Browsing by Author "Powell, Chante Melissa"
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- ItemSpecies identification, lifestyles and mitogenomics of the elusive wasp assemblage associated with wild and cultivated olives in the Western Cape(Stellenbosch : Stellenbosch University, 2019-12) Powell, Chante Melissa; Van Asch, Barbara; Rhode, Clint; Stellenbosch University. Faculty of Agrisciences. Dept. of Genetics.ENGLISH ABSTRACT: While the international olive industry is greatly affected by the olive fruit fly (Bactrocera oleae), South African commercial crops are marginally affected. The rich assemblage of native parasitoid wasps found in the region may contribute to maintain B. oleae populations at low levels and has potential applications in biocontrol. Furthermore, agricultural losses in the Western Cape province are mainly due to the activity of olive seed wasps (OSW) associated with premature fruit drop; however, the status of several species as phytophagous, parasitoid and hyperparasitoid remains uncertain. Moreover, the genus Psyttalia (Braconidae: Opiinae) includes parasitoid species with potential for biocontrol of fruit-infesting tephritid pests such as B. oleae. In addition to the native Mediterranean tephritid parasitoid, Psyttalia concolor, two sub-Saharan parasitoid species; Psyttalia humilis and Psyttalia lounsburyi, are of particular interest as they can be utilized in exotic biocontrol applications of B. oleae. The aim of this study was to generate a comprehensive catalogue of the entomofauna associated with olive fruit by identifying all species affecting the fruit, confirming the status of putative olive seed wasps as phytophagous and contributing to the phylogeny of the family Braconidae. The comprehensive survey combined morphological and DNA-based methods in which four Braconidae species and six Chalcidoidea species were identified. Furthermore, morphological identifications were congruent with DNA data for all species, as neighbour-joining and maximum-likelihood trees correctly placed all sequences either at the genus or species level, depending on the available taxa coverage, and low genetic distances strongly supported conspecificity. These results can be used for early DNA-based species identification of wasp larvae in olives, and to further investigate their biology and ecology. In addition, a DNA-based identification tool was developed to identify immature specimens collected from olive seeds and for the simultaneous detection of five putative chalcid OSW (Eupelmus spermophilus, Eurytoma oleae, Eurytoma varicolor, Neochrysocharis formosus and Sycophila aethiopica). Eupelmus spermophilus, E. oleae and S. aethiopica were identified in olive seeds, and confirmed as phytophagous. This method can be used as a diagnostic tool for pest detection at an early stage of infestation when morphological identification is not feasible. Furthermore, it can provide new biological insights into the lifestyles of these elusive species. The near-complete mitochondrial genomes of Psyttalia concolor, Psyttalia humilis, and Psyttalia lounsburyi, three important parasitoids, were recovered using Sanger sequencing and next-generation sequencing. The three Psyttalia species had a particular gene arrangement involving tRNAs, different from all other Braconidae. Gene rearrangements varied substantially among Braconidae, potentially being useful for clarification of the complex phylogeny of the group. Phylogenetic reconstruction within the family Braconidae confirmed the division of two major lineages of cyclostome and non-cyclostome braconids. Furthermore, our analyses corroborated subfamily Aphidiinae as a sister group to the cyclostome braconids, a group previously thought to be a separate family (Aphidiidae). Overall, this study advances the knowledge of insects associated with olive fruit in the Western Cape, the status of phytophagous OSW, which was previously undetermined, and contributes to the phylogeny and understanding of gene rearrangement in the family Braconidae.