Wild-caught Rats Research Articles

Inheritance of resistance to warfarin in Rattus rattus L.

Breeding experiments with Rattus rattus indicate that the inheritance of resistance to the rodenticide warfarin has a multifactorial basis. In resistant × resistant and resistant × susceptible crosses between wild-caught rats, averages of 25 and 17% respectively of the offspring were resistant. In F 1 backcrosses to the susceptible, less than 1% were resistant. Susceptible rats bred true. Significant inter-family variation was observed in resistant crosses. The implications of the results for the development and containment of resistant populations in the field are discussed.

Some Behavioral Tests of Domestication in Norway Rats

AbstractFive experiments with wild and domestic rats (Rattus norvegicus) were designed to assess behavioral effects of domestication. The results, which must be considered preliminary, are supportive of the notion that domestication in the Norway rat has induced an adaptive fitness rather than degeneration: 1. Scar-marked captives showed the poor reproductive success typical of traditional attempts at initial laboratorization. In 10 such pairs, three of the females killed prospective mates and five of the six who produced litters cannibalized all or some of the offspring. Unscarred captives, assumed to represent higher social status in the wild population, produced litters in eight of ten pairings with no abnormal breeding or maternal behaviors. 2. Scar-marked captives were least dominant in water competition and were most likely to show abnormal behaviors, new wounds, and mortalities. Similar competitive groupings of domestic rats showed the expected difference in social behavior; fighting was less intense, social distance was less, and threat signals were rare compared to wild rats. Where wild and domestic rats were housed together, however, the intensity of social behaviors in the latter increased, even leading to deaths, although interaction was almost segregated between the two kinds of rats. 3. In an avoidance learning situation, wild-caught and wild F1 (laboratory raised) rats were markedly inferior in performance compared to domestic rats in paradigms with internally or externally cued warnings. 4. In another avoidance learning context, wild rats showed limited evidence of a passive style of learning while domestic rats showed clear evidence of active avoidance learning. These data suggest that learning styles may differ in the two kinds of rats and that definitive evidence of a learning difference will be difficult to obtain. 5. Daily patterns of responding for drinking water were more resistant to change in the wild rats, even at a substantial cost in water obtained, suggesting that domestication may have induced greater behavioral flexibility.

The Duration of Efficacy of the Insecticide Dieldrin Against the Chigger Vectors of Scrub Typhus in Malaya 1

Dieldrin, when applied to the surface of the ground and to low-lying vegetation by means of a high pressure spray or Swing-fog apparatus at the rate of 2.5 pounds to the acre, effectively controlled the chigger vectors of scrub typhus, Trombicula (Leptotrombidium) deliensis Watch and T. (L.) akamushi Brumpt, for at least 26 months. In experiments in a field of lallang (kunai grass), Imperata cylindrica , at Subang, Selangor, Malaya, the Chigger Index or average number or chiggers per wild-caught rat, Rattus rattus jalorensis (Bonhote), before application of insecticide, was more than 360 per rat, and 10 days after treatment the index was 9 in the sprayed area and 13 in the Swing-fogged area, respectively. The index ranged from 2 to 12 in the sprayed plots and from 4 to 25 in the Swing-fogged plots during checks made over a period of 52 weeks, while the mites remained prevalent in the control area. At the termination of the experiment at 113 weeks, the reduction in the numbers of chiggers on rats in the treated areas as compared with the controls was 92% or greater. The actual duration of efficacy has not been determined. The use of dieldrin for disinfestation of terrain in hyperendemic areas of scrub typhus is recommended where relatively large numbers of non-immunes lire a risk, as in military camps, rubber plantations and the like. A severe grass fire drastically reduced the numbers of chiggers, found on rats, but the effect was only temporary, and in 2 or 3 months the chigger index was as high as ever. The fire did not appreciably affect the rate at which live rats were trapped even 1 week after the grass was burned. The lallang although completely burned over, started to grow rapidly from unaffected rhizomes within a few days of the fire. Shrubs were apparently killed, and were replaced by lallang.

Studies on the Transmission of the Filarial Worms of the Cotton Rat 1

SummaryA method is described for infecting groups of cotton rats with relatively constant numbers of the filarial worms, Litomosoides carinii, all of which are of the same age. The infections were produced by exposing the rats in metal tanks to counted numbers of mites whose percentage of infection had been determined. Such rats are superior for chemotherapeutic studies and for studies on immunity to wild caught rats with infections of various numbers of worms of mixed ages. Further improvement along this line is needed, however, and to indicate possible lines of procedure the factors in the variability observed in these experiments are analyzed.

A Laboratory Infection of the Rat with Filarial Worms 1

Summary Successful transmission of infections of Litomosoides carinii, a filarial parasite of the cotton rat Sigmodon hispidus texianus, has been accomplished in all of three trials made by housing together infected and uninfected rats in a moist environment into which freshly gathered grass nests of cotton rats had been introduced. Altogether 15 out of 16 cotton rats became infected as well as the only white rat tried, while 24 control cotton rats and 4 control white rats remained uninfected. The only biting arthropods found in the experimental units were fleas, Rhopalopsyllus gwyni, and two species of mites, viz. a new species of Atricholaelaps and Liponyssus bacoti. On the grounds of abundance both in the units and on wild-caught rats either the fleas or the former species of mites seemed indicated as the vector, but 100 and 500 dissections respectively revealed no developing larvae. L. bacoti was rare both on wild rats and in the units and too few were dissected for conclusions, but this species seems to be incriminated by the elimination of other possibilities.