Recommendations for Estimating Pesticide Effects on Nontarget Organisms during Mosquito Eradication Programmes in New Zealand

Health officials commissioned a report on the need to monitor nontarget effects of mosquito control agents, and to present a plan to monitor such effects if a nontarget study was deemed necessary.

The report finds that the two pesticides used in New Zealand's Mosquito Eradication Programme are among the least environmentally damaging, according to a report prepared for the Ministry of Health.

The pesticides S-methoprene and Bacillus thuringiensis israelensishave been used as part of the programme to eradicate the southern saltmarsh mosquito Ochlerotatus camptorhynchus in the North and South Islands.

The report, by American ecotoxicologist J. D. Stark, says these pesticides should not result in long term negative effects to the ecosystem as they have little effect on other species including birds, fish and non-insect invertebrates. Repeated applications may greatly reduce communities of insects living under water (benthic insect populations), particularly chironomid midges, which make up a large part of the diet of organisms that inhabit wetlands. However overseas studies have found organisms that feed on chironomids are able to switch to other food sources.

The report considers a nontarget study in New Zealand to be unnecessary, as the primary effect is on chironomid midge populations and this will be only temporary. Midge populations should remain high in surrounding untreated areas, providing enough food for waterfowl and other species that feed on midges.

As the pesticides are being applied to relatively small areas, any organisms unintentionally affected will be rapidly recolonised from surrounding untreated areas.