Rodent Bait Research Articles

Rodents as vehicle for delivery of transgenic bacteria to make paratransgenic sand fly vectors of cutaneous leishmaniasis in field condition

Vector-borne diseases, among them leishmaniasis, cause more than 700,000 deaths annually. The lack of an effective vaccination and the increasing resistance of sand flies to insecticides require the urgent development of innovative approaches to contain the disease. The use of engineered bacteria that express anti-parasite molecules (paratransgenesis) shows much promise. However, a challenge for implementation of this strategy is to devise means to introduce modified bacteria into sand flies in the field. In this study, we use rodent food bait as a delivery strategy to introduce two mCherry-fluorescent bacteria, Serratia AS1 and Enterobacter cloacae, into adult sand flies in field settings. Bacteria-infected food was provided to Rhombomys opimus rodents. These bacteria transiently pass through the rodent alimentary tract and are delivered to larval habitats with the rodent feces. The feces are ingested by sand fly larvae and, in the case of Serratia AS1, are trans-stadially transmitted to adults. This is the first report of targeting delivery of Serratia AS1 in a paratransgenic system to control transmission of leishmaniasis under field condition. This novel strategy shows promise for delivering transgenic bacteria to Leishmania vectors in the field.

The Ecological Origins and Consequences of the Rodent Bait Station: From WWII Britain to Contemporary California

ABSTRACT This article describes the origin of the rodent bait station, a globally distributed system for controlling rats, currently creating a secondary ecological crisis affecting wildlife who eat rats that have eaten the poison. I argue that this system is tied to settler colonial places like California and that banning poison will not address the crisis. It details the history of this box as a scientific ecological solution to rat control, created by Charles Elton and his research group during WWII. I pair this account with an account of contemporary science into the ecological crisis of rodenticides.

Assessing pig farm biosecurity measures for the control of Salmonella on European farms.

Salmonella spp. is a common zoonotic pathogen, causing gastrointestinal infections in people. Pigs and pig meat are a major source of infection. Although farm biosecurity is believed to be important for controlling Salmonella transmission, robust evidence is lacking on which measures are most effective. This study enrolled 250 pig farms across nine European countries. From each farm, 20 pooled faecal samples (or similar information) were collected and analysed for Salmonella presence. Based on the proportion of positive results, farms were categorised as at higher or lower Salmonella risk, and associations with variables from a comprehensive questionnaire investigated. Multivariable analysis indicated that farms were less likely to be in the higher-risk category if they had '<400 sows'; used rodent baits close to pig enclosures; isolated stay-behind (sick) pigs; did not answer that the hygiene lock/ anteroom was easy to clean; did not have a full perimeter fence; did apply downtime of at least 3days between farrowing batches; and had fully slatted flooring in all fattener buildings. A principal components analysis assessed the sources of variation between farms, and correlation between variables. The study results suggest simple control measures that could be prioritised on European pig farms to control Salmonella.

Large scale systemic control short-circuits pathogen transmission by interrupting the sand rat (Psammomys obesus)-to-sand fly (Phlebotomus papatasi) Leishmania major transmission cycle.

Systemic control uses the vertebrate hosts of zoonotic pathogens as "Trojan horses," killing blood-feeding female vectors and short-circuiting host-to-vector pathogen transmission. Previous studies focused only on the effect of systemic control on vector abundance at small spatial scales. None were conducted at a spatial scale relevant for vector control and none on the effect of systemic control on pathogen transmission rates. We tested the application of systemic control, using Fipronil-impregnated rodent baits, in reducing Leishmania major (Kinetoplastida: Trypanosomatidae; Yakimoff & Schokhor, 1914) infection levels within the vector, Phlebotomus papatasi (Diptera: Psychodidae; Scopoli, 1786) population, at the town-scale. We provided Fipronil-impregnated food-baits to all Psammomys obesus (Mammalia:Muridae; Cretzschmar, 1828), the main L. major reservoir, burrows along the southern perimeter of the town of Yeruham, Israel, and compared sand fly abundance and infection levels with a non-treated control area. We found a significant and substantial treatment effect on L. major infection levels in the female sand fly population. Sand fly abundance was not affected. Our results demonstrate, for the first time, the potential of systemic control in reducing pathogen transmission rates at a large, epidemiologically relevant, spatial scale.

