沙漠研究 19-1, 379- 382 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Bio-ecologic Observations on Rhinoceros Beetle Oryctes agamemnon (Burmeister1847) on the Palm Dates Oasis of Rjim Maatoug in South-western Tunisia
M’hammed EHSINE*1, Mohamed Sadok BELKADHI1, Mohammed CHAEIB2
Abstract: The culture of date palms (Phoenix dactylifera L.) plays a very important role insouthern Tunisia both at socio-economic and ecological levels. It plays a major role in thenational economy. However, palm trees are still facing many problems and constraints thathave undoubtedly negative impacts on their normal growth and production. Today, a relatively
new pest is assuming alarming proportions: the rhinoceros beetle, O. agamemnon Burm
weakens the root system and renders the trees susceptible of falling off. O. agamemnon Burmis a Coleoptera insect of the family of Scarabeidae. The insect passes from egg into an adultby three larval instars, a prepupa and a pupa. The monitoring of the biological cycle of theinsect at the laboratory and on ground showed that the pupal phase is carried out without hull.
The sexual dimorphism is evident only with the big individuals. The most noticeable damage
is caused by the larvae. The adult can cause damage on the trunk, on the trunk base and onother organs of the plant. The study of the stratification of the insect on the palm tree showedthat the larvae are concentrated on the level of the collar and the root system, but alsofrequently set out along the trunk. The monitoring of the state of the infestation of manure
showed that it is a very favourable medium for the multiplication of Oryctes. The study ofpopulation dynamics of adult revealed that the activity of adult of O. agamemnon in the oasisof the region starts by the beginning of June until mid-November.
Keywords: Adult activity, Date palm, Larva, Manure, Oryctes agamemnon

1. Introduction
The culture of date palms (Phoenix dactylifera L) plays a very important role in southern Tunisia bothat socio-economic and ecological levels. It plays by now an undeniable role in maintaining humanpopulations in arid regions where natural resources are limited and living conditions are difficult. So it is astabilizer of economy in these regions, allowing the survival of about 4.5 million people worldwide (Dutuitet al., 1991). In Tunisia there are about 10% of the population who earn their living from the palm dates’
sector (EL Hadrami et al., 1998). Date Palms play a crucial role in the struggle against desertification,
maintaining an ecological balance and contributing to the conservation of a fragile ecosystem. In addition,
this tree can grow under conditions of temperature ranging from 12 to 50 ˚C with little or no moisture andcan be irrigated with very alkaline water (Leroy, 1958). It is also a shelter for many indigenous plant andanimal species. Moreover, the Tunisian oasis is characterized by a considerable genetic wealth as
evidenced by the presence of at least 250 cultivators listed (Rhouma, 1994). In spite of the great efforts tooptimize production, palm trees are still facing many problems and constraints that have without any doubt
negative impacts on their normal growth and production. Those problems include water stress, excess of
salinity, drainage and many diseases and pests. Some major pests of date palms are present in Tunisia(Dhouibi, 1991). The mite Oligonychus afrasiaticus affects essentially the fruit. The white scale
Parlatoria blanchardi colonizes all parts of the tree. The larva of the moth Ectomyelois ceratoniae infests
the dates internally. Several fungal diseases of date palms are known in Tunisia. Mycosphaerella tassiana
causes brown spots on midribs, leaflets and thorns. Diplodia phoeniceum affects essentially leaves ofoffshoots and the lethal disease: “Brittle leaf disease” or, in French, “Maladie des feuilles cassantes”(MFC) that has affected or killed up to 40,000 date palm trees in the Djerid region of Southern Tunisia
since the 1980s (Takrouni et al., 1988; Triki et al., 2003). Today, a relatively new pest, is assuming
alarming proportions: the rhinoceros beetle, O. agamemnon weakens the root system and renders the trees
susceptible of falling off. Rhinoceros beetle of the genus Oryctes are important pests of palms, inSoutheast Asia, North Africa and some Pacific islands. (Hallet et al., 1995; Rochat et al., 2004). O.
12Institute of Arid Regions – kebili, BP 32, 4200, Kebili, Tunisia. * Corresponding: ehsine_mhammed@yahoo.fr
Science Faculty of Sfax, BP 802 3018. Sfax, Tunisia.

