J. Manlm. Soc. Japan 20 (2) : 157-158 December 1995

Short Communication Fat Deposits in rattus, R. losea, Bandico ta bengalensis, and B. indica

Tatsuo YABE, Ram C. POUDEL*, Poorna D. D. SHRESTHA*, Tsutomu KUWAHATA** and Tyuzi KUSANO**

Kanagawa Prefectzlral Pzl blic Health La boratories, Asahi- kzl, Yokohama 241, Japan * Agricultzlral Research Coz~ncil,Entomology Division, Khzlmaltar, Lalitpur, Kathmandu, Nepal **Tropical Cont~~olCommittee, c/o Overseas Ag?icultzlral Development Association, Akasaka, Minato - kzl 107, Japan (Accepted 31 August 1995)

Four of , the roof rat Rattus rattus, the lesser ricefield rat R. losea, the lesser -rat bengalensis, and the greater bandicoot-rat B. indica were the focus of a study in and Nepal. R. rattus is a typical commensal rat, but it can also be found feeding in fields during the cropping season in the Kathmandu valley, Nepal. B. bengalensis occurs in fields and stores huge amounts of food (Vander Wall 1990), the only species to do so among the four species studied. R. losea and B. indica occur generally in fields throughout the year. Yabe (1994) suggested that three types of energy sources are available to rats during the winter, or the dry season, when the food supply is insufficient. These sources are : commensalism, fat deposition, and food hoarding. We examined, therefore, whether R. losea and B. indica store body fat and whether R. rattus and B. bengalensis deposit fat, in addition to com~nensalismor food hoarding.

Materials and Methods

Specimens of R. rattus and B. bengalensis were collected from villages in the Kathmandu valley, in the latter part of November 1994. At that time of the dry season, cereals such as rice, wheat, and corn have been harvested, and rape (Brassica sp.) covers the fields. Rats were caught indoors using mesh traps, and in fields using snap traps baited with potatoes or baked coconut. Specimens of R. losea and B. indica were collected from a burnt rice-field in a village near Bangkok, Thailand, during the dry season in mid-February 1988. The amount of perirenal fat present on specimens was assessed visually using Taylor and Green's (1976) method because of its simplicity and suitability for a field study. No fat scored 0. A trace of fat largely obscured by the kidney scored 0.5, a fat deposit level with the greatest circumference of the kindney scored 1, whereas fat obscuring up to one quarter of the ventral surface ,158 Ynbe et al. of the kidney scored 2, and fat obscuring more than one quarter of the ventral surface of the kidney scored 3. Fat index levels (FIs) were calculated by averaging the fat records from all adults. Fifty-one R. losea and four B. indica were collected in Thailand. Sixty- one R. rattus were trapped in farmhouses in Nepal, of which 13 adults were randomly sampled for the FI calculation. These were identified as R. rattus brunneus from their underpart color, skull length, and toothrow length. Nine B. bengalensis were caught around corn ricks and embankments in fields, and one was caught inside a farmhouse.

Results and Discussion

We found that all R. losea (n=22) and all B. indica (n=4) stored fat, the specimens had FIs (kSD) of 3.01-0 for both species. All individuals had abdominal cavities filled with fat. In contrast, no perirenal fat was found in R. rattus or B. bengalensis, except pregnant or lactating individuals, which had FI scores of 0.5. FIs for R. rattus were 0.12k0.22 (n= 13, including three pregnant or lactating females), and for B. bengalensis 0.06f 0.18 (n=8). R. losea and B. indica clearly store fat during winter, whereas R. rattus and B. bengalensis do not. R. rattus presuinably moves into houses to feed during the winter because it neither stores fat nor food. R. losea and B. indica may well be able to survive moving about in the fields owing to their body fat stores. B. bengalen- sis, on the other hand, which is neither a commensal nor stores fat remains restricted to a narrow home range in the immediate vicinity of its burrow system (Posamentier 1988), and is aggressive even intraspecifically (Roberts 1977), presumably to safeguard its own food cache. We conclude, that generally, in the areas suveyed, R. rattus maintains its energy supply through the winter by commensalism, B. bengalensis by food hoarding, and R. losea and B. indica by fat deposition.

Acknowledgments

This study was partly supported by the Japan International Cooperation Agency (JICA) and the Tropical Rat Control Committee, Minato-ku, Tokyo.

References

Posamentier, H. 1988. Integrated pest management, principles in control. In Rodent Pest Management. (I. Parkash, ed.) pp. 427-439. CRC Press, Florida. Roberts, T. J. 1977. The of Paltistan. Ernest Benn, London, 361 pp. Taylor, I<. D. and M. G. Green. 1976. The influence of rainfall on diet and reproduction in four African rodent species. J. 2001. London 180 : 367-389. Vander Wall, S. B. 1990. Food Hoarding in . Univ. of Chicago Press, Chicago, 445 pp. Yabe, T. 1994. Fat deposits for wintering in the Norway rat, Ratfils ~zo~uegiczci.J. Mamm. Soc. Japan 19 : 129- 133.