no economic damage.In recent studies James and Warren (2007) recorded L. canaliculatum on grass, cotton, soil among turnips and associated with damaged peach trees.Hagstrum (2009) recorded L. canaliculatum on soybeans feed on grass roots.Leichenum pulchellum pulchellum was found in a narrow strip of the seashore beside a sand dune (Fattorini 2002).Mouna et al. (2009) recorded this species in the sandy beaches.
Using of Scanning Electron Microscope (SEM) is extremely useful for studying the detailed morphology of very small structures on insect cuticle (Watson, 2015).The SEM enables quick, accurate representation with high resolution, threedimensional clarity, and great depth of field.Legner and Kogan (1969) confirmed that, the rigid exoskeleton of insects is especially suitable for electron microscopy because the specimen usually retains its shape under vacuum.
The SEM provides an excellent and detailed morphological overview (Zhang et al., 2012).
Ubero-Pascal (2010) reported the reasons of limitation of using SEM technique and stated that it is expensive and requires specialized preparation of the material to be studied.
Taxonomic studies on the species of genus Leichenum very scarce, especially L. mulleri which is probably only briefly studied by Penrith (1984), and other few studies carried out L. pulchellum.Hence the present study aimed to present an attempt to review the taxonomic status of the Egyptian species of genus Leichenum and contribute towards confirming or cancelling the old taxonomic characters, previously suggested by ancient taxonomists, also the study used SEM technique which offer high magnification and high-quality micrographs enabling the researchers to describe precisely and take the right decisions.

Insects
The present study is carried out on preserved insects of two species which belong to genus Leichnum, obtained from the side collection of the Plant Protection Research Institute, Dokki, Giza governorate, Egypt.

Scanning Electron Micrograph
The specimens were coated by gold sputter coater (PSI-Module, USA).A fully computer-controlled scanning electron microscope (Model: JSM-5500 LV; JEOL, Ltd.-Japan).Using high vacuum, it was scanned with the electron beam at 30 kV from different angles.Images of dorsal surface, mouthparts, eyes, mentum, pronotum, fore tibia, elytra, ventral surface, intercoxal process and the abdominal segments were taken.The SEM photograph was conducted at the Regional Center of Mycology and Biotechnology, Al-Azhar university, Cairo, Egypt.
-Pronotum with very dense setae dorsally, with not incised anterior margin (Fig. 1 d  Vertex bare, wrinkled medially, with widely sparse setae laterally above the dorsal margin of eyes, gena and above the antennal insertion with dense setae longer than that at vertex; eye with dark brown, erect scales surrounding each eye facet (Fig. 3 a); pronotum with widely sparse, greyish seta, brown at midline, anterior margin bordered with dense seta directed forwardly, sub-lateral strip with sparse setae, slightly broadened to apex, laterally with sparse setae, longer than that at sub-lateral strip, cylindrical, slightly gradually thickened to apex (Fig. 1 b); posterior margin with row of dense setae, longer than that of anterior margin, surface of pronotum wrinkled (Fig. 3 b).
Elytra with whitish-grey and yellowish-brown setae, arranged in rows, equidistant from each other, intervals between rows broad (Fig. 3 c); laterally with setae similar to that at the lateral margin of pronotum but longer (Fig. 3 d), elytral surface ornamented with scale -like shapes.Ventrally, submentum with sparse setae, mentum, maxillae, labial and maxillary palpi with dense setae; labium with widely sparse setae (Fig. 3 e); prosternum with dense setae, apical margin with row of setae, prosternal process bare, wrinkled, with sparse punctures; mesosternum and mesosternal process densely punctate, metasternum slightly dense punctate with few number of setae; abdominal segments bare, slightly dense punctures.Head relatively small (about 0.7 time length of pronotum).Vertex convex, without depressions (Fig. 3 a).Eyes rounded, slightly prominent, its diameter about half length of head.Gena brown and thick at apex.Pronotum transverse (width 1.8 times its length), maximum width is at the middle, slightly arched laterally, incised anteriorly with sharp, prominent anterior angles; anterior margin narrowly serrate; posterior margin shallowly bisinuate, with obtuse posterior angles, not project laterally; pronotum with lateral depressions at its basal fourth, scutellum subquadritic, visible, flat (Fig. 1 a & Fig. 3 b).Elytra with raised striae, intervals between striae wide and concave, punctate laterally and basally; anterior angles rounded and prominent.Legs with setae and truncated at apex; anterior tibia with large outer tooth in both sexes; in male with two stout pointed teeth externally at middle and a perpendicular tooth at inner apical angle; in female, the fore tibia with stout teeth externally at middle and straight tooth at inner apical angle.Ventrally, submentum convex medially, sloping laterally forming broad antennal groove beneath eyes (Fig. 3 e).Prosternal intercoxal process cordate, passes above procoxae, raised above level of prosternum, arched above procoxae, not bent down apically, reaches to mesosternun, with shallow median sulcus at its apical half, pointed apically (Fig. 4

