Morphology and Ultrastructure of the Sensilla of Larval Antennae and Mouth Parts of the Mediterranean Flour Mouth, Ephestia kuehniellazeller (lepidopetra: pyrilidae)

Citation: Egypt. Acad. J. Biolog. Sci. (A. Entomology) Vol.9 (3)pp. 1319(2016) 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
E. kuehniella (Mediterranean flour moth) caterpillars are a common pest, infesting grain, flour, baked goods and cereal products.They cause damage by eating especially the germ and bran from grain, and leaving frass, webbing, and body parts in stored dried foods.They are found in households as well as mills, warehouses, and processing plants.They are prolific spinners of silk which has made them a serious pest in flour mills.If left uncontrolled, the species may reach extreme population densities in suitable locations, such as mills, and the copious webbing which they produce blocks milling machinery, and interferes with production; large clumps of webbed flour also provide harbourage for other insect pests (Rees, 2003).In the Lepidopetra, the sensilla on the antennae and mouthparts have been documented in many pest speices for adult stage, since they are involved in semiochemical reception and are related to food seeking and food acceptance (Zacharuk and Shields, 1991).
The goal of the present study is to investigate the ultrastructure of the sensilla on the antennae and mouthparts of the larvae in E. kuehniella.

MATERIAL AND METHODS
The E. kuehniella larvae were obtained from infested wheat flour in Zagazig, Sharqia, Egypt.About ten fifth instar larvae were selected for analysis using scanning electron microscopy (SEM) investigation.All larvae were washed several times with distilled water and fixed in 10% formalin for a period of 12 h, dehydrated in various grades of alcohol, cleared in acetone, dried and fixed on metallic stub at different angels.Mouth parts fixed on stub were processed for gold coating and scanned under the Jeol/ EO, Version 1.0 (Instrument JSM-5500) Scanning Electron Microscope (SEM) at the regional center for Mycology and Biotechnology, Al-Azhar University, Egypt.

RESULTS
The head of the E. kuehniella mature larvae is strongly sclerotized capsule, oval in shape, and hypognathus, with the mandibulate mouth parts directed downwards.The frontal portion of the head capsule is supplied with the antennae and mouth parts (Fig. 1).The paired antennae are short and arise from a prominent membranous membrane base.The mouth parts are composed of labrum, a pair of mandible, a pair of maxillae, a labium and a hypopharynx.On each side of the head capsule there is a group of six stemmata, which are arranged in a loose circle above and lateral to the antennal base (Fig. 1).

Antennae
The antennae are paired, segmented appendages that articulate with the cranium in the antennal socket (Fig. 2a).Three parts can usually recognized; the basal, or the first segment is the scape; the second segment is the pedicel; and the remaining segment is the flagellum (Fig. 2b).The sensillae are primarily on the tips of pedicel and flagellum.The basal scape is the broadest and longest segment, and devoid of any sensillae.The pedicel is long and carries three sensillae basiconica (B1-B3) and two sensillae chaetica (C1-C2) at its apex.B2 is much shorter than B1 and B3.Both C1 and C2 are located at the distal margin of the pedicel.The apical flagellum is greatly reduced and borne distally along the dorsal margin of the pedicel.The flagellum bears an elongate sensillum styloconicum and three basiconica (B4-B6) (Fig. 2c).

Labrum
The labrum is well developed and roughly trapezoid, proximally articulated with the anteclypeus.The ventral margin of the labrum is slightly notched medially with six pairs of sensillaechaetica (C1-C6), (Fig. 3).

Mandibles
The mandibles are strongly developed and sclerotized, slightly excavated on the inner side and convex on the outer side.The apex of the mandible is strongly dentate, with five prominent incisor cusps (T1-T5).
Each mandible bears long sensilla chaetica (C1-C2) situated on the basal part of the outer surface along the anterior margin (Fig. 4).

