The natural decline of an introduced species following its initial increase in abundance; an explanation for Ommatoiulus moreletii in Australia

Summary The black Portuguese millipede, Ommatoiulus moreletii, an exotic species first reported in Australia in 1953, shows a pattern of initial eruption and subsequent decline in abundance following its introduction to sites in South Australia. Comparative sampling of new, erupted populations and older, declined populations was done in an attempt to find testable hypotheses to account for the decline. We report on laboratory and field experiments which show that a native rhabditid nematode appears to be the causal agent for the decline of populations of O. moreletii in South Australia. Implications for the biological control of introduced species are discussed in terms of this work.