Demography, fecundity and natural enemy dynamics of rubber vine (Cryptostegia grandiflora) in riparian and upland sites of north Queensland

I.J. Radford, CSIRO Sustainable Ecosystems, Davies Laboratory, PMB PO, Aitkenvale, Queensland 4814, Australia.

Corresponding address: Botany Department, University of Otago, PO Box 56, Dunedin, New Zealand.


Summary

Rubber vine (Cryptostegia grandiflora) is a major weed in the wet- and dry-tropics of north Queensland. It invades riparian and non-riparian habitats. Two species, a moth (Euclasta whalleyi) and a fungal rust (Maravalia cryptostegiae) have been released for the control of this species. Little data are available on either the relative importance of habitat in rubber vine demography or on the incidence of biocontrol agents. In this study, we present demographic and agent incidence data to determine how habitat influences rubber vine invasion patterns and the occurrence of attack by rubber vine rust (M. cryptostegiae), rubber vine moth (Euclasta whalleyi) and native crow butterfly (Euploea core corinna).

Riparian populations were found to have more complex population size structure and higher seedling emergence than non-riparian populations. This is despite there being no difference in density or seed production in riparian versus non-riparian populations. Rust infection was found to be more severe in riparian than non-riparian populations during July, November and February. Insect damage caused by rubber vine moth larvae and native crow butterfly larvae was minor over all months except October and severity was unrelated to habitat type. Comparison of fecundity and seedling emergence pre- and post-biological control suggests that bio-control agents may be having major impacts on rubber vine. Reduced fecundity is discussed in relation to rubber vine invasibility.

 

Plant Protection Quarterly(2003) 18 (4) 138-142.