Urban Rats in Wellington: Estimating Home Ranges, Population Densities and Detection Probabilities

<p><b>The ship rat (Rattus rattus) and Norway rat (Rattus norvegicus) are prolific pest species with a near- global distribution. Their spread has had serious public health repercussions as carriers of disease and by causing considerable agricultural losses. They are also invasive to many native ecosystems, degrading ecosystem processes, and preying upon native species, resulting in significant losses to biodiversity. </b></p><p>This study aims to guide more effective rat management strategies through an increased understanding of the spatial ecology of rats in an urban environment. Three separate studies were conducted, all located in Wellington, New Zealand: </p><p>1) A radio-telemetry study looked at the home range and spatial behavior of 10 urban ship rats. Results showed comparatively small home ranges (0.01 - 0.45 ha at 100% minimum convex polygons) with maximum linear distances within a home range of 19-74m. There was significant spatial overlap between home ranges– up to 90% (between two adjacent home ranges); co-nesting behavior between both sexes; frequent diurnal activity amongst ship rats (9 of 10 rats); and two longer distance dispersal events (~120m) by ship rats. Implications for rat management include: a need for tighter spacing of devices in urban habitats for control and detection of survivors, potentially every 20-25m if eradication is the goal. </p><p>2) A capture mark re-sight study to estimate the minimum density of ship rats in an 0.63 ha urban bush fragment. A total of five rats were live caught in cage traps and uniquely marked before release. An additional eight wild rats were uniquely identified on cameras based on distinctive features of their appearance. A conservative Lincoln-Petersen estimate was used to estimate the number of rats within the bush fragment: this produced an estimate of 14.6 rats with 95% confidence intervals [7.69-55.6], which translates to a density of 23.2 rats/ha [12.2-88.25]. These densities are significantly higher than those found in most mainland studies and more comparable to those in island habitats. This could be because ship rats are subsidizing their diet with human-derived foods, although this was not confirmed here. </p><p>3) A detection probability study investigated the sensitivity of three devices (wax tag, chew card and bait station) to ship rat presence and examining age-related differences in detection. The bait station was found to have the highest detection probability (0.5 detections/sighting) followed by the wax tag (0.44 detections/sighting) and chew card (0.37 detections/sighting) although results were based on data retrieved from a low sample size of devices (n=2 of each type). The bait station showed a sharp difference between the adult (0.1 detections/sighting) and adolescent populations (0.89 detections/sighting) detection probability. Furthermore, this difference in detection probability was found, although less pronounced, in both the wax tag and chew card. Implications for rat management include: a recommendation that wax tags be used as the primary means of ship rat monitoring; a need for further behavioral studies looking at detection probabilities across a range of kill and monitoring devices so that the most effective ones can be identified; and the development and testing of devices that are attractive to adult rats that may have become “trap shy”. </p><p>These three studies together provide useful insights into urban rat ecology with implications for pest management. However, a more comprehensive study with larger sample sizes is recommended to fully substantiate this work. </p>

Urban Rats in Wellington: Estimating Home Ranges, Population Densities and Detection Probabilities

