Rodent Control in China

Rodent pest problems and their control in China are reviewed. Three commensal species, Rattus norvegicus, R. flavipectus and Mus musculus, are important pests both in urban and rural regions. Mus musculus is the most widely distributed species in China. Its population density is cyclic, unique for a commensal species in being found in the arid Xinjiang (Sinkiang) Autonomous Region in Northwest China. In South China, R. losea and Bandicota indica are serious problems in rice and cane fields. Many different genera of field rodents are considered pests to agriculture and/or are reservoirs of rodentborne diseases. These include Citellus, Marmota, Meriones, Cricetulus, Microtus, Apodemus, Ochotona, Myospalax, Clethrionomys, Sciurus, and Eutamias. The ecology and control of these rodents are included. There are a series of efficient administrative organizations responsible for rodent control. Most campaigns of commensal rodents have relied on a combination of rodenticides and different types of traps, but in the case of field rodents the reliance is heavily placed on poison baits. Diphacinone (Na-salt) is most frequently used for control of commensal species. Zinc phosphide, fluoroacetimide (1081), sodium fluoroacetate (1080), glyftor and 0.2% diphacinone (Na-salt) are used for field rodent control. Information is supplied on the susceptibility of important rodents in China to different rodenticides, including difenacoum and brodifacoum, and on other means of rodent control. China is mainly located in the north temperate zone. Geographically, the landform is very complex including large plains, high mountains, plateaus, grasslands, deserts, forests, etc. The vertebrate fauna is very rich, but most species of Rodentia cause harm to agriculture, industry and/or transmit human diseases. Commensal rodents, Rattus norvegicus, R. flavipectus and Mus musculus, are the most important pests both in urban and rural regions. In the tropical and subtropical region of South China, R. losea and Bandicota indica are a serious problem both in rice and sugar cane fields. Many different genera of field rodents are considered pests to crops and/or reservoirs of rodent-borne diseases in Northern China. These are Citellus spp., Marmota spp., Meriones spp., Cricetulus spp., Microtus spp., Apodemus spp., Ochotona spp. and Myospalax spp. Pests to forestry include Clethrionomy rufocanus, Sciurus vulgaris and Eutamias sibiricus. They damage the red pine seeding, often making reforestation impossible. Before the founding of New China in 1949, there were no rodent control organizations or rodent control programs, except for some locally made traps used for rat control. Since then the Government has paid great attention to rodent control. Large-scale rodent control campaigns have been conducted every year since 1956, and they have made good progress. A brief review on rodent control in China follows: THE ORGANIZATION OF RODENT CONTROL Rodent control is a complicated, practical, ecological problem which deals with a wide range of knowledge, as well as habits and customs of people. It is a job for everyone to keep rodent damage at a low level. In order to push the work forward, there is a great need for an efficient administrative organization to spread propaganda among the masses and to establish effective inspection and enforcement methods. In our country each province and county has its own Antiepidemic Station responsible for implementation and consultation of rodent control. Another system is a series of committees of patriotic public health campaigns at central, provincial and county level, which are responsible for spreading propaganda, training and supervising the operation of the street committees and for procuring the rodenticides and traps. THE MANUFACTURE AND SUPPLY OF RODENTICIDES Zinc phosphide and diphacinone (Na-salt) are important rodenticides used in the control of both commensal and field rodents. They are manufactured in China and available in markets. Fluoroacetimide (1081), sodium fluoroacetate (1080), glyftor and Vacor are made locally and used mainly in field rodent control. The fumigants commonly used in warehouses, ships and rodent burrows are chloropicrin, methyl bromide and aluminum phosphide. Alpha naphthylthiourea and Promurit were used for control of rats and some field rodents years ago before some of the current rodenticides became available. 1984, Proceedings Eleventh Vertebrate Pest Conference 47 (D.O. Clark, Ed.). Printed at Univ. of California, Davis, Calif COMMENSAL RODENT CONTROL R. norvegicus, R. flavipectus and Mus musculus are the most important commensal species in China. R. norvegicus is distributed over a large area, especially in North China except the Xinjiang (Sinkiang) Autonomous Region and Tibet. R. flavipectus is mainly found in South China, south to the Yangtze River, whereas Mus musculus is the most widely distributed species; and what is unique for a commensal species, it is even found in the Xinjiang Autonomous Region and Tibet. In North China R. norvegicus is also an important agriculture pest in the warm season. When the field crops are grown, it migrates from dwelling houses to the fields. It is a prolific breeder, averaging six to eight per litter and four to five litters per year. There are two peaks of breeding, one between March and May, another between September and October. The reproductive activity generally ceases in the cold winter months. There is an exception; they maintain their reproductive activity in cold storage when food is plentiful. R. flavipectus is the most important species in South China and Southwest China. In Leizhou (Leichow) Peninsula, Guandong (Kwangtung) Province, of 155,200 individuals of small mammals caught in dwelling houses, 135,895 were identified as R. flavipectus (87.6%). In the tropical region of China they are found living in the wild. Mus musculus is the most widely distributed of the commensal rodents in China. In Xinjiang and Tibet, they are common inhabitants of grassy and cultivated lands and have adapted well to living in dry deserts without any free water, where we do not find other commensal species. Mus musculus may breed all year-round with peaks in spring and fall. It was found that they did not cease breeding even during the cold winter in Xinjiang. The incidence of pregnancy of female accounted for 46.5% (272/585) from March to September. The average litter size was 5.7 ranging from 1 to 10, and 2 to 4 litters were recorded per year. There is seasonal migration in Xinjiang. They move back and forth between crops which are harvested at different times. Wheat and alfalfa fields, sesame fields, maize fields, and dwelling houses is the order of their migration. This ability to adapt to an extreme environment is of great benefit to their population. Weather, food and cover are all factors causing migration, but mature crops that provide cover for Mus musculus are most important. In Xinjiang Mus musculus populations are cyclic in nature, reaching high numbers every 6 or 10 years. The extraordinarily high population densities occurred in North Xinjiang in 1967 to 1970. Almost all of the crops and grasses were devastated at that time. It was estimated that 300,000 tons of cereals were damaged in 1967. A problem of particular concern is the presence of numerous Mus musculus and R. flavipectus in trains and ships, where they are extremely difficult to control. Research is underway on commensal rodent control. These investigations include raising and breeding rats and mice in the laboratory for ecological observation and control tests, for synthesizing and screening new rodenticides, and for planning integrated control programs. Chinese millet was found to be attractive to commensal rats and mice. The preference tests showed that it was preferred to other dry cereals, including corn meal, wheat, oat meal, rye, barley, etc. Several rodenticide samples have been synthesized. Among these are warfarin, diphacinone, Pival, Norbormide, UK786, RH945, RH787, and recently reported second-generation anticoagulants, difenacoum and brodifacoum (Table 1). Table 1. LD50 (mg/kg oral) toxicity tests. A combination of rodenticides and traps are used in the urban area, but in rural areas reliance is placed on poisoned baits. The baits containing 1 to 3% zinc phosphide and 0.025% diphacinone (Na-salt) are most frequently used. The bait material used in North China is usually corn meal, and in South China rice containing 2% vegetable oil as sticker; also sweet potatoes are often used.