Hotspots Research Summary

  

This summary  reports some of the key findings of recent Hotspots research: 

 

Detailed maps of spatial risks for each mosquito are not reported here. See ‘Publication page’ for the full text of research reports (including relevant spatial risk descriptions and maps) and references

  
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1        Summaries of findings of the Oc. camptorhynchus (Southern salt-marsh mosquito) case study

1.1         Comments and conclusions regarding Oc. camptorhynchus incursion events and responses

The case study has allowed an extensive review of the Oc. camptorhynchus risk and incursions in New Zealand from prior to 1998 to 2004. This has been done with the benefit of hindsight, direct field experience and investigation of affected sites, access to reported studies and current knowledge of Oc. camptorhynchus in New Zealand - as well as the benefit of advanced spatial analytical methods available in Hotspots that have enabled investigation of climatic and habitat risk attributes of areas. The lessons learnt in this retrospective study provide opportunity to help inform future risk planning for other exotic mosquitoes that pose a risk to New Zealand. The key observations and conclusions are noted below: 

  • Prior to 1998, the potential for arboviral vectors to arrive and establish in New Zealand was well-recognised.
  • Prior to 1998, biosecurity measures in terms of potential entry of exotic mosquitoes of public health significance were largely based on expert opinion that provided a broad overview of potential risks and identified at-risk ports. This analysis was largely qualitative and descriptive in nature. It was not feasible at that time with the readily available technology to provide a rigorous, systematic, spatial analysis of risks for each vector of concern.
  • Consequently prior to 1998 there was active surveillance for exotic mosquitoes at city ports that were deemed to be at-risk. Surveillance of wider mosquito habitats was negligible, geographically limited and not systematic.
  • It was however noted that Oc. camptorhynchus had the potential to colonise ‘the Northland - Coromandel inter-tidal zones of New Zealand’. This was a useful but incomplete description of the spatial extent of risk in New Zealand and has since, with the benefit of hindsight,  been found to be an erroneous description of the type of breeding sites and habitat typically preferred by Oc. camptorhynchus in New Zealand.
  • Following public complaints of a nuisance biting mosquito, Oc. camptorhynchus was first discovered in Napier in December 1998 and in several other localities (including Kaipara Harbour) on the North Island over the next 5 years. In 2004 it was discovered in Marlborough – the first finding on the South Island.
  • It is thought possible that Oc. camptorhynchus was present in Napier for up to about two years before being discovered. It is reasonable to suspect that its discovery in other infested areas was also belated.
  • Most of the subsequent positive sites were found by reactive intense surveillance efforts, however the planning and effective execution of surveillance is a time and resource intensive task with many of the smaller sites being difficult to find.
  • Even with enhanced awareness following detection of the Napier infestation, the use of enhanced methods and tools for surveillance, and systematic surveillance initiatives, larger sites such as those of the extensive habitat in the Kaipara Harbour were not readily found until the infestation was widespread through the entire harbour system.
  • Delayed identification and delimitation of large sites (such as Kaipara Harbour) is a risk assessment and management deficiency that raises concern of a high potential risk of non-remediable widespread colonisation with its attendant arboviral health risks. Rapid identification of all at-risk habitat, but especially large, or potentially large, zones and sites, is crucial to the overall health strategy of keeping New Zealand free of endemic populations of arboviral vectors and locally transmitted arboviral disease.

 

1.2         Comments and conclusions on current surveillance for Oc. camptorhynchus

Several points are noteworthy regarding the current organisation, planning and implementation of surveillance: 

  • The current surveillance approach is sophisticated in terms of methods and tools available to assist the process of identifying at-risk areas. These include the use of topographical maps, aerial photographs, GIS maps, helicopter flyovers and fieldwork.

·        While surveillance activities have found most of the known sites, there is some concern that the large affected tracts in the Kaipara Harbour area were found only after infestation was well established. 

