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Ultrastructure of Sensory Receptors on the Antennae and Mouthparts of the Adult, Sitophilus oryzae L. and Sitophilus granarius L. (Coleoptera: Curculionidae) ( 25 )

ABSTRACT

KEYWORDS

Ultrastructure of Sensory Receptors on the Antennae and Mouthparts of the Adult, Sitophilus oryzae L. and Sitophilus granarius L. (Coleoptera: Curculionidae).

Fouda, M.A.; Al-Dali, A.G. & Ghannam, I.S.

Received: 15/03/2016

Accepted: 05/04/2016

E.mail:[email protected]

Ultrastructure, Antennal sensilla, Mouthparts sensilla, Sitophilus sp. and Scanning electron microscopy (SEM).

J. Nucl. Tech. Appl. Sci, Vol. 4, No. 1, PP. 25 : 33 (2016)

Journal of

NUCLEARTechnology in Applied ScienceISSN 2314-8209 e-ISSN 2314-8217

1. Department of Zoology and Entomology, Faculty of Science, Al-Azhar University, Cairo, Egypt.

The ultrastructure of sensilla on the antennae and mouthparts of adult Sitophilus oryzae L. and S. granarius L. (Coleoptera: Curculioni-dae) were examined using scanning electron microscopy. Two types of sensilla trichoidea (ST1 & ST2), two types of sensilla basiconica (SB1 & SB2) and one type of sensilla chaetica (SC) were observed on the an-tennae of the two weevils species. Mouthparts in both species have two sub-types of sensilla basiconica (SB1 & SB2) and one type of sensilla chaetica (SC).

INTRODUCTION

Insects are considered as primary pests of stored products and cause damage to stored grains by direct feeding on the grain at some point in their lifecycle. Primary pests attack grains that are intact and stable, while, secondary pests generally feed on grains that are damaged or going out of condition. (Adel, 2012). Loss of

weight and quality of stored grains due to seed beetles is a very serious problem for farmers and traders (Rees, 2004).

From the coleopteran that attack stored grains is Sitophilus sp. (Fam-ily: Curculionidae) which are infested seeds of cereal crops such as wheat, corn, rice, and sorghum and are important economic pest species in stored grain. The species share the same life history, but do have a number of differences in their seed exploitation strategies (Longstaff, 1981).

Fouda, M.A. et al.( 26 ) J. Nucl. Tech. Appl. Sci., Vol. 4, No. 1

The antennae of adult insects have various types of sensilla with different functions, and play an im-portant role in various behaviors during adult life. Antennal sensilla are important sensory receptors implicated in host location and discrimination be-haviors (Ochieng et al., 2000).

Although insect mouthparts are adapted for the ingestion of many types of food, the most distin-guishing characteristic of an insect’s behavior lies in their functional mouthparts (Moon et al., 2008 & 2014). The fine structure of stored grain weevils – mouthparts and their associated sensilla have been nearly neglected until now.

Thus, the present study aims to identify the mi-crostructure of antennae and mouthparts, and their associated sensilla in the two weevils; Sitophilus ory-zae and Sitophilus granarius. In order to understand the behavior of these pests to stored products, it was necessary to characterize and determine the abun-dance and distribution of the antennal and mouth-parts sensilla of the two coleopteran species studied using the scanning electron microscopy (SEM).

MATERIALS AND METHODS

Insects used:

The adult stages of stored grain weevil’s species were used in this work: The rice weevil, Sitophilus oryzae Linnaeus and the granary weevil, Sitophilus granarius Linnaeus (Coleoptera: Curculionidae). They were obtained from stock cultures maintained in Plant Protection Department, Faculty of Agricul-ture (Boys), Al-Azhar University, Cairo.

Scanning electron microscopy:

Samples are prepared for scanning electron mi-croscopy examination according to the method given by Harrison, (2012). Cut heads of adult stages were fixed separately for 24 h. in 2.5% glutaraldehyde solution in phosphate buffer of PH (7.4). Follow-

ing fixation the specimens were washed twice with phosphate buffer, distilled water and dehydrated by serial dilution of ethanol from 50% to 100% and air-dried using CO2 critical point drier and finally coated with thin layer of gold in sputtering unit for examination by using scanning electron microscopy (JEOL-JSM-5500 LV) using high vacuum mode at the Regional Center of Mycology and Biotechnol-ogy, Al-Azhar University, Cairo, Egypt.