Maxillae
Each maxilla consists of a cardo, stipes, galea, and maxillary palp.The cardo and stipes each bears a sensillum chaeticum (Fig. 5a).The galea and the palp each carry an apical cluster of pegs.The galea carries seven sensilla on its distal surface: Two sensillaechaetica (C1 and C2), three flattened elongated sensilla basiconica (B1-B3), and two sensilla styloconica (St1 and St2) (Fig. 5b).Both of the sensilla styloconica have a small slender peg on the top of an elongate thick base.The maxillary palp is two segmented.The basal segment is long and wide at the base.The distal segment is long and carries eight sensilla on its terminal surface.Seven basiconica (B1-B7) and one styloconicum (St), (Fig. 5c).

Labium
The labium bears a pair of palps and a long tube-like spinneret, from which silk can be secreted by the larvae (Fig. 6a).The labial palp bears a long sensillum styloconicum and a short cone shaped sensillum chaeticum (Fig. 6b).

DISCUSSION
Insect sensilla play an important role in olfactory and gustatory sensation.The main function of antennae is olfactory in Lepidopteran larvae.The mouthpart of Lepidopetra larvae consists of various types of sensilla and play an important role in feeding behaviours during larval life.In this study, sensilla on the larval antenna and mouthparts were examined in E. kuehniella with scanning electron microscopy.The types, numbers, and distribution of sensilla were similar to Grapholita molesta (Song et al., 2014) and to Crposina sasakii (Liu et al., 2011).Each antenna possesses three sensilla basiconica and two sensilla chaetica on the pedicle; three sensillabasiconica and one sensillum styloconicum on the distal flagellum.This results similar to Pentateucha inouei (Lin, 2002) even the morphological appearances are different.This kind of sensilla is reported to possess olfactory function (Hanson and Dethier,1973 ;Zacharuk, 1985).The sensilla chaetica are involved in tactile stimulus reception (Schoonhoven, 1967;Albert, 1980;Zacharuk, 1985;Baker et al., 1986;Faucheux, 1995) and sensilla styloconica are suggested as thermal detectors (Schoonhoven, 1967).We propose that the sensilla on E.kuehneilla larvae may also be involved in these functions.
The sensilla on the larval mouth parts of E. kuehneillaare partly similar to other lepidopteran insects, but differ somewhat in the sensillum number, distribution, and external morphology in comparison with other Lepidopterans.The most notable variation exists on the maxillae on each maxillary palp,E.kuehneilla possesses eight apical sensilla, seven sensilla basiconica and one styloconicum in contrast with eight sensilla basiconica in other Lepidoptera (Grimes and Neunzig, 1986b;Faucheux, 1995).The presence of apical basiconica on the maxillary palp might be playing similar role and function as gustatory.They are probably related to olfactory functions (Schoonhoven, 1972;Devitt and Smith, 1982) and may also have mechanoreceptory functions (Schoonhoven and Dethier, 1966).The sensilla styloconica plays a major rolein food recognition Ishikawa et al. (1969) as well as it is gustatory in nature.The sensilla styloconica and sensilla basiconica on the galea have been shown to be important chemosensory function for modifying feeding behavior (Albert, 1980).The sensilla chaetica of the maxillae are tactile (Schoonhoven and Dethier, 1966;Hanson, 1970).In E. kuehneilla larvae, group of microtrichia is present on the maxilla and labium are similar to microtrichia described on the labrum of Acheta domesticus (Rohr, 1882).On the labrum, there are six pairs of sensilla chaetica, which are similar to other Lepidoptera and are reported to have mechanical function (Davis et al., 2008;Kent and Hildebrand, 1987;Nielsen and Kristensen, 1989).The two sensilla chaetica on the mandible are mechanoreceptors (Albert, 1980;Kent and Hildebrand, 1987).Each mandible bears five teeth for cutting offpieces of food and crushing them.The two sensilla on labial palps were shown to be mechanoreceptors (Albert, 1980;Devitt andSmith, 1982 andFaucheux, 1995).
The description and illustration of sensilla types in E. kuehneilla will consider as abases for future aiming to understand feeding behavior and preferences with a promising to the development of future control method.