Macroinvertebrate community responses to mammal control - Evidence for top-down trophic effects

<p>New Zealand’s invertebrates are characterised by extraordinary levels of endemism and a tendency toward gigantism, flightlessness and longevity. These characteristics have resulted in a high vulnerability to introduced mammals (i.e. possums, rats, mice, and stoats) which are not only a serious threat to these invertebrates, but have also altered food web interactions over the past two-hundred years. The establishment of fenced reserves and the aerial application of 1080 toxin are two methods of mammal control used in New Zealand to exclude and reduce introduced mammals, respectively. Responses of ground-dwelling invertebrates to mammal control, including a consideration of trophic cascades and their interactions, remain unclear. However, in this thesis, I aimed to investigate how changes in mammal communities inside and outside a fenced reserve (ZEALANDIA, Wellington) and before-and-after the application of 1080 in Aorangi Forest, influence the taxonomic and trophic abundance, body size and other traits of ground-dwelling invertebrates on the mainland of New Zealand. I also tested for effects of habitat variables (i.e. vegetation and elevation), fluctuations in predator populations (i.e. mice, rats and birds) and environmental variables (i.e. temperature). Additionally, I investigated how squid-bait suspended over pitfall traps influenced the sampling of ground weta and other invertebrates in Aorangi and Remutaka Forests. Contrary to my expectations, there were no differences in abundance or body size of invertebrates within ZEALANDIA (which excludes introduced mammals except mice) relative to the outside, except for Staphylinidae which were more abundant outside the fence. Differences in the agents of predation pressure from mainly mammals, outside the reserve, to mostly birds within ZEALANDIA, but potentially little change in net predation pressure, may explain this apparent similarity in ground-invertebrates. No differences in invertebrate communities were also recorded in the 1080-treated area (Aorangi Forest) after one year of the aerial application of 1080. It could imply that the use of this toxin does not produce any apparent detriment to invertebrates at a population level. The application of 1080 usually leads to changes in insectivorous predator (birds and introduced mammals) dynamics in the short-term mainly due to meso-predator release, which may affect invertebrate communities as a result. Temporal and spatial variation of different components of the ecosystem appear to be more significant drivers of invertebrate dynamics, than 1080 mammal control. For example, rats (Rattus spp.) limited the abundance and body size of large invertebrates (i.e. ground weta, cave weta and spiders) in Aorangi and Remutaka Forests. Smaller invertebrates such as gastropods, weevils and springtails were affected directly by spatial factors such as vegetation, while dung beetles responded to an increase in mouse density. Based on a comparison of pitfall trapping methods, I suggest the use of squid baiting as an effective method for sampling ground weta (Hemiandrus spp.) in New Zealand, as they responded positively to these baits. Finally, I propose ground weta and spiders as suitable indicators of rat predation, as they are abundant in forests and easily recognised by non-specialists, and they respond negatively to rat densities. This thesis underlines the importance of studying the effect of introduced mammal dynamics derived from mammal control in an ecosystem approach, to achieve conservation goals both in the short- and long-term, especially considering the New Zealand Government’s ambitious goal of eradicating three of the most prevalent mammal predators (rats, possums and stoats) by 2050.</p>

Macroinvertebrate community responses to mammal control - Evidence for top-down trophic effects