380agamemnon (Coleoptera, Scarabaeidae) was accidentally introduced in the southwestern oases of Tunisia.
It was identified for the first time in 1995 in Tozeur (Khoualdia et al., 1997), and introduced to Rjim
Maatoug after the creation of new oases. Its introduction without the natural controlling factors allows it toreproduce quickly and spread to become a serious pest. Thus, it is necessary to study the bio-ecology ofOryctes in order to develop methods that may help fight this pest.
2. Materials and methods
Our investigations started at the beginning of 2003 in the oasis of Rjim Maatoug. It is an area whichlies within 120 kilometres in the south west of kebili. It is characterized by a continental Saharan climate,an average rainfall lower than 100 mm/year, an average temperature of 21˚C with extremes of +55˚ insummer in the shade and -7 ˚C in winter, ETP = 2200 to 4300 mm/year and a very filtered sandy ground.
Our study reached the entire oasis of production in this area (Rjim Maatoug 1 and 2, Ferdaws 1 and 2 andNasr 1 and 2), occupying a total surface area of 1452 hectares. The study of bio-ecology of the Oryctes
was carried out by visiting the oasis to follow the state of the infestation, to collect the various stages of theinsect and carry out a research about their different biotopes. The larvae and adults were collected alive inplastic vats. The rearing of larvae and adults collected was undertaken at the laboratory on an artificialsubstrate. The dynamics of the populations of the insect in the oasis ecosystem was conducted based on
the capture of the adults using a luminous trap over the year 2005. The collection of trapped adults wasrealized every week. In what concerns measurements of different biological stages of Oryctes, we used arule and a binocular magnifying glass type Euromex.
3. Results and discussion
3.1. Description and biology of Oryctes
Oryctes is an insect with complete metamorphosis. Its reproductive cycle consists in five instars: theegg, the larva, the prepupa, the pupa and the adult. The insect has brown shining colour. It is cylindrical,lengthened and very convex. It also possesses a characteristic cephalic horn which is larger for males.
Measurements carried out on some adults at the level of laboratory showed that males have these
dimensions: 25-39mm long and 13-19 mm breadth whereas females are 22-38mm long and 12-19 mm
breadth. Our observations at the laboratory confirm what is said by, Rochat (unpublished), that the sexual
dimorphism is not obvious only for the bigger individuals and it is possible to recognize undoubtedly themale and female through the examination of the end of the abdomen ventral face. For the male the last
segment is narrow with more or less parallel edges and with a notch in the middle of the posterior edge,
whereas for the female the last segment is clearly triangular with a point in the middle of the posterior edge.
The egg is of white opaque colour and oval form to the laying. Progressively with incubation it becomesalmost round. Its sizes are on average 3.14 mm length and 2.22 mm width. The eggs are generally foundeither lonely or grouped (2 to 4) in the same galleries on the level of the collar and the base of the dry
petiole on the stem (Fig. 2). The larva of Oryctes is lengthened, cylindrical and thick, curved in arc ofcircle having three pairs of thoracic leg and crushing mouth. Measurements at the laboratory showed thatits length varies between 6.4 and 87 millimetres. The prepupa is a stage of preparation to the pupal phaseand the shift to this stage is marked by the absence of sloughing. Thus, we can say that, when the larvae
reach the maximum growth point in the late third instar phase, they stop feeding and begin the preparation
for the pupal phase. This cessation of breeding is accompanied by many transformations such as theregression of size, a contraction of the legs etc.. This stage was not mentioned by Lepesme (1947), butduring our work either on field or at the laboratory we met this stage, as indicated by Balachowsky (1962)
and Soltani et al. (2008 a). The pupa is characterized by the differentiation of the majority of the externalbodies and a white colouring which changes gradually into yellow then into orange and at the end reaches
clear brown. According to taken measurements we note that the nymph can reach a 40.8 mm length and awidth of 16,8mm. According to Lepesme (1947), the phase of pupa occurs in hulls built from remains
agglomerated by the larva of the last stage; or our observations on fields and at the level of rearing at thelaboratory did show that the phase of pupa is carried out without a pupal cell. We noted only the presenceof tegument of the prepupa after his metamorphosis into nymph and the tegument of the nymph followinghis transformation into an adult. The follow-up of the insect on oases shows that the larvae of this beetle