Detections of house mice on Gough Island approach zero within days of aerial baiting

Context House mice (Mus musculus) on temperate Gough Island (6500 ha) are known for their large size, boldness, and tendency to kill large prey such as albatross chicks and even adults. To remove this threat, a mouse eradication operation was implemented in June–August 2021. How mice react to bait during eradications is not well understood, so we capitalised on this operation and conducted the first study with wild house mice during an actual eradication. Aim To document how rapidly mouse activity declined after application of rodent bait, to improve eradication guidelines. Methods We set up a monthly monitoring regime using 10 trail cameras without lures, active for three nights in various habitats around a research station, because this area supported the highest abundance of mice and was logistically feasible. Monitoring commenced before the mouse eradication operation (January–May 2021), and continued when rodent bait was spread (from June 2021), when mouse activity was monitored for 17 consecutive nights, starting the day before baiting. In addition, an increasing number of cameras (up to 15) associated with lures were set further afield in July–August to detect survivors. Key results In the months before bait application, mean daily mouse activity was 3.2 detections/camera (range: 0–56 detections/camera). Immediately after the first bait application, detection rates declined dramatically, from 9.6 to zero detections/camera per day on Day 4 post-baiting. From 1 week post-baiting, mouse detections were extremely rare on both cameras with and without lures. Our last mouse record, 27 days after the first bait application, may be related to initial rapid bait disappearance. Opportunistic camera traps first detected surviving mice 6 months after the first bait drop. Conclusions The rapid decline in detections suggests that most mice consumed bait as soon as it became available, which is faster than what laboratory trials suggest. Future similar operations can expect that mouse activity will decline sharply within 1 week, although some mice may survive longer. Implications Documenting similar declines in mouse activity using cameras could inform operational decisions such as timing of a second bait application or non-target monitoring on future eradication projects. Cameras, particularly with attractive lures, are an effective addition to the mouse detection toolkit, and facilitated a timely confirmation of eradication outcome.

A lesson for planning rodent eradications: interference of invasive slugs during the Gough Island mouse eradication attempt in 2021

Context House mice (Mus musculus) are the main drivers of biodiversity declines on Gough Island (6500 ha; 40°21′S, 009°53′W), central South Atlantic. A mouse eradication operation was planned, the largest global attempt targeting only this species. Understanding and managing challenges of operating at such scales are crucial for maximising the chance of eradication success. The Gough Island mouse eradication attempt was implemented between June and August 2021, after years of planning and trials. We expected poor weather and negligible non-target bait consumption. Aims We aimed to assess the impact of expected and unexpected challenges faced during the eradication operation on Gough Island, namely poor weather and rapid bait disappearance. Methods We set up bait degradation plots across the primary habitats to monitor the impact of expected heavy rain on bait pellets. In contrast, bait availability monitoring and slug laboratory trials were set up ad hoc in response to unexpected observations of high bait consumption by invasive slugs in the lowlands, where both slugs and mice are more abundant. Key results Bait degradation rates were very different between the highlands and the lowlands, with bait in the highlands lasting about six times longer, despite bait pellets receiving more precipitation and the highlands being persistently under cloud. Bait availability in the lowlands dropped by &gt;80% within a few days of the second and third bait application, down to critically low levels (~2 kg ha−1). Importantly, mouse activity was negligible by this time. Non-native slugs appeared to be the main cause of such a sudden drop in rodent bait availability. Conclusions The expected rainy weather was not a significant direct cause of bait degradation in the short term. In contrast, the unexpected slug interference, overlooked in earlier planning trials, resulted in major adjustments of the baiting strategy. Indeed, the rapid bait disappearance in the lowlands triggered the third bait application over this area, at a higher rate. This was not enough, as mice are still present. Implications This is the first report of slug interference during aerial rodent eradications. Our results illustrate how interference by non-target species could affect future pest eradications using baits and should, as far as possible, be assessed early during planning.

