Our research

A leaf feeding beetle (Gratiana boliviana) has been successfully employed as a weed biological control agent against tropical soda apple in Florida USA where the insect has proven to be host specific and effective in providing control of this weed. Although the insect has been extensively tested for its safety in the USA against native and agriculturally important Solanaceae (such as potato, tomato and eggplant) it had not been host tested against native Australian Solanaceae. It was therefore not known if this leaf-feeding beetle is a viable option for release into the Australian environment.

The purpose of this project was to determine if the leaf feeding beetle (Gratiana bolviana) was suitable for use as a biological control for tropical soda apple in Australia. The project assessed if the beetle was safe for release into the Australian environment by determining if it would harm other species in Australia, in particular those that are closely related to tropical soda apple. To do this the project imported the beetle from Florida USA and conducted host testing against native Australian Solanaceae plant species and related families, in quarantine facilities in Australia. During this testing some feeding and limited oviposition and incomplete development was observed on a few native Australian Solanum species.

Previous research

In 2017, tropical soda apple was approved as a biological control target by the Australian Government Department of Agriculture IPAC (Invasive Plants & Animal Committee), now called the EIC (Environment and Invasives Committee). A collaboration with the University of Florida was established to maintain a small colony of the insects for export to Australia.

In January 2018, the first importation of Gratiana boliviana into the quarantine research facility at CSIRO in Dutton Park, Qld to establish a culture occurred.

A host test list was also developed with Solanaceae specialist Dr Laurence Haegi, Botanic Gardens SA. Solanaceae plant species were sourced, and host testing began in quarantine at CSIRO in Dutton Park, Qld, early in 2018.

Collaborators at the University of Florida conducted open field specificity tests, involving native Australian Solanum species and varieties of eggplant (Solanum melongena) available in Australia. The first experimental trial was completed in November 2018 and the final trial commenced in April 2019.

By June 2019, host specificity testing of imported Gratiana boliviana was completed. Twenty species from the family Solanaceae were included in adult non-choice tests (1-6 replicates each), and twenty species from the family Solanaceae were included in larval non-choice tests (1-6 replicates each).

Plans for the future

This project has resulted in the development of a strong collaboration with the University of Florida. We intend to maintain this collaboration to undertake additional risk analyses. Further research is required to better quantify the risk to closely related native Australian Solanums within the Leptostemonum subgenus. Phylogenetic assessments of relationships between Australian native Solanums would be useful as this data will help to ensure we select native species for future testing which are closely related to those on which we have observed some feeding and limited oviposition and development. Further open field specificity testing will also help to better quantify risk associated with G. boliviana. We also intend to investigate if any of the other insects identified during previous native range surveys on tropical soda apple might be promising for future risk assessments in collaboration with the University of Florida.

A collaboration with the University of Queensland has also been established with the aim to genetically screen leaf samples of tropical soda apple collected in Australia, South America and the southern USA. The aim of this screening is to ensure that the genetics of the invasive population present in Australia is like that present in the USA, and to possibly determine the origins of the Australian populations of tropical soda apple. Screening of populations in this way enables us to determine the potential efficacy of any future biological control programme on this weed.