Lack of pre-dispersal seed predators in introduced Asteraceae in New Zealand

The idea that naturalised invading plants have fewer phytophagous insects a ssociated with them in their new environment relative to their native range is often assumed, but quantitative data are few and mostly refer to pests on crop species. In this study, the incidence of seed-eating insect larvae in flowerheads of naturalised Asteraceae in New Zealand is compared with th at in Britain where the species are native. Similar surveys were carried ou t in both countries by sampling 200 flowerheads of three populations of the same thirteen species. In the New Zealand populations only one seed-eating insect larva was found in 7800 flowerheads (0.013% infected flowerheads, a ll species combined) in contrast with the British populations which had 487 (6.24%) flowerheads infested. Possible reasons for the low colonization le vel of the introduced Asteraceae by native insects in New Zealand are 1) th e relatively recent introduction of the plants (100-200 years), 2) their ph ylogenetic distance from the native flora, and 3) the specialised nature of the bud-infesting habit of the insects.