HISTORICAL ANALYSIS OF RODENT DYNAMICS AND DAMAGE USING QUEENSLAND SUGARCANE INDUSTRY MONITORING DATA

TWO native rodent species, Rattus sordidus (cane-field rat) and Melomys burtoni (grassland melomys) are significant vertebrate pests within the Queensland sugarcane industry. A comprehensive management strategy exists for R. sordidus and includes annual monitoring by various Cane Productivity Services (CPSs) during the early stage of the crop cycle between Sarina in the central coast region and Mossman in the north. Various non-crop and in-crop site characteristics are recorded along with species trapped and the number of males and females captured. We analysed 5 years of monitoring data from 2000 to 2004 including a total of 26 383 trap nights, conducted across 1482 sites between Sarina and Mossman. Of the 2408 rodents captured, 87% were R. sordidus and 11.7% were M. burtoni. The highest damage level and trap success for R. sordidus across the entire region occurred in sugarcane adjacent to other sugarcane blocks, particularly where these blocks had high levels of in-crop weed. In contrast, capture rates of M. burtoni were significantly higher in the wet tropics than the dry tropics, with the greatest captures in either area in sugarcane adjacent to open forest and grassland. Trap success for M. burtoni correlated significantly with weed levels within both the crop and harbourage in the wet tropics, but not in the dry tropics. However, the level of damage was significantly greater at sites with high in-crop and harbourage weed levels in both the wet and dry tropics. The historical data collected by industry provide results consistent with previous studies on the dynamics of each species within the sugarcane crop cycle. Results suggest that in-crop weed cover facilitates movement of M. burtoni within the crop cycle. Similarly, a high level of weed cover in adjacent habitats contributes to high trap success of M. burtoni within the wet tropics. The potential to manipulate non-crop habitats to minimise the source of M. burtoni colonists and manage the level of weed cover in-crop to reduce damage should be examined in future studies.