By understanding how populations of specific rodent species interact, simple and environment-friendly methods can be developed to control rats in lowland irrigated crops.
This video, produced by the Irrigated Rice Research Consortium (IRRC; http://irri.org/index.php?option=com_... ), explains the breeding dynamics of the rice field rat and its relation to the rice planting season. It introduces ecologically based rodent management and highlights effective community actions to control rice field rats, such as the trap barrier system.
* Rodent outbreaks: Ecology and impacts on Google Books: http://books.google.com/books/irri?id...
Each rodent pest species has different behavioral characteristics, breeding dynamics, and habitat preferences.
Some species breed regularly, some breed throughout the year, and others breed at very specific times.
The ricefield rat, for example, breeds only when the rice is in the reproductive phase—if there is one planting season per year, they have one breeding season, if there are two, they will have two, and, if they have three crops a year, they will have three breeding seasons.
Female rats are pregnant for 21 days and can mate the day after they give birth. One female can give birth to three litters—with 12 young per litter—during a rice crop, resulting in a total of 36 rats.
These young will not breed until the next crop unless neighboring farmers plant their crops more than 2 weeks apart. This will extend the breeding season, allowing the rats (six females) from the first litter to also breed (rats breed at 7 weeks of age). Therefore, one adult female could potentially give rise to 120 rats in a single rice-growing season.
Scientists have also been studying where rats live at different times of the year in agricultural landscapes. This then enables them to target rat populations when they have aggregated in easily assessable habitats.
Ecologically based rodent management—the ideal rat trap
Once the ecology of a major pest species is understood, scientists and extension specialists can work closely with farmers to develop ecologically sound, cost-effective management strategies that fit with usual farming practices, including traditional rat-catching methods.
Studies in Indonesian and Vietnamese villages have clearly shown that rat populations can be successfully managed if farmers work together as a community—applying their control at the right time and in the right habitats. Such ecologically based actions have also led to a 50% reduction in the use of chemical rodenticides.
Effective community actions include:
• Keeping irrigation banks less than 30 cm wide to make it difficult for rats to build nests;
• 3Conducting community campaigns using local methods to control rats within 30 days of planting the crop, which is before the main breeding season for rats in rice fields. These community actions should focus on village gardens, main irrigation channels, and roadsides, where the rats gather in small corridors when the land is being plowed in preparation for planting;
• If control is left later, then the rats would have already dispersed throughout the rice crops, making it much more time-consuming and costly to control them over a vast area.
• Cleaning up any grain spills at harvest; and
• Synchronizing planting so that crops are planted within 2 weeks of each other.
Rats are highly mobile -- they can travel a distance of 1 km a night. If farmers do not act together and only one farmer is effective in controlling rats, then rats will invade his crop from the fields where no control was done.
One simple technology added to the armory of rice farmers is a trap-and-fence system known as the trap barrier system (TBS). Used across much of Southeast Asia, the TBS comprises a plastic fence surrounding a small rice crop planted 2--3 weeks earlier than the surrounding crop, with traps set into the plastic.
Rats have a very well-developed sense of smell. At night, rats will be attracted to the smell of the early developing rice within the fence. This rice acts as bait. The rats reach the fence and then follow the line of the plastic until they reach a hole, which they enter to reach the rice. They are caught in the trap and removed the next morning.
One TBS can protect up to 10 hectares. For smallholder farmers who have less than 2 hectares of rice, the TBS requires community action to share in the cost and daily checking of traps. Therefore, scientists refer to this method as community trap barrier system. This method is very cost-effective for managing rat populations.