Nematode parasites of free-living rabbits, Oryctolagus cuniculus (L.) in eastern Australia III. Variations in the numbers of Passalurus ambiguus (Rudolphi)

Abstract

Numbers of Passalurus ambiguus occurring in each of four geographically and climatically widely separated regions of Australia were studied by regular sampling over 1-3 yr; P. ambiguus was present in varying numbers and incidence in each site. At Snowy Plains, a subalpine site in south-eastern New South Wales, P. ambiguus was present in large numbers and showed a regular cycle of changes in numbers during each of 3 years. The main feature was a peak in numbers of Passalurus during mid-winter, followed, in males, by a gradual fall to a trough in late autumn. In females a second peak in numbers occurred during the breeding period when, for a period of up to several months, the geometric mean count of Passalurus was up to 1000 times greater in females than in male rabbits. This was followed by a drop in numbers until autumn when males and females had similar low numbers of Passalurus. At Urana in the riverine plains of southern New South Wales and at Tero Creek in semi-arid far north-west New South Wales numbers of Passalurus remained low and no definite annual changes were apparent. At Mitchell in subtropical south-central Queensland the numbers of Passalurus also remained low for most of the year but a sharp rise during the spring months suggested that a regular annual pattern might be detectable by more prolonged study.