A systematic review of rodent pest research in Afro-Malagasy small-holder farming systems: Are we asking the right questions?

Abstract

Rodent pests are especially problematic in terms of agriculture and public health since they can inflict considerable economic damage associated with their abundance, diversity, generalist feeding habits and high reproductive rates. To quantify rodent pest impacts and identify trends in rodent pest research impacting on small-holder agriculture in the Afro-Malagasy region we did a systematic review of research outputs from 1910 to 2015, by developing an a priori defined set of criteria to allow for replication of the review process. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We reviewed 162 publications, and while rodent pest research was spatially distributed across Africa (32 countries, including Madagascar), there was a disparity in number of studies per country with research biased towards four countries (Tanzania [25%], Nigeria [9%], Ethiopia [9%], Kenya [8%]) accounting for 51% of all rodent pest research in the Afro-Malagasy region. There was a disparity in the research themes addressed by Tanzanian publications compared to publications from the rest of the Afro-Malagasy region where research in Tanzania had a much more applied focus (50%) compared to a more basic research approach (92%) in the rest of the Afro-Malagasy region. We found that pest rodents have a significant negative effect on the Afro-Malagasy small-holder farming communities. Crop losses varied between cropping stages, storage and crops and the highest losses occurred during early cropping stages (46% median loss during seedling stage) and the mature stage (15% median loss). There was a scarcity of studies investigating the effectiveness of various management actions on rodent pest damage and population abundance. Our analysis highlights that there are inadequate empirical studies focused on developing sustainable control methods for rodent pests and rodent pests in the Africa-Malagasy context is generally ignored as a research topic.

Fig 1. PRISMA statement for the publications retained in the review.

Fig 2. Temporal trend of rodent pest studies in Afro-Malagasy agricultural systems from 1960 to 2015.

Fig 3. Spatial distribution of rodent studies in the Afro-Malagasy agricultural systems during the period 1960–2015.

Map is limited to countries in which rodent pest studies were registered and shading represents number of studies (see legend). Map created by LHS.

Fig 4. Proportional breakdown by research theme of studies on rodent pests in Tanzania and other Afro-Malagasy countries published between 1960 and 2015.

Fig 5

Range of crop losses (a) and median point estimates for crop losses (b) as reported for different crop stages and storage. Asterisks denote significant differences, whiskers minimum and maximum values, box plot indicate third and first quantile and median. n = number of data points.

Fig 6. Median crop losses for different crops at maturity stage.

Whiskers represent minimum and maximum values, box indicate first quantile, third quantile and median while n = number of data points.