CORE Metadata, citation and similar papers at core.ac.uk ProvidedJournal by PubMed of Insect Central Science: Vol. 8 | Article 57 Soltani et al. Descriptive study of damage caused by the rhinoceros beetle, Oryctes agamemnon, and its influence on date palm oases of Rjim Maatoug, Tunisia Rasmi Soltani1a, Chaieb Ikbel1, and Med Habib Ben Hamouda1 1Department of Biological Sciences and Plant Protection, Agronomics Sciences Institute of Chott Meriam 4042 Sousse, Tunisia Abstract Oryctes agamemnon (Burmeister 1847) (Coleoptera, Scarabaeidae) was accidentally introduced in the southwestern oases of Tunisia (Tozeur) around 1980 and spread to the Rjim Maatoug region. In these areas O.agamemnon was specific to date palm trees causing severe damage that can result in potential danger due to collapse of the tree. This study was conducted from April 2004 to March 2006 in 4 sites in the region of Rjim Maatoug. Different levels of palm tree attack were determined, ovioposition sites were identified, and pest damage was described in detail to specify their relative importance and to indicate factors governing palm tree attack. Eggs were individually oviposited in the attacked parts. Dead parts of palm trees were the main target of O. agamemnon including the respiratory roots, tough, trunk bark, dry petiole and the periphery of the crown. The crown itself was not attacked. Feeding by larvae caused significant damage. The biggest danger occurred when heavy attacks of larvae invaded the respiratory roots at the level of the soil, and secondarily on the periphery of the crown, which can result in fungal diseases. Several cases of Deglet Nour date palm tree collapse were caused by this pest in Rjim Maatoug. Attacks on other parts of the tree were without danger for the palm tree. In the absence of pest management, application of a quarantine program combined with field cultivation techniques could help farmers significantly decrease attack of O. agamemnon on palm trees. Keywords: Scarabaeidae, offshoots, oviposition, palm tree collapse Correspondence: [email protected] Received: 24 May 2006 | Accepted: 24 December 2007 | Published: 8 October 2008 Copyright: This is an open access paper. We use the Creative Commons Attribution 3.0 license that permits unrestricted use, provided that the paper is properly attributed. ISSN: 1536-2442 | Volume 8, Number 57 Cite this paper as: Soltani R, Ikbel C, Ben Hamouda M. 2008. Descriptive study of damage caused by the rhinoceros beetle, Oryctes agamemnon, and its influence on data palm oases of Rjim Maatoug, Tunisia. 11pp. Journal of Insect Science 8:57, available online: insectscience.org/8.57 Journal of Insect Science | www.insectscience.org 1 Journal of Insect Science: Vol. 8 | Article 57 Soltani et al. Introduction Materials and Methods In southwestern region of Tunisia, the date palm is often Study site prone to phytophagous attacks caused by various insects, Observations started at the beginning of April 2004 in in particular in the zones of high date production of the area of Rjim Maatoug located in Kebili governorate, Djerid (Gouvernorat of Tozeur), and Nefzaoua 120 km in the south-western area of this city, just south (Gouvernorat of Kebili). The three principal species of Chott El Djerid. This area was characterized by a con- threatening date production are the carob moth, Ectomy- tinental Saharan climate, an average rainfall lower than eloïs ceratoniae (Zeller 1839), the white scale, Parlatoria blan- 100 mm/year, an average temperature of 21°C with ex- chardi (Targioni Tozzetti 1892), the acarina Boufaroua, tremes of 55°C in the shade in summer and 7°C in Oligonychus afrasiaticus (McGregor 1939), and a new pest, winter, sandy ground and desert vegetation limited the beetle Oryctes agamemnon (Burmeister 1847) mainly to the species Ephedra alata alenda (Stapf), Spartidium (Coleoptera, Scarabaeidae). The latter is an exotic pest saharae (Cosson and Durieu) and date palm trees within originating from the Middle East (Baraud 1985). It was oases. introduced accidentally for the first time in the late 1970s to the early 1980’s into the palm plantations of Mrah lah- Currently, the zone comprises 5 oases in production ouar in Tozeur. It came from the countries of the Golf (Rjim Maatoug, Ferdaous 1 and 2 and Nasr 1 and 2) cov- region and was disseminated by offshoots of the variety ering a total surface of 1440 hectares where observations Deglet Nour to the oases of Ibn Chabbat of the same took place. Oases in this area are continental and of the area (Anonymous 2000). By the middle 1980’s O. agamem- moderntypewithameanplantingspaceof9x9m.The non had reached the Rjim Maatoug zone after new oases principal vegetation was date palm trees with a marked were installed using biological material from infested predominance of the Deglet Nour variety and very