Since becoming a pest in graminaceous crops in Africa, the African sugarcane stalkborer Eldana saccharina Walker has been the subject of much study. Its very cryptic habits have precluded more commonly available control measures being used against it. Biological control is regarded as a viable control option, but the apparent paucity of parasitoids in graminaceous crops leads to E. saccharina being regarded as lacking parasitoids, and thus not a good candidate for biological control in the classical sense. In contrast, this project argues that interactions in indigenous hosts of E. saccharina had been ignored, and that classical biocontrol principles and basic ecological theory could be applied by the discovery, collection and introduction of parasitoids from its indigenous habitat to its newly adapted habitat, sugarcane. The habitat offered by Cyperus papyrus L. was shown to be heterogenous both temporarily and spatially. Umbels, from young through mature to senescent, were available in the same proportion for colonisation throughout the year. Umbels with sexual reproductive stages (seeds) were present from early spring into late summer, and provided an additional component to the already heterogenous environment. Young umbels, in addition, developed from rhizomes in an environment regarded as sub-optimal for photosynthesis, until they reached the canopy. All stages of umbels were attacked by E. saccharina, but larvae were only found in rays of umbels and in the apex of the culm, which was the meristematic area for rays, both high nutrient areas. Young umbels were never found with borer pupae, only smaller larvae, indicating that E. saccharina development matched growth of young umbels until they reached canopy height. Also, the majority of borings found were occupied, indicating that infestation of young umbels was recent. All stages of E. saccharina development were found in mature umbels, which were also most abundant at anyone time. Numerous empty borings were found in addition to those occupied, indicative of past occupation by E. saccharina. Very few young larvae were found in old umbels, the majority of life stages found being pupae or empty pupal cases, and also many empty borings, showing that old umbels were not suitable for E. saccharina development. A guild of parasitoids which comprised Orgilus bifasciatus Turner, the most common parasitoid of small and smaller medium E. saccharina larvae, Goniozus indicus Ashmead the most common parasitoid of larger medium and large larvae, and an entomogenous fungus Seauveria bassiana (Sals.) Vuill. attacking all life stages of E. saccharina was found. Three uncommon parasitoids of smaller saccharina were also found, viz. Sassus sublevis (Granger), Iphiaulax sp. and Venturia sp. The former three natural enemies were instrumental in depressing a major outbreak within two months of it being observed and then maintaining the host population at a lower level in C. papyrus. G. indicus and B. bassiana were most effective during the summer and autumn months, and O. bifasciatus most effective during the winter months. This study supports the hypotheses that the apparent paucity of parasitoids and lack of biological control success thus far against E. saccharina in sugarcane has been because very little was known about its ecology and biology in its numerous indigenous host plants, and that studies of the latter factors coupled with ecological theory could enhance biological control programmes against this borer. As more indigenous host plants are investigated in the same way as has been done with C. papyrus, more will become known of natural enemies of E. saccharina. Parasitoid guilds could be selected, even from rare parasitoids in the more stable indigenous habitats, which would provide control in the unstable habitat of sugarcane. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

Eldana saccharina Walker (Lepidoptera: Pyralidae) is an indigenous insect widely distributed throughout Sub-Saharan Africa that is a major pest of sugarcane in southern Africa. Studies have shown that populations from West Africa have distinct behavioural differences compared to populations from eastern and southern Africa. In addition, the parasitoid guilds attacking populations in these regions are markedly different. This marked behavioural and parasitoid guild variation evoked a hypothesis of genetic diversification. To evaluate this hypothesis a project on the phylogeography of E. saccharina was initiated. The project was planned to include sampling of as many regions as possible in its known range in Africa, to obtain specimens of E. saccharina for genetic analysis. When these surveys were initiated in Ethiopia, it was found that there was no published literature available on the occurrence of stem borers in Ethiopian sugarcane. It was thus clear that no stalk borer/parasitoid surveys had been completed in either sugarcane or any large grass and sedge indigenous hosts in Ethiopia. The study was thus expanded beyond the investigation of only the genetic diversity of E. saccharina, to include area-wide surveys to determine ecological aspects of the borer complex in suspected host plants, including sugarcane, in Ethiopia. In this way the host plant range and distribution of E. saccharina and other sugarcane borers in