The interaction of native and introduced insect species in New Zealand

[First paragraphs...]
Initially, it is desirable to define the word "introduced" in terms of time. Most of the species which concern us are ones which have received assistance from man, but we must allow the possibility of recent introductions unaided in this manner.
The advent of the more recent spectacular introductions such as the white butterfly (Pieris rapae (L.)) and the European wasp (Vespula germanica (F.)) is clearly dated, but there is no definite information for most of the species which arrived last century. A hundred years ago, when quarantine was a relatively minor consideration, and traffic with our nearest neighbour, Australia, was quite considerable, it is not difficult to imagine many species being unwittingly introduced with plants and produce from that country. It will be recalled that much of this shipping arrived in northern parts, especially the Bay of Islands—a climate ideally suited to the reception and establishment of many Australian insects. Some species, now common to both countries, are shrub-loving ones with a poor capacity for flight. A number of these are now more plentiful here than in Australia, indicating a relative freedom from controlling agents, features strengthening the probability of their recent arrival.