Rodent was hitherto a problem in agricultural and horticultural crops. However, it took a different shape with increasing human population, urbanization, dwindling resources for solid waste management, spurt in zoonotic diseases, development of food and hospitality industry and industries with sensitive infrastructure including electronic appliances. As local bodies struggle economically, less money is available for urban waste disposal, maintenance of city sewer and storm water systems, subway tunnels, parks, vacant housing, unhygienic road side restaurants leading to congenial environment for rodent breeding. Net result is that rodents’ invasion in residential buildings, restaurants and neighbourhoods and become potential hazard in spreading zoonotic diseases; damage structures and can disrupt power or start fires by gnawing on wiring.
Rodent pest/vector species
In world scenario, three rodent species are commensal co-existing with humans in urban situations. They include Sewer rat, Rattus norvegicus, House rat, Rattus rattus and House mouse, Mus musculus. The latter two have wider distribution all through the Globe and contribute for structural damages including electronic installations, disease transmission to humans and farm animals, and food adulteration through faeces and hair.
The nibbling habits and smaller body size make House mice as potential threat to cables and storage commodities. In Indian scenario, the spread of Lesser bandicoot, Bandicota bengalensis and Larger bandicoot, Bandicota indica in urban areas accentuated the rodent related problems. The bandicoots are replacing the house rats in most of the urban situations in the country, due to expansion of colonies in the agricultural areas and their aggressive behaviour.
Potentiality for Structural Pest Management Industry
The sectors which provide more revenue for rodent pest management include
i) Food Industry contributing to 14% of manufacturing GDP i.e. `280,000 crores,
ii) Hospitality Industry with an estimated growth from `74 billion to `119 billion from 2010-13, and
iii) IT Industry contributing to 7.5% to GDP and market of US$ 50 billion and expected to double its growth in 2011-12
Rodent Pest Management Options
With regard to rodent pest management, basic difference exists in agricultural and industrial or domestic situations. In most of the industrial situations, rodents are to be excluded totally from certain areas to avoid damage to sensitive installations or expensive equipment. Even a single mouse could cause loss of several lakhs of rupees and can create technical snags in aircrafts. In agricultural situations, their number should be kept below the threshold level. Integration of different methods gives the desired management success. A number of options exist for their management with each option having its own limitation.
Trapping is an age old method adopted for rodent control in residential premises. Live traps – wonder and box type are used in domestic/industrial situations. Kill or Snap traps are also used, which will kill the rodents instantly on touching the trigger. These traps are effective for tackling localized rodent infestations. Trap shyness of rodents and pheromonal communication among rodents often impact the efficacy of trapping method. Non poisonous sticky traps are effective to remove traces of mouse/rat infestations in expensive/sensitive establishments. Hence, they gained popularity as a tool in excluding localized infestations effectively. However, their usage is restricted recently by Ministry of Environment and Forests on cruelty issues arising out of struggle by the rodents on the glue boards.
Although Predators like cats are often reared in domestic situations, they are found to remove effectively surplus rat/mouse populations that are immigrating in to the premises from adjoining areas. The local established rats/mice are un effected. Further, the predators posed a threat of zoonotic diseases and this tool was to be abandoned in Cairo by the Government, after its legal implementation over couple of years in early 1980s.
Ultrasound devices producing sound vibrations above 20kHz are being used to prevent the immigration of rodents in closed door storage situations. The commensal rodents acclimatize to the ultra sound on continuous exposure. Hence their usage has its own limitations.
Attractants and repellents were tried for rodent management, but so far no effective repellent could be developed in urban situations. Although evidence suggests usage of rodent pheromones as promising to increase/decrease their populations, no attempt is seriously made to identify, isolate and synthesize those pheromones.
Effective chemosterilants are not available. Effort is being made to introduce a male sterilant in India. But due to biotechnology implications, the registration process is at slow pace.
Rodenticides, boon or bane
Rodenticides are most commonly used tool against commensal rodents. They are potential in tropical situations with long future, but much remains to be done to optimize their use. In India, only zinc phosphide and bromadiolone are available in market. Although aluminium phosphide pellets are recommended for rodent burrow fumigation, it needs permission from CIB&RC for use within India.
Due to toxicity and environmental safety reasons, the use of zinc phosphide is not advocated in domestic areas. However, in open fields it is recommended at 2.5% TG in cereal baits. Neophobia and bait shyness are limitations to use this rodenticide. Ready-to-use formulations are not available with this acute rodenticide and such formulations can reduce the risk of exposure of non-target species to higher concentrations.