Response of small rodents to manipulations of vegetation height in agro-ecosystems

Some small mammal populations require human interference to conserve rare or threatened species or to minimizeadverse effects in plant production. Without a thorough understanding about how small rodents behave in theirenvironment and consideration of how they react to management efforts, management will not be optimal. Socialbehavior, spatial and temporal activity patterns, predator avoidance and other behavioral responses can affect pestrodent management. Some of these behavioral patterns and their causes have been well studied. However, theirimpact on pest rodent management, especially for novel management approaches, is not always clear. Habitatmanipulation occurs necessarily through land use and intentionally to reduce shelter and food availability and toincrease predation pressure on rodents. Rodents often respond to decreased vegetation height with reducedmovements and increased risk sensitivity in their feeding behavior. This seems to result mainly from an elevatedperceived predation risk. Behavioral responses may lessen the efficacy of the management because the desiredeffects of predators might be mediated. It remains largely unknown to what extent such responses can compensateat the population level for the expected consequences of habitat manipulation and how population size and cropdamage are affected. It is advantageous to understand how target and non-target species react to habitatmanipulation to maximize the management effects by appropriate techniques, timing and spatial scale withoutcausing unwanted effects at the system level.

Impact of fertility versus mortality control on the demographics of Mastomys natalensis in maize fields

The multimammate mouse,Mastomys natalensis,is the most common rodent pest species in sub-Saharan Africa.Currently,rodenticides are the preferred method used to reduce the population of rodent pests,but this method poses direct and indirect risks to humans and other non-target species.Fertility control is a promising alternative that has been argued to be a more sustainable and humane method for controlling rodent pests.In this study,we compared the effectiveness of fertility control bait EP-1(quinestrol(E)and levonorgestrel(P),10 ppm)and an anticoagulant rodenticide bait(bromadiolone,50 ppm)on the population dynamics of M.natalensis in maizefields in Zambia during 2 cropping seasons.M.natalensis was the most abundant species in maizefields(77%of total captures).Fertility control reduced the number of juveniles and suppressed population growth of M.natalensis at the end of the 2019–2020 cropping season.The population density initially decreased after rodenticide treatment,but the population rapidly recovered through immigration.None of the treatments influenced maize damage by rodents at germination(F2,67=1.626,P=0.204).Applying the treatments during the maize seeding time was effective at suppressing population growth at the end of the cropping season than application the month before maize seeding.This research indicates that a single-dose delivery of EP-1 and rodenticide have comparable effects on the population dynamics of M.natalensis.Thesefindings are important in developing fertility control protocols for rodent pest populations to reduce maize crop damage and improve yields.

Fertility control of Rattus nitidus using quinestrol:effects on reproductive organs and social behavior

Fertility control has been identified by studies in the laboratory and the field as a more appropriate and long-term control strategy for rodent pests than lethal control.In this study,we investigated the effects of quinestrol on mass of reproductive organs and on social behaviors in female and male Himalayan field rats(Rattus nitidus).A total of 16 adult females and 16 adult males were randomly assigned to 4 groups.One male and one female group were fed rice with 0.005%quinestrol by weight for 7 days,and another 2 groups were fed rice only.After 7 days,rats were assigned to 10 min dyadic encounters between groups,and investigation,aggression,defense and attack latency were quantified.All animals were killed on day 10,and reproductive organs were dissected and weighed.Dyadic encounter data showed that there were obvious changes in social behaviors of quinestrol-treated rats.Quinestrol significantly inhibited the investigative behavior of quinestrol-treated males toward control females in Rattus nitidus,but seldom affected investigation between control males and quinestrol-treated females.Aggression of control females toward quinestrol-treated males was higher than that of quinestrol-treated females,and defense of quinestrol-treated males toward control females was more remarkable than that of control males.Quinestrol remarkably decreased wet masses of epididymis and spermotophore in males and ovaries in females,but had no effect on wet masses of testes and uteri after quinestrol treatment.These results indicate that the anti-fertility effects of quinestrol on R.nitidus are attributed to not only suppressing reproductive organs but also impacting social behaviors associated with territory defense and mate choice.

Relationships among rat numbers,abundance of oil palm fruit and damage levels to fruit in an oil palm plantation

The relationships between vertebrate pests and crop damage are often complex and difficult to study.In palm oil plantations rodents remain the major pests,causing substantial monetary losses.The present study examined the numerical and functional responses of rodents to changes in the availability of oil palm fruit and the damage associated with that response.For the study,200 traps were set in pairs on a 10×10 trapping grid for 3 consecutive nights in each of 6 study plots at 8-week intervals in a 2569 ha oil palm plantation at Labu,Negeri Sembilan state in Peninsular Malaysia over 14 months.A total of 1292 individual rats were captured over 25200 trap-nights.Animals were identified,aged,sexed,weighed and measured.An index of the relative abundance of rats was calculated based on trapping success.Damage to infructescences was assessed at each trap point.Regardless of the age of palms,there were positive and significant relationships between the relative abundance of rats and numbers of infructescences.The levels of damage to infructescences were significantly correlated with the relative abundance of rats.A steep increase in damage was observed with an increase in mature infructescences,indicating a feeding preference of rats for mature infructescences.For both males and females of all rat species,there were weak and non-significant correlations between body condition and infructescence numbers.These results indicated that there was a numerical and a functional response by rats to the availability of palm fruit and a resulting increase in depredation of oil palm fruits.The ways in which this information might aid in future pest control are discussed.

Habitat evaluation for outbreak of Yangtze voles(Microtus fortis)and management implications

Rodent pests severely damage agricultural crops.Outbreak risk models of rodent pests often do not include sufficient information regarding geographic variation.Habitat plays an important role in rodent-pest outbreak risk,and more information about the relationship between habitat and crop protection is urgently needed.The goal of the present study was to provide an outbreak risk map for the Dongting Lake region and to understand the relationship between rodent-pest outbreak variation and habitat distribution.The main rodent pests in the Dongting Lake region are Yangtze voles(Microtus fortis).These pests cause massive damage in outbreak years,most notably in 2007.Habitat evaluation and ecological details were obtained by analyzing the correlation between habitat suitability and outbreak risk,as indicated by population density and historical events.For the source-sink population,96.18%of Yangtze vole disaster regions were covered by a 10-km buffer zone of suitable habitat in 2007.Historical outbreak frequency and peak population density were significantly correlated with the proportion of land covered by suitable habitat(r=0.68,P=0.04 and r=0.76,P=0.03,respectively).The Yangtze vole population tends to migrate approximately 10 km in outbreak years.Here,we propose a practical method for habitat evaluation that can be used to create integrated pest management plans for rodent pests when combined with basic information on the biology,ecology and behavior of the target species.