Scanning electron morphological studies of Tribolium confusum Jacquelin du Val (Coleopteran: Tenebrionidae)
© The Author(s) 2017
Received: 30 May 2017
Accepted: 21 August 2017
Published: 26 September 2017
The confused flour beetle Tribolium confusum Jacquelin du Val (Coleopteran: Tenebrionidae) is the most destructive pest of stored products worldwide. It is the most common pest of wheat flour.
This study describes and illustrates the larvae, pupae, and adults of T. confusum using scanning electron microscopy. The first larval instars are 5.0–5.1 mm long and 0.5–0.6 mm wide whereas the last larval instars are 5.75–6.9 mm long and 0.75–0.95 mm wide. Adults of T. confusum are reddish brown elongate beetles (4.0–4.5 mm in body length and 1.0–1.2 mm in width). Electron micrographs revealed the structure of the mouth parts during the larval, pupal, and adult stages as well as the structure of thoracic and abdominal appendages. Results indicated that the setiferous sex patches which were reported in males can often be used for sexing specimens. A specific feature of the first instar larvae of T. confusum is the extreme shortened antenna with a reduced number of antennomeres and the presence of well-developed and moderately long legs.
SEM examination may help us not only discover and understand new morphological details as the pits with spine on the elytra and the spikes on the membrane wings which will facilitate the identification of this species but also clarify the functions of various body parts.
KeywordsColeoptera Tenebrionidae Larva Pupa Adult Scanning electron microscopy Tribolium confusum
Tenebrionidae is one of the most diverse families within Coleoptera (beetles) and is very difficult to classify (Aalbu, Triplehorn, Campbell, Brown, Somerby, et al., 2002).
Studies of immature and adult stages of insects are very important and useful for classification of particular groups which were seeing several times (Beutel & Friedrich, 2005).
Taxonomic studies on immature stages of the family Tenebrionidae are rare because the knowledge about the developmental stages of this family is very limited (Jia, Ren, & Yu, 2013). This is particularly true for tenebrionid pupae and larvae. For the tenebrionid pupae, several workers have made their contributions as (Daggy, 1946; Abdulla, 1964; Spilman, 1966, 1969; Bouchard & Steiner, 2004; Cherney, 2006; Gosik, 2007; Dunford & Steiner, 2007; Simoes et al., 2009; Matthews et al., 2010 and Jia et al., 2013), but few studies including the tribe Optrini, was reported by Cherney (2005) and Cherney and Fedorenko (2006).
The red flour beetle, Tribolium confusum (Coleoptera: Tenebrionidae), is the most widespread and withering major insect pest of stored cereals in the world. Hana (2013) had reported the percentage of damages of these insects ranging from 5 to 30% of the world’s total agriculture production. Freeman (1973) had reported that the success of the spreading of these insects is due to different evolutionary adaptations to the actions of humans who transport them through the world and give a protective habitat for stored food stuffs.
The aim of the present work was to study the morphology of different stages of T. confusum to explore new morphological details which will facilitate the identification of different stages of this species.
All experiments were done according to the guidance and animal care ethics of Sohag University, Egypt. Larvae, pupae, and adults of T. confusum were collected from the flour in the laboratory and fixed in 70% alcohol. Pupae were examined using binocular microscope to differentiate between male and female pupae. Specimens were prepared for examination by subjecting them to dehydration series of 90%, 95%, and absolute alcohol. Specimens were then critically point dried and coated with gold using sputter coating for examination using a scanning electron microscope (SEM), JEOL, JSM 5300.
General body shape of the larvae is as follows: elongate, cylindrical, body mostly white, weakly sclerotized surface with sparse vestiture of whitish setae, segment IX dorsally forming divided sclerite (pygidium) (Fig. 7a–d). Urogomphi are appendages of tergum IX of beetle larvae of T. confusum which are reported for the first and last larval instars (Fig. 7c, d). Segment X is not visible in dorsal view; it is inserted on the ventral side posterior to sternum IX and may be represented by two lobes (Fig. 7c, d) and (Fig. 9b) which is probably developed as a pygopod. In the larval stage, there were three pairs of legs each of them consists of five segments (Figs. 7a and 9a); these are coax, trochanter, femur, tibia, and tarsus, and a single claw is present in the first and last instar larvae.
Experiments carried out by Huet and lenoir-Rousseaux (1976) and Daly and Sokoloff (1965) on the tenebrionid beetle Tenebrio molitor demonstrated that the entire larval appendage developed to the adult appendage and that specific adult structures within each appendage generally arise by transformation of their corresponding larval structure. Thus on the basis of its relatively close relationship with Tenebrio (Daly & Sokoloff, 1965) on T. castaneum (David, Frank, Ariel, Moto, & Elizabeth, 2012), the adult mouth parts are assumed to be formed by transformation of their larval precursors. This contrasts with Drosophila, where larval appendages exist as small sensory organs and adult appendages develop from imaginal discs that are set aside during embryonic development (David et al., 2012).
