A risk-based detection survey for the predatory mirid <i>Macrolophus pygmaeus</i> in New Zealand

<p dir="ltr"><i>Macrolophus pygmaeus</i>, a predatory mirid used to manage greenhouse whitefly, was illegally imported into New Zealand, and for a time was reared and sold to commercial tomato growers. We designed and implemented a risk-based detection survey to determine whether <i>M. pygmaeus</i> was still present in New Zealand a decade later. The survey was designed to have an 80% chance of detecting a single low density (0.05 per lineal metre of host plants) population within 1 km of known points of introduction. The survey was implemented between 8 and 15 March 2018. Local habitat constraints meant that the planned sampling had to be modified but this was accounted for in the subsequent analysis. No <i>M. pygmaeus</i> were found in the samples, but 93 specimens from seven other mirid taxa were detected, validating the sample methods. The survey gives 60% confidence that <i>M. pygmaeus</i> was not present at a mean density of 0.05 per lineal metre of habitat. It gives 80% confidence that a population at 0.1 m−1 was not present and 90% confidence that no population exists at >0.18 m−1. Though there are no published data on typical field population densities of <i>M. pygmaeus</i>, for related species the survey would have had high confidence in detecting any medium to high density population present. Therefore, it is likely that <i>M. pygmaeus</i> is no longer present in New Zealand, but if extant within the sampled areas then we have high certainty that it was at low densities compared to other predaceous mirids.</p>