**1. Introduction**

228 Gamma Radiation

Zakri, A.H., and Jalani, B.S. (1998). Improvement of soybean through mutation breeding.

International Atomic Energy Agency.

Improvement of grain legume production using induced mutations. Proceedings of a workshop Pullman Washington, USA,1-5 July 1986.pp 451-461.Vienna, Austria,

> Palm beetles (Coleoptera: Curculionidae) are harmful pests for cultivated palm – oil, date or coconut palms (Bedford, 1980, Giblin-Davis *et al,* 1996). The red palm weevil (RPW) *Rhynchophorous ferrugineus* (Oliv.) is the most important pest of the date palm in the Middle-East (Abraham & Pillai*,* 1998). The insect was discovered in Saudi Arabia in the mid-1980s (Gush, 1997 & Faleiro *et al*., 1999). Since then it has spread over most of the date palm areas (Bokhari & Abuzuhira 1992 & Vidyasagar *et al.*, 2000), due to the transfer of infested offshoots and palm trees.

> It was introduced accidentally into the Gulf states from Pakistan in 1985, from whence it spread throughout the Arabian Peninsula. It was first reported in Egypt in 1992. It infested the governorates Ismailia and Sharkia, an area with an estimated one million palm trees (Salama & Abdel Aziz, 2001). lthough they have been known as major pests for a long time, efficient and acceptable methods of controlling them are still lacking in many cases. In addition, the selection of plants for oviposition is determined by the physical nature of their surface and by chemical factors which are detected after contact (Fenomore, 1980, Chadha & Roome, 1980). As such, the identification of olfactory and contact chemoreceptors in insects has received the attention of many workers (Albert, 1980, Bland, 1984 & Salama *et al*., 1987).

> Antennae in insect are organs of taste, smell and stimulation (Wiggles worth, 1972). Other authors (Stubbs, 1980, Nakamuta, 1985 & Obata, 1986) have suggested a possible role of sensory stimuli (olfactory, gustatory or mechanical) in prey, or mate detection. The antennae also play kinetic roles and normally keep the nervous system in a state of tone in which it responds to stimuli of all kinds. Antennae of insects vary greatly in length, overall size, size of the individual segments, segmentation, setation and other aspects with the structures being closely related to their function ( Srivastava & Omkar , 2003). Notably, some authors studied the ultrastructurally effects of gamma rays on the features of normal antennal sensilla of *R. Ferrugineus* as Oland *et al*., (1988); El-kholy & Mikhaiel (2008) and El- Akhdar & Afia, 2009.

Ultrastructure Alterations in the Red Palm Weevil Antennal Sensilla Induced By Gamma Irradiation 231

at the base of the rostrum. It consists of three segments, (scape, pedicel, and flagellum)

It is the longest segment; it measures more than one-third of the length of the antenna. Proximally, it has a hook fitting in the antennal groove, while distally it is somewhat

The pedicel has a small triangular base that fits in a comparatively large cavity at the distal

It consists of six segments; the first five segments known as the funicle (resemble the pedicel in form), while the sixth flagellar segment is known as the club (Fig.1). Six subtypes of sensillae were recognized on the funicle, S. trichodea 1, 2, 3, S. chaetica 2 and S. coeloconic 1,

It is the last segment of flagellum (similar to funnel in shape), longer and broader than other antennal segments (Fig.1). The light microscopic observation revealed that the sensilla are densely and homogenously packed on this area. Also, the electronic microscopic study revealed the presence of four types (seven subtypes) of sensilla highly crowded over the

Fig. 1. General morphology of adult antenna *Rhynchophorus Ferrugineus* showing: Scape (S),

Pedicel (P), Funicle (F) and Club (C). [Scale bar indicate 1 mm]

3. The characteristic morphological features of sensilla are shown in figures (2D, 3A).

end of the scape (Fig.1). Two subtypes of sensilla were distinguished

differing in size and shape (Fig.1).

**3.1 The scape** 

thickened (Fig.1).

**3.3 The flagellum** 

**3.4 The club** 

whole of this segment.

**3.2 Pedicel** 

Despite the importance of sense organs on the antennae of red palm weevil (for oviposition, feeding and mating) there is little information about it. Therefore, the objective of current study is to describe the distribution, types of sensillae in *Rhynchophorus ferrugineus* using scanning electron microscopy, and estimate the effects of gamma radiation on them. This information may be useful for controlling the pests.