Ethiopia in particular could be determined, samples for a larger phylogeography project could be collected, and the insect's impact on sugarcane could be assessed. Quantified area-wide surveys of the sugarcane estates and small-scale farmer fields of Ethiopia were conducted between December 2003 and February 2004. The surveys verified the presence of four lepidopteran stem borer species on Ethiopian sugarcane. These were Chilo partellus Swinhoe (Lepidoptera: Crambidae), Sesamia calamistis Hampson (Lepidoptera: Noctuidae), Busseola fusca Fuller (Lepidoptera: Noctuidae) and Busseola phaia Bowden (Lepidoptera: Noctuidae). The surveys indicated that Busseola species are the major and most widely distributed sugarcane stem borers in sugarcane farms of Ethiopia. Over 70% of the peasant sugarcane fields visited were infested by these borers, with the highest levels of infestation (35% and 50%) being in the northern and western part of the country, respectively. Busseola was also the predominant stem borer of sugarcane in two of the three estates (Wonji and Finchawa). Chilo partellus and S.calamistis were recovered in very low numbers at all the commercial estates and from peasant farms in the western part of Ethiopia. However, C. partellus was the predominant sugarcane stem borer in lowland areas of northern, southern and eastern parts of the country. Eldana saccharina was recovered from large sedges in waterways of Metehara and Wonji sugar estates in the central part of the country, and sedges growing around lakes in northern and southern Ethiopia, but not from sugarcane anywhere in Ethiopia. The phylogeographic study conducted on E. saccharina populations from eleven countries of Africa clearly showed the population structure of the insect within the continent. Five hundred and two base pairs of the mitochondrial DNA (mtDNA), corresponding to the Cytochrome Oxidase subunit I (COl) region, were sequenced to clarify phylogenetic relationships between geographically distant populations from eastern, northern, southern and western Africa. Results revealed that E. saccharina is separated into four major populations corresponding to their geographical location, i.e. West African, Rift Valley and two southern African populations. Sequence divergence between the four populations ranged from 1% to 4.98%. The molecular data are congruent with an isolation by distance pattern except for some of the specimens from eastern and southern Africa where geographically close populations are genetically distant from each other. Geographical features such as the Rift Valley and large water bodies in the continent seem to have a considerable impact on the genetic diversity in E. saccharina. Identification of field-collected stem borer specimens was done using classical taxonomic techniques, except for Busseola spp. where DNA barcoding was used. As field-collected larval material of Busseola died before reaching the adult stage, identification of species using adult morphology was not possible. 'Sequence divergence in the COl gene was used as a tool to identify the species of Busseola attacking Ethiopian sugarcane. Partial COl sequences from Ethiopian specimens were compared with sequences of already identified noctuid species from the East African region. Results of the sequence analysis indicated that the Busseola species complex in Ethiopian sugarcane comprised B. fusca and B. phaia. Sequence divergences between Ethiopian Busseola species was as high as 5.0 %, whereas divergences within species were less than 1% in both species identified. Several larval parasitoids, bacterial and fungal diseases of stem boring caterpillars were also recorded in Ethiopian sugarcane. Amongst these was Cotesia flavipes Cameron (Hymenoptera: Braconidae). This exotic parasitoid has been introduced into several African countries for the control of C. partellus in maize and sorghum, but had never been released in Ethiopia. To investigate the origin of C. flavipes in Ethiopian sugarcane, molecular analyses were conducted on Ethiopian specimens from sugarcane and specimens of C. flavipes from different countries of Africa released from the Kenyan laboratory colony, again using COl sequences. Results of the analysis revealed that the C. flavipes population that had established in sugarcane fields of Ethiopia was similar to the south east Asian populations released against C. partellus in maize in other parts of Africa, and different from other populations of this species, providing evidence that the Ethiopian C. flavipes is likely to be a descendant of the original Pakistani population that was released in different parts of Africa. The study reveals the importance of lepidopteran stem borers in sugarcane production in Ethiopia and highlights the role of molecular methods in species identification and determining phylogenetic relationships. More importantly, this study establishes the continental phylogeographical pattern of the indigenous moth, E. saccharina. The impact of geological events, geographic barriers and cropping systems on the evolution, distribution and abundance of stem borers are discussed. Future areas of research for understanding more about the phylogeographic relationships of E. saccharina and management of stem borers are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.