·        Even with nearly five years of awareness and experience, and availability of advanced surveillance methods and tools (including GIS mapping) a site such as that of the Wairau estuary in Marlborough was only discovered incidentally because of the prudent actions of a member of the public. While public notifications and incidental findings have played, and will probably continue to play, an important role in detecting infestations, each of these occurrences represents a failure of organised pro-active surveillance processes and methods.  

·        The planning and successful implementation of surveillance is clearly a difficult task and costly in terms of time and resources. Successful pro-active surveillance and early infestation detection have been difficult goals to achieve in New Zealand and this may be partly explained by inconsistencies and difficulties in their local implementation. 

  • Any new, additional tools, such as Hotspots, that facilitate decision-making for exotic mosquito incursion management must produce efficiency gains in surveillance planning, and also support an ongoing increase in knowledge, expertise and awareness.

 

1.3         Summary of Hotspots performance for Oc. camptorhynchus in New Zealand

Hotspots was used in a desktop study to analyse risk for Oc. camptorhynchus in the Hawkes Bay and Gisborne regions. In this retrospective study to evaluate Hotspots’ performance, the aim was to simulate how the model could have been used for proactive risk analysis had it been available prior to the incursions of Oc. camptorhynchus.  The study made use of existing reported expert knowledge, existing field data from Australia and laboratory data. Used in this way, in the Hawkes Bay and Gisborne regions, Hotspots was able to: 

  1. Directly identify approximately two thirds of Oc. camptorhynchus positive sites; and,
  2. Identify all the geomorphological and/or ecological zones that were positive for Oc. camptorhynchus.

 

With subsequent field experience in Hawkes Bay and Gisborne regions, field testing and parameter fitting using Hawkes Bay and Gisborne historical distribution data, the performance of Hotspots was readily increased and, in a separate validation exercise, analyses were used to predict risk in Auckland and Northland regions. It was found that: 

  1. Hotspots directly identified approximately three-quarters (73%) of the positive sites in Auckland and Northland regions.
  2. Approximately one quarter of the positive sites (24%) were not identified by the model apart from identification of the wider geomorphological and/or ecological zone. These sites tended to be small isolated pockets in the wider Kaipara Harbour system.
  3. Only one site (3%) was completely missed by the model with no meaningful zone identification.

  

In terms of using the model to plan surveillance these results suggest that: 

  1. The model validates well using the Auckland and Northland region distribution data.
  2. Using the model prospectively for surveillance is likely to directly identify about three-quarters of the positive sites.
  3. For the remaining one-quarter of sites, the model is likely to correctly identify their zone or provide some indirect indication of the possibility of a positive site.
  4. There is likely to be the occasional site that this modelling approach will ‘miss’ entirely.

For mapping potential Oc. camptorhynchus distributions, Hotspots now provides a validated and ‘ground-truthed’ modelling approach that is useful for surveillance planning and delimitation studies in New Zealand. It is likely to directly identify the majority of potentially positive sites and when combined with experience, local knowledge and additional tools (such as, where available, aerial photographs and topographical maps) is likely to assist with the identification of almost all potentially positive sites.

 

 1.4         Hypothetical role of Hotspots (from pre-1998 to 2004) with respect to Oc. camptorhynchus risk and incursions

 

In a review of the incursion events and with the hypothetical scenario of Hotspots risk capability having been available at the time of the pre-1998 risk assessments, the case study has shown that this analysis capability would have been valuable in finding sites, planning surveillance and assisting with management decisions.

 A hypothetical ‘pre-1998’ Hotspots analysis using first principle and reported data (without the benefit of local field experience) would have indicated that: 

·        Favourable climate for Oc. camptorhynchus exists throughout the coastal areas of the North Island and the more northern coastal areas of the South Island.

·        Ports with highest entry risks include Auckland, Tauranga, Whangarei, Christchurch, Invercargill and Wellington.

·        Substantial zones of suitable habitat exist in several coastal areas of the North Island including Auckland and Northland regions (especially Kaipara Harbour, Whangarei and areas north of Whangarei), the Coromandel Peninsula and Bay of Plenty (including Tauranga Harbour), Gisborne and Hawkes Bay regions.

