Is there local adaptation in Drosophila-parasitoid interactions?

Local adaptation has received little attention in host-parasitoid associati ons. Here we combine data on the outcome of parasitism in 20 sympatric popu lations of Drosophila melanogaster and its parasitoid Asobara tabida. We pr esent data on resistance and virulence when each host is tested against a s ingle allopatric strain of parasitoid, and when each parasitoid is tested a gainst a single allopatric strain of host. We argue that the extent to whic h these allopatric interactions can be used to predict sympatric interactio ns sets an upper bound to the importance of local adaptation. In a statisti cal model, we found that 56% of the variance in the outcome of sympatric in teractions could be explained by parasitoid virulence and host resistance m easured using the allopatric reference strains, with the former being the m uch more important of the two. The geographical distance between the proven ances of the sympatric and reference parasitoid (but not host) populations was also statistically significant and increased the variance explained to 69%; but against expectation, parasitoid success was negatively correlated with distance. We also explore the factors determining the frequency with w hich neither host nor parasitoid survive. We conclude that, although the cr itical tests have yet to be performed, the available evidence points toward s local adaptation not being of major importance in this system.