This species differs from L. mulleri in the following characters:
Vertex covered with very dense setae-like scales.Eye with dark brown, with recumbent scales cover most of eyes (Fig. 6 a).Pronotum furnished with very dense, oval, recumbent scales; with sparse, medium, suberect, greyish seta, anterior margin bordered with very dense seta, not directed forwardly (lie horizontally along the margin); laterally pronotum with slightly sparse setae, depressed dorsoventrally broadened to apex; posterior margin with widely sparse setae, as long as that of anterior margin, surface of pronotum scaly (Figs. 1 b).Elytra, intervals between rows of setae narrow (Fig. 6 b); elytral surface invisible, laterally setae similar to that on pronotum but longer (Fig. 6 c).Ventrally, apical margin of prosternum with row of setae longer than that on surface of prosternum (Fig. 6 d); prosternal process with slightly dense, very dense posteriorly, broadened at apex setae; without punctures (Fig. 6 d).Mesosternum and mesosternal process with slightly dense setae, without punctures; metasternum with slightly dense setae, without punctures (Fig. 7 a); abdominal segments with slightly dense setae, without punctures (Fig. 7 b).Head relatively small (about 0.5-time length of pronotum).Vertex with broad, slightly deep lateral depressions.Eyes, prominent, surrounded by deep groove (Fig. 6 a).Gena brown and thick at apex.Pronotum transverse (width 1.5 its length), strongly arched laterally, constricted basally, anterior angles extended anteriorly; anterior margin not serrate; posterior margin slightly deeply bisinuate, with acute posterior angles, forming spine-like projection extend laterally; pronotum with very small depression at posterior margin (Fig. 1 d); scutellum shield-shape, hardly visible.Elytra, with flat striae; intervals narrow and flat, punctat (Fig. 6b).Legs, fore tibia broad and toothed outside, its inner apical angle with small spines and teeth at middle of external margin; meso-and metatibiae externally with relatively strong and pointed spins.

DISCUSSION
The members of the genus Leichenum are cosmopolitan, small and scarcely studied insects.These beetles occur at sandy areas, along beaches (Mouna et al., 2009), lake and river shorelines (James and Warren, 2007).Alfeiri (1976) and El-Torkey et al. (2009) classified genus Leichenum within subfamily Opatrinae, tribe leichenmini, while Aalbu and Triplehorn (1985) removed Leichenum from Opatrini and the genus is currently the only representative of the tribe Leichenini (Aalbu et al. 2002).
The Leichenini are distinguished from the Opatrini by the possession of ocular scales, short antennae with a four-segmented club, and a unipartite tegmen of the aedeagus (Penrith, 1984).Medvedev (1973) concluded that the setae located between the facets of the Leichenum c. variegatum are to protect the eyes from damage when they burrow into the sand.This can be applied on the two Egyptian species of Leichenum as their eyes provided with scales.The ocular scales are found in other Tenebrionidae, as Drosochrini and Cryptochilini, and also occur in other families, e.g., Dasytidae, Colydiidae (Penrith, Australian Faunal Directory (2007) stated that Leichenum pulchellum Küster, 1849 is the synonym to the Madagascar beetle, Leichenum canaliculatum variegatum (Klug) 1833, and described the latter as having eyes slightly emarginated, with erect setae between facets, the present study found that eyes not emarginated and eyes facets surrounded by scales instead setae.
Applying SEM micrographs in the present study adding a number of distinguishing characters differentiating the two Egyptian Leichenum spp.as, detail description of the body vestitures i.e. setae and scales shapes, body topography, i.e. depressions, grooves, convexity etc.
Present knowledge of Leichenum is not sufficiently extensive for a serious consideration of relationships within the genus, but the evidence so far available is presented.

CONCLUSIONS
The scanning electron microscope is a very useful tool for observing minute, three dimensional structures of small insects, and some of these details can only be seen under the SEM.Like setae and hairs.Although the preparation of specimens for viewing under the SEM is time-consuming and expensive, the effort is worthwhile because the detailed information obtained is useful to solve some difficult aspects of tenebrionids beetle's taxonomy.