Colonization of host patches following long-distance dispersal by a goldenrod beetle, Trirhabda virgata

1. The arrival of the chrysomelid beetle Trirhabda virgata on isolated patches of its host Solidago altissima was closely monitored to determine how conspecific density and host condition influence colonization.
2. Experimental host patches, which were set on the roof of a four-storey building located 0.7 km from the nearest naturally occurring hosts, were frequently colonized by beetles over a 2-week dispersal period.
3. Females preferred lush host patches that were free from simulated Trirhabda chewing damage. Females colonized lush patches more often than defoliated patches at two spatial scales, when patches were 2 m and 25 m apart. Males did not show a strong preference for lush plants.
4. Males aggregated on plants that already contained adult conspecifics, apparently increasing their reproductive success. Females did not respond to the presence of adults on the patch.
5. Ninety-five per cent of the females arriving on the isolated plants had mated before flying, indicating that lone females are able to colonize empty stands.
6. By avoiding heavily defoliated plants, females should dissipate local outbreaks and spread their offspring away from over-exploited areas.