Physical Control of Rats in Developing Countries We have determined the ideal size range ... the degree of asynchronous planting of rice for a TBS for farmers (G.R. Singleton and crops; and Sudarmaji, unpublished data), but not the ... the variety of other crops grown in the area. optimum spatial distribution of these in the landscape. Although there was much This information requires detailed variation between seasons in the extent of studies of the population ecology and the halo of protection provided to crops by a behaviour of Rattus argentiventer and good TBS+ Te we recommend that a 25 x 25 m documentation of farming practices. There TBS would significantly reduce rat damage are some data available on the first two dot in the surrounding 10-20 ha of rice crop. points. For instance, banks along the Therefore, at a village level we that margins of rice fields and the banks of the one TB5+ TC would be sufficient for every 15 major irrigation canals provide important ha of rice crop. This recommendation has not habitats for rats to take refuge in during non­ been tested. breeding seasons, and for rats to nest and breed in after the crop reaches the maximum The spatial distribution of physical tillering stage (see Leung et al., Chapter 14). methods for controlling rat numbers is an Also, the breeding season of R. argentiventer important issue given the ability rats have to is linked to the reproductive stage of the rice re-colonise areas where their densities have crop (Lam 1983; Murakami et al. 1990). been reduced. In rice fields, rats move Therefore, asynchronous planting of hundreds of metres in a night, especially neighbouring crops will extend the breeding once the developing crop reaches the season of rats. Although we require more booting stage (Singleton et al. 1994; P. detailed knowledge of the population Brown, pers. comm.). To reduce this ability ecology and biology of R. argentiventer, what of rats to compensate for control activities, we already know has had an important management needs to be approached influence on the development of initially at the village level and then at the management strategies for this species. Our district level. A good extension program efforts to manage this species would be with strong grower participation is considerably strengthened if we had a better fundamental for a community-based control understanding of the processes that campaign to be successful (FAO 1997). influenced whether a rat did or did not enter a trap of a TBS. Towards this end, we need to At the village level, the spatial develop a better awareness of the distribution and number of TBS sites will not behavioural responses of rats to a TBS+ TC simply be determined by the area of land and of the factors that may influence this under rice production. Important response. considerations will be how rat populations respond to: CONCWDING REMARKS ... the heterogeneity of the habitat (the In closing, the biggest hurdle facing the seasonal dynamics in habitats where rats successful use of physical methods for can take safe refuge and/ or breed); managing rodent pests is the ability of 195 Ecologically-based Rodent Management rodent populations to compensate for Leung et al., Chapter 14, for discussion of reductions in population size through other actions). immigration, increased survival and/ or How the use of physical barriers plus better breeding performance. The early traps has evolved in our endeavours to studies of Oavis (1953) clearly demonstrated manage the rice-field rat highlights the the ability of rat populations to recover to imperative of having sound ecological original levels following poisoning studies in progress before embarking on operations. Similarly, H. Leirs (pers. comm.) broad scale management programs of a has shown that a 50% reduction in a rodent pest (Leirs et a1. 1996; Singleton 1997). Mastomys natalensis population, through the Further population studies of rodent pests use of chemical rodenticides, has little are planned for Indonesia, Vietnam and Lao impact on the yield loss of crops. However, PORI and they will complement our sustained harvesting of rats from a progress towards optimising the use of trap population can lead to the collapse of that barrier systems and trap crops. population, presumably because of a decline in the age structure of the breeding ACKNOWLEDGMENTS population (Oavis and Christian 1958). The TBS studies in Indonesia and Vietnam Together, these studies indicate that one-off were part of a multi-country study on the uses of physical control, especially when management of rodent pests in Southeast rodent densities are high, may have little to Asia, funded by the Australian Centre for no impact on rat populations. In contrast, International Agricultural Research (Project sustained use of physical control methods numbers ASl/9420 and ASl/9679). We over an appropriate spatial scale may be acknowledge the efforts and commitment of both cost effective and environmentally the support staff from the Research Institute sustainable. for Rice, Indonesia, and the Institute of Two methods which warrant further Animal Sciences and National Institute of study are the use of TBS+ TC and the targeting Plant Protection, Vietnam. We also thank of bounty seasons at appropriate times of the Monica van Wensveen, Ms Rahmini, Ir year. The timing of the latter needs to be Rochman, Nguyen Manh Hung, Nguyen dictated by our understanding of the Viet Quoc, Nguyen Phu Tuan, Lam Yuet population biology of the rat rather than the Ming and Luke Leung for their support, phenology of the crop. For both methods, input and ideas. We greatly appreciated the success will revolve around coordinated, comments of Oavid Freudenberger and Alan synchronised actions at a village or district Buckle on an earlier draft of this chapter. level and their ability to be adopted as part of an integrated approach to rodent management Singleton 1997; 196 Physical Control of Rats in Developing Countries REFERENCES Bell, A 1998. Integrated rodent management in FAO 1997. Community based IPM case studies. post-harvest systems. Eschborn, Germany, Food and Agriculture Organization Inter­ Deutsche Gesellschaft fUr Technische Zusam­ country Programme for the Development of menarbeit (GTZ), leaflet, 8p. 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