RESULTS

Scanning electron microscopy of antennal sensillaSitophilus oryzae L. (Coleoptera: Curculionidae)

General description of antennae

The antennae of this species consist of the scape, pedicel and six flagellomeres. Scape is the longest segment of antennae followed by a short pedicel. The width of flagellomeres increase distally where the widest (6 flagellomere) are present (Fig. 1-A). All antennal segments are covered by scales-like structures (Figs. 1-B, 1-C and 1-D).

Types of sensilla

Based on shape, size, distribution and cuticular attachment, one type of sensilla chaetica (SC) are distributed on the all segments; two types of sensilla trichoidea (ST1 & ST2) present on the tip of the 6th flagellomere with basiconic sensilla (SB) (Figs. 1-B, 1-C and 1-D) were identified.

Sensilla trichoidea (ST1): The ST1 are sharp-tipped, nearly straight or slightly curved.

Sensilla trichoidea (ST2): The ST2 are a blunt-tipped, shorter than ST1.

Sensilla chaetica (SC): They occur on each an-tennomere of the antennae, they are characterized by grooved surface and blunt tip.

Sensilla basiconica (SB): The SB are character-ized by smooth cuticle and blunt tip.


Sitophilus granarius L. (Coleoptera: Curculioni-dae)

General description of antennae

As in S. oryzae, the antennae consist of scape (the longest segment), short pedicel and six flagello-meres. All antennal segments are covered by scales-like structures (Figs. 1-E).

Types of sensilla

Three types of sensilla were distinguished on the antennal segments of S. granarius; sensilla chaetica (SC) which distributed on all segments (Fig. 1-E), sensilla trichoidea (ST1 & ST2) and sensilla basi-conica (SB1 & SB2) on the tip of flagellomere 6 (Fig. 1-F).

Fig. (1): (A-D): Scanning electron micrographs of antenna in the adult of S. oryzae (A) antenna 120x; (B) scape and pedicel 370x; (C) various sensilla types on the antennal segments 650x; (D) the distal antennal segment 350x. Scape (S), pedicel (P), flagellum (F), sensilla chaetica (SC), sensilla basiconica (SB), sensilla trichoidea types 1&2 (ST1&ST2).


Scanning electron microscopy of mouthparts and their associated sensilla Sitophilus oryzae L.

General description of mouthparts

Scanning electron microscopic examination showed that the mouthparts of this weevil is adapted for chewing solid food and is surrounded by spe-cialized structures for grasping and grinding. These structures consist of a labrum, a pair of mandibles, a pair of maxillae and a labium. This weevil has a distinct snout (rostrum) and the jaws are at the end of the snout (Figs. 2-A and 2-B).

Types of sensilla

Based on size, shape, distribution and cuticular attachment, the sensilla associated with mouthparts of S. oryzae were basiconic sensilla (SB) which dis-tinguished into two sub-types: SB1 (short pegs with blunt tips) and SB2 with biforked tips. Those basi-conic sensilla are distributed on the snout and the mouthparts at the distal end of snout (Figs. 2-B and 2-C).

In addition to the basiconic sensilla there were striaghted leaves-like structures sensilla (SC) which condensed at the base of the snout (Fig. 2-D).

Sitophilus granarius L.

General description of mouthparts

Scanning electron microscopic observations showed the same structure of mouthparts in S. ory-zae. The mouthparts of this weevil species consist of a labrum, a pair of mandibles, a pair of maxillae and a labium (Fig. 2-E).

Types of sensilla

Figure (2-E) showed only one type of sensilla basiconica (SB) which divided into two sub-types as in S. oryzae (SB1 & SB2). Those sensilla are dis-tributed on the snout (Figs. 2-E and 2-F). In addi-tion to those sensilla, sensilla chaetica (SC) which are leaves-like structures and are distributed on the mid and basal parts of the snout (Figs. 2-G and 2-H).

Fig. (1): (E-F): Scanning electron micrographs of antenna in the adult of S. granarius. (E) antennal sensilla on the flagel-lomere 3, 1500x; (F) various sensilla types on the tip of flagellomere 6, 900x. Sensilla chaetica (SC), sensilla trichoidea types 1&2 (ST1&ST2), sensilla basiconica types 1&2 (SB1&SB2).


Fig. (2): (A-D): Scanning electron micrographs of mouthparts and associated sensilla in the adult of S. oryzae (A) head (lateral view) 60x; (B) ventral view 500x; (C) snout (mid part) 800x; (D) snout (base part) dorsal view 430x. Snout (SN), sensilla chaetica (SC), sensilla basiconica subtype 1&2 (SB1&SB2).

Fig. (2): (E-H): Scanning electron micrographs of mouthparts and associated sensilla in the adult of S. granarius. (E) mouthparts 550x; (F) snout (lateral view) 1700x; (G) snout (mid part) dorsal view 550x; (H) snout (base part) dorsal view 370x. Sensilla chaetica (SC), sensilla basiconica subtype 1&2 (SB1&SB2).