Effects of Biopolymers from Cassava Implanted with Rodent Bait on Wistar Rats

Effects of Biopolymers from Cassava Implanted with Rodent Bait on Wistar Rats

The effect of COVID19 pandemic restrictions on an urban rodent population

Shortly after the enactment of restrictions aimed at limiting the spread of COVID-19, various local government and public health authorities around the world reported an increased sighting of rats. Such reports have yet to be empirically validated. Here we combined data from multi-catch rodent stations (providing data on rodent captures), rodent bait stations (providing data on rodent activity) and residents’ complaints to explore the effects of a six week lockdown period on rodent populations within the City of Sydney, Australia. The sampling interval encompassed October 2019 to July 2020 with lockdown defined as the interval from April 1st to May 15th, 2020. Rodent captures and activity (visits to bait stations) were stable prior to lockdown. Captures showed a rapid increase and then decline during the lockdown, while rodent visits to bait stations declined throughout this period. There were no changes in the frequency of complaints during lockdown relative to before and after lockdown. There was a non-directional change in the geographical distribution of indices of rodent abundance suggesting that rodents redistributed in response to resource scarcity. We hypothesize that lockdown measures initially resulted in increased rodent captures due to sudden shortage of human-derived food resources. Rodent visits to bait stations might not show this pattern due to the nature of the binary data collected, namely the presence or absence of a visit. Relocation of bait stations driven by pest management goals may also have affected the detection of any directional spatial effect. We conclude that the onset of COVID-19 may have disrupted commensal rodent populations, with possible implications for the future management of these ubiquitous urban indicator species.

Impact of contraceptive hormones on the reproductive potential of male and female commensal black rats (Rattus rattus).

The black rat is considered one of the world's top pests. With increased restrictions on rodenticides, new alternatives to manage rats are urgently needed. Research on the use of contraceptive hormones, levonorgestrel (LE), and quinestrol (QU), have been evaluated against some rodent species, and this research is the first study to assess these on black rats. Hormones were incorporated into rodent bait at 10 and 50 ppm concentrations singly and in combination (EP-1). Groups of 10 animals of each sex were fed the baits over 7days. Lower bait consumption was observed with slight body mass reductions. On dissection, it was observed that the uterus was in a state of edema and male reproductive organs weighed less with reduced sperm counts/motility. The 2 most promising baits, 50 ppm QU and EP-1, were used to assess impact on pregnancy and litter size. Pregnancy was reduced from 70% success when both males and females consumed untreated bait, down to 30% when males had consumed contraceptive bait but females had not, and down to 0% when females had consumed contraceptive bait, regardless of whether they had paired with a treated or untreated male. Litter size in the untreated pairs was 8 pups, but only 4 pups in those cases where the male only had consumed the contraceptive. Further studies should investigate how long the effect lasts and its reversibility. Field studies at the population level may also shed light on the practicality of using contraceptive baits for black rats in different habitats.

Monitoring and Controlling House Mouse, Mus musculus domesticus, Infestations in Low-Income Multi-Family Dwellings.

