The phenology and impact of the gorse seed weevil, Exapion ulicis, on gorse, Ulex europaeus, in Tasmania

The patterns of gorse pod production, the phenology of Exapion ulicis and its impact on gorse seed production were assessed in a field study conducted at two sites over 20 months in Tasmania, Australia. The production of gorse pods varied considerably between the two sites as did the impact of E. ulicis on mature gorse seed production. At Stonehenge, a site in Tasmania’s eastern midlands, green pods were produced in spring and summer and black pods were produced in late spring, summer and early autumn, the timing of which was well synchronised with E. ulicis seed feeding activity. At Lymington, a coastal site in southern Tasmania, both green and black pods were produced almost all year, the timing of which was not well synchronised with E. ulicis seed feeding activity. As a result, the average percentage of mature seeds that were damaged by E. ulicis was 2.7 times higher at Stonehenge (45.5%) than at Lymington (16.7%). These levels of seed destruction were much lower than the levels (i.e. 75–85%) that were considered necessary by previous workers to cause a decline in gorse densities. The results show that additional agents are needed to act in combination with E. ulicis and reduce seed production further if seed feeding biological control agents are to have an impact on plant densities in Tasmanian gorse populations.