**4. Discussion**

The microscopic observations of the *R. Ferrugineus* antennae revealed four types (eleven subtypes) of hair- like structures and have not shown any sexual dimorphism. These observations are in agreement with behavioral responses of *R. palmarum* to odors in the laboratory and in the field, males and females respond with the same sensitivity to hynchophorol and sugarcane juice in a four-armed olfactometer (Said *et al*., 2003).

The first type of sensilla is coeloconic which large abundance on the scape and pedicel. The morphology of S. C 1 is distinct from the other olfactory sense organs (Jhaveri *et al*., 2000).

Fig. 7. SEM photomicrographs of irradiated adult antenna of *Rhynchophorus Ferrugineus* with 20 Gy of gamma rays. (A): Abnormal sensilla chaetica1 (Ch1) on the lateral side of club, (B): Shrunken and swollen sensilla chaetica 2 (Ch2) on the surface of club, (C): Sensilla chaetica 1 (Ch1) on the surface of club. [Scale bars indicate 20 µm (A, C) and 50 µm (B),

The microscopic observations of the *R. Ferrugineus* antennae revealed four types (eleven subtypes) of hair- like structures and have not shown any sexual dimorphism. These observations are in agreement with behavioral responses of *R. palmarum* to odors in the laboratory and in the field, males and females respond with the same sensitivity to

The first type of sensilla is coeloconic which large abundance on the scape and pedicel. The morphology of S. C 1 is distinct from the other olfactory sense organs (Jhaveri *et al*., 2000).

hynchophorol and sugarcane juice in a four-armed olfactometer (Said *et al*., 2003).

respectively]

**4. Discussion** 

Coeloconic sensilla often consist of a peg whose wall is composed of numerous parallelruning fingers (Keil, 1997). Also, Ameismeier (1985) illustrated that some of the fingerlike projections remained interstitial while some ones combined with each other and remained longitudinal grooves on the surface of the sensilla wall. Hunger and Steinbrecht (1998) observed the coeloconic sensella to be double walled, multiporous, rich in neurons and excessive contact interfaces. Other authors even considered that this type of sensilla may participate in receptivity to heat and humidity (Cuperus, 1983). Olson & Andow (1993) suggested an olfactory function of this sensillar type in *Trichogramma nubilale*, but as revealed in several insect species (Altner *et al*., 1983), this sensillar type may be involved in thermo- or hygroreception. Coeloconica sensilla are found in many Hymenoptera belonging to several families and have been described by different terminologies, such as, small sub terminal sensilla, (Weselow, 1972), multiporous grooved sensilla (Barlin *et al.*, 1981), bulb sensilla (Cave & Gaylor, 1987) and smooth basiconica sensilla (Norton & Vinson, 1974).

Sensilla trichodea 1 has been described in different insects as having putative mechanoreceptive functions, such as in the perception of mechanosensory stimuli (Onagbola & Fadamiro, 2008). Keil (1999) cited that trichoid sensilla may be olfactory, but sensilla found on the pedicel are usually mainly mechanoreceptive. Schneider (1964) suggests that trichoid sensilla may be dye-permeable and so may posses chemoreceptivity. The great occurrence of the sensilla trichodea on the antennae of male *O. elegans* relative to the females may indicate a probable role in mate location, possibly for the detection of females sex pheromones (Onagbola, *et al*., 2008).

Sensilla trichodea1 was found on the antennae of *Bembidion* species. These bristles are innervated by a single sensory neuron, ending with the typical tubular body, attached to the base of the hair shaft. This indicates a mechanosensory function (Zacharuk, 1985).

Sensilla similar to sensilla trichodea 2 have been described on several species of curculionid beetles (Alm & Hall 1986 and Isidoro & Solinas, 1992). In electrophysiological experiments with *H. abietis*, Mustaparta (1975) found that this sensillar type was electrophysiologically responsive to odours. Merivee *et al.,* (1999) suggested that they probably function as sex pheromone receptors. In the ground beetle, *Platynus dorsalis*, it might indicate that these sensilla probably respond to aggregation pheromone (Merivee *et al.,* 2001).

Sensilla similar in external morphology to the sensilla trichodea 3 on *R*. *Ferrugineus* are found on other alticinid species (Ritcey & McIver, 1990). The short sensilla trichodea, recorded from *Synempora* by Davis & Nielsen (1980) are in fact microtrichia, which are very frequently found on flagellomeres. They superficially resemble multiporous small sensilla basiconica which so far have been described only from Agathiphagidae among Lepidoptera (Faucheux, 1990).

