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Rodents infest urban environments, causing damage and acting as vectors for disease transmission. Currently, anticoagulants are the most widely used chemical rodenticides, and their extensive and widespread use can contaminate the environment. To ensure effectiveness and avoid accumulation of rodent baits in the environment, it is important to evaluate how long rodent baits maintain their palatability and efficacy. In rodent control programs, rodent baits are placed in locations such as sewers, but after a few days, baits appear altered, causing doubts about the control efficacy. For this reason, baits are replaced periodically, which increases costs and generation of chemical waste. The objective of this study was to evaluate the palatability and efficacy of commercial paraffin-type rodent bait blocks placed in sewers in São Paulo City over a period of 90 days. Bait blocks were placed in sewers and collected after 30, 60, and 90 days. Additionally, in a laboratory two-choice test, wild-caught urban Norway rats were offered 40-60 g of bait and an equal volume of standard rat pellets. The amount of bait and rat pellet consumed was registered, the palatability was calculated, and the efficacy was measured as the percentage mortality over 14 days. The results showed that, even when they had an altered appearance, bait blocks remained palatable to the rats and were effective after at least 90 days. Leaving bait blocks for longer periods could be an effective strategy for reducing costs and could help to ensure the control of urban rodents in an environmentally sustainable way.

Urban Norway rat (Rattus norvegicus) populations can carry the bacteria methicillin-resistant Staphylococcus aureus (MRSA). There are numerous knowledge gaps in the epidemiology of MRSA in these populations that limit understanding of its ecology in urban environments. For example, fecal shedding of MRSA, which may increase environmental contamination, has been reported in other species; however, it is unknown whether Norway rats carry the bacteria rectally. Furthermore, while intermittent MRSA shedding has been shown in other species and may dictate when the risk of transmission is highest, duration of carriage has not been examined for Norway rats. Previous work has shown that lethal animal-control methods may increase the level of pathogens within reservoir populations, possibly by disrupting ecological patterns. However, the impact of rodent-control on potentially environmentally acquired pathogens like MRSA has not been tested. Using capture-mark-recapture methods in an inner-city neighborhood in Vancouver, Canada, we show that rats intermittently carry MRSA both in the rectum and oropharynx. By assessing the prevalence of MRSA before and after enacting a pest-control intervention, we report that kill-trapping had no impact on the prevalence of carriage of this environmentally-acquired agent., (© 2018 Blackwell Verlag GmbH.)

Paraffinized rodent baits developed initially for use in control of Norway rats in sewers by Lloyd Plesse of San Jose, California, an experienced bait formulator for Santa Clara County, significantly enhanced longevity and effectiveness of toxic rodent baits. Within a couple of years, this paraffin type molded bait’s moisture resistant qualities and proven efficacy, especially for sewer rat (Norway rat) control, was the subject of several published articles. Those first three articles, 1959-1961, were responsible for rapidly launching this new paraffinized bait formulation into national usage, at first, mostly by health departments. The structural pest control operators and agricultural interests were soon to follow, using them initially for out-of-doors control of rats and indoors where high humidity normally caused bait deterioration. Recognizing the potential of paraffinized rodent baits, along with the published how-to information, commercial bait manufacturers were quick to get into production and distributors eager to market. Paraffinized rodent baits soon came into common usage and literally revolutionized rodent baits by not only making them more moisture and weather resistant but more convenient to use and versatile in applications. This resulted in greatly expanding the conditions under which commensal rodents could be more effectively controlled. The chronology and evolution of paraffinized rodent baits and their practical uses are followed from their beginning throughout much of their early existence, as are the changes in their manufacturing processes. The factors contributing to development and rapid acceptance for rodent control are enumerated, as are their advantages and disadvantages. The greatest emphasis is placed on the first two decades (1960s and 70s) of the existence of paraffinized rodent baits.

An alternative rodent control technology is presented. The patented discovery that specific plant-derived structural carbohydrate polymers are inhibitory to the water retentive mechanisms of rodents is discussed. Specifically, it has been discovered that when natural complex structural carbohydrates are formulated into a palatable pellet, target species of rodents (rats, mice, and ground squirrels), after ingesting the polymers, become less active and eventually die after 3 - 10 days. Captivity and in situ tests on the Norway rat have indicated the lethal dose for rats to be approximately 35 - 50 g consumed over a period of 72 - 96 hours, whereas for house mice it is 7 - 10 g over the same period. Captive trials on California ground squirrels have indicated a similar lethal dosage to that of rats, specifically 35 - 50 g consumed over 72 - 96 hours. The commercial product is exempt from registration in many countries including the U.S. This paper discusses laboratory and field test results on rodents to date and field use experiences.

In laboratory experiments, carbon disulfide (CS2) increases the attractiveness of feeding stations to rats and mice. Bait consumption is also increased, and the effects are more pronounced for females than for males. The present study was designed to assess whetherCS2 would enhance consumption of a standard bait formulation by wild Norway rats (Rattus norvegicus). The results showed that consumption was tripled when bait was paired with CS2. We speculate that CS2 could similarly enhance the effectiveness of rodenticide bait formulations to which it is applied. Extensive field tests of CS2 as a rodent attractant appear warranted.

Current rodent control practices for the Hawaiian sugar industry revolve around the use of single grain baits containing anticoagulants in bait stations and zinc phosphide for aerial applications. Neither type of control programs as they are now applied has been very effective against the Norway rat (Rattus norvegicus) which is becoming a major problem species for the industry. As a result, we have sought a more effective anticoagulant, to which the Norway rat is more susceptible, and an improved method of bait distribution. With a knowledge of the month-to-month variation in the field rodents' gestation rate, a new control program is being developed which involves the distribution of diphacinone oats in plastic bags to precede the major annual gestation peaks.

A detailed description of problems of Norway rat infestation of sanitary sewer systems is provided, as well as a review of control methods and materials. Design and maintenance of urban sewer systems can reduce rat problems, but ongoing effective rat control programs typically must include use of rodenticides. Commonly used active ingredients are discussed, as is the formulation and application of baits appropriate for use in sewer systems. The need for prebaiting when using acute toxicants is noted, as is the desirability of including mold inhibitors into bait formulations when using paraffin baits or anticoagulant baits, which require repeated feeding to be lethal. A method for locating rodents burrows that are connected to main sewer lines or laterals is described, using smoke bombs and portable blowers to force smoke through sewer systems and reveal locations where rats have points of access. Components of an effective strategy to control Norway rat infestations in sewers are discussed, and literature citations are provided.