Targeting biological control across diverse landscapes: the release, establishment, and early success of two insects on mesquite (Prosopis spp.) insects in Australian rangelands

Biological control agents are frequently expected to perform over a wide geographic and climatic range, or to target high priority regions with specific climates. Biological control of mesquite (Leguminosae: Prosopis spp.) in Australia is one such example. Mesquite is widely distributed across Australia, but is currently a more serious weed in some areas than others. We document the mass-rearing, release, and establishment of two new biological control agents native to the same region in north-west Argentina. We also determine whether climate-matching, a frequently used method for helping identify well-adapted agents, would have predicted establishment and relative performance of each agent. Release and evaluation sites were selected to represent the diverse climates in which mesquite is a serious weed. One insect, the leaf-tier Evippe sp. #1 (Lepidoptera: Gelechiidae), established widely. Densities of this species were highest in the warmest region, which was 4.7 °C hotter than the point of origin, and low where climate is most similar to the point of origin. Significant impact from Evippe sp. is likely in the warmest region (Pilbara, WA), but was not assessed quantitatively. In contrast, the other insect, the psyllid Prosopidopsylla flava, is only tenuously established at the two coolest sites, one of which was climatically most similar to the point of origin. Both climate and ant predation probably play a role in the failure of psyllids to reach damaging densities, and to become established at other sites. Climate of the areas where the insects were collected in their native range was therefore a poor predictor of performance of at least one of these two insects. Techniques other than climate-matching are therefore required to improve our prediction of relative performance at the regional level.