Adaptation in an insect host–plant pathogen interaction

Jenny S. Cory* and Judith H. Myers Molecular Ecology and Biocontrol Group, NERC Centre for Ecology and Hydrology, Mansfield Road, Oxford OX1 3SR, UK Department of Zoology and Faculty of Agricultural Sciences, Centre for Biodiversity Research, University of British Columbia, 6270 University Boulevard, Vancouver, Canada *Correspondence and present address: Jenny S. Cory, Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands. E-mail: [email protected] Abstract Selection on parasites to adapt to local host populations may be direct or through other components of the system such as vectors or the food plant on which the parasite is ingested. To test for local adaptation of nucleopolyhedrovirus among island populations of western tent caterpillars, Malacosoma californicum pluviale, we compared virus isolates from three geographically distinct sites with different dominant host plants. Pathogenicity, speed of kill and virus production of each isolate were examined on the three food plants. Virus isolates from the two permanent host populations had the fastest speed of kill on the host plant from which they were isolated. This was not the case for a caterpillar population that goes extinct when populations are regionally low. Virus isolates on some plant species combined rapid speed of kill with high virus yield. Infection of hosts by mixed microparasite populations could facilitate local adaptation in response to differing food plant chemistry.