The fourth type of trichodea sensilla are found only on the club of *R*. *ferrugineus* in few number are similar to type V sensilla found on the club of *R. palmarum* ,which characteristics of olfactory trichodea sensilla (Said *et al.,* 2003).Such sensilla were found to house neurons tuned to the pheromone component in *Ips typographus* L. and *Hylobius. abietis* (Mustaparta,1973,1975).

Shields & Hildebrand (2001) showed that every type -trichoid sensilla -of the female sphinx moth *M.sexta* was innervated by two olfactory receptor cells and could respond to aromatic

Ultrastructure Alterations in the Red Palm Weevil Antennal Sensilla Induced By Gamma Irradiation 243

into different directions, irregularity in shape, swollen in some parts and some sensilla gathered into dense collections. Similar works on the effects of gamma radiation have been recorded by many authors in other insects ; Oland *et al*.,(1988) illustrated the comparison between normal and irradiated *Manduca sexta* with 2.64 Gy revealed that features of normal antennal sensilla were present in irradiated ones with presence some cuticular disruption. Also, El-kholy & Mikhaiel (2008) revealed that gamma irradiation of full grown male pupae of *Galleria mellonella* with the sterile dose 400 Gy and the two substerile doses 100 and 150 Gy showed malformations in the F1 male antennal sensilla less than that in the parents irradiated with the dose 400 Gy . Besides, the irradiated pupae with the sterilizing dose in *Bactrocera zonata* produced adults with different malformation on the antennal sensilla (El-

The present study showed that the malformations in the antennal sensilla induced from exposed of adult with the dose rate 15 Gy were very few, while the dose rate 20 Gy affected on high number of antennal sensilla. And so, the used of high dose (20 Gy) must be turned off because this dose will affect on the behavior of insects. These previous results are compatible with our study in using gamma radiations (15Gy) as part of an Integrated Pest

The antennal sensilla of unirradiated and irradiated red palm weevile, *Rhynchophorus Ferrugineus* (Oliv.) (Coleoptera; Curculionidae) were investigated by using a scanning electrone microscope. The antenna was composed of three segments; scape, pedicel and flagellum (funicle, club). Four different sensillar types were distinguished. Eleven subtypes, these were; three subtypes of sensilla coeloconica, four subtypes of sensilla trichodea, two subtypes of sensilla basiconica, and two subtypes of sensilla chaetica. The position of these sensilla on the antenna was discussed. These types are used by insects as mechanoreceptor, sex pheromone, aggregation pheromone, olfactory, mate location, thermo-hygroreceptor,

There are differences in lengths and diameters of some types of sensilla were recorded as a result of irradiated adult with two doses of gamma rays (15, 20Gy). In the higher dose (20 Gy) more effects of sensilla were recorded for the sensilla chaetica followed by sensilla

Abraham, V.A. & Pillai, G.B.(1998). Red palm weevil – a dreaded enemy of coconut palm.

Albert, P. J. (1980). Morphology and innervation of the mouth-part sensillae in the larvae of

Alm, S. R. & Hall, F. R. (1986). Antennal sensory structures of *Conotrachelus nenuphur*

(Coleoptera: Curculionidae). *Ann. Entomol. Soc.Am*., 79: 324-333.

the spruce budworm, *Choristoneura fumiferana* (Clem.) (Lepidoptera: Tortricidae).

Akhdar & Afia, 2009).

**5. Conclusion** 

coeloconica.

**6. References** 

Management program for controlling this pest.

and receptivite to heat, and humidity.

*Indian Farmers` Digest* 7(1):15-20.

*Can.J. Zool*., 58: 842-851.

or terpenoid odorants. Similarly, the sensory neuron membrane protein of the wild silk moth *Antheraea polyphemus* was most prevalent in neurons and was localized to receptor membrane of the dendrite cilia presumed to perform the role of olfactive conduction (Rogers *et al*., 2001).

Sensilla chaetica 1 of *R. ferrugineus* are ascribed to mechano-chemoreception in coccinellids,*Semiadalia undecimnotata*, *Coccinella transverguttata* and *P.tsugae* (Jourdon *et al*., 1995; Wipperfurth *et al*.,1987; Broeckling & Salom 2003). In neopseustids, it cannot be excluded that the hair is connected to the considerably elevated socket by a flexible joint membrane and, in this case, the sensilla would be contact mechanoreceptors (Faucheux *et a*l., 2006).