In the present study, a specific feature of the first instar larvae of T. confusum is the extreme shortened antenna with a reduced number of antennomeres; these results agree with that reported by Ross and Pothecary (1970), Beutel and Hornschemeyer (2002), and Margarita et al. (2015). Another feature is the presence of well-developed and moderately long legs; these results agree with that reported by Ross and Pothecary (1970) and Margarita et al. (2015).
Urogomphi are appendages of tergum IX of beetle larvae of T. confusum which are reported for the first and last larval instars. Urogomphi are prominences of tergum IX of beetle larvae (e.g., Lawrence et al., 2010). In some alticine (e.g., Chaetocnema and Psylliodes) and galerucine (e.g., Diabrotica duodecimpunctata, D. vittata) larvae, a pair of simple curved urogomphi is present. A single median terminal process occurs in larvae of Phyllotreta cruciferae, P. atra, and P. vittula (Boving, 1930; Cox, 1988; Cox, 1981). Yi et al. (2014) reported that segment IX is dorsally forming undivided semicircular and subtriangular sclerite (pygidium) for galerucine and alticine larvae.
In the present study, after describing the different stages of T. confusum, the urogomphi of the pupae are diverging from each other, these results agree with that reported by Jia et al. (2013) who identified two main types of urogomphi in the Optartini pupae. The urogomphi in Scleropotrum horridum horridum, Gonocepholum reticulatum, Opatrum (Opatrum) subaratum, Penthicus (Myladion) alashanicus, Penthicus (Myladion) nojonicus, and Melanesthes (Optroneshes) rugipennis are identical. In these species, the urogomphi are diverging from each other. Also, Jia et al. (2013) reported that the urogomphi in Eumylada potonini, Eumylada punctifera, Melanesthes (Melanesthes) maxima maxima, Melanesthes (Melanesthes) jintaiensis, and Myladina unguiculina are parallel to each other.
Also, Steiner (2014) described the pupa of Glyptotus cribratus which is bearing large divergent urogomphi. The urogomphi of pupa of Cibdelis blaschkei are long, wrinkled at base, gradually tapered to divergent sharp apices.
In the present study, T. confusum on the first and last larval instar, segment X is not visible in dorsal view, it is inserted on the ventral side posterior to sternum IX and may represented by two lobes which are probably developed as a pygopod. These results agree with that reported by Margarita et al. (2015) who reported the structure of segment X for the first larval instar of Tenomerga mucida that the greatly reduced segment X is inserted on the ventral side posterior to sternum IX, it is represented by two pairs of flattened, sclerotised anal flaps, the larger flap bears two long setae, the smaller ventromesal flap one long seta, and several short ones along its rounded posterior edge; the latter are fused basally but divided by a deep median cleft.
In contrast to Steiner (2014) who reported the absence of pygopods on the mature larva of Glyptotus cribratus, the abdominal segment X is small, ventral, transverse, semi-circular, convex, three times wider than long, with row of six fine setae across width. Also, Steiner (2014) described the mature larva of Cibdelis blaschkei in which abdominal segment X is small, ventral, transverse, semi-circular, convex, 2.5× wider than long, with a row of six fine setae across width, and pygopods absent.
Beutel and Hornschemeyer (2002) reported that the eversible ventral lobes of segment IX are composed of a weakly sclerotized proximal part and a largely membranous distal element is present in larvae of Micromalthus and Cupedidae (Lawrence, 1991). Beutel and Hornschemeyer (2002) reported that the eversible ventral lobes of segment IX may facilitate locomotion in galleries. Also, Beutel and Hornschemeyer (2002) reported that segment X is not visible externally in all larvae of Archostemata. It is exposed in larvae of most other groups of Coleopteran (e.g., Adephaga, Staphyliniformia) (Frank, 1991; Newton, 1991).
Beutel and Hornschemeyer (2002) reported the absence of urogompi from tergum IX of all larvae of Archostemata but they are present in most larvae of Adephaga, in Torridincolidae (Beutel, 1999b) and in larvae of many groups of Polyphaga (e.g., Hydrophiloidea, Histeroidea, and Staphylinoidae) (Frank, 1991; Newton, 1991).
In the present study, the presence of setiferous patches on the fore, middle, and hind femur of the legs were reported in male of T. confusum. Their basic structure, comprising a depression-containing dense, fluted or grooved setae, and numerous pores, is similar to that found in the setiferous sex patches of other Coleoptera (Faustini & Halstead, 1982).
So, using SEM examination add some knowledge about morphological details of different stages of T. confusum, the setiferous sex patches in males, the structure of the mouth parts of adult and larval stage, the pits with spine on the elytra, and the spikes on the membrane wings which will facilitate the identification of T. confusum and may help to clarify the functions of various body parts.
Based on the current results, the future work will concern mainly with the morphological, histological, and biochemical studies of this species and others.
I would like to express my thanks to the SEM unit, Assuit University, for their efforts in specimen preparation. Great thanks to the Dean of Faculty of Science (Sohag University) for funding this work.
NMHZ is the main author only for this manuscript.
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