Simple SummaryThe house mouse is a very common pest in low-income multi-family residential dwellings. They cause significant property damage and produce allergens that are linked to asthma and allergy. Current mouse management practices in these dwellings are not effective. This study attempted to gain insights into residents’ impressions of house mice, develop more effective mouse detection methods, and evaluate the effectiveness of building-wide mouse management programs. The programs were implemented by researchers for 63 days and the results were monitored for up to 12 months. Significant differences were found in the efficacy of two commercial blank baits for detecting house mouse activity. Chocolate spread was significantly more effective than both commercial blank baits for detecting house mice. Between the two commercial toxic rodent baits tested, FirstStrike® (0.0025% difethialone) was more palatable than Contrac® (0.005% bromadiolone) rodent bait. A building-wide mouse control program resulted in an 87% reduction in mouse activity after three months in two buildings. After 12 months, the number of infestations decreased by 94% in one building, but increased by 26% in another building. Long-term house mouse control requires continuous efforts and the incorporation of multiple strategies.The house mouse, Mus musculus domesticus, is a common pest in multi-family residential apartment buildings. This study was designed to gain insights into residents’ impressions of house mice, develop more effective house mouse detection methods, and evaluate the effectiveness of building-wide house mouse management programs. Two high-rise apartment buildings in New Jersey were selected for this study during 2019–2020. Bait stations with three different non-toxic baits were used to detect house mouse activity. Two rodenticides (FirstStrike®—0.0025% difethialone and Contrac®—0.005% bromadiolone) were applied by researchers over a 63-day period and pest control operations were then returned to pest control contractors for rodent management. There were significant differences in the consumption rates of non-toxic baits and two toxic baits tested. A novel non-toxic bait, chocolate spread, was much more sensitive than the two commercial non-toxic baits for detecting mouse activity. The house mouse management programs resulted in an average 87% reduction in the number of infested apartments after three months. At 12 months, the number of infestations decreased by 94% in one building, but increased by 26% in the second building. Sustainable control of house mouse infestations requires the use of effective monitoring strategies and control programs coupled with preventative measures.

A computer-vision approach to bait level estimation in rodent bait stations

The continual management of pest species and their preventative elimination is an ongoing, labour-intensive problem. Bait stations are pivotal in this management process as they are the point of contact between the rodents and the process, since the rodents need to enter the bait stations to consume the poisoned bait. Monitoring of these bait stations provides feedback of the effectiveness of the management process. However, there is a significantly large cost associated with periodically sending pest control experts to check the level of bait in the bait stations. This becomes even more apparent over a large geographical area. In this paper we present a method of reducing the labour component associated with regular bait level monitoring by placing a camera in the bait stations and using machine vision to provide an estimate of the amount of bait remaining and the type of bait in the station. Images of four common bait types were captured under provided artificial light in a closed bait station, and the computer vision algorithms proved effective in identifying the type of bait as well as providing an estimate of the bait level.

Risks posed by rat reproduction and diet to eradications on tropical islands

Removing invasive rodents from islands has many ecological and social benefits. However, eradications fail more frequently on tropical than on temperate islands, and causes for these failures are not yet well understood. We addressed two major plausible reasons for eradication failure, testing whether actively reproducing females and pre-weaned pups may not consume bait during an experimental eradication of Rattus exulans on a tropical island (22 ha). We tested four hypotheses, namely that: (1) lactating female rats take longer than non-lactating conspecifics to consume rodent bait, (2) pre-weaned rats orphaned following bait application survive when their mother dies, (3) surviving pre-weaned rats are not exposed to rodent bait and (4) lactating females have different natural diets than non-lactating females. Our experimental eradication was successful, despite conditions that are typically associated with eradication failures: rat density was high (95% CI 65–153 rats/ha), rats were breeding and juveniles of all age-classes were present, land crabs were abundant, bait was only widely available for two nights after bait application (i.e. > 90% of bait disappeared within 36 h; bait was undetectable after 60 h), and alternative foods (e.g. coconut) were abundantly available. We found no evidence to support hypotheses that rat breeding and diet specialisation limit bait uptake because all rats consumed bait. Rat eradication was achieved with a relatively low bait application rate (32 kg/ha; 16 kg/ha per application) and a short (7 day) interval between the two bait applications. We recommend further experimental eradications targeting R. exulans and other invasive Rattus and Mus species on larger islands, but conclude that with comprehensive bait coverage eradications on tropical islands can be successful despite abundant natural food and a high density of reproductively active rats.

First record of the development of Sitophilus oryzae on two rodent bait formulations and literature overview of stored product arthropods infestations in rodent baits

It is known that rodent baits can be a source of stored product pests in grain stores and food industry facilities. However, a global inventory of stored product arthropod species that infest rodent baits does not exist. This overview showed that at least 7 species from two orders (Lepidoptera and Coleoptera) are able to develop in toxic rodent baits, and no records have been published for mites (Acari) or psocids (Psocoptera). No records were found for arthropods in non-toxic baits. Here, we report for the first time the development of internally feeding Sitophilus oryzae in two cereal formulations of anticoagulant rodent baits: wax block and mixed-diet baits (pellets + grains). The adults of S. oryzae that developed in the mixed-diet bait were significantly smaller than those that emerged from the wax blocks, indicating that the latter is a more suitable formulation for pest development.

