The influence of secondary metabolites on the host range selection of <i>Suleima skinnerana</i> , a potential biocontrol agent for <i>Tithonia diversifolia</i>

A Mexican stem-boring moth, Suleima skinnerana (Lepidoptera: Tortricidae), was imported to South Africa as a candidate biocontrol agent for invasive Tithonia diversifolia (Asteraceae). To determine the suitability of the moth for release as a biocontrol agent, we conducted host range tests and examined the influence of plant secondary metabolites on the utilisation of closely related plant species. During no-choice tests, the moth utilised three Tithonia spp., four cultivars of Helianthus annuus and Xanthium strumarium for feeding and development. During multi-choice tests, only the target weed T. diversifolia, one cultivar of H. annuus and X. strumarium were utilised by S. skinnerana. The overall performance of the moth was relatively poor on T. rotundifolia, the congener of the target weed. Amongst all Tithonia species tested in this study, T. rotundifolia had the lowest concentration of both phenols and flavonoids. Limited performance of S. skinnerana on T. rotundifolia suggests that host range may not always be consistent with plant phylogeny, where the closest relatives are expected to be the most acceptable for feeding and development. We recommend that the species with a similar volatile profile to the target weed be prioritised for host range testing as they are likely to be utilised as hosts. The moth was rejected as a biocontrol agent for T. diversifolia in South Africa since it attacked cultivars of sunflower.