The researchers' hopes rest on the biological agents the clear-winged carmenta moth and the seed-feeding smicronyx weevil and they have big plans for these small insects.

Biosecurity Queensland principal entomologist, Kunjithapatham Dhileepan, said the researchers centred their attention on Central Queensland, where parthenium is well established, to monitor the spread of these biological control agents.

"One of the worst weeds, parthenium, causes allergic reactions such as dermatitis, hayfever and asthma in people and is toxic to cattle, costing Queensland producers an estimated $16 million per year," Dr Dhileepan said.

Parthenium is a major weed in many African countries including Ethiopia and South Africa and these researchers hope to follow Queensland's lead in implementing a similar control strategy.

"Our visitors accompanied us on our annual field survey to the Rockhampton and Dysart areas, providing them with the opportunity to see the carmenta moth and smicronyx weevil in action."

Dr Dhileepan said results from the recent field survey were promising.

"We found very high populations of the smicronyx weevil in all survey sites and we have not seen such high populations in the field until now," he said.

The South African researchers are particularly interested in the carmenta moth, which they collected together with the weevil to take back to Africa for testing and eventual release.

While the impact of the moth will not be known for some years yet, early signs are promising - the population has grown considerably and the moth has now spread to seven sites in Central Queensland, including two non-release sites.