Evaluating the effectiveness of an integrated tick management approach on multiple pathogen infection in Ixodes scapularis questing nymphs and larvae parasitizing white-footed mice.

We investigated the effectiveness of integrated tick management (ITM) approaches in reducing the burden of infection with Borrelia burgdorferi, Babesia microti, and Anaplasma phagocytophilum in Ixodes scapularis. We found a 52% reduction in encountering a questing nymph in the Metarhizium anisopliae (Met52) and fipronil rodent bait box treatment combination as well as a 51% reduction in the combined white-tailed deer (Odocoileus virginianus) removal, Met52, and fipronil rodent bait box treatment compared to the control treatment. The Met52 and fipronil rodent bait box treatment combination reduced the encounter potential with a questing nymph infected with any pathogen by 53%. Compared to the control treatment, the odds of collecting a parasitizing I. scapularis infected with any pathogen from a white-footed mouse (Peromyscus leucopus) was reduced by 90% in the combined deer removal, Met52, and fipronil rodent bait box treatment and by 93% in the Met52 and fipronil rodent bait box treatment combination. Our study highlights the utility of these ITM measures in reducing both the abundance of juvenile I. scapularis and infection with the aforementioned pathogens.

Availability and Nature of Commercial Tick Control Services in Three Lyme Disease Endemic States

In an update of earlier surveys conducted in Connecticut and New Jersey in the mid-1990s, an online survey of private commercial pest control firms engaged in residential tick control showed that the application of synthetic acaricides continues to be the primary method of control used. The carbamate and organophospate acaricides, previously the most commonly used against ticks, have given way to synthetic pyrethroids and, to a lesser extent, the use of natural product/organic acaricides. Typical costs for a single acaricide application today ($100-$200 for a 1 acre [0.4 ha] property) remain similar to those reported from the earlier surveys, although the frequency of applications and, therefore, also the overall annual cost has increased. The application habitats within residential properties, life stages targeted, and application equipment used have not changed appreciably since the mid-1990s. While most survey respondents expressed knowledge of natural product acaricides and Damminix Tick Tubes, many reported that they either did not employ or knew very little about other alternative tick control methods (including entomopathogenic fungus and topical application of acaricides to tick hosts via 4-Poster deer treatment stations or Select TCS rodent bait boxes). This suggests either a failure to adequately inform the pest management industry and their potential client base of the availability of alternate methods, and/or industry concerns about cost and effectiveness of the alternatives.

Rodenticide efficacy in sewers in São Paulo, Brazil.

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.

Field assessment of insecticide dusting and bait station treatment impact against rodent flea and house flea species in the Madagascar plague context.

Bubonic is the most prevalent plague form in Madagascar. Indoor ground application of insecticide dust is the conventional method used to control potentially infected rodent fleas that transmit the plague bacterium from rodents to humans. The use of bait stations is an alternative approach for vector control during plague epidemics, as well as a preventive control method during non-epidemic seasons. Bait stations have many advantages, principally by reducing the amount of insecticide used, lowering the cost of the treatment and minimizing insecticide exposure in the environment. A previous study reported promising results on controlling simultaneously the reservoir and vectors, when slow-acting rodenticide was incorporated in bait stations called “Boîtes de Kartman”. However, little evidence of an effective control of the fleas prior to the elimination of rodents was found. In this study, we evaluated bait stations containing insecticide powder and non-toxic attractive rodent bait for their potential to control rat fleas. Its efficacy was compared to the standard method. The impact of both methods on indoor and outdoor rodent fleas, as well as the human household flea Pulex irritans were analyzed at different time points after treatments. Bait stations did not cause any significant immediate or delayed reduction of rat fleas and increasing the number of operational bait stations per household did not significantly improve their efficacy. Insecticide ground dusting appeared to be the most efficient method to control indoor rat fleas. Both methods appeared to have little impact on the density of outdoor rat fleas and human fleas. These results demonstrate limited effectiveness for bait stations and encourage the maintenance of insecticide dusting as a first-line control strategy in case of epidemic emergence of plague, when immediate effect on rodent fleas is needed. Recommendations are given to improve the efficacy of the bait station method.