few oases of Tozeur. market-gardening or fodder practices for farmer consumption. The gradual acclimatization of O. agamemnon to Tunisian oases conditions was simultaneously accompanied by a Localization of oviposition and breeding sites change in the date palms hosts. The Deglet Nour variety, in nature which is the most cultivated within these oases, became Determination of oviposition sites was carried out while its principal target. Consequently, it has became an im- looking for various instars of the insect. This was done portant pest of date palm trees. Currently, the most signi- three times per week during the summer, for three years ficant pest danger has occurred in certain oases of from 2004 to 2007. Eggs were collected from different Tozeur and Kebili states. Although it has not had any oviposition sites of the palm tree. Breeding sites were de- direct effect on production, it directly affects some sensit- termined using the same methodology but was done ive parts of the date palm tree. Thus after many years of weekly during the entire year. infestation, attacked parts can become weak threatening the sudden fall of the whole palm (Soltani 2004). Damage localization, symptoms and damage description In the absence of biological and/or chemical control A general survey of all sites of the region was done to methods, O. agamemnon became acclimatized, and in- identify the principal existent categories of oases, the re- creased its population size to the point that it became dif- partition of the species within it and also to determine at- ficult to control. The problem was discovered at the end tacked parts of palm tree where different instars of the O. of 1990s, but by this time they had become uncontrol- agamemnon lived. Sampling for the second part was real- lable. In spite of the danger that O. agamemnon is likely to ized in a systematic way, during the entire period of the present for the future of date palm culture in the region, study, by choosing palm trees within the oases situated at it has been neglected and no serious study has been de- each corner and in the middle. Samples were composed voted to it (Soltani 2004). of hundreds of palm trees. The objectives of this study were to do a detailed examin- Simultaneously, exterior examination of all invaded parts ation of damage, determine larval feeding behaviour, was done in different sites of the region to determine all adult oviposition sites, dispersal methods, and effects on symptoms of attack by this pest. Damage description was palm trees in the oases of Rjim Maatoug. Methods that based on meticulous observations of hundreds date palm could be used to prevent dispersion were also examined. trees and offshoots between 2004 and 2007, including percent infestation, and distribution of the attack. Journal of Insect Science | www.insectscience.org 2 Journal of Insect Science: Vol. 8 | Article 57 Soltani et al. Results Also, damage was not externally visible on the attacked parts. Organization of the date palm Root system Larval instars were nourished on secondary parts, with Being a monocotyledon, the date palm has no tap root. little effect on the date palm tree. In the oases of the re- Its root system is fasciculated and roots are fibrous, simil- gion, palm tree attacks were localised mainly at the base, ar to a maize plant. The date palm root system is divided particularly at the superficial part of the root, known as into four zones (Oihabi 1991; Zaid et al. 2002): respiratory part and secondary on higher trunk levels in- cluding different components of the dry petiole levels and Zone I, the respiratory zone, the respiratory zone is the the periphery of the crown (tough, dry petiole, stem bark base of the palm no more than 25 cm depth and laterally and fronds base of the crown). It should be noted that ini- a maximum of 0.5 m away from the stipe. The roots in tial damage to the tree was localised as a result of the at- this zone are mainly primary and secondary type with a tack sites of the female beetle in obscure sites that were respiratory role. wet and well protected. Zone II, the nutritional zone, is large with the highest pro- Regular surveys enabled a detailed description of damage portion of primary and secondary roots. These roots are to determine favourable conditions for pest attack. The between 0.90 and 1.50 m depth and project laterally bey- attack of O. agamemnon on the palm tree causing symp- ond the tree's canopy. toms of damage that are very specific and can pass un- perceived during the first years of invasion because larvae Zone III, the absorbing zone, is usually found at a depth live in obscure and well protected places between hairy of 1.5 to 1.8 m. These primary roots are present with de- or fibrous roots and tough layers protected by the dry creasing density from top to bottom.