Review and analysis of the surveys for natural enemies of Mimosa pigra: What does it tell us about surveys for broadly distributed hosts?

Mimosa pigra L. (Mimosaceae), a serious weed in Australia and Asia, has been the target of a biological control project for 25 years. This woody legume occurs naturally in all tropical American countries from Mexico to Argentina and on many Caribbean islands. In this paper, we analysed the results of surveys for natural enemies of M. pigra conducted in seven countries by several different collectors and which revealed ∼420 species of insects and five of fungi. We assessed the survey effort relative to the natural distribution of the host-plant to show that large areas of the natural distribution were not covered. We examined the known distribution of the natural enemies to show that most natural enemies occur over the majority of the range of the host, although the Isthmus of Panama is a barrier to many species. This indicates that few potential agents were missed. We show species accumulation curves for three sites to estimate the number of visits required to find most species at a site. Although the species accumulation curves continued to rise, even after 28 collections and 101 insects found at one site, the species utilised for biological control were found relatively early. We expect that these general conclusions (that those insects with potential for biological control are widely distributed and relatively quickly discovered) are applicable to biological control surveys of any target that occurs continuously over a wide geographic range, but possibly not to targets that occupy disjunct distributions.