Morphological and molecular studies of tortricid moths of economic importance to the South African fruit industry

Timm, Alicia Eva (2005-12)

Thesis (PhD (Agric) (Conservation Ecology and Entomology))--University of Stellenbosch, 2005.


Six tortricid species are of major economic importance to the South African fruit industry. They are the codling moth Cydia pomonella, the oriental fruit moth Grapholita molesta, the false codling moth Thaumatotibia leucotreta, the macadamia nut borer T. batrachopa, the litchi moth Cryptophlebia peltastica and the carnation worm Epichoristodes acerbella. For phytosanitary purposes and to aid the management of population levels of the aforementioned species, their identities at species and population level were investigated using morphological and molecular genetic techniques. Morphological characteristics were used to distinguish and differentiate between the final instar larvae and pupae of the six species. For this purpose the morphology of the final instar larvae and pupae of the Afrotropical species T. leucotreta, T. batrachopa, Cr. peltastica and E. acerbella was described and illustrated using line drawings and scanning electron micrographs. Taxonomic characters found to be useful for the identification of the larvae were the presence and structure of the anal comb and the number and arrangement of crochets on the prolegs. The pupae could be distinguished based on the presence or absence of a distinct cremaster, the shape of the spiracle, the position of the setae on the anal rise, the structure of the mouthparts and the length of the procoxa in relation to that of the protarsus. These characters were used to develop keys to distinguish between the tortricid species occurring on tropical and subtropical fruit (T. leucotreta, T. batrachopa and Cr. peltastica) and deciduous fruit (E. acerbella, C. pomonella, G. molesta and T. leucotreta). At population level, molecular techniques were employed to compare geographic populations of each of the six species. Amplified fragment length polymorphism (AFLP) analysis with five selective primer pairs was used to investigate genetic diversity. In addition, host populations of species were compared where relevant. No evidence was found to suggest that populations from different hosts were genetically differentiated. However, geographic populations were found to be genetically distinct in each of the six species, with extensive genetic divergence apparent over local geographic scales and significantly high estimates of population differentiation ranging between Gst = 0.2625 and 0.3778. Factors influencing the genetic population structure of the six species were investigated by comparing the amount and distribution of genetic variation between oligophagous and polyphagous species as well as introduced and native species. Results indicated that host range and population history did not have a major effect on population genetic structure. It was therefore suggested that other factors such as limited dispersal were responsible for the extensive genetic divergence observed between geographic populations of each of the six tortricid species. These results should be incorporated into existing pest management programs and taken into consideration when designing new control strategies. This is the first report of its kind to identify, with a high level of accuracy, the aforementioned tortricids and the first to determine the population genetic structure of these species.

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