Antioxidant and cytoprotective effects of N-acetylcysteine against subchronic oral glyphosate-based herbicide-induced oxidative stress in rats.

It is claimed that oxidative stress has a prominent role in the mechanism of toxic effects formed by glyphosate-based herbicide (GBH) in living systems. A strong thiol compound, N-acetylcysteine (NAC), has antioxidative and cytoprotective properties. The objective in this subchronic toxicity study was to identify the prophylactic effect of NAC over histopathological changes and oxidative stress induced by GBH in blood, renal, liver, cardiac, and brain tissues. A sum of 28 male Wistar rats were divided into four equal groups, each containing 7 rats. During the study, group I (control group) was supplied with normal rodent bait and tap water ad libitum. The applied agents were 160mg/kg NAC to group II, 375mg/kg as equivalent to 1/10 of lethal dose 50% (LD50) of GBH to group III, and 160mg/kg of NAC and 375mg/kg of GBH together once per day as oral gavage to group IV for 8weeks. While GBH decreased the levels of GSH in blood, liver, kidney, and brain tissues, it considerably increased malondialdehyde levels. On the contrary, these parameters happened to improve in the group supplied with NAC. Besides, it was seen that NAC was observed to improve the histopathologic changes in rat tissues induced by GBH. It was concluded that NAC protects oxidative stress and tissue damage induced by GBH in blood and tissue and this prophylactic effect could be attributed to its antioxidant and free radical sweeper character.

Novel edible coatings to improve longevity of rodent baits

ABSTRACTRats and mice cause severe biodiversity impacts worldwide, including in New Zealand, where poisoning campaigns are undertaken on the mainland and offshore islands using cereal-based baits. However, bait stations are often irregularly serviced so wildlife managers require a bait that would remain palatable to rodents for at least 6 months in the field. One potential way to improve the field life of baits is by coating them in materials that reduce water uptake and subsequent mould growth. However, these coatings must be palatable to the rodents. This report investigates the palatability to captive Norway rats (Rattus norvegicus) and mice (Mus musculus) of both weathered and unweathered rodent food pellets coated with various polymer solutions. When compared with uncoated alternatives, fresh baits coated with shellac or polyvinyl butyral (PVB) in ethanol solvent were preferred by the rats. The use of acetone rather than ethanol solvent did not affect bait palatability. A combination of shellac and PVB reduced palatability compared with shellac alone. Weathered shellac-coated baits remained more palatable than uncoated fresh pellets to rats for up to 6 months and outperformed the PVB and combination coatings. Overall, the palatability of fresh-coated baits was lower for mice. The PVB-coated baits had lower mean palatability scores than the shellac-coated baits but none of the bait types was significantly less palatable than uncoated baits. The shellac-coated baits remained palatable to mice for up to 4 months. Shellac is recommended as a coating for multi-species rodent baits.

Urban Field Efficacy of a New Cholecalciferol-based Soft Bait on Commensal Rats in New Orleans, Louisiana, USA

Author(s): Jordan, Kyle K.; Riegel, Claudia; Bauder, Friederike M.; Smith, Philip L. L. | Abstract: Selontra® Rodent Bait (BASF, Ludwigshafen, Germany) is a cholecalciferol-based soft bait that exhibits high palatability both in the lab and field. Because of the attributes and mode of action of cholecalciferol, isolated field populations of rodents can often be controlled by Selontra within one week after initial bait exposure. Baiting trials were established at five sites in the city of New Orleans, Louisiana to investigate the field efficacy of Selontra against roof rats (three sites) and Norway rats (two sites). Comparison of pre- and post-baiting census data indicates an average control rate of 97.7% for roof rats and 88.5% for Norway rats.