DISCUSSION

Insects antennae are mobile, segmented, paired head appendages and are found in nearly all insects groups (Gullan and Cranston, 1994). Numerous sensilla occurred on antennae in the form of hairs, pegs, pits or cones.

Based on shape, size, distribution and cuticular attachment, two types of sensilla trichoidea (ST1 & ST2), two types of sensilla basiconica (SB1 & SB2) and one type of sensilla chaetica (SC) were observed in the antennae of the two weevils species; S. oryzae and S. granarius. These types of sensilla are in great harmony with those reported for other beetles spe-cies (Merivee et al., 2002; Lopes et al., 2002; Said et al., 2003 and Hu et al., 2009).

Comparing the ultrastructure of these sensilla with those described in other insect species (Altner and Prillinger, 1980; Zacharuk, 1980 & 1985; Mc-Iver, 1985), those sensilla are capable of responding to various stimuli i.e. olfactory, gustatory, tactile as well as thermo- and / or hygroreception. The distri-bution patterns of the sensilla types provide evidence for the importance of the distal antennal segments (particularly the terminal segment) in behavioral studies (Sen and Mitchell, 1995).

Sensilla trichoidea 1 (ST1) has been described in different insects as having putative mechanorecep-tive functions, such as in the perception of mechano-sensory stimuli (Pettersson et al., 2001; Roux et al., 2005; Onagbola and Fadamiro, 2008). However, Keil, (1999) stated that trichoid sensilla may be ol-factory, while sensilla found on the pedicel are usu-ally mainly mechanoreceptive.

Sensilla trichoidea 2 (ST2) which are common on the antennal flagella of insects, Merivee et al., (1999) suggested that they probably function as sex pheromone receptors.

Sensilla chaetica (SC) are believed to have a dual function of mechanoreception and contact che-moreception (Jourdan et al., 1995). While, Merivee et al., (1999) suggested that their function are che-moreceptors.

Sensilla basiconica 1and 2 (SB1 & SB2) are suggested to be sex pheromone receptor or olfactory function (Hu et al., 2009).

Insect mouthparts have become diversely modi-fied to perform the function of ingestion. Although there are several types of mouthparts such as chew-ing, cutting, piercing, sucking and siphoning, there are two general categories: 1) mouthparts adapted for biting and chewing solid food; 2) mouthparts adapted for sucking fluids (Gullan and Cranston, 2010).

While most beetles have mouthparts designed for chewing solid food, many beetles of the super-family Curculionidea have a distinct snout that can bore into wood and chew seeds (Danho et al., 2002). At the end of the snout found the mouthparts that can be used for penetration and feeding and for bor-ing hol for egg laying (Moon, 2015).

The present study indicated that only the ba-siconic sensilla types are distributed on the distal end of snout. In addition to these sensilla, sensilla chaetica were distributed on the base of snout in the two weevils; S. oryzae and S. granarius. These ob-servations are in great harmony with that obtained by Dinută et al., (2008) for S. granarius and Moon, (2015) for S. zeamais.

In conclusion, the present study has identified and characterized the different sensilla types on the antennae and mouthparts of Sitophilus oryzae and S. granarius. However, further studies on the func-tional morphology of the antennal and mouthpart sensilla using transmission electron microscopy (TEM) coupled with electrophysiological recordings will confirm the functions of the different sensilla identified in this study.

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الدقيق للمستقبالت احلسيه على قرون إستشعار و أجزاء فم سوسة األرز و سوسة الرتكيب احلبوب البالغني )غمديات األجنحه: السوسيات احلقيقيه(.

حممد عبد احلي فوده – عالء جوده الدالي – إبراهيم سعيد غنام

الرتكيب الدقيق للشعريات احلسيه على قرون إستشعار و أجزاء فم سوسة األرز و سوسة احلبوب

املاسح. اإللكرتوني امليكروسكوب بإستخدام ُفحص احلقيقيه) السوسيات األجنحه: (غمديات البالغني

(ST2&sensilla trichoidea (ST1 وقد لوحظ على قرون اإلستشعار لنوعني السوس , نوعني من

ونوعني من SB2&sensilla basiconica (SB1) ونوع من sensilla chaetica (SC) . أجزاء الفم

sensilla لكال النوعني متتلك نوعني فرعيني من SB2&sensilla basiconica (SB1) و نوع من

. (chaetica (SC

)2016( ، 33 : جملد 4 ، عدد 1 ، ص 25

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