Laboratory and field investigations aimed to characterize the chemical communication system of the date palm pest Oryctes agamemnon. Live males or extracts of male effluvia attracted conspecifics in an olfactometer, whereas female effluvia attracted only males. Volatile emissions from adults feeding on sugarcane were sampled and analysed by gas chromatography (GC) and GC/mass spectrometry (GC/MS). Males emitted a blend of 1) ethyl 4-methyloctanoate, 2) 4-methyloctanoic acid, 3) 4-methyloctanyl acetate, and 4) 4-methyloctanol in variable ratio. Single sensillum recordings demonstrated that compounds 1, 2, and 3 are detected by specific olfactory receptor neurons. Olfactometric experiments showed that compounds 1 and 3 attract both sexes of O. agamemnon, but females are more attracted by compound 1 and males by compound 3. Compound 2 was more attractive for females, especially virgin ones. Field experiments confirmed that compound 1 and compound 2 attracted O. agamemnon of both sexes and showed synergy with palm odors. No clear activity of compound 3 was observed. A mix of compounds 1 and 2 with date palm core odor was significantly the most attractive, and captured more females than males. The male aggregation pheromone of O. agamemnon appears therefore to be based on a mixture in contrast to previously identified Oryctes pheromones. Our results provide the basis for developing mass trapping to control this pest.

Studies to determine the relative abundance and distribution of stemborer species and their associated parasitoids in maize and sorghum were carried out during the 1995-1996 and 1999-2000 cropping seasons on Unguja and Pemba, the two main islands of Zanzibar. Three stemborer species were found on both islands in maize and sorghum, with the exotic species Chilo partellus (Swinhoe) (Crambidae) being the irtDst abundant and widely distributed species, accounting for 75.3 % of stemborer attack. It was followed by Sesamia calamistis Hampson (Noctuidae) and Ch. oriclialcociliellus Strand (Crambidae). Stemborer abundance was significantly higher in Pemba (1.47 ± 0.20) than Unguja (0.85 ± 0.05). Overall stemborer density in Zanzibar, during the period of study, was 1 03 ± 0.08 stemborers per plant. Stemborer infestation was significantly higher during the short rainy season than long rainy season but it did not vary between maize and sorghum or coral rag and plantation areas. The i adigenous parasitoids recorded included ten larval parasitoids: Bassus sp., Cltelonus sp., Cotesia sp., Cotesia sesamiae (Cameron), Cotesia ruficrus (Haliday),;Dolichogenidea sp., Dolichugcnidea aethiopica Wilkinson, Dolichogenidea polaszeki Walker, Megaselia sp. and an unidentified Tachinidae. Among these, the braconid Co. sesamiae was the most common parasitoid, attacking all the stemborer species and recorded from 85.2 % of parasitised larvae. However, parasitism was low-3.9 % on Unguj-i and 1.9 % on Pemba. In addition, the efficiency of Co. sesamiae was reduced by two hyperparasitoids-Aphagnomus fijiensis Ferriere and Elasmus sp. Seven pupal parasitoids were recorded, namely Dentichasmias busseolae Heinrich, Brachymeria sp. Westwood, Brachymeria olethria Waterston, Pediobius furvus Gahan, Psilochalcis soudanensis Steffan, Syzeuctus ruberrimus Benoit and an unidentified Chalcididae. The differences in species diversity between the two islands are discussed in the context of the equilibrium theory of biogeography and the geographical size. Classical biological control of the introduced stemborer Ch. partellus using^ the exotic parasitoid Co. flavipes to supplement the indigenous parasitoids in population regulation is proposed as a potentially useful option for Zanzibar. 335 336 E. I. NIYIBIGIRA et al. Hampson (Noctuidae) et Ch. orichalcocilielhis Strand (Crambidae). L'abondance des borers etait plus eleve dans l'ile de Pemba (1.47 ± 0.20) que dans celle d'Unguja (0.85 ± 0.05). En general la densite des borers a Zanzibar pendant la periode d'etude etait de 1.03 ± 0.08 foreurs par plant. L'infestation par les borers etaient particulierement eleve pendant la courte saison des pluies, mais n'a pas variee entre le mais, le sorgho, ou entre les plantations et les banes de coraux. Dix parasitoids locaux ont ete collectes parmi lesquels, Bassus sp., Chelonns sp., Cotesia sp., Cotesia sesamiae (Cameron), Cotesia ruficrus (Haliday), Dolichogenidea sp., Dolichogenidea aethiopica Wilkinson, Dolichogenidea polaszeki Walker, Megaselia sp., et un Tachini...

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The root borer (Rhinoceros beetle), Oryctes agamemnon (Burmeister, 1847) is an invasive coleopteran pest of date palm trees in southwestern Tunisia introduced accidentally in "Mrah Lahwar" (Department of Tozeur), spread out into "Rjim Maatoug" (Department of Kebili), then into most oases of Tozeur and Kebili departments, where it is now causing a serious damage. We used 101 samples of O. agamemnon collected from 7 oases and 2 date palm varieties, in order to assess several invasion parameters (e.g. level and distribution of genetic diversity, degree of gene flow between populations and number of introduction events). Analysis of molecular variance (AMOVA) of the random amplified polymorphic DNA (RAPD) markers exhibited no significant genetic differentiation in relation with departments (Tozeur vs. Kebili) or host plant varieties (Deglet Nour vs. Kenta), raising the hypothesis that a limited number of founder genotypes would have been at the origin of invasion. A substantial gene flow was revealed among populations, suggesting that the expansion of O. agamemnon, in Tunisian southwestern oases, has been most likely facilitated by human agency, through the propagation of date palm. These preliminary results would provide a framework for more detailed studies on introduced populations of O. agamemnon, in order to help the development of optimized management methods of this insect.