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Rodent pest management traditionally relies on some form of lethal control. Developing effective fertility control for pest rodent species could be a major breakthrough particularly in the context of managing rodent population outbreaks. This laboratory-based study is the first to report on the effects of using fertility compounds on an outbreaking rodent pest species found throughout sub-Saharan Africa. Mastomys natalensis were fed bait containing the synthetic steroid hormones quinestrol and levonorgestrel, both singly and in combination, at three concentrations (10, 50, 100 ppm) for 7 days. Consumption of the bait and animal body mass was mostly the same between treatments when analysed by sex, day and treatment. However, a repeated measures ANOVA indicated that quinestrol and quinestrol + levonorgestrel treatments reduced consumption by up to 45%, particularly at the higher concentrations of 50 and 100 ppm. Although there was no clear concentration effect on animal body mass, quinestrol and quinestrol + levonorgestrel lowered body mass by up to 20% compared to the untreated and levonorgestrel treatments. Quinestrol and quinestrol + levonorgestrel reduced the weight of male rat testes, epididymis and seminal vesicles by 60-80%, and sperm concentration and motility were reduced by more than 95%. No weight changes were observed to uterine and ovarian tissue; however, high uterine oedema was observed among all female rats consuming treated bait at 8 and 40 days from trial start. Trials with mate pairing showed there were significant differences in the pregnancy rate with all treatments when compared to the untreated control group of rodents. [ABSTRACT FROM AUTHOR]

The breeding dynamics of three species of rodents, Mastomys natalensis, Aethomys chrysophilus and Gerbilliscus vicina were investigated in a seasonal environment (wet versus dry) in Berega in the eastern parts of central Tanzania. Berega has a distinct unimodal rainfall pattern, with most rainfall from November to April/May. We hypothesized that breeding of rodents in central Tanzania would be confined to the wet season, when unlimited resources would be available for reproduction. We provide evidence of breeding discontinuity in the three species, showing that breeding was seasonally restricted to the wet season and early in the dry season. The observed discontinuity could largely be ascribed to variation in primary productivity between the wet and dry seasons. Reproductively active females were found in the population as early as November, a month into the rainy season, but when early rains occurred, some individuals were already breeding in October. Breeding was more intensive in the latter part of the wet season (March-May) and completely ceased during the dry season. For M. natalensis, survival was highest in the wet period and low in the dry season. The study provides knowledge on the breeding dynamics of rodents in central Tanzania, which can help farmers to take proactive rodent management decisions to prevent high rodent densities and reduce crop damage in the fields. Application of control measures by the community early in the season when populations of reproductive females is lowest will be most rewarding. [ABSTRACT FROM AUTHOR]

As part of a three-year study to develop ecologically-based rodent management (EBRM) in southern Africa, a capture-mark-recapture study was carried out in Tanzania, Namibia and Swaziland to establish the demographic patterns and population dynamics of rodents. Two study grids were established in each country. In Tanzania, ten species of rodents and one shrew (Crocidura sp.) were identified in the study area. The rodent species consisted of Mastomys natalensis, Aethomys chrysophilus, Arvicanthis neumanni, Gerbilliscus vicina, Acomys spinosissimus, Lemniscomys griselda, Lemniscomys zebra, Rattus rattus, Graphiurus sp. and Mus minutoides. Mastomys natalensis was dominant and contributed more than 70% of the captures. In Namibia, five species were captured, namely Mastomys natalensis, Gerbilliscus leucogaster, Saccostomus campestris, Mus minutoides and Steatomys pratensis. Mnstomys natalensis contributed about 50% of the captures. In Swaziland, only M. natalensis was captured in the study grids. There was a clear pattern in the population dynamics, with breeding confined to the wet seasons in the three countries. Mastomys natalensis was the dominant pest species, for which EBRM should focus on. The highest population density of M. nutalensis occurred during and after the rains, which coincided with the most susceptible phenological stage of crops. The breeding seasonality and density fluctuations observed in the three countries conform with observations made elsewhere in Africa, which support the hypothesis that rainfall events promote primary productivity on which murid rodents depend. Development of EBRM in these countries will be determined by the local conditions and how they influence the demographic processes of the rodent populations. EBRM should make use of the available ecological knowledge of the local rodent pest species and the focus should be on (ecological) management practices applicable at the community level including community based intensive trapping, field hygiene, removing cover and sources of food for rodents. [ABSTRACT FROM AUTHOR]

Studies of populations of the multimammate rat Mastomys natalensis in Morogoro, Tanzania, show that soil texture appears to influence the population abundance and distribution of these rats in agricultural fields. The lowest rodent population abundance was found on sandy clay soils ( F(2, 5)= 8.42; P= 0.025). The population abundances of M. natalensis on sandy clay loam and sandy loam soils did not differ significantly ( P≤ 0.05), possibly because these soils have a very similar texture. The results of this study suggest that M. natalensis prefers loam-textured soils with a high percentage of sand, which are probably better than clay soils for burrowing and nesting, particularly in the rainy season. The lower preference for clay soils is probably related to the poor aeration in these soils and the waterlogging that occurs during the wet season. [ABSTRACT FROM AUTHOR]

The multimammate rat, Mastomys natalensis Smith 1834, is a dominant species in agro-ecosystems in Sub-Saharan Africa, but adapts quickly to changes in non-agricultural landscape, particularly woodlands and forests. In this study we report on reproduction and population dynamics of M. natalensis in deforested high elevation localities in the Usambara Mountains, north-east Tanzania. We conducted Capture-Mark-Recapture studies in 2002-2004, and established that reproduction of M. natalensis takes place in the extended wet season between February and June, and the population density peaks in June-August. Reproduction cease in July to January and population density drops from July onwards. Reproduction and population density fluctuations are linked to the duration and amount of rainfall. In years when rainfall was below average and the wet season was short, the population density was significantly lower (below 10 animals/ha and 60 animals/ha in 2003 and 2004 respectively, compared to >100 animals/ha in 2002 when rainfall was above the seasonal average) (Fdf 2,13= 9.092, p < 0.01 for in between years variations and Fdf 12,15= 5.389, p < 0.01 for effect of cumulative annual rainfall on population density). These densities were much lower than in the lowland savannah habitats in central and southwest Tanzania. A comparison between the farmland/fallow mosaic fields and agro–forestry areas showed higher population densities in the former, which have similarities to the preferred habitats in the lowland savannahs. The increasing abundance of M. natalensis in the Usambara could have some consequences: M. natalensis is major pest and is involved in the plague cycle in the western Usambara Mountains. Mastomys natalensis is also a strong competitor and the impact on endemic rodent species, e.g. Lophuromys flavopunctatus and Praomys delectorum is unknown. [ABSTRACT FROM AUTHOR]