<p>New Zealand’s invertebrates are characterised by extraordinary levels of endemism and a tendency toward gigantism, flightlessness and longevity. These characteristics have resulted in a high vulnerability to introduced mammals (i.e. possums, rats, mice, and stoats) which are not only a serious threat to these invertebrates, but have also altered food web interactions over the past two-hundred years. The establishment of fenced reserves and the aerial application of 1080 toxin are two methods of mammal control used in New Zealand to exclude and reduce introduced mammals, respectively. Responses of ground-dwelling invertebrates to mammal control, including a consideration of trophic cascades and their interactions, remain unclear. However, in this thesis, I aimed to investigate how changes in mammal communities inside and outside a fenced reserve (ZEALANDIA, Wellington) and before-and-after the application of 1080 in Aorangi Forest, influence the taxonomic and trophic abundance, body size and other traits of ground-dwelling invertebrates on the mainland of New Zealand. I also tested for effects of habitat variables (i.e. vegetation and elevation), fluctuations in predator populations (i.e. mice, rats and birds) and environmental variables (i.e. temperature). Additionally, I investigated how squid-bait suspended over pitfall traps influenced the sampling of ground weta and other invertebrates in Aorangi and Remutaka Forests. Contrary to my expectations, there were no differences in abundance or body size of invertebrates within ZEALANDIA (which excludes introduced mammals except mice) relative to the outside, except for Staphylinidae which were more abundant outside the fence. Differences in the agents of predation pressure from mainly mammals, outside the reserve, to mostly birds within ZEALANDIA, but potentially little change in net predation pressure, may explain this apparent similarity in ground-invertebrates. No differences in invertebrate communities were also recorded in the 1080-treated area (Aorangi Forest) after one year of the aerial application of 1080. It could imply that the use of this toxin does not produce any apparent detriment to invertebrates at a population level. The application of 1080 usually leads to changes in insectivorous predator (birds and introduced mammals) dynamics in the short-term mainly due to meso-predator release, which may affect invertebrate communities as a result. Temporal and spatial variation of different components of the ecosystem appear to be more significant drivers of invertebrate dynamics, than 1080 mammal control. For example, rats (Rattus spp.) limited the abundance and body size of large invertebrates (i.e. ground weta, cave weta and spiders) in Aorangi and Remutaka Forests. Smaller invertebrates such as gastropods, weevils and springtails were affected directly by spatial factors such as vegetation, while dung beetles responded to an increase in mouse density. Based on a comparison of pitfall trapping methods, I suggest the use of squid baiting as an effective method for sampling ground weta (Hemiandrus spp.) in New Zealand, as they responded positively to these baits. Finally, I propose ground weta and spiders as suitable indicators of rat predation, as they are abundant in forests and easily recognised by non-specialists, and they respond negatively to rat densities. This thesis underlines the importance of studying the effect of introduced mammal dynamics derived from mammal control in an ecosystem approach, to achieve conservation goals both in the short- and long-term, especially considering the New Zealand Government’s ambitious goal of eradicating three of the most prevalent mammal predators (rats, possums and stoats) by 2050.</p>

High spatial resolution fluorescence imagery for optimized pest management within a Huanglongbing-infected citrus grove

Huanglongbing (HLB), or citrus greening disease, has significantly decreased citrus production all over the world. The disease management currently depends on the efficient application and adequate distribution of insecticides to reduce the density of the disease vector, the Asian citrus psyllid. Here, we use a novel fluorescent-based method to evaluate insecticide distribution in an HLB-infected citrus grove in Florida. Specifically, we evaluated six different locations within citrus trees, the top and bottom sides of leaves, the effect of application approach (tractor vs airplane), and different application rates. We found that despite the insecticide distribution being highly variable among the different locations within a tree, the top of the leaves received an average increase of 21 times more than the bottom of the leaves. Application by tractor also resulted in a 4- to 87-fold increase in insecticide coverage compared to aerial application, depending on the location in the tree and side of leaf. When taken into context regarding the type of insecticide that is applied (systemic vs contact), these results can be used to optimize a pest management strategy to effectively target psyllids and other pests while minimizing the time and money spent on insecticide application and reducing risk to the environment.

Evaluation of a Methoprene Aerial Application for the Control of Culiseta melanura (Diptera: Culicidae) in Wetland Larval Habitats

Eastern equine encephalitis virus (EEEV) is an arbovirus endemic to the eastern United States. Human cases are rare but can be serious. The primary enzootic vector is Culiseta melanura (Coquillett) (Diptera: Culicidae), an ornithophagic mosquito. We conducted an aerial application of a granular methoprene formulation in Hockomock Swamp (Massachusetts), which represents a focus of EEEV transmission. Water collected from inside and outside Cs. melanura crypts was evaluated in bioassays of early fourth instar Cs. melanura larvae using treated and untreated water. Adult eclosion rates were 36% significantly lower in treated compared with untreated water (P &lt; 0.05). Eclosion rates for water collected from inside crypts were significantly higher (62%) than rates from outside crypts (30%) (P &lt; 0.05), indicating higher efficacy outside crypts. We tested whether reduced methoprene efficacy inside the crypts was due to reduced chemical penetration into this habitat. Chemical water analyses confirmed that methoprene concentrations were lower inside the crypts (0.1 ± 0.05 ppb) compared to water from outside crypts (1.79 ± 0.41 ppb). The susceptibility of Cs. melanura to methoprene was also determined to allow for comparison against concentrations observed in water collected from the field (LC-95: 1.95 ± 0.5 ppb). Overall, methoprene-treated water prevented mosquito development for up to 4 wk, but with a reduction in efficacy between 4- and 6-wk post-application. Our results suggest that aerial methoprene applications can effectively treat open water in wetlands but may not provide efficacious control of Cs. melanura due to an inability to penetrate larval habitats.

