added 2 research items
Rodent Management in Northern Laos
A field and a household survey, the latter of which included inspections and interviews with the residents of a total of 1370 properties, were conducted in 2004 in 30 villages of the city of Luang Prabang, Lao PDR, in order to assess the degree of rodent infestation and to identify potential factors influencing infestations. Roof rats, Rattus rattus, and the Polynesian rat, Rattus exulans, were the only rodents found in the city, and trapping results showed a clear dominance of roof rats (80-90% of all individuals). Measurements of rodent activity using tracking patches correlated positively with the trapping data, and revealed a significantly higher degree of rat infestation during the rainy season (September) than during the dry season (November). If households in the vicinity of the sampling locations were considered, villagers' accounts of indoor rodent infestations recorded during the household survey correlated positively with measurements of rodent activity. At least every second household reported indoor infestations. Using explorative statistical analyses (classification trees, factor analysis) we checked the predictive or explanatory value of up to 28 variables assessed during household inspections for villagers' observations on rodent infestation as the dependent variable. Trophic factors such as exposed food (indoors) and garbage (outdoors), and structural features such as open ceilings (indoors) and rat harborage in gardens (outdoors) ranked highest as explanatory variables. Assessment of a small sample of roof rat droppings collected inside houses revealed the presence of the potential disease agents Salmonella javiana, Cryptosporidium parvum, Giardia duodenalis and the parasitic nematode Calodium hepaticum (syn. Capillaria hepatica). These results underline the need for an appropriate rodent management strategy for the city, whereby simple sanitation and rodent-proofing measures could be cheap means of reducing rat infestation rates.
This study followed up on results of an integrated rodent management program that was implemented from 2010 to 2011 in 18 treatment and 18 control villages in three provinces of Northern Laos. The program's impact on reducing rodent damage to upland rice was reported previously. Here, we focused on the efficiency with which upland villagers applied the proposed rodent control methods (snap traps, biological control using the protozoan parasite Sarcocystis singaporensis, community hunts) by comparing control effort (inputs) to an output of more than 73,000 rodents (mainly black rats) culled in Houphanh (HP) province. We also hypothesized that rice yields of a given crop year (2009) could predict rat damage in the three provinces in following years (2010, 2011). A survey of flowering of bamboo and fagacean 'nut' trees in 2011 was used to check for a potential influence of flowering events on rodent infestation. Using regression analysis we observed that efficiency (cumulative culls method-1) of snap traps and biological control decreased significantly with increasing field size of upland rice fields, while the opposite trend was apparent with regard to paddy fields. Numbers of rodents culled by hunting and trapping increased with rising numbers of hunting villagers, but culls household-1 declined with increasing village size. We developed multiple regression models that predicted rodent culls by the paddy/upland rice area ratio and rodent control effort and explained >90% of the variation. Rat damage to wet season rice in 2010 and 2011 (and rodent culls ha-1) increased with increasing village rice yields of 2009, while the treatments' regression line was positioned at a 5.5% lower rat damage level, in parallel to the controls. Integration of the observed relationships using the General Linear Model (GLM) allowed predicting rat damage under different treatment and seasonal scenarios. Surprisingly, 99.8% of the variation in rodent culls ha-1 in HP could be explained by a combination of rodent control effort, rice productivity, and flowering events. Herewith, we provide predictive and explanatory models that could be useful for future rodent management in the uplands. The observed relationships are discussed in view of potential forecasting of chronic rodent infestation and, ultimately, outbreaks.