<p><b>The ship rat (Rattus rattus) and Norway rat (Rattus norvegicus) are prolific pest species with a near- global distribution. Their spread has had serious public health repercussions as carriers of disease and by causing considerable agricultural losses. They are also invasive to many native ecosystems, degrading ecosystem processes, and preying upon native species, resulting in significant losses to biodiversity. </b></p><p>This study aims to guide more effective rat management strategies through an increased understanding of the spatial ecology of rats in an urban environment. Three separate studies were conducted, all located in Wellington, New Zealand: </p><p>1) A radio-telemetry study looked at the home range and spatial behavior of 10 urban ship rats. Results showed comparatively small home ranges (0.01 - 0.45 ha at 100% minimum convex polygons) with maximum linear distances within a home range of 19-74m. There was significant spatial overlap between home ranges– up to 90% (between two adjacent home ranges); co-nesting behavior between both sexes; frequent diurnal activity amongst ship rats (9 of 10 rats); and two longer distance dispersal events (~120m) by ship rats. Implications for rat management include: a need for tighter spacing of devices in urban habitats for control and detection of survivors, potentially every 20-25m if eradication is the goal. </p><p>2) A capture mark re-sight study to estimate the minimum density of ship rats in an 0.63 ha urban bush fragment. A total of five rats were live caught in cage traps and uniquely marked before release. An additional eight wild rats were uniquely identified on cameras based on distinctive features of their appearance. A conservative Lincoln-Petersen estimate was used to estimate the number of rats within the bush fragment: this produced an estimate of 14.6 rats with 95% confidence intervals [7.69-55.6], which translates to a density of 23.2 rats/ha [12.2-88.25]. These densities are significantly higher than those found in most mainland studies and more comparable to those in island habitats. This could be because ship rats are subsidizing their diet with human-derived foods, although this was not confirmed here. </p><p>3) A detection probability study investigated the sensitivity of three devices (wax tag, chew card and bait station) to ship rat presence and examining age-related differences in detection. The bait station was found to have the highest detection probability (0.5 detections/sighting) followed by the wax tag (0.44 detections/sighting) and chew card (0.37 detections/sighting) although results were based on data retrieved from a low sample size of devices (n=2 of each type). The bait station showed a sharp difference between the adult (0.1 detections/sighting) and adolescent populations (0.89 detections/sighting) detection probability. Furthermore, this difference in detection probability was found, although less pronounced, in both the wax tag and chew card. Implications for rat management include: a recommendation that wax tags be used as the primary means of ship rat monitoring; a need for further behavioral studies looking at detection probabilities across a range of kill and monitoring devices so that the most effective ones can be identified; and the development and testing of devices that are attractive to adult rats that may have become “trap shy”. </p><p>These three studies together provide useful insights into urban rat ecology with implications for pest management. However, a more comprehensive study with larger sample sizes is recommended to fully substantiate this work. </p>

EFFICACY OF COMMERCIAL ATTRACTIVE TOXIC SUGAR BAIT STATION (ATSB) AGAINST AEDES ALBOPICTUS

The use of toxic sugar baits is a new paradigm in mosquito control. A commercial product of attractive toxic sugar bait station (Spartan Mosquito Eradicator) contains a toxic sugar bait with sodium chloride as the active ingredient and yeast as an attractant. We studied the efficacy of the device against adult Aedes albopictus Skuse. The study composed of a laboratory and a field component with treatment and control cohorts. The treatment in the laboratory experiment resulted in nonsignificant mortality of adult mosquitoes compared with untreated mosquitoes. Neither laboratory nor field components of the study showed significant evidence that the commercial product could reduce the abundance of Ae. albopictus in the natural environment. The device may need to be improved and further evaluation conducted.

FIELD EVALUATIONS OF ATTRACTIVE TOXIC SUGAR BAIT STATION AND VEGETATION SPRAY APPLICATIONS FOR CONTROL OF AEDES AEGYPTI IN KEY LARGO, FLORIDA

