Biological control of bellyache bush: Native range surveys in South America

Abstract

Bellyache bush (Jatropha gossypiifolia), a deciduous shrub introduced as an ornamental from tropical America, is a major and expanding weed of rangelands and riparian zones in northern Australia. Biological control that complements existing control techniques (e.g. herbicide, mechanical and fire) is needed for cost-effective and long-term control of the weed. Surveys in Mexico, Central and northern South America and the Caribbean for potential biological control agents resulted in release of the seed feeding bug Agonosoma trilineatum (which failed to establish) and prioritisation of a leaf-rust Phakopsora arthuriana (previously known as P.jatrophicola) for host-specificity testing (ongoing). Prospects of gaining new agents from Mexico, Central America and the Caribbean are unlikely. Hence, further surveys were conducted in South America, at 42 sites in Peru, 15 sites in Bolivia and 16 sites in Paraguay. Natural populations of bellyache bush (green leaf form) were seen only in the arid regions of Bolivia. Ornamental populations (purple leaf form) were seen in Peru, Paraguay and Bolivia. A total of 14 agents (12 species of insects, one mite species and one rust fungi) were collected from Peru, Bolivia and Paraguay. The insects were exported to a quarantine facility in South Africa, where they were reared through to adults and sent to relevant taxonomic experts for identification. Identifications of the leaf-mining gracillariid moth Stomphastis thraustica from Bolivia and Peru and the leaf-feeding cecidomyiid Prodiplosis sp. near longifila from
Paraguay have been confirmed, while the identification of the shoot-tip/leaf galling cecidomyiid (?Prodiplosis sp.) from Bolivia is in progress. None of the notodontid
larvae from Paraguay developed into adults in the quarantine facility in South Africa.
A leaf-rust was also recorded from both Bolivia and Peru. The leaf was exported to CABI (UK) and DAFF (Brisbane) where it was identified as P. arthuriana. The limited
number of insect species found on bellyache bush in the arid regions in Bolivia was probably due to the timing of surveys which were undertaken late in the dry season.
Further exploration needs to be conducted in Bolivia during the wet season to study the field host range and damage levels of the previously identified agents and to look
for any new agents. Based on the restricted field host range in South America, an application to import the Jatropha leaf-miner (S. thraustica) in to a quarantine in
Brisbane, Australia for host-specificity testing has been submitted to relevant regulatory authorities in Australia.