630 US ISSN 0271-9916 NOVEMBER, 1980 RESEARCH-EXTENSION SERIES 002

RODENTS AND CONTROL IN Barry M. Brennan

University of Hawaii at Manoa HAWAII INSTITUTE OF TROPICAL AGRICULTURE AND HUMAN RESOURCES AND RODENT CONTROL IN HAWAII

Barry M. Brennan Department of Agricultural Biochemistry University of Hawaii at Manoa Honolulu, Hawaii 96822

The and its cousin, the mouse, have been im­ known but is probably related to an abundance of portant pests to man since ancient times. They are food and shelter before and during the critical especially important as disease carriers. They also breeding cycle, followed by disappearanceof these cause enormous destruction and loss of food and essentials with the onset of drought conditions, property. Their control is not easy due to their which forces the migration of mouse populations. ability to adapt to changes and their capacity to reproduce. IDENTIFICATION OF RODENTS Rodents are carriers of a number of important Roof rat ( rattus)-Medium to large rat, diseases including plague, murine typhu&, lepto­ body 5 to 7 inches long. Tail slender and always spirosis, and salmonellosis. The Hamakua coast longer tha·n head and body combined. Body color area on the Big..Island and Makawao district on varies from grey to jet black; underside grey, grey­ Maui were former plague endemic areas, but the white, or white. Nose sharply pointed, large eyes, last reported human case occurredin 1949 (Hama­ large, thin ears; in female, five pairs of nipples. kua). However, plague is still kept under surveil­ Expert climber and wire scaler; frequents cane lance by the Department of Health Vector Control fields, macadamia nut, coffee, papaya, and bana­ Program. Although murine typhus and leptospi­ na groves; nests in attics of buildings, trees, bana­ rosis are known to occur throughout the islands, na. bunches, and abandoned burrows of Norway only sporadic cases have been reported.. rat. Moderately susceptible to plague infection. Rodents consume, contaminate, and cause ex­ Norway rat (Rattus norvegicus)-Largest of tensive damage to food andagricultural crops. For in Hawaii, weighs 10 to 18 ounces, measures every $2.00 worth of food they eat, they cause 8 to 10 inches long. Tail stout, shorter than head $20.00 worth of damage. In Hawaii, state and pri­ and body combined. Body color reddish brown to vate agencies spend more than $600,000 annually grey to black; underside whitish color. Head wide, to control rodents. nose blunt, ears small, eyes small, chunky in There are four rodents of economic importance appearance; in female, six pairs of nipples. A bur- . in Hawaii: the roof or , the Norway or rowing species in ground, rubbish piles, garbage , the polynesian (Hawaiian) rat, and the dumps, and under walks and docks; frequents house or field mouse. The roofrat is found in agri­ sewers, pig styes, and coops. May cause cultural a~eas, wooded gulches, kiawe forests, and great damage to cane fields. Vicious. High degree in both wet and dry forests. This species has now of resistance to plague infection. displaced the Norway rat as the most common rat (Rattus exulans)-Compara­ found close to human habitations and especially tively small in size, weighs 2 to 3 ounces, measures in wet areas such as stream beds, drainage canals, 4 to 5 inches long. Tail as long as orslightly long- and sewers. The polynesian rat is the smallest of er than head and body combined; bristles along the three rats and it apparently prefers agricul­ tail give the appearance of faint, narrow rings. tural lands, range, and wooded areas (including Body color is cinnamon-brown to cinnamon-huff gulches) up to 2500 feet. Like the Norway rat, it to grey; stiff black guard hairs on back and sides; may cause considerable damage to cane. The underside light buff or grey. Nose roundly point­ is smaller than the rats and is found ed, ears rather short, eyes medium size, hind feet both in urban and rural areas. On Maui, Hawaii, dark on underside; in fema1e, four pairs of nip­ and Oahu, there have been cyclic mouse "out­ ples. A field rat, rarely found near buildings in breaks" every few years. The cause is not wholly Hawaii; nests in burrows, gulches, rock piles, rock" I 3 walls, wastelands, fields, and embankments. removing access to food, water, or shelter, or Causes great damage to sugarcane, pineapple, limiting· their accessibility with physical barri­ macadamia nuts, coconuts, coffee, and other fruit ers such as screens, will result in a population de­ and