Perspective: Agricultural Aerial Application with Unmanned Aircraft Systems: Current Regulatory Framework and Analysis of Operators in the United States

HighlightsThe FAA has used two exemptions (17261 and 18009) as precedents for approval of numerous agricultural operations for unmanned aircraft systems (UAS).While many operators have received exemptions, a significant portion have not received an agricultural aircraft operator certificate (AAOC), despite the need for both to operate UAS in agricultural operations.Operators who have both an exemption and an AAOC tend to be clustered in geographic areas, with many states without a single such operator.Abstract. Unmanned aircraft systems (UAS) have seen rapid growth in many industries in the U.S. since the introduction of small UAS regulations (14 CFR § 107). However, adoption of UAS for agricultural aerial application has been limited. Two landmark regulatory exemptions by the Federal Aviation Administration (FAA) have laid the foundation for commercial agricultural aerial application with UAS. Since the initial introduction of these exemptions, the pace of new exemptions for agricultural aerial application with UAS has remained steady. By the end of 2019, 64 operators had received exemptions in which the FAA cited one of the two landmark exemptions as a precedent. This study analyzed these exemptions to determine geographic distribution, aircraft manufacturer, number of employees, and time to operator certification. Results indicate that less than half of operators who received an exemption from the FAA became certified for aerial application. Additionally, certified operators were not evenly distributed throughout the U.S. despite the broader distribution of exemption holders. Two UAS manufacturers dominated the market, with over 80% of exemptions requesting UAS from one or both manufacturers. While regulatory hurdles for agricultural aerial application with UAS have been substantially reduced through the introduction of standardized exemptions, this has not resulted in the anticipated influx of certified operators. There are additional impediments preventing operator certification, including technological limitations of currently available UAS, which need to be addressed to improve the rate of UAS integration into agricultural aerial application. Keywords: Chemical applications, Drone, Precision agriculture, UAS, UAV, Unmanned aerial vehicle, Unmanned aircraft systems.

Aerial Application Methods for Control of Weed Species in Fallow Farmlands in Texas

Prolific growth of weeds, especially when followed by abundant rainfall, is common in Texas farmlands during early winter and progresses into spring when farmers begin chiseling and disking operations for spring-seeded cropping. This research sought to develop aerial application technologies designed to control unwanted vegetation in croplands left fallow until spring. The aerial nozzles used in the study were conventional hydraulic (CP), rotary atomizer, and electrostatically (ES) charged nozzles. Glyphosate at 0.4145 kg ae·ha−1 was applied on weeds using a fixed-wing aircraft equipped with various aerial nozzles used as treatments. The spray application rate for the conventional and rotary atomizer nozzles was 28.1 L·ha−1, while that for the ES charged nozzle was 9.4 L·ha−1. Aerial and ground-based remote sensing and visual estimates quantified weed vigor and canopy health. Both the CP and rotary atomizer nozzles were efficacious in suppressing weeds. ES charged on nozzles at one-third of the spray application rate of the CP and the rotary atomizer nozzles were equally effective in reducing weed vigor. More aerially applied replicated field research trials conducted over time and space are needed to unravel the differences between aerial spray nozzle technologies for controlling weed populations in Texas farmlands.

Spray Deposition on Weeds (Palmer Amaranth and Morningglory) from a Remotely Piloted Aerial Application System and Backpack Sprayer

This study was designed to determine whether a remotely piloted aerial application system (RPAAS) could be used in lieu of a backpack sprayer for post-emergence herbicide application. Consequent to this objective, a spray mixture of tap water and fluorescent dye was applied on Palmer amaranth and ivyleaf morningglory using an RPAAS at 18.7 and 37.4 L·ha−1 and a CO2-pressurized backpack sprayer at a 140 L·ha−1 spray application rate. Spray efficiency (the proportion of applied spray collected on an artificial sampler) for the RPAAS treatments was comparable to that for the backpack sprayer. Fluorescent spray droplet density was significantly higher on the adaxial surface for the backpack sprayer treatment than that for the RPAAS platforms. The percent of spray droplets on the abaxial surface for the RPAAS aircraft at 37.4 L·ha−1 was 4-fold greater than that for the backpack sprayer at 140 L·ha−1. The increased spray deposition on the abaxial leaf surfaces was likely caused by rotor downwash and wind turbulence generated by the RPAAS which caused leaf fluttering. This improved spray deposition may help increase the efficacy of contact herbicides. Test results indicated that RPAASs may be used for herbicide application in lieu of conventional backpack sprayers.