Host range tests cast doubt on the suitability of Epiblema strenuana as a biological control agent for Parthenium hysterophorus in Africa

Parthenium hysterophorus (Asteraceae: Heliantheae) (parthenium weed), one of the most aggressive terrestrial weeds, has wide-ranging negative impacts on crop and animal production, biodiversity conservation, and human and animal health in Africa, Asia and Australia. In 2010, South Africa imported the biological control agent, Epiblema strenuana (Lepidoptera: Tortricidae), into quarantine for testing. It is one of the most widespread and damaging agents to have established on parthenium weed in Australia and China. However, it was rejected in India for completely developing on Guizotia abyssinica (Asteraceae: Heliantheae) during laboratory testing. Although G. abyssinica is not cultivated in South Africa, if E. strenuana were to be released here, there are concerns that the moth could readily reach East Africa (where G. abyssinica is an important native commercial oil crop in some countries) due to its dispersal ability and broad host acceptance across several genera. As a matter of responsibility, initial host-range testing in South Africa focussed on determining the susceptibility of selected Ethiopian cultivars of G. abyssinica. Under no-choice conditions, E. strenuana completed development on only one of five test cultivars. However, significant larval feeding damage was recorded on all cultivars. During multiple-choice studies, E. strenuana did not complete development on any of the cultivars, and significantly reduced larval feeding damage was recorded as compared to damage in no-choice tests. Larval development studies showed gall formation and adult eclosion on four cultivars. The interpretation of these results concluded with a decision by South African researchers in 2012 to deprioritise E. strenuana as a potential biological control agent, at least until its host range and potential impact on non-target species in Africa were resolved through field host range trials in Australia.