  • Assuming appropriate motivation and adequate resources, relevant biosecurity and surveillance policy would have reasonably supported pro-active surveillance of the larger tracts of habitat near and associated with international ports being those of the Auckland Harbours, Tauranga Harbour, Kaipara Harbour, Whangarei, Napier and Gisborne.

If not surveyed pro-actively, the 1998 Napier finding would have ideally triggered immediate re-active surveillance in the high-risk areas identified above. The analyses of the case study show that, assuming the first discovery was indeed at Napier in 1998 rather than another site through active surveillance, the Hotspots risk analysis capability would have been likely to: 

    • Highlight the other positive sites in the Hawkes Bay region and on the North Island including those of Porangahau estuary, Mahia, Gisborne and Kaipara Harbour.
    • Provide impetus and rationale for the early deployment of surveillance in large habitat tracts such as provided by the Kaipara Harbour area.
    • Facilitate delimitation studies and enhanced surveillance activities and help to find rapidly most (approximately three-quarters) of the other sites.
    • Highlight all positive zones on the North Island (apart from that of the Whangaparoa Peninsula site).
    • Identify the Wairau estuary on the South Island as at risk.
    • Possibly augment analysis informing key management decisions such as the eradication decision for Kaipara Harbour - and so possibly help avert delays in management.

As the route or routes of Oc. camptorhynchus arrival in New Zealand and mechanisms of spread are unknown, as are the sequence and timing of site infestations, it is not possible to speculate as to how earlier detection at key sites may have limited the pattern and extent of infestation in New Zealand. However, an infestation becoming well established in large habitat zones such as Kaipara Harbour is clearly a scenario that should be avoided for spread of the vector to be minimised, if eradication operations are to be affordable and successful, and for long-term arboviral transmission risks to be averted. 

It should be borne in mind that many of the factors that hindered detection of sites were partly due to various shortfalls in process, expertise and resources. It is difficult to speculate to what extent modelling capacity with its ability to explore and develop an understanding of various components of risk (such as vegetation type, topography, climate and points of entry) may have helped risk management in the absence of consistently high levels of expertise, determination and resourcing to respond to, and address, the risk pro-actively.

 

 

  

2    Aedes albopictus

Synopsis of Hotspots risk profile and analyses: 

  • Ae. albopictus is a competent vector of dengue fever, Ross River virus and yellow fever.
  • Ae. albopictus is cold tolerant and is found in many temperate countries.
  • It is widely distributed globally and found in many countries with which New Zealand has close travel and trade links.
  • Although originally found in natural  forest, Ae. Albopictus has adapted to exploit a range of habitats and environments, including modified environments and urban and sub-urban environments.
  • Ae. Albopictus  has proven ability to colonise countries very rapidly after introduction - if climatic conditions are suitable.
  • As a container breeder with desiccation resistant eggs, Ae. albopictus has a high risk of introduction into New Zealand  - especially via the shipping ports.
  • For the above reasons it has been identified as a significant biosecurity health risk for New Zealand.
  • The parameters used in Hotspots to model potential Ae. albopictus distributions in New Zealand are well supported by the literature and evidence derived from climatic preferences and tolerance limits of known global populations.
  • Although it is a mosquito that is cold tolerant, in New Zealand climatic factors on average would probably preclude even temperate strains of Ae. albopictus from establishing in most of the southern and central parts of the North Island and all of the South Island – it would seem that this is mostly due to insufficient summer warmth rather than low temperatures in winter.
  • However, Northland, Auckland, parts of the Waikato and coastal areas of the  Coromandel peninsula, Bay of Plenty, Gisborne and Hawkes Bay are at risk.
  • Auckland, Whangarei and Tauranga are the most at risk ports given their introduction risks and suitability of climatic conditions including their availability of sufficient degree-days per year to support viable long-term populations.
  • While Christchurch has a high risk of introductions occurring, its current climate is not likely to support long-term viable Ae. albopictus populations – but this does not preclude the occurrence of transient populations especially in warmer than usual summers.

