Effect of herbivory pressure on Chinese tallow growth in Louisiana: Prospects for biological control

Chinese tallow (Triadica sebifera (L.) Small) is an aggressive invader of wetlands and upland habitats, forestlands and disturbed habitats in the southeastern United States. A biological control agent, the flea beetle Bikasha collaris (Baly) (Coleoptera: Chrysomelidae), is currently being considered against this invasive tree. Pre-release studies were conducted to: 1) determine the impact of local natural enemies, and 2) the effect of simulated herbivory and soil fertility on tallow growth in Baton Rouge, Louisiana (2018, 2019). Insecticide treatment was used to exclude insects in half of the plants, and tallow growth (e.g. basal stem diameter, plant height) and insect damage (percent) were measured monthly (objective 1). A factorial experiment was established with fertility (slow release fertilizer) and herbivory (artificial damage) as factors, and plant growth was recorded monthly (objective 2). The leaf miner Caloptilia triadicae (Hubner) was the main insect herbivore found on Chinese tallow but had little impact on plant growth. Simulated herbivory did not affect tallow growth when growing under high soil fertility in 2018. However, multiple herbivory events over a two-year period significantly reduced tallow growth under low or high soil fertility by end of the experiment (November 2019). Therefore, the release of biocontrol agents may help managing Chinese tallow in Louisiana and elsewhere. Results from these studies will be used to make recommendations to park managers, foresters and other stakeholders during the implementation of biological control in Louisiana.