They are resemble in their external sensilla chaetica in *Coccinella transversalis* Fabricius (Coccinellidae) (James, 2001),"chetiform sensilla type I" in *Semiadalia undecimnotata* (Coccinellidae) (Jourdon *et al.,* 1995,"sensilla chaetica type I" in *Agriotes obscurus* Elateridae) (Merivee, 1992) .Some authors treat these also as sensilla trichodea. They are classified, for example, as sensilla trichodea type I in *Carabus fiduciaries saishutoicus* (Carabidae) (Kim & Yamasaki, 1996), and flea beetles (Alticidae) (Ritcey & McIver, 1990).

Sensilla chaetica II could be observed in the antenna of *Cawjeekelia pyongana* (Polydesmida: Paradoxmatidae) (Chung & Moon,2007,2009) and on the labrum of *Synempora andesae* (Neopseustidae),the aporous bifurcate sensilla chaetica could constitute an autapomorphy but would need to be described further in other species of that family (Faucheux 2008).

In the present study the sensilla basiconica 1 and 2 are found on the pedicel and the surface of club. Okada *et al.,* 1992 on the cigarette beetles; *Lasioderma serricorne* and Daly & Ryan, 1979 on the ground beetle, *Nebria brevicollis*, they demonstrated that the wall of these sensilla is perforated by numerous tiny pores. The numerous pores and branched dendrites are considered to be evidence that these basiconica sensilla function as olfactory receptors (Altner & Prillinger, 1980 and Zacharuk,1985).The sensilla basiconica of *Hylobius abietis* were responsive to odours in electrophysiological experiments (Mustaparta, 1975). Moreover, a small groove or depression, not characteristic for mechanoreceptive pegs, at the tip of tiny sensilla basiconica 3 indicate that they propaply function as chemoreceptors (Ploomi *et al.,* 2003).

Curculionid, scolytid and coccinellid beetles have been reported to bear antennal sensilla similar to the sensilla basiconica described here (Alm & Hall, 1986; Bland, 1981; Isidoro & Solinas, 1992, Jourdan *et al*., 1995). Non-articulated blunt-tipped basiconica sensilla, which resemble sensilla basiconica 1, 2 of *Bembidion lampros, B. properans* and *Platynus dorsalis* are common on the antennal flagellum of most insects (Ploomi *et al.,* 2003).

Besides the sensory organs abundant cuticular pores, obviously openings of the antennal glands, penetrate the surface of the antennae of *R. Ferrugineus*. Differences in the size and placement of these pores may suggest differences in the function of respective cuticular glands. In some other insects, antennal glands may have enzymatic activity, degrading molecules of pheromones (Taylor *et al.,* 1981). In Chrysomelidae, antennal glands may produce pheromone (Bartlet *et al*., 1994).

A few ultrastructurally obvious effects of irradiation in the features of normal antennal sensilla of *R. Ferrugineus* could be observed*.* Typically seen as shrunken, curved of sensilla into different directions, irregularity in shape, swollen in some parts and some sensilla gathered into dense collections. Similar works on the effects of gamma radiation have been recorded by many authors in other insects ; Oland *et al*.,(1988) illustrated the comparison between normal and irradiated *Manduca sexta* with 2.64 Gy revealed that features of normal antennal sensilla were present in irradiated ones with presence some cuticular disruption. Also, El-kholy & Mikhaiel (2008) revealed that gamma irradiation of full grown male pupae of *Galleria mellonella* with the sterile dose 400 Gy and the two substerile doses 100 and 150 Gy showed malformations in the F1 male antennal sensilla less than that in the parents irradiated with the dose 400 Gy . Besides, the irradiated pupae with the sterilizing dose in *Bactrocera zonata* produced adults with different malformation on the antennal sensilla (El-Akhdar & Afia, 2009).

The present study showed that the malformations in the antennal sensilla induced from exposed of adult with the dose rate 15 Gy were very few, while the dose rate 20 Gy affected on high number of antennal sensilla. And so, the used of high dose (20 Gy) must be turned off because this dose will affect on the behavior of insects. These previous results are compatible with our study in using gamma radiations (15Gy) as part of an Integrated Pest Management program for controlling this pest.