vegetable crops. Very susceptible to plague cline. Mechanical control achieved with the use infection. of traps may also be important. Physical, mechan­ House mouse (Mus musculus)-Smallest of the ical, and environmental control should be used in four rodent species, weighs about 1/2 ounce, conjunction with chemical control. measures 6 to 7inches longfrom nose to tipof tail. are the most effective means of Slender tail as long as or longer than head and controlling large and small rodent populations. body combined. Body color varies from yellowish However, their use entails hazards to other mam­ dirty tan to dusky grey, darker over back, lighter malian life, including man (especially small chil­ underneath. Body slender, ears large, eyes small, dren), pets, and domestic . Some poisons nose pointed; in female, five pairs of nipples. have a secondary effect which may affect animals Nests in any type of shelter, inside buildings, rock which consume dead or nearly dead rodents. walls, rock piles, under boards, in burrows, under Thus, it is imperative that strict safety precau­ cane plants, and in truck-crop fields. Damage may tions be used in the preparation, broadcast, or be extensive to truck crops, flowers, etc. Degree of placement and disposal of poison baits for ro­ resistance to plague in Hawaii has not been deter­ dents.. mined. Rodenticides are broadly categorized as either multi-dose or single-dose poisons. Multi-dose RAT BIOLOGY poisons act as sub-acute rodenticides and require The rat is prolific. The young rat is sexually repeated exposures. Rodents generally do not de­ mature at four months. Sexual activity and repro­ velop "baitshyness" to anti-coagulants. Themore ductive potential are continuous until death. Rat common sub-acute rodenticides in use are war­ behavior is influenced by thirst, hunger, sex, ma­ farin (warfacide), prolin, fumarin, pival, and ternal instinct, and curiosity. Rats cannotgo with­ diphacin. out water for more than 48 hours or without food Single-dose rodenticides act as acute poisons for more than four days. Thirstyor hungry rats be­ and include Red squill and zinc phosphide. Zinc come desperate and are therefore easier to control phosphide has a pungent odor which repels pets because they are less wary. Judici9uS use of traps, and birds, but is attractive to rodents. Although poisons, and other control measures thus become these poisons are very effective when used prop­ doubly effective. Rats are nocturnal and tend to erly, their toxicity and physical characteristics develop behavior patterns which become habitu­ often place limits on their use. al. They have a keen and , After conducting a thorough rodent survey, pre­ and a fair sense of sight with ability to see in the poisoning bait trials should be conducted to de­ dark. termine which foods and baits are most desirable to the rodent. This information and the type and lo,cation of bait containers must be recorded RODENT CONTROL throughout the course of the control program. Rodent control is dependent upon recognition After two days of negative feeding, the bait sta­ of a rodent infestation. The most common signs tions should be removed and the records reviewed. are droppings, rubmarks, runways, tracks, gnaw­ The survey should be repeated in about two ings, live or dead rats, nests, and rodent odors. months, the approximate interval for a second Control programs must be aimed at controlling generation. Properly utilized environmental and the entire population, not individual rodents. physical controls will prevent rapid infestation Programs must include a survey to: (1) identify the and population build-up. species causing the problem, (2) determine the approximate size of the population, and (3) iden­ tify the characteristics of the infected area. Rodents establish a home range which provides REFERENCE food, water, shelter, and reasonable protection I. Watanabe, Walter. Rodents. In: Vector Con­ from predators. Cleaning up the environment by trol Training Manual Chapter XIV. 1975. 4 Identifying Rats and Mice

ROOF RAT Rattus rattus

Longer than head and body Light Slender Large / I TAIL BODY EAR EYE NOSE I \ Small / \ "'"Small Blunt Shorter than head and body

Tail whitish underneath

NORWAY RAT Rattus norvegicus

YOUNG RAT ~=44 Large Large / \ FEET HEAD POLYNESIAN (Hawaiian) RAT Rattus exu/ans \ I --====&n~

HOUSE MOUSE Slightly longer Mus musculus than head and body Light Medium Rounded Slender

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