The Rhinoceros Beetle Oryctes agamemnon arabicus in ... - Iresa

DEVELOPMENT SITESThe availability of development orbreeding sites and the knowledge of theirnature and quality are determinant in theexistence of any insect population in agiven area. Indifferently of the infestedoasis in Southwest Tunisia, it has beenfound that the breeding sites of O.agamemnon arabicus are the same both inthe Djerid and Rjim Maatoug zones. Allthe stages develop in live standing palmtrees. The large number of beetles, eggsand larvae were collected from respiratoryroots both on the ground and in the aerialpart, on the external dead wood throughthe stem as the matrixes of fibrilium, thebark of stem and basal part of dry petioles(13, 14, 15).In Oman, O. agamemnon arabicus isconsidered as a fruit stalk borer whichlarvae are usually found inside the deadand weaken offshoots. In Saudi Arabia,larvae of O. elegans were found betweenthe frond bases and trunks (1). However,the most favored breeding sites for O.rhinoceros in Pacific area are deadstanding palms which die from old age,dead coconut trunks and stumps, anddecaying cocoa pod humus (2, 16).As with all beetles, larvae of O.agamemnon arabicus hatch from eggs anddevelop into nymphae, and theseultimately develop into adult beetles. Eggsare deposited directly on the area of futuretarget. However, female burrows to lay theeggs singly 5 to 10 cm below the surfacebetween fibrous of respiratory roots,through the stem eggs are laid betweentough layers. In both cases and in newtargeted place, female chewed and reducethe fibrous roots or the matrixes offibrilium on small granules used to preparechipboard of firm material where eggs arelaid. However, when firm material exists,eggs are laid at intervals along the tunnelmade in it. Each female lays at mean 27eggs in single or several clutches (14).Favored breeding sites are standingalive date palm trees in the goodentertained oases, weakened palms areless attacked than vigorous ones. In thezone of Tozeur, where the species firstlyappeared, targeted parts of standingvigorous palm trees are preferred tounhealthy and dead standing ones (13).DAMAGES, THREAT ANDECONOMIC IMPORTANCEIn Southwest Tunisia, O.agamemnon arabicus was localizedinside plantations of less than 30 yearsold and damage caused by this pest, areirreversible, particularly in respiratoryroots part, and may result in one of thefollowing symptoms, perceived throughsight, depending upon the stage ofinfestation (14):i) Occurrence of chewed planttissues on the ground beside the attackedside and on the upper surface of toughlayers,ii) Weakened bases of fibriliummatrixes and dry petioles made them easyto pull up,iii) Heavily attacks on offshootslinked to mother plant let them partiallydry with wrinkled aspects of palms.Damages are localized from thebottom to the top of the plant on therespiratory roots, external components ofthe stem and the basal levels of old greenpalms. Larvae of O. agamemnon arabicusconstitute the mainly harmful stages (14)and not the adult beetle like for O.rhinoceros (2, 3, 12, 16) and O. elegans (1,11). The concealed nature of the pestmakes detection of infested palms adifficult task.In respiratory roots, larvae move bycutting into fibrous roots. Through thestem, matrixes of fibrilium, frond midribsand stem bark are the interested part ofattack and larvae are never seen inside thestem. Basal part of crown, represented byTunisian Journal of Plant Protection 184 Vol. 5, No. 2, 2010