Background and findings of the 1993-94 New Zealand mosquito survey

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Abstract
Early 1993 interceptions of four species of exotic Culicidae, three of them alive and healthy, were followed by New Zealand's largest-ever survey of larval mosquito populations. This took place from spring 1993 to autumn 1994, concentrating on the northern North Island and the hinterlands of container ports in Hawkes Bay, Wellington and Canterbury. Priority was given to artificial habitats, notably used tyre casings. These, mostly packed into shipping containers, were the source of the above interceptions from imported consignments off-loaded at Wellington, Lyttelton and Port Chalmers. The sampling of 9,408 larval habitats during the survey revealed no evidence of new exotic mosquito establishments, suggesting that prompt control measures and tightened quarantine requirements had proved effective. Two long-established exotics, Culex (C.) quinquefasciatus Say, and (especially) Aedes (Finlaya) notoscriptus (Skuse), were found to have recently dispersed southwards from the northern North Island. The causes of this dispersal and southern establishment include intermittent surface-temperature oscillations over the past 25 years, lately coinciding with greatly augmentcd artificial larval habitat availability due (1) to the burgeoning international and national trade in used tyres, and (2) to a distinctively New Zealand use of them — weighting down the polythene sheeting covering farm silage piles and pits. These trends favour future spread of imported tyre-utilizing mosquito pests/arbovirus vectors, should they elude quarantine precautions and become established.