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

[摘要] Six tortricid species are of major economic importance to the South African fruit industry. They are thecodling moth Cydia pomonella, the oriental fruit moth Grapholita molesta, the false codling mothThaumatotibia leucotreta, the macadamia nut borer T. batrachopa, the litchi moth Cryptophlebia peltasticaand the carnation worm Epichoristodes acerbella. For phytosanitary purposes and to aid the managementof population levels of the aforementioned species, their identities at species and population level wereinvestigated using morphological and molecular genetic techniques. Morphological characteristics wereused to distinguish and differentiate between the final instar larvae and pupae of the six species. For thispurpose 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 scanningelectron micrographs. Taxonomic characters found to be useful for the identification of the larvae were thepresence and structure of the anal comb and the number and arrangement of crochets on the prolegs. Thepupae could be distinguished based on the presence or absence of a distinct cremaster, the shape of thespiracle, the position of the setae on the anal rise, the structure of the mouthparts and the length of theprocoxa in relation to that of the protarsus. These characters were used to develop keys to distinguishbetween the tortricid species occurring on tropical and subtropical fruit (T. leucotreta, T. batrachopa andCr. peltastica) and deciduous fruit (E. acerbella, C. pomonella, G. molesta and T. leucotreta). Atpopulation level, molecular techniques were employed to compare geographic populations of each of thesix species. Amplified fragment length polymorphism (AFLP) analysis with five selective primer pairswas used to investigate genetic diversity. In addition, host populations of species were compared whererelevant. No evidence was found to suggest that populations from different hosts were geneticallydifferentiated. However, geographic populations were found to be genetically distinct in each of the sixspecies, with extensive genetic divergence apparent over local geographic scales and significantly highestimates of population differentiation ranging between Gst = 0.2625 and 0.3778. Factors influencing thegenetic population structure of the six species were investigated by comparing the amount and distributionof genetic variation between oligophagous and polyphagous species as well as introduced and nativespecies. Results indicated that host range and population history did not have a major effect on populationgenetic structure. It was therefore suggested that other factors such as limited dispersal were responsiblefor the extensive genetic divergence observed between geographic populations of each of the six tortricidspecies. These results should be incorporated into existing pest management programs and taken intoconsideration when designing new control strategies. This is the first report of its kind to identify, with ahigh level of accuracy, the aforementioned tortricids and the first to determine the population geneticstructure of these species.

[发布机构] Stellenbosch University