Population dynamics, diet and pest status of the grassland melomys (Melomys burtoni) in northern Queensland sugarcane crops

Abstract

Context In far-northern Queensland, Melomys burtoni and M. cervinipes occur within sugarcane crops and adjacent habitats and are potentially damaging to sugarcane. Aims To examine the population dynamics and diet of Melomys spp. within sugarcane crops so that, in conjunction with cane-stalk damage assessments, their pest status could be determined and information provided relevant to the development of sustainable pest-management tools. Methods Eight sites within sugarcane fields, four adjacent to grassland and four adjacent to closed forest, were established around Tully in far-northern Queensland. We examined demographic characteristics of all rodents (the two Melomys spp. and Rattus sordidus) within the crops by capture–release studies. Snap-trapping and dissection studies, along with weed-biomass surveys, were conducted for diet analysis, whereas damaged stalk counts were undertaken to understand the damage process. Fieldwork commenced within a fully developed crop, then continued through the annual harvest period and all subsequent crop growth stages to the next harvest. Sampling was undertaken monthly from February 2005 to April 2006. Key results Melomys cervinipes was rarely caught in sugarcane and should not be regarded as a pest. In contrast, M. burtoni feeds on sugarcane and was responsible for damage to ~6% of stalks. In sites adjacent to closed forest, R. sordidus was found in higher numbers than was M. burtoni in Crop stages 2–4. However, at sites adjacent to grassland, numbers of M. burtoni increased in Crop stage 4, and before crop harvest, M. burtoni was found in higher numbers than was R. sordidus. M. burtoni colonised sugarcane at later stages of crop development than did R. sordidus. Although the level of M. burtoni reproduction was lower than that of R. sordidus, the highest proportion of pregnant M. burtoni individuals occurred during the later stages of crop development, corresponding directly with the highest proportion of juvenile recruitment. Conclusions Of the two Melomys species found in northern Queensland sugarcane crops, only M. burtoni should be regarded as a pest. This rodent breeds and feeds within the crop, primarily after canopy closure. M. burtoni captures were roughly equivalent irrespective of adjacent habitat type, whereas R. sordidus, the traditionally recognised major pest of sugarcane crops, was found in significantly higher numbers in sugarcane adjacent to closed forest. Implications The integrated pest-management (IPM) strategy developed for R. sordidus is centred on the early stages of crop development and includes population monitoring, in-crop weed control, harbourage management and strategic use of permitted rodenticides. The late colonisation and lower breeding potential of M. burtoni mean that the IPM strategy for R. sordidus will not be directly transferable to M. burtoni.