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meet on the base of the trunk of the palm trees (collar) and on the stem. They are particularly harmful tothe roots; especially the third instar; since it is the longest developmental stage of larvae; which can devour
the tissue and the root on the level of the collar anyway and constitutes larger holes (Figs. 3 and 4). The
repetition of the phenomenon, over many years, constitutes a potential danger to the whole palm tree andcan result in an unbalance by the weakening of its basal support, and as a consequence, increasing the riskof collapse (Fig. 5). They are also harmful to the new planted offshoots by reducing the percentage ofresumption (Fig. 6). We met damage on the basis of the palms, into the base of cluster of fruits. Thisdamage might be caused by the adult which, according to Lepersme (1947), seeks the tender wood.
3.2. Stratification of damage
When the problem first appeared, all the orientations were concentrated on the buried zone of thepalm tree (Figs. 3 and 4) where we met the greatest number of larvae and where the damage is easier toobserve; especially at an advanced attack; following the appearance of a brown powder similar to compost,that was scattered on the ground at the level of the trunk base. For this reason, the intervention bycollection and destruction of various bio-stages of the beetle was exclusively at this level. But ourinvestigations revealed that the larvae are distributed along the stem by arranging galleries (Fig. 1) whichpass unperceived, especially that they are protected by the dry base leaf. This prevents us fromdetermining the trunk situation, whether it is infested or not. Our results correspond to the results cited by
Soltani et al. (2008 b) that the existence of larvae in the stem is not very dangerous to the palm tree but it
constitutes a nest for the breeding of this insect.

14

2

35

6Figs. 1 to 6. (1) damage of larvae on the dry petiole and sheath at the level of stem; (2) eggs on the stem; (3 and4) damage of larvae at the base of stem; (5) collapse of date palm; (6) offshoots damage.

3.3. Control of the state of manure infestation
The manure is largely used in the oasis by the farmers to fertilize their oasis. To explore the different
biotopes of the insect, we gave a special attention to this. The analysis on the level of the manure put in thetrench in the oasis showed us the presence of larvae of Scarabeidae which have a very great similarity to
the larvae of Oryctes. In order to determine the species, we collected some larvae which reared at thelaboratory. In a few weeks, the larvae have become adults. This result enabled us to confirm that this isthe Oryctes, specifically O. agamemnon. As such, the manure and organic matter in a general way is afavourable environment for the development of Oryctes and is very dangerous since it increases the spreadof the insect.
3.4. Adult activity
Population monitoring has been carried along the year 2005 (Fig. 7). A total of 740 beetles werecaptured by one luminous trap. Weekly captures, which were nil in January, February, March, April, andMay have increased from the beginning ofJune until the mid-July. Then, they have
oscillated around that level until the third
week of September with a sharp peak of
capture at the beginning of August (135beetles) and decreased regularly to become
again nil at mid-November.

n u m b er o f ad u lts trap p ed

382

160
140
120
100
80
60
40
20
0

4. Conclusion
6/1
6/3
6/5
6/7
6/9
6/11
The culture of palm dates plays a very
date of control
important role in the southern part ofFig.
7.
Activityof
theadultsofOryctes
agamemnon.
Tunisia both at the socio-economic andecological scales. It is a stabilizer for theeconomy in these regions, and a real front against the wandering desert. However, palm trees are stillfacing many problems and constraints that have without any doubt negative impacts on their normal
growth and production. A relatively new pest is leading to alarming proportions: the root borer, O.
agamemnon weakens the root system, and renders the trees susceptible of falling off. The observations
that we have undertaken on Oryctes show that the larvae of the insect exist on palm trees throughout theyear and they are more harmful to the tree than adults. Manure is a favourable environment for theproliferation of Oryctes and is a very dangerous means of propagation of this pest. The study of adultdynamics has shown that the adult population of O. agamemnon in the oases begins from the beginning ofJune until mid-November. Currently we are interested in an indigenous entomopathogenic nematodewhich is the subject of a study that can be used in an integrated Program to fight against the pest.
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