An experimental field study to assess the effectiveness of bait containing the parasitic protozoan Sarcocystis singaporensis for protecting rice crops against rodent damage

Replicated large-scale field trials in two seasons in Thailand with the protozoan parasite Sarcocystis singaporensis showed that damage due to rats was reduced significantly. Biological as well as conventional (local practice using electric fences and zinc phosphide) rodent control reduced the mean proportion of rat-cut tillers in the first (biological 0.5%; conventional 1.6% and 1.1%) and second season (biological 0.2%; conventional 0.6%) compared with untreated controls (5.8% and 5.5%, respectively). At sites that received rodent control in the first season, activity of rats (Rattus argentiventer, R. losea, Bandicota indica) declined towards harvest. Biological as well as conventional rodent control resulted in yield increases of 18% and 20%, respectively, although in the second season weed problems confounded yield data. Economic analysis showed that biological rodent control was more economic than conventional control at an average damage level of 5%, whereby yield increases of 2-3% paid back the costs.