·        The extent of potential distribution of Ae. albopictus in New Zealand is highly sensitive to climate – with potential distribution and suitability increasing markedly in warm years and with projected future climate change.

·        Climate change would extend the areas at risk of permanent populations to include most areas of the North Island apart from central inland areas, and to include the warmer areas of the South Island with suitable conditions for Ae. albopictus populations possible as far south as Christchurch – and so, allowing Christchurch to become another high risk entry point for colonisation.

In conclusion, under current climatic conditions, Auckland, Whangarei and, to a lesser extent, Tauranga are of most concern given the high entry risks in these areas. Christchurch is likely to be a high risk entry point in warmer than usual climate conditions - and in the future with climate change. Auckland and Whangarei – with their high entry risks and the associated extent of suitable climatic and habitat conditions in the greater Auckland region and Northland regions - are a major concern and these ports and associated at-risk regions would represent the epicentres of current Ae. albopictus risk in New Zealand.

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3   Aedes aegypti

 

Synopsis of Hotspots risk profile and analyses:

 

·        Ae. aegypti is widespread through tropical and sub-tropical areas of the world but has also been found in some more temperate countries.

·        There is a high risk of introduction into New Zealand and there have been previous interceptions at New Zealand ports.

·        The ports at most risk of introduction are Auckland, Whangarei, Christchurch and Invercargill and to a lesser extent Tauranga, Napier, Wellington and Dunedin.

·        While habitat for Ae. aegypti is abundant, under current climatic conditions it is unlikely that Ae. aegypti would be able to establish long-term populations in New Zealand.

·        However, in warmer than usual years there may be some areas in Northland and Auckland regions that are able to support populations of Ae. aegypti.

·        In addition, climate change would allow some areas in Northland and Auckland regions to support long-term populations of introduced Ae. aegypti populations.

·        Under climate change conditions and warmer than usual conditions the ports of Auckland and Whangarei and their immediate surrounding areas are most at risk for Ae. aegypti colonisation. These areas are also likely to be the focus of any transient populations that may survive under current warmer than usual conditions.

  

4   Aedes polynesiensis

Synopsis of Hotspots risk profile and analyses:

 

  • Ae. polynesiensis is abundant in many of New Zealand’s neighbouring countries in the Pacific with which it has strong travel and trade links.
  • The ports at highest risk for entry of this vector are Auckland and Christchurch but Whangarei, New Plymouth and Invercargill have moderate risk while other New  Zealand ports have lower risk.
  • The northern coastal areas of the North Island and especially the Northland and Auckland regions have climates that are tolerable and at times possibly close to optimal for Ae. polynesiensis.
  • In other areas of New Zealand – and especially inland areas and the cooler areas of the South Island – the climatic suitability for this mosquito is marginal.
  • Warmer than usual years and seasons may provide climatic conditions that support transient populations especially in the warmer areas and in these warmer areas such an event may provide a foothold predisposing to long-term establishment of the vector.
  • Ae. polynesiensis is a container breeder that makes use of a wide range of natural and artificial container breeding sites and therefore it is likely to find suitable habitat in most areas of New Zealand and in most types of common land-cover.
  • While Ae. polynesiensis has successfully colonised most other Pacific Island countries, it is reasonable to suggest that in the past climatic conditions have prevented Ae. polynesiensis from colonising New Zealand even though undetected accidental introductions may have occurred.
  • Because climate is possibly a main limiting factor and New Zealand currently appears to be on the limits of the potential distribution of Ae. polynesiensis, the effect of climate change and any associated warming of local climates would have a pronounced effect on the risk of this mosquito successfully propagating following an introduction.
  • Should Ae. polynesiensis be introduced and propagate in New Zealand in warmer climate conditions  - especially as indicated by future climate change – the extent of its suitable habitat would make it extremely difficult, if not impossible, to eradicate or even control.

 

5    Ochlerotatus japonicus

Synopsis of Hotspots risk profile and analyses: 

  • Oc. japonicus has proven ability to be transported internationally and establish in new regions.
  • Oc. japonicus has previously and will continue to be accidentally imported into New Zealand from areas where it is established.
  • The ports most at-risk of entry are Auckland, Christchurch and Tauranga.
  • Oc. japonicus is indigenous to, and established in, countries and regions of the world that are temperate.
  • For most of the North Island, especially its northern and warmer coastal areas, climate will not be likely to prevent this mosquito surviving and breeding if it were introduced. The regions most at risk are Northland, Auckland, Waikato and Bay of Plenty. Some of the warmer and northern coastal areas of the South Island have climate that is compatible with Oc. japonicus infestation.
  • Given the vast areas of suitable habitat where breeding sites are likely to be found and the large areas of land with suitable climate, Oc. japonicus would be extremely difficult to eradicate or even control should it establish breeding populations following an accidental introduction.
  • Climate change and warmer periods would exacerbate these risks.

 

6   Ochlerotatus vigilax

Synopsis of Hotspots risk profile and analyses:

 

  • Oc. vigilax is widely distributed in neighbouring countries including Australia.
  • Oc. vigilax is most likely limited in its southern distribution in Australia by the cooler climate (particularly winter cold) in these areas.
  • Oc. vigilax breeds in coastal habitat that is periodically flooded and has specific habitat preferences that include coastal wetlands, salt marshes and mangroves.
  • Auckland, Whangarei and Tauranga are the ports and areas most at-risk given their entry risks, available habitat and their location in the more climatically suitable regions.
  • Regions with suitable climatic conditions for Oc. vigilax and that are most at-risk include Northland, Auckland, the Coromandel peninsula and to a lesser extent the Bay of Plenty, Gisborne and Hawkes Bay.
  • Transient summer populations are possible in most warmer and coastal areas of New Zealand including warmer parts of the South Island.
  • Climate change would greatly increase the extent of regions with suitable climate for Oc. vigilax to almost all coastal areas of the North Island and to some of the most northern coastal areas of the South Island.

Local area Hotspots analyses to identify specific sites and areas with both suitable climatic conditions and habitat in high risk regions have been documented in Hotspots research reports and form a basis for further risk  analysis work should it be required.  

 

7  Culex annulirostris

Cx annulirostris is widespread in neighbouring countries with which New Zealand has close trade and travel connections - including many Pacific Island countries and Australia. Hotspots analyses allow useful characterisation of the extent and attributes of the risk to New Zealand, and provide the following key insights: 

  • Auckland, Whangarei, Christchurch and Invercargill are the most likely ports of entry for Cx annulirostris while Tauranga, Wellington and Dunedin are at more risk than other New Zealand ports. However average climatic conditions are only likely to be favourable and allow propagation following introduction in Auckland, Whangarei and Tauranga. 
     
  • The potential distribution of Cx annulirostris in New Zealand is likely to be restricted, in prevailing climatic conditions, to the warmer areas of the Northland and Auckland regions and, while it may survive in other warmer areas of the North Island and maybe even of the South Island, it would not thrive in these areas and in those of the South Island it would be very marginal. The potential distribution and potential abundance would be greatly increased in warmer than usual years.
  • Climate change would have a profound impact on the overall risk of establishment following an undetected introduction in New Zealand and on the potential extent of area in which Cx annulirostris would thrive and on its potential abundance in these areas.

Cx annulirostris is a competent vector of several arboviral diseases. Cx annulirostris is a freshwater mosquito that can breed in a wide range of habitats including containers and in diverse environments from natural riverine areas to urban areas.  Currently in New Zealand the potential distribution of Cx annulirostris is not likely to be constrained by land-cover, habitat or environments but is likely to be constrained by climatic conditions (i.e. temperature). The overall risk of successful colonisation following an introduction would be low to moderate given current climate conditions and location of likely ports of entry.  These risk are likely to increase greatly and become ideal in many parts of the country during warmer years and also as a result of climate change. Where climatic conditions are favourable, eradication and control would be exceptionally difficult given the extent of suitable habitat for this mosquito.