Aedes aegypti and Aedes albopictus, vectors of many arboviruses including Zika, dengue, and chikungunya, are difficult to control with traditional methods. We tested two novel approaches utilizing attractive toxic sugar baits (ATSB) against Ae. aegypti in the upper Florida Keys. Residential sites on the island of Key Largo were systematically selected using Google maps. Sites received either bait stations or vegetation spray application with ATSB. An untreated control site was selected to monitor mosquito populations. Adult and egg counts were monitored through baited BiogentsSentinel and oviposition traps. The treatment evaluation lasted 28 days following a 14-day pre-treatment evaluation. Treatment efficacy was evaluated using regression models to estimate the percent reduction of mosquitoes over time. Post-treatment, Ae. aegypti mosquito populations were reduced by 81% and 74% at days 7 and 28 (p<0.05) at the bait station site, while mosquito populations at the spray treatment site for the same period (7 to 28 days) were reduced by 66% and 82% (p<0.05), respectively. Treatment and time had no significant effect on the proportion of eggs collected after the application of the ATSB treatments. This is the first residential field trial against the Zika vector, Ae. aegypti, in South Florida that demonstrated successful reduction of female and males using both ATSB stations and vegetation spray treatments. The findings suggest that 1) ATSB stations and vegetation spray applications can reduce populations of Ae. aegypti in residential and semi-tropical areas at least up to 28 days and 2) Ae. aegypti female mosquitoes in South Florida feed on sugar, and their sugar-feeding behavior can be exploited to enhance control strategies.

Foraging behavior and bait station preference in scavenging termite, Odontotermes obesus (Blattodea: Termitidae)

Termites are a significant pest of buildings, agriculture, and trees, and are mainly controlled by baiting. However, baiting systems are available for only lower termites (Rhinotermitidae) not for higher termites (Termitidae). Termite foraging behavior associated with baiting systems varies among species and families, and plays a significant role in baiting success. Here, foraging behavior of Odontotermes obesus (Blattodea: Termitidae: Macrotermitinae), a fungus-growing higher termite, was investigated relative to three bait-station sizes (small, medium, and large) containing different quantities of food. Significantly more workers recruited to large stations (470/station) compared to medium (246/station) and small (124/station) stations. Abundance of O. obesus in large and medium stations significantly positively correlated with relative humidity whereas negative but non-significant correlations were observed with temperature in large and medium stations. Total and continuous contacts with the stations increased with time and were greater in large stations. Station abandonment due to disturbance was significantly less in large stations (3%) followed by medium (9%) and small stations (20%). Our results suggest that large stations (≈8 litres volume) work best for population management of O. obesus and other related fungus-growing higher termites.

An IoT Smart Rodent Bait Station System Utilizing Computer Vision

Across the world billions of dollars of damage are attributed to rodents, resulting in them being classified collectively as the biggest animal pest in the world. At a commercial scale most pest control companies employ the labour intensive approach of deploying and manually monitoring rodenticide bait stations. In this paper was present, RatSpy, a visual, low-power bait station monitoring system which wirelessly reports both on bait station levels and intruders entering the bait station. The smart bait stations report data back to a custom designed cloud platform. The system performance was evaluated under realistic field conditions (on an active cattle farm) with initial results showing significant potential in terms of reducing manual labour, improving scalability and data.

Camera traps are an effective method for identifying individuals and determining the sex of spotted-tailed quolls (Dasyurus maculatus gracilis)

We compared two bait station techniques for determining the sex and identifying individual spotted-tailed quolls (Dasyurus maculatus gracilis) using images taken by camera traps. One method used bait in a plastic mesh bag and the other was a new method using a raised bait canister to entice the quolls to stand on their hind legs and present their ventral surface to the camera. Individuals were identified from multiple images of their unique spot pattern, and sex was determined from ventral images. The bait bag method was better for detecting quolls and both methods performed similarly in allowing observers to identify individuals from images. However, the bait canister method was superior for determining sex of individuals. Using this new bait canister method, individual identification was possible in 202 out of 206 detection events and the sex of 81% (47 of 58) of identified individuals was confidently assigned from multiple detections. This bait station design can therefore provide additional data on individual quolls and reduces the need for more invasive live-trapping techniques. This methodology could be adapted for other mammals in Australia and worldwide.

Testing a pyriproxyfen auto-dissemination station attractive to gravid Anopheles gambiae sensu stricto for the development of novel attract-and-kill strategies for malaria vector control

Background Larval source management is an effective supplementary tool for malaria vector control although it is not used widely in sub-Saharan Africa. This study explored whether an attract-and-kill strategy could contaminate gravid Anopheles gambiae sensu stricto with the insect growth regulator, pyriproxyfen, at a bait-station, for dissemination to larval habitats. Methods A bait-station comprising an artificial pond, containing water was treated with 20 ppm cedrol, an oviposition attractant, was covered with pyriproxfen-treated netting. Three identical semi-field cages were used to assess the potential of gravid Anopheles gambiae sensu stricto to transfer pyriproxyfen from the bait-station to three open ponds. Gravid females were released in the test and one of the control cages that had no pyriproxyfen on its bait-station. No mosquitoes were released in the third cage with a pyriproxyfen-treated station. Transfer of pyriproxyfen to open ponds was assessed by monitoring emergence of late instar insectary-reared An. gambiae sensu stricto larvae introduced into the open ponds. Liquid chromatography-mass spectrometry was used to quantify the amount of pyriproxyfen carried by a mosquito and the amount transferred to water. Results 86% (95% CI 81-89%) of larvae introduced into the open ponds in the two control cages developed into adults. Transfer of pyriproxyfen to the test cage depended on the distance of the pond from the bait-station. While only 25% (95% CI 22-29%) adult emergence was observed in larvae introduced into ponds 4.4 m from the bait-station, the emergence rates increased to 92% (95% CI 89-94%) in larvae introduced in ponds 10.3 m away. Each mosquito was contaminated with 112 µg (95% CI 93-123 µg) pyriproxyfen, whilst 230 ng/L (95% CI 180-290 ng/L) was transferred by a single female to 100 ml of water. Conclusions Pyriproxyfen was auto-disseminated by gravid females from attractive bait-stations, but mainly to aquatic habitats near the bait station. To make this approach feasible for malaria vector control, stronger attractants and better pyriproxyfen delivery systems are needed.

Testing a pyriproxyfen auto-dissemination station attractive to gravid Anopheles gambiae sensu stricto for the development of novel attract-and-kill strategies for malaria vector control

Background Larval source management is an effective supplementary tool for malaria vector control although it is not used widely in sub-Saharan Africa. This study explored whether an attract-and-kill strategy could contaminate gravid Anopheles gambiae sensu stricto with the insect growth regulator, pyriproxyfen, at a bait-station, for dissemination to larval habitats. Methods A bait-station comprising an artificial pond, containing water was treated with 20 ppm cedrol, an oviposition attractant, was covered with pyriproxfen-treated netting. Three identical semi-field cages were used to assess the potential of gravid Anopheles gambiae sensu stricto to transfer pyriproxyfen from the bait-station to three open ponds. Gravid females were released in the test and one of the control cages that had no pyriproxyfen on its bait-station. No mosquitoes were released in the third cage with a pyriproxyfen-treated station. Transfer of pyriproxyfen to open ponds was assessed by monitoring emergence of late instar insectary-reared An. gambiae sensu stricto larvae introduced into the open ponds. Liquid chromatography-mass spectrometry was used to quantify the amount of pyriproxyfen carried by a mosquito and the amount transferred to water. Results 86% (95% CI 81-89%) of larvae introduced into the open ponds in the two control cages developed into adults. Transfer of pyriproxyfen to the test cage depended on the distance of the pond from the bait-station. While only 25% (95% CI 22-29%) adult emergence was observed in larvae introduced into ponds 4.4 m from the bait-station, the emergence rates increased to 92% (95% CI 89-94%) in larvae introduced in ponds 10.3 m away. Each mosquito was contaminated with 112 µg (95% CI 93-123 µg) pyriproxyfen, whilst 230 ng/L (95% CI 180-290 ng/L) was transferred by a single female to 100 ml of water. Conclusions Pyriproxyfen was auto-disseminated by gravid females from attractive bait-stations, but mainly to aquatic habitats near the bait station. To make this approach feasible for malaria vector control, stronger attractants and better pyriproxyfen delivery systems are needed.