Poison-Based Commensal Rodent Control Strategies in Urban Ecosystems: Some Evidence Against Sewer-Baiting

Abstract

Sewers are historically considered the main reservoir for commensal rodents, posing threats to urban ecosystem health. Aboveground rodent signs are often assumed to give clues to high sewer infestation, which can chronically restock surface areas. Thus, current sewer-baiting programmes are mostly reactive, responding to increased surface infestation. Conversely, proactive sewer-baiting (regardless of infestation levels) is often disregarded because cost-effectiveness is not always addressed. We explored the extent to which the surface infestation is related to rodent feeding activity on sewer and surface baits by analysing a set of proactive bait records in Bologna city, Italy. Sewer bait intakes were significantly lower than surface ones, suggesting that proactive sewer-baiting is generally less effective. As surface infestation increased, probability of recording surface bait intake increased significantly but this was not reflected by increased sewer bait intake, suggesting that surface infestation is not always a reliable indicator of sewer infestation. This should discourage the use of reactive sewer-baiting as a routine strategy. Poison-based control programmes by themselves are scarcely predictable and strategically limited, and ideally they should be handled within an ecologically based integrated pest management approach for achieving satisfactory results.

Rats About Town: A Systematic Review of Rat Movement in Urban Ecosystems

“…Indeed, Tanaka and Kawashima (1951) observed rats moving among three to four houses in a city block over the course of a single week. Additionally, rats may travel between surface and sewer locations (Colvin et al, 1998;Heiberg et al, 2012), but not in all cases (Gras et al, 2012). In contrast, rats do not appear to travel between adjacent, but separate, sewer systems (Heiberg et al, 2012).…”

Monitoring of Rattus norvegicus based on non-toxic bait containing encapsulated fluorescent dye: Laboratory and semi-field validation study

“…Traditionally, in the grain stores, food industry premises and urban sewers, toxic baits have been used for both rodent control and monitoring (e.g., see Patergnani et al, 2010;Mughini et al, 2012). The rate of bait consumption indicates population trends or the efficacy of the treatment.…”

SARS-CoV-2 surveillance in Norway rats (Rattus norvegicus) from Antwerp sewer system, Belgium

“…They are considered true commensals, often living in close proximity to humans, increasing the risk of pathogen transmission, as they are a source of a wide range of viral, bacterial and parasitic zoonoses (Himsworth et al 2013). In Europe, Norway rats are well adapted to a synanthropic lifestyle and thrive in urban environments, including city sewer systems, where they find food, water and shelter (Mughini Gras et al 2012, Pascual et al 2020). Considering that many studies have detected SARS-CoV-2 in wastewater from the sewage system globally (e.g.…”