Preventing the establishment of exotic mosquitoes in New Zealand
Figure 1: Suspected exotic mosquito
interception. 16/5/2007. This blue drum
contained damaged larvae of Culex
pervigilians and Cx. quinquefasciatus.
Photo: Shaun Yu, Auckland DHB
By Rachel Cane, Amy Snell and Mark Disbury, New Zealand Biosecure
Exotic mosquitoes pose a potential risk to public health, the economy and New Zealand's native fauna. They are intercepted at our borders every year, entering the country using a variety of pathways which must be monitored to prevent them from establishing.
Within the port environment, import pathways include incoming aircraft and ships, risk cargoes such as used cars and machinery, and passenger luggage (Frampton, 2004). Points of entry are no longer confined to ports, but have extended to include de-vanning sites where shipping containers are opened, inspected and unloaded at many locations around the country. Systems which direct the monitoring and response activities have been established to minimise the likelihood of an exotic mosquito successfully establishing in New Zealand.
Interception responses involve collaboration between several organisations cooperating to prevent the establishment of exotic mosquitoes within New Zealand. The Environmental Health Protection Guidelines produced by the Ministry of Health detail each organisation's responsibilities to ensure a rapid response each time there is an interception.
Port surveillance
Routine mosquito surveillance at air and sea ports is conducted as both a preventative measure and means of early detection of exotic mosquitoes. This work is carried out by local public health units (PHUs) for the country's 12 district health boards (DHBs) under direction from the Ministry of Health (MoH). Carbon dioxide-baited light traps, ovitraps and tyre traps are utilised, in addition to larval sampling and regular treatment of all suitable breeding habitats within the port environs. Traps are generally put throughout the ports, but higher-risk zones such as risk good inspection areas are targeted for increased surveillance.
The port surveillance system proved its worth in March this year when a routine collection from a light trap at the Ports of Auckland produced an adult male Aedes albopictus (= Stegomyia albopicta) (the Asian Tiger mosquito).
Mosquito larval specimens are often collected at ports, in artificial container habitats such as tyres and drums
(Figure 1). Although the specimens collected in these containers are usually species already present in New Zealand, the containers also provide habitat for any container-breeding exotic species which may arrive at the ports. It is therefore important to remove all containers where possible, or alter them so they can no longer retain water and become a breeding site. Examples of modifying containers so they no longer provide suitable mosquito habitat include filling them with soil or sand and/or drilling holes at the base of the containers so water cannot accumulate.
Figure 2: Interception of live Aedes
albopictus larvae found on a garbage truck
at the Ports of Auckland, imported
PHU Health Protection Officers (HPOs) conduct regular audit surveys of potential mosquito breeding habitats at air and sea ports, in an attempt to control the number of containers and reduce the amount of habitat available for exotic mosquitoes. This is usually less of an issue within airport environments, which generally have fewer containers lying about.
All mosquito specimens are collected, processed and forwarded to the MoH-contracted mosquito entomologists at the Southern Monitoring Services New Zealand Biosecure Entomology Laboratory (NZBEL) for identification. The results of the audit surveys and identifications of any mosquitoes found are forwarded to the Port Manager and the removal or modification of risk containers discussed. The Port Manager arranges for the removal of any risk containers, where possible.
An audit survey carried out at the Ports of Auckland in April 2007 identified a range of potential mosquito breeding habitats. Many of the containers surveyed were found to contain live mosquito larvae in large amounts of water (Parkinson, 2007).
De-vanning sites
Exotic mosquito interceptions also occur at de-vanning sites. The insects fly out of shipping containers when they are opened for inspection or are being unloaded. All mosquito specimens collected at these locations are treated as potential exotic interceptions until they have been identified by the NZBEL entomologists.
Container habitats which are suitable for mosquito breeding are often found within de-vanning site environments. Operators are encouraged to keep these environments as clean as possible to minimise the chance of an incursion at their site and reduce the number of false alarms.
Interception responses
The MoH has a memorandum of understanding with MAF Biosecurity New Zealand (MAFBNZ, which incorporates the former MAF Quarantine Service) to look for mosquito biomass during routine shipping and cargo inspections (Figure 2) (Ministry of Health, 2004). If any mosquito specimens are found by MAFBNZ during these inspections they are treated as a potential exotic species. An HPO from the local PHU is contacted to coordinate the initial response under the direction of the MoH (Senior Adviser John Gardner, or in his absence, the Environmental Health Team Leader Sally Gilbert) as outlined in the Environmental Health Protection Guidelines (Ministry of Health, 2004). The initial response generally includes:
Figure 3: Photograph showing a
key taxonomic characteristic for identifying
exotic mosquito specimens. Aedes
alternans
- commencing an activity log
- advising the MoH (if not already informed), MAFBNZ and the NZBEL
- collecting the sample from the MAFBNZ staff if they have one or collecting one themselves
- processing the sample for shipment and forwarding it by same-day courier (where possible) to the NZBEL
- entering the sample details into the online national mosquito surveillance database (Cane and Disbury, 2007)
- contacting any other stakeholders affected by the event, e.g., local port authority if at a port or landowner/occupier if elsewhere
- undertaking an urgent delimiting survey of the area including checking all existing traps, inspecting and treating, mitigating or eliminating potential habitat
- establishing enhanced surveillance of the area by placing additional traps and maintaining enhanced monitoring
- organising immediate treatment of risk goods through the MAFBNZ or interception site as required
- identifying owners of risk goods
- confirming availability of treatment products and equipment and sampling gear
- assessing human resource requirements
- responding appropriately, depending on the mosquito life stages present
- contacting the shipping agent and obtaining voyage details including transit ports and onward destinations (domestic and foreign)
- advising another PHU if a contaminated shipping vessel has moved on to berth or unload in their area
- producing a situation report (SITREP) of the incident which is forwarded to the Chief Technical Officer and the NZBEL as soon as possible.
Following preliminary identification from the entomologists, the MoH provides advice on treatment and enhanced surveillance to the PHU. If all specimens are identified as New Zealand native or endemic mosquitoes, then relevant parties are notified that no further response action is required and the enhanced surveillance is terminated. However, if an exotic species is identified, knowledge of the behaviour and life history of that species is used to target the enhanced surveillance. For example, the chemical octenol would be used to attract female Aedes vigilax (= Ochlerotatus vigilax) but not Aedes aegypti (= Stegomyia aegypti), while ovitraps would be used to attract egg-laying female Ae. aegypti but not Ae. vigilax. Following a confirmed interception, enhanced surveillance is carried out by the local PHU for three to four weeks.
Specimen identification
The NZBEL has a well-established system for responding to suspected interceptions. Specimens are forwarded by same-day courier where possible, frequently on nights and weekends. An on-call roster ensures there is always a qualified mosquito entomologist available.
The on-call entomologist collects the specimens direct from the Wellington Airport cargo depot and takes the specimens to the NZBEL in Lower Hutt, avoiding extra delays with couriers. All specimens are examined using either a stereo (adults) or compound (larvae) microscope and identified as native (or established), or exotic. The entomologist is required to provide a preliminary identification to the MoH as soon as possible after receiving the specimens. After telephoning this through, all species are identified in full using dichotomous keys.
Figure 4: Interception of
live Tr. bambusa, Ur.
Photographs are taken of relevant taxonomic characters of identified exotic mosquito specimens (Figure 3) and these are emailed to an Australian mosquito expert for confirmation (Disbury et al., 2007). Once received, the MoH is contacted with the confirmed identification and the result is entered into the online national mosquito surveillance database (Cane and Disbury, 2007).
Often more than one species is intercepted. It is therefore important to accurately identify all specimens to enable targeted treatment and surveillance programmes for the exotic species which represents the largest threat. This was highlighted in March 2005, when large numbers of mosquito larvae were found in water contained on a concrete pump truck at the Ports of Auckland (Figure 4). It was discovered there were three exotic species present: Tripteroides bambusa (179 larvae), Uranotaenia novobscura (five larvae) and one larva of the disease vector species Aedes (Finlaya) japonicus. The response needed to be targeted towards Ae. japonicus, which is an unwanted organism and poses the highest public health risk.
Recent interceptions
Since January 2007, there have been 16 mosquito interception responses from New Zealand air and sea ports and de-vanning sites. Six of these have involved exotic mosquito species: Ae. albopictus has been intercepted three times, Culex sitiens twice, and Ae. aegypti, Ae. vigilax (Figure 5) and Aedes alternans (=Mucidus alternans) all intercepted once. Four of the exotic interceptions occurred at the Ports of Auckland, involving three collections of larvae from risk goods and one adult caught in a light trap (Ae. albopictus mentioned previously). The remaining two interceptions each involved two species of live adults captured on a plane ex Australia arriving at Christchurch International Airport. The planes were being disinsected on arrival and these interceptions emphasise why disinsection of aircraft is so important.
It is important that surveillance of air and sea ports continues to protect New Zealand’s borders. To ensure that vigilance in the detection of exotic mosquitoes is maintained, reviews of surveillance activities at these sites should be conducted by experienced personnel.
Acknowledgements
We would like to acknowledge the officers from the PHU, DHB and MAFBNZ for their involvement with each interception and to thank John Gardner and Sally Gilbert of the MoH for reviewing this article. Thanks also to Shaun Yu (Auckland DHB) and Garry Higgins (MAFBNZ) for permission to use their photographs, and Abnesh Chetty and Shaun Yu for their assistance with some of the procedural details.
References
Figure 5: Blood-fed Aedes vigilax
female collective live on a flight
from Australia at Christchurch International
Airport on 4 March 2007
- Cane, R. and Disbury, M. 2007. Online national mosquito surveillance database. Biosecurity 73(2): 24–25.
- Disbury, M., Cane, R.P. and Russell, R.C. 2007. Remote identification of exotic mosquito specimens using digital photography. Australian Journal of Entomology (in press).
- Frampton, E.R. 2004. Pathways of entry and spread of exotic mosquitoes with particular reference to southern saltmarsh mosquito, Ochlerotatus camptorhynchus. Ministry of Health, Wellington.
- Ministry of Health. 2004. Environmental Health Protection Guidelines, Version 4.0: June 2004. Internal Report.
- Parkinson, M. 2007. Audit survey for mosquito habitats at Ports of Auckland on 23 April 2007. Internal Report for Auckland Regional Public Health Service Ref: Q080_15_05.
- Snell, A., Cane, R.P. and Disbury, M. An update on exotic mosquito interceptions in New Zealand (in prep).
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Page last updated: 30 April 2008