BACKGROUND: In the Australian southeast, the saltmarsh mosquito Aedes vigilax (Skuse) is the focus of area-wide larviciding campaigns employing the biological agent Bacillus thuringiensis var. israelensis (Bti). Although generally effective, frequent inundating tides and considerable mangrove cover can make control challenging. Here, we describe the efficacy and persistence of an aqueous Bti suspension (potency: 1200 International Toxic Units; strain AM65-52) within a mixed saltmarsh-mangrove system and the use of affordable unmanned aerial systems (UAS) to identify and map problematic levels of mangrove canopy cover. RESULTS: High mangrove canopy density (>40% cover) reduced product deposition by 75.2% (0.01 ± 0.002 ∼L cm-2 versus 0.05 ± 0.006 ∼L cm-2), larval mortality by 27.7% (60.7 ± 4.1% versus 84.0 ± 2.4%), and ground level Bti concentrations by 32.03% (1144 ± 462.6 versus 1683 ± 447.8 spores mL −1) relative to open saltmarsh. Persistence of product post-application was found to be low (80.6% loss at 6 h) resulting in negligible additional losses to tidal inundation 24 h post-application. UAS surveys accurately identified areas of high mangrove cover using both standard and multispectral imagery, although derived index values for this vegetation class were only moderately correlated with ground measurements (R 2 = 0.17-0.38) at their most informative scales. CONCLUSION: These findings highlight the complex operational challenges that affect coastal mosquito control in heterogeneous environments. The problem is exacerbated by continued mangrove transgression into saltmarsh habitat in the region. Emerging UAS technology can help operators optimize treatments by accurately identifying and mapping challenging canopy cover using both standard and multispectral imaging.

Coastal development is expanding globally in response to mass human migration, yet urban planning guidelines often overlook the problems that human encroachment on or near coastal mosquito habitat may cause. This study aimed at elucidating the frequency and magnitude of dispersal of highly vagile saltmarsh mosquitoes from productive off-shore bay islands to adjacent coastal human developments. Inter-population dynamics and daily host-seeking activity of saltmarsh mosquitoes were monitored daily at 15-minute intervals within a productive bay island and adjacent coastal development in southeast Queensland, Australia, using emerging smart trap technology over a 2-month period of high mosquito activity. The regulation of mosquito dispersal and host-seeking activity by local environmental factors, e.g. temperature, relative humidity and hourly wind patterns, were also investigated. The data show that the primary saltmarsh mosquitoes Aedes vigilax (Skuse) and Culex sitiens (Wiedemann) disperse from offshore breeding sites to neighboring mainland areas in high numbers and in highly synchronized waves despite unfavorable wind patterns and the need to traverse a considerable expanse (ca. 1.4 km) of open water. Patterns of host-seeking activity within each site were also remarkably similar despite notable differences in the local environment demonstrating a consistency in host-seeking activity across disparate habitats. These findings demonstrate that distant saltmarsh habitats, including offshore breeding sites, are likely to be primary sources of mosquito nuisance for coastal housing developments. This observation highlights the need to develop new planning and regulatory guidelines that alert urban planners to the risks of encroaching on habitats close to the sources of highly vagile mosquito species.

Commercially available ‘smart’ trap technology has not yet been widely used to evaluate interventions against mosquitoes despite potential benefits. These benefits include the ability to capture data continuously at fine temporal scales without the human resources usually required for conventional trap deployment. Here, we used a commercially available smart trap (BG-Counter, Biogents) to assess the efficacy of an insecticide barrier treatment (BiFlex AquaMax) in reducing mosquito nuisance in a logistically challenging coastal environment in Queensland, Australia. Adoption of smart trap technology permitted us to conduct a uniquely detailed assessment of barrier treatments, ultimately allowing us to demonstrate significant reductions in mosquito collections from treated properties over all temporal scales. On average, daily mosquito collections from treated properties were reduced by 74.6% for the duration of the post-treatment period (56 d). This observation was supported by similar reductions (73.3%) in mosquito collections across all hours of the day. It was further found that underlying mosquito population dynamics were comparable across all study sites as evidenced by the high congruence in daily collection patterns among traps (Pearson r = 0.64). Despite limitations related to trap costs and replication, the results demonstrate that smart traps offer new precision tools for the assessment of barrier treatments and other mosquito control interventions.

Little is known regarding the comparative source–sink relationships between primary mosquito breeding sites (source) and neighboring (sink) environments in heterogeneous landscapes. An exploration of those relationships may provide unique insights into the utility of open-space buffer zone mitigation strategies currently being considered by urban planners to reduce contact between mosquitoes and humans. We investigated the source–sink relationships between a highly productive mosquito habitat and adjacent residential (developed) and rural (undeveloped) coastal environments. Our results suggest that source–sink relationships are unaffected by environment. This conclusion is supported by the high level of synchronicity in daily saltmarsh mosquito abundance observed among all surveyed environments (β = 0.67–0.79, P < 0.001). This synchronicity occurred despite the uniqueness of each surveyed environment and the considerable distances of open water and land (2.2–2.6 km) between them. Trap catches, which we interpret as expected mosquito biting nuisance, were high in both residential and rural coastal landscapes (309.4 ± 52.84 and 405.3 ± 62.41 mosquitoes/day, respectively). These observations suggest that existing and planned open-space buffer zones will do little to reduce the biting burden caused by highly vagile saltmarsh mosquitoes. This strengthens the need for empirically informed planning guidelines that alert urban planners to the real risks of human residential encroachment on land that is close to highly vagile mosquito habitat.

AbstractCoastal development is expanding globally in response to mass human migration, yet urban planning guidelines often overlook the problems that human encroachment on or near coastal mosquito habitat may cause. This study aimed at elucidating the frequency and magnitude of dispersal of highly vagile saltmarsh mosquitoes from productive off-shore bay islands to adjacent coastal human developments. Inter-population dynamics and daily host-seeking activity of saltmarsh mosquitoes were monitored daily at 15-minute intervals within a productive bay island and adjacent coastal development in southeast Queensland, Australia, using emerging smart trap technology over a 2-month period of high mosquito activity. The regulation of mosquito dispersal and host-seeking activity by local environmental factors, e.g. temperature, relative humidity and hourly wind patterns, were also investigated. The data show that the primary saltmarsh mosquitoes Aedes vigilax (Skuse) and Culex sitiens (Wiedemann) disperse from offshore breeding sites to neighboring mainland areas in high numbers and in highly synchronized waves despite unfavorable wind patterns and the need to traverse a considerable expanse (ca. 1.4 km) of open water. Patterns of host-seeking activity within each site were also remarkably similar despite notable differences in the local environment demonstrating a consistency in host-seeking activity across disparate habitats. These findings demonstrate that distant saltmarsh habitats, including offshore breeding sites, are likely to be primary sources of mosquito nuisance for coastal housing developments. This observation highlights the need to develop new planning and regulatory guidelines that alert urban planners to the risks of encroaching on habitats close to the sources of highly vagile mosquito species.