Sympatric/parapatric speciation via differential host plant utilisation in the tephritid fly Tephritis conura

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The tephritid fly Tephritis conura is used to test hypotheses of sympatric and parapatric speciation in herbivorous insects. The fly feeds on seeds of at least nine thistle species, all of the genus Cirsium. Allozyme analyses and ecological studies indicate a relationship between T. conura and some Cirsium species with respect to allele frequencies (locus HK), host attraction and survival of larvae. The study emphasis is put on behavioural and population genetic aspects of host shifts. We exemplarily study T. conura populations from three host plant species, Cirsium heterophyllum, C. oleraceum, and C. erisithales. Plants are sampled from pure and mixed stands, and from localities where only one of several alternative host plant species is attacked. Field and laboratory experiments are designed to test the relative importance of temporal flowering, host attraction and mate recognition for reproductive isolation. Furthermore, experiments are designed to test viability on alternate hosts. Population genetic analyses (nuclear genes, mtDNA) are used to quantify whether biotypes (host associations) are stable or diverging in their reproductive and dispersal behaviours, including possible selection linked to the enzyme HK. MtDNA is of interest because females choose the oviposition site and the genealogy may reveal the directionality of plant colonisation. We aim to elucidate causal explanations for divergence in an incipient, by insect-plant interactions mediated process of species radiation.