Progress 08/01/18 to 03/31/19

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Objectives 1.1-1.3 Develop and test different prototype long-lasting formulations to encapsulate the different doses of the five proprietary rat semiochemical compounds and their blends. Two different dispenser mechanisms were evaluated, a monolithic bubble cap dispenser, and a semi-flowable SPLAT formulation. Bubble Caps. The release rate of bubble capsis strongly dependent of the concentration of the semiochemicals in the mineral oil solution, as well as the porosity of the plastic membranes to the different semiochemical components. The most likely mechanism of semiochemical release is that the chemical placed in the bubble cap initially as a pure liquid vaporizes into the atmosphere within the bubble cap and then releases through the membrane into the surrounding outside atmosphere. The vapor pressure inside the bubble cap is usually close to the saturation vapor pressure, whereas the vapor pressure outside the membrane is usually negligible, because the semiochemicals are quickly removed by atmospheric movement and turbulence. Release rates, therefore, were controlled by the saturation vapor pressure and the chemical porosity of the membrane, which should remain constant unless the membrane integrity is disrupted. Our experience is that the saturation of the vapor pressure inside the bubble cap reservoir increases exponentially with temperature. Three different combinations of A4 membrane sheeting were trialed to observe their effect on the release rates of the attractant compounds (Table 2). SPME injections were made into static headspaces containing the bubblecap samples. All analyses were undertaken using a manual SPME injection apparatus fitted with a pre-conditioned Supelco (St. Louis, MO, USA) 50/30 μm DVB/CAR/PDMS Stableflex™ 2cm 24 gauge SPME fibre. The SPME fibre was exposed to the sample vial headspace for 17.5 minutes at 25°C. The fibre was then removed and immediately injected into the GC-MS injector port and desorped for 2 minutes at 270°C. Results showed that the release rate could be adjusted based on the type of membrane being used in the production of the bubble caps. SPLAT® Formulation. The SPLAT wax dispenser formulations belong to a "matrix-type" or "monolithic" category of controlled-release devices. These are defined as devices wherein the active ingredient is dispersed or dissolved in a polymer matrix. The property of the active agent having the greatest influence on its release rate is its molecular weight. Generally, larger molecules take more time to make their way through the free space of a matrix. Branching in a molecule can also decrease its rate of diffusion through a matrix. The partition coefficient of the active agent between the matrix and the environment can also influence the release rate of that agent. If the agent readily partitions to the environment, then its rate of release will be diffusion-controlled and first order. If, however, partitioning of the active agent to the environment is relatively slow, then its partition coefficient will determine its release rate from the matrix and the device will exhibit zero order release kinetics. The partitioning of the active agent to the environment is a function of the solubility of the active agent in the matrix; compounds more soluble in the matrix partition to the environment more slowly. SPLAT emulsions that form the basis of the proposed rat lure formulations, exhibit diffusion-controlled release in a field environment. The surface area of the point source or SPLAT dollop also influences its release rate where dispensers with larger surface areas will release the rat semiochemical active ingredients at faster rates. The release rate of any SPLAT-based formulation containing a fixed amount of semiochemical can be modulated simply by changing a few of parameters in the formulation, including the type of components used (e.g., wax composition, emulsifiers), their proportion in the formulation (e.g., percentage of water, oil or wax content), the stage in the manufacturing at which the different components are added, the rheology, and finally the characteristics of application of the material in the field (e.g., applied as small-dollop or a large dollop). SPLAT formulations were made for each of the five attractants, at predefined AI concentrations. The formulation was extruded into 1g dollops, and conditioned. Release rates were determined for each of the five formulations. Objective 2.0: Conduct field trials to evaluate our semiochemical lure's impact on rat behavior. Lures were presented to wild, free-ranging rats in tracking tunnels used for monitoring rats. Inked tracking cards were placed in each tunnel to quantify visitations and the identity of species visiting lures. Tracking tunnels were installed along transects that followed walking tracks for ease of accessibility, speed of tracking tunnel installation and safety during in-?eld work. Tracking tunnels were installed between 2 and 15 m (into the forest) from pathways and fixed to the ground using metal mat pins. Each tracking tunnel was constructed and deployed by an operative wearing a new pair of single use gloves (Ansell micro-touch Nitrile powder-free). This avoided human scent transmission to tracking tunnels and microtubes and in-field cross-contamination between tunnels from unpacking and handling semiochemicals. Tracking tunnels were cleaned after each trial using tap water, rinsed with rainwater and left to air-dry outdoors. Tracking tunnels that received rat interactions, such as extensive chewing and/or urine marking or those where the lure was subjected to rat interactions (e.g., biting) were not used in future trials and replaced with new, pre-conditioned tunnels. Each trial was made up a single stratified transect. Lures were spaced at 50 m. A control (the lure medium only) and standard (peanut butter) were assigned to each transect. The order of transects and that of the samples within each transect was randomised for each trial. All lures were left in situ for two rain-free nights. Each semiochemical lure was scored for four behavioural responses: attraction, marking, biting and intensity. Attraction was scored using the presence/absence of rat tracks on inked tracking cards to provide a proportion of tracking cards receiving species-specific visitations and hereafter termed the 'tracking rate'. I also recorded (1) the presence of urination and/or faecal marking/communication on or in the tracking tunnel and hereafter termed 'marking' (2) the presence of chew or bite marks on the microtube and/or tracking tunnel and hereafter termed 'biting' and (3) the area tracked with footprints on each tracking card that received a visitation and termed 'intensity'. This was measured using a 10 x 47 cm Perspex sheet with a grid made up of 1 x 1 cm squares. The number of squares with species-specific tracks provided an intensity score that was designed to identify semiochemical lures that generated a strong investigatory response by an individual or that elicited visits from multiple individuals. Six field locations were used around New Zealand with between 2-4 area at each location, with a total of 15-17 replicates for each treatment. The areas were; the Wainuiomata Recreation Area (WRA), the Tunnel Gulley (TG), the Karapoti Gorge (KG), Victoria University (VUW), Akatawara Forest (AKA), and Wright's Hill (WH). Four different types of lures were used, each with one of the two best performing active ingredient blends (I, and BI). Peanut butter controls were also used. The main measure of interaction was a presence/absence of observed tracks in each tunnel trap. Of all the treatments, the BI bubble cap performed best, with a tracking rate (0.47) significantly higher than the peanut butter control (0.24). None of the treatments were significantly less than the peanut butter control